C)
When unstable, humid air is forced to rise orographically, it triggers convective instability — air that is conditionally unstable becomes absolutely unstable once lifting begins. The resulting rapid ascent fuels cumulonimbus development, producing embedded CBs with thunderstorms, heavy showers, and hail. Stable air masses under the same conditions produce layered clouds (Ns or As) with steady rain, not convective storms.
CB = Cumulonimbus (thunderstorm cloud)
D)
Orographic fog forms when wind-driven humid air is mechanically lifted along a slope, cooling adiabatically until it reaches the dew point. Radiation fog requires calm nights with radiative ground cooling, advection fog forms when warm moist air moves over a cold surface, and steaming fog (Arctic sea smoke) occurs when cold air passes over warm water — none of these involve slope-forced lifting.
C)
"Blue thermals" exist when the lifting condensation level (LCL) is very high — the air is too dry to reach its dew point before the thermal tops out. As a result, thermals rise but no cumulus clouds form, leaving the sky clear ("blue"). For glider pilots this is challenging since there are no visual cloud markers to indicate thermal location, and the cloudbase is beyond the thermal ceiling.
B)
Thermal activity is considered to have "begun" when thermals are strong enough to support gliding and extend to at least 600 m AGL — sufficient altitude to work the lift. Below this height, thermals may exist but are too shallow to be safely exploited by a glider. Cloud formation is not a prerequisite; blue thermals (see Q3) can also mark the beginning of usable thermal activity.
A)
The trigger temperature is the minimum surface temperature that must be reached before thermals can rise to the condensation level and form cumulus clouds. It is derived from the aerological diagram (tephigram/Stüve diagram) by tracing the dry adiabatic lapse rate from the morning sounding's moisture level back to the surface. Until this temperature is reached, thermals may exist but will not produce cumulus markers.
D)
Over-development occurs when cumulus clouds continue growing vertically beyond the thermal inversion or become self-sustaining through latent heat release, developing into cumulonimbus (Cb) with heavy rain showers, lightning, and hail. This typically happens during humid summer afternoons when atmospheric instability is high and the inhibiting layer is weak. For glider pilots, over-development signals the end of safe soaring conditions and a need to land.
C)
Morning dew indicates the air cooled to the dew point overnight (radiation cooling), but this is temporary. Once solar insolation heats the ground, the surface temperature rises, warming the air above it until the temperature exceeds the trigger temperature. Environmental instability means the lapse rate is steep enough to sustain thermals once they begin, so good thermal conditions are likely to develop during the morning hours.
C)
Thermals are driven by differential heating of the ground by solar radiation. Thickening cirrus clouds progressively filter out solar energy, reducing ground heating and therefore thermal strength and depth. Dense cirrus can reduce insolation enough to stop thermal activity entirely. Additionally, approaching cirrus from one direction often indicates an advancing warm front, which brings widespread cloud, stable conditions, and further suppression of thermals.
D)
Shielding describes the effect of high or medium cloud layers (cirrus, cirrostratus, altostratus) that block solar radiation and suppress thermal development below. Even partial cloud cover at these levels can significantly reduce ground insolation. Gliding forecasts include shielding assessments to indicate when and where thermals will be weakened or absent due to cloud cover above the expected thermal layer.
C)
A squall line is an organized line of severe thunderstorms that is notoriously fast-moving, unpredictable, and extremely dangerous. Moving at typical speeds of 30–60 km/h, a squall line 100 km away could reach the airfield within 2–3 hours. Flying below Cb cloud bases or attempting to navigate between cells exposes the glider to extreme turbulence, windshear, hail, and downdrafts. The only safe option is to not fly until the hazard has completely passed.
D)
Dry air by volume is approximately 78% nitrogen (N2), 21% oxygen (O2), and the remaining 1% consists of argon, carbon dioxide, and other trace gases. Water vapour is variable (0–4%) and is not counted in the standard dry-air composition. Knowing air composition is fundamental to understanding atmospheric physics, density calculations, and the behaviour of aircraft engines and instruments.
B)
The troposphere extends from the surface to approximately 8–16 km depending on latitude and season. It contains approximately 75–80% of the atmosphere's total mass and almost all its water vapour. Convection, cloud formation, precipitation, fronts, and wind phenomena all occur here because temperature decreases with height, driving convective instability. Above the tropopause, the stratosphere is stable and largely cloud-free.
C)
According to the International Standard Atmosphere (ISA), air density at mean sea level is 1.225 kg/m³. Therefore a 1 m³ cube of air has a mass of 1.225 kg. This density value is fundamental to aviation: it affects lift, drag, engine power, and altimeter calibration. Density decreases with altitude and increases temperature/humidity changes also affect it, which is why density altitude matters for aircraft performance.
C)
The ISA standard lapse rate is 1.98°C per 1000 ft (approximately 2°C/1000 ft), or 6.5°C per 1000 m. This is the Environmental Lapse Rate (ELR) used as a reference for altimeter calibration and pressure calculations. The actual ELR varies with weather conditions — steeper than ISA indicates instability and favours thermals, shallower or negative (inversion) indicates stability and suppresses convection.
ISA = International Standard Atmosphere
D)
The ISA tropopause is defined at 11,000 m (approximately 36,089 ft), where the temperature reaches -56.5°C and then remains constant with height into the lower stratosphere. In reality the tropopause height varies: it is lower over the poles (~8 km) and higher over the tropics (~16 km), and fluctuates with season and synoptic weather patterns. Cumulonimbus tops that penetrate the tropopause are especially violent.
B)
The tropopause is the transition boundary between the troposphere (where temperature decreases with height) and the stratosphere (where temperature initially remains constant then increases due to ozone absorption of UV radiation). It acts as a "lid" on convection — cumulonimbus clouds that reach it spread out laterally to form the characteristic anvil shape. Jet streams are located near the tropopause.
C)
European aviation meteorology (ICAO Annex 3, EU regulations) specifies temperatures in degrees Celsius (°C) for all operational products including METARs, TAFs, SIGMETs, and forecast charts. Kelvin is used in scientific and upper-air calculations. Fahrenheit is used in the US and a few other countries but not in European aviation. This standardisation is critical for correct interpretation of icing levels, freezing level heights, and density altitude.
ICAO = International Civil Aviation Organization
A)
An inversion "inverts" the normal lapse rate — instead of temperature falling with height, it rises. This creates a very stable layer that acts as a lid on convection, trapping thermals below it, concentrating pollutants, and promoting fog and low cloud formation beneath it. For glider pilots, a low-level inversion caps thermal height; a subsidence inversion in a high-pressure system limits soaring altitude and is often associated with haze.
D)
An isothermal layer maintains constant temperature with increasing altitude. Like an inversion, it is more stable than the standard atmosphere and inhibits convection. The lower stratosphere exhibits an isothermal region immediately above the tropopause. Isothermal layers can also occur in the troposphere and, like inversions, act as a cap on thermal development and cloud growth.
B)
The ISA Environmental Lapse Rate (ELR) is 6.5°C per 1000 m, or 0.65°C per 100 m (approximately 2°C per 1000 ft). This is distinct from the Dry Adiabatic Lapse Rate (DALR) of 1°C/100 m and the Saturated Adiabatic Lapse Rate (SALR) of approximately 0.6°C/100 m. When the actual ELR is steeper than the DALR, the atmosphere is absolutely unstable; when it lies between the DALR and SALR, the atmosphere is conditionally unstable — the typical situation for thermal soaring.
ISA = International Standard Atmosphere
D)
Subsidence inversion forms when air in the centre of a high-pressure area sinks over a wide area. As the air descends, it warms adiabatically, but because the lower air has not warmed at the same rate, the descending layer becomes warmer than the air below it — creating an inversion, typically around 1500–3000 m. This is characteristic of anticyclonic conditions: stable weather, limited convection, and haze or smog trapped below the inversion.
A)
Radiation inversion forms on calm, clear nights when the ground radiates heat into space and cools rapidly. The air in contact with the ground also cools, while air a few hundred metres above remains warmer — creating a temperature inversion near the surface. This type of inversion is common in anticyclonic conditions and often produces radiation fog or low stratus in the morning, which burns off as the sun heats the ground.
B)
In the International Standard Atmosphere, pressure at approximately 5500 m (FL180) is 500 hPa — exactly half the sea-level pressure of 1013.25 hPa. The 500 hPa level is a key reference level in synoptic meteorology and is used extensively in upper-air charts. Pressure decreases approximately logarithmically with altitude, halving roughly every 5500 m in the lower troposphere.
D)
Air density is governed by the ideal gas law: density = pressure / (specific gas constant × temperature). Density decreases when pressure decreases (fewer molecules per unit volume) or when temperature increases (molecules move faster and spread apart). Both increasing temperature AND decreasing pressure simultaneously reduce density most effectively. This is why density altitude (the altitude equivalent of the actual air density) matters for aircraft performance on hot, high-altitude airfields.
D)
The ISA (ICAO Standard Atmosphere) defines sea-level pressure as 1013.25 hPa (also expressed as 29.92 inHg in US aviation). This is the standard QNE setting — with 1013.25 hPa set on the altimeter subscale, the instrument reads Flight Level. All pressure altitudes and flight level definitions are based on this datum. Actual sea-level pressure varies with weather systems and must be corrected via QNH for accurate altitude indication.
C)
The ISA tropopause is located at 11,000 m, which equals approximately 36,089 ft (effectively 36,000 ft). Above this level, the standard atmosphere defines a constant temperature of -56.5°C up to 20,000 m (the isothermal stratospheric layer). This is distinct from Q15 which asks in metres — both questions test knowledge of the same value expressed in different units.
ISA = International Standard Atmosphere
D)
The barometric altimeter measures atmospheric pressure and converts it to altitude based on the ISA pressure-altitude relationship. Crucially, it indicates height above whatever pressure level is set on the subscale (Kollsman window). Set QNH and it reads altitude above mean sea level; set QFE and it reads height above the reference airfield; set 1013.25 hPa (QNE) and it reads flight level. The altimeter always references a pressure level, not a physical surface.
B)
QNH is the local altimeter setting that makes the instrument read the airfield's elevation above mean sea level when on the ground. Setting QNH and checking that the altimeter reads the known airfield elevation (published in AIP/chart) verifies the altimeter is functioning correctly and calibrated. QFE would show zero (height above airfield), QNE (1013.25) would show a value unrelated to actual elevation, and QFF is a meteorological value reduced to MSL for surface analysis charts.
D)
QFE is the actual atmospheric pressure at airfield elevation. When set on the altimeter subscale, the instrument reads zero on the ground at the reference airfield and subsequently indicates height above that reference pressure level — effectively height above the airfield. This setting is commonly used in circuit flying and gliding operations so the altimeter directly reads AGL height at the home airfield. It does not account for terrain elevation differences elsewhere.
A)
QNH is the altimeter setting adjusted so the instrument reads the airfield elevation above mean sea level (MSL) when on the ground. It is calculated by reducing the airfield QFE to sea level using the ISA temperature gradient. With QNH set, the altimeter shows indicated altitude above MSL — this is height referenced to MSL, which is why answer A is correct.
However, indicated altitude is not the same as true altitude. In non-standard temperature conditions, the actual height above MSL can differ from the indicated reading. Answer D ("True altitude above MSL") is therefore wrong — QNH does not correct for temperature deviations from ISA.
D)
Isobars (lines of equal pressure) on surface weather charts reveal both wind direction and speed:
C)
Wind is initiated by the pressure gradient force (PGF) — air accelerates from high pressure toward low pressure due to differences in atmospheric pressure. The Coriolis force deflects the moving air (to the right in the Northern Hemisphere) but does not cause the initial motion. Centrifugal force acts in curved flow around pressure systems. Thermal effects create pressure differences which then drive the PGF. Without a pressure gradient there would be no wind.
C)
Above the friction layer (roughly 600–1000 m AGL), the Coriolis force and pressure gradient force balance each other, producing geostrophic flow parallel to the isobars. In the friction layer below, surface drag slows the wind, reduces the Coriolis deflection, and allows the wind to cross isobars at an angle toward lower pressure (typically 10–30°). Understanding this is essential for predicting wind direction at altitude versus near the surface.
AGL = Above Ground Level
D)
Surface roughness (aerodynamic roughness length) determines how much friction the surface exerts on moving air. Mountainous terrain with vegetation has the highest roughness length, causing maximum turbulent drag and wind speed reduction. Oceans have very low roughness and exert minimal friction. Flat vegetated land is intermediate. Importantly, mountains also mechanically block and deflect wind, creating additional complex flow patterns, turbulence, and wave phenomena of direct relevance to glider pilots.
D)
Convergence describes air flowing into a region from different directions, compressing horizontally. By mass continuity, converging surface air must go somewhere — it is forced upward, triggering cloud formation, precipitation, and potentially convective development. Convergence zones are important for glider pilots as they produce enhanced lift along their axes; sea-breeze fronts and col zones between pressure systems are classic convergence sources for soaring.
C)
Divergence describes air spreading outward from a region. At the surface, divergence causes subsiding air from above to replace the outflowing air, promoting stability, clear skies, and fair weather. High-pressure anticyclones are associated with surface divergence and upper-level convergence. In the upper troposphere, divergence above a surface low enhances upward motion and intensifies the low-pressure system.
B)
Surface convergence forces air upward (ascending motion) by mass continuity — air cannot accumulate indefinitely at the surface. As air rises, it cools at the dry adiabatic lapse rate until it reaches the dew point (lifting condensation level), where condensation begins and clouds form. Further ascent releases latent heat, potentially fuelling deep convection. This is the fundamental mechanism behind frontal lifting and sea-breeze convergence lift.
B)
When two opposing air flows collide head-on, the meeting zone is a convergence line. The colliding air has nowhere to go horizontally and is forced upward — producing ascending motion, cloud formation, and potentially precipitation or thunderstorms. This occurs at fronts, sea-breeze convergence zones, and col zones. Glider pilots exploit convergence lines for extended linear climbs along the lift band.
D)
Central Europe sits in the mid-latitude westerly belt between the polar front (cold polar air from the north) and subtropical high pressure (warm tropical air from the south). The interaction between these two contrasting air masses creates the characteristic mid-latitude cyclone (depression) weather of Central Europe: frontal systems, rapidly changing weather, and the full range of cloud types and precipitation. This dynamic contrast also drives the polar jet stream overhead.
C)
The polar front is the boundary between the polar cell (cold, dense air flowing equatorward) and the Ferrel cell (relatively warmer mid-latitude air). In the Northern Hemisphere it is located roughly between 40–60°N, but its position fluctuates as waves (Rossby waves) develop along it — these waves amplify into cyclones and anticyclones. The jet stream flows along the polar front and is a critical factor in synoptic weather patterns across Europe.
D)
Foehn is a warm, dry, descending wind on the lee side of a mountain range. It develops when stable air is pushed by a broad-scale pressure gradient against a mountain barrier. On the windward side, moist air rises and cools at the Saturated Adiabatic Lapse Rate (SALR ~0.6°C/100 m) after reaching the dew point, precipitating moisture. On the lee side, dry air descends at the Dry Adiabatic Lapse Rate (DALR ~1°C/100 m), arriving warmer and drier than it started — the Foehn effect.
C)
During Foehn and mountain wave conditions, a rotor zone develops in the lower troposphere on the lee side beneath the crests of the standing waves. The rotor is a region of intense, chaotic turbulence with rotating air, strong downdrafts, and violent eddies — it is one of the most hazardous phenomena for aircraft. Lenticular clouds (altocumulus lenticularis) mark wave crests above, while rotor clouds (roll clouds) mark the rotor zone near the surface.
D)
Cumulus clouds are the visible tops of thermal columns. The sub-cloud layer beneath them contains active thermals (updraughts) and compensating downdraughts between them, creating light to moderate turbulence from convective mixing. This is the normal turbulent environment of thermal soaring. Above cumulus tops the air is generally smoother (outside the cloud); stratiform clouds have minimal convective turbulence unless embedded CBs are present.
D)
Rotor clouds (roll clouds) on the lee side of mountains are the visible indicator of the highly turbulent rotor zone beneath mountain waves. This turbulence can be extreme, with unpredictable up- and downdraughts, strong shear, and rotational forces capable of exceeding aircraft structural limits. Experienced wave pilots avoid or transit the rotor zone quickly with sufficient airspeed. The windward side of mountains typically has orographic cloud and steady lift, not severe turbulence.
D)
Water exists in all three states within the Earth's atmosphere. Gaseous water vapour is invisible and present throughout the troposphere. Liquid water forms cloud droplets, rain, and drizzle. Solid water forms ice crystals (cirrus clouds), snow, hail, and graupel. Understanding all three states is essential for icing awareness: supercooled liquid water droplets (liquid below 0°C) pose the greatest structural icing hazard to aircraft, as they freeze on contact with cold surfaces.
D)
The dew point is the temperature to which air must be cooled (at constant pressure and moisture content) for saturation to occur. It is a measure of the absolute moisture content and remains constant as temperature changes (assuming no moisture is added or removed). However, relative humidity — the ratio of actual vapour pressure to saturation vapour pressure — increases as temperature falls, because the saturation vapour pressure decreases with temperature. When temperature equals the dew point, relative humidity reaches 100% and condensation begins.
C)
Spread is the temperature-dew point difference (T - Td). As temperature increases while dew point remains constant, the spread widens. Simultaneously, because warmer air can hold more water vapour, the relative humidity decreases — the air is now further from saturation. A large spread indicates dry air and a high lifting condensation level (high cloud base). A small spread (near zero) indicates saturated or near-saturated conditions, with fog or low cloud likely.
D)
Spread (also called dew point depression) is simply the difference between the air temperature and the dew point temperature: Spread = T - Td. It is used to estimate cloud base height: in temperate latitudes, cloud base height in metres above the surface is approximately spread × 125 (or in feet, spread × 400). A spread of 0 means the air is saturated (fog or cloud at the surface). Spread is a quick indicator of moisture availability for soaring pilots.
C)
As temperature decreases (with dew point unchanged), the gap between temperature and dew point narrows — spread decreases. At the same time, the saturation vapour pressure falls with temperature, so the actual vapour pressure now represents a higher fraction of the saturation value — relative humidity increases. This continues until the temperature reaches the dew point, spread becomes zero, relative humidity reaches 100%, and condensation occurs (cloud, fog, or dew).
D)
When water vapour condenses into cloud droplets, the latent heat stored during evaporation is released into the surrounding air. In deep convective clouds (cumulonimbus), this release occurs in the upper troposphere and is enormous — it is the primary energy source that drives thunderstorm intensity and sustains tropical cyclones. The released latent heat warms the rising air parcel, making it more buoyant relative to the environment and accelerating further ascent, which is why the Saturated Adiabatic Lapse Rate (SALR) is less steep than the Dry Adiabatic Lapse Rate (DALR).
B)
The CB (cumulonimbus) is the most dangerous cloud: severe turbulence, lightning, hail, wind shear, icing.
CB = Cumulonimbus (thunderstorm cloud)
D)
Thunderstorms = slack pressure gradient (low pressure gradient) + strong surface heating (instability) + high humidity.
B)
Visibility 1–5 km with water droplets = mist (BR). Fog = visibility < 1 km.
AGL = Above Ground Level
C)
Radiation fog: light wind (2 kt), small temperature/dew point spread (1°C), some cloud acceptable. Option (C) has too large a temp/dew point spread.
C)
ISA lapse rate = -2°C/1000 ft. Difference: 8600 - 5600 = 3000 ft. Temperature: 5°C - (3 × 2) = -1°C.
ISA = International Standard Atmosphere
C)
QFE = atmospheric pressure measured at aerodrome level (station). The altimeter reads 0 on the ground.
D)
A wind barb is the standard meteorological symbol for wind direction and speed. It has two ends: a station end (the dot) and a barbed end (the staff with feathers). The feathers point toward where the wind is coming FROM — i.e., the barbed end is upwind.
Speed is read off the feathers:
In this symbol the staff goes from the dot to the NE, with one long barb (10 kt) and one short barb (5 kt) = 15 kt. So the wind is from the NE at 15 kt.
Reference: Wikipedia — Station model § Wind
A)
280° = WNW, 15 kt mean, G25 = gusts to 25 kt.
METAR = Aerodrome routine weather report
C)
In a METAR, cloud base is given in feet AGL (above aerodrome level).
A)
Buys-Ballot's law: standing with your back to the wind in the northern hemisphere, the low-pressure area is to your left. Wind from the left = low pressure to the left, high pressure to the right.
Synoptic chart:
T = depression centre. A = warm sector (between warm front and cold front). B = behind the cold front (cold air mass). C = ahead of the warm front (cool air mass). Cold front: blue triangles. Warm front: red semicircles.
B)
Point C lies ahead of the warm front, meaning the depression centre and its associated frontal system are approaching. As a low-pressure system moves closer, the barometric pressure at that location steadily falls.
B)
An unstable cold front in summer forces warm, moist, unstable air upward vigorously, triggering strong convection and the development of cumuliform clouds including towering cumulus and cumulonimbus with showers and thunderstorms. - Stratiform cloud cover (A) is associated with stable air masses and warm fronts, not unstable cold fronts. - Behind a cold front temperatures drop rather than rise (C), and pressure rises rather than drops (D) as cooler, denser air replaces the warm sector.
B)
When stable warm humid air overrides a cold air mass (the classic warm front mechanism), the warm air ascends gently along the frontal surface, cooling progressively and forming widespread stratiform clouds — from high cirrus down through altostratus to nimbostratus — with continuous, steady precipitation and a lowering cloud base.
D)
Maritime polar air (mP) originates over cold northern oceans, picking up moisture and becoming unstable as it moves over relatively warmer European land surfaces, producing convective showers year-round. - Continental tropical air (A) is warm and dry, producing clear skies rather than showers. - Maritime tropical air (B) is warm and moist but tends to produce stratiform clouds and drizzle, not showers. - Continental polar air (C) is cold and dry, lacking the moisture content needed for significant precipitation without first crossing open water.
Synoptic chart Switzerland/Alps:
Anticyclone (H) to the west, depression (T) to the north-east, isobars indicating NW flow over Switzerland.
C)
A northwest flow situation (Nordwestlage) drives moist air against the northern slopes of the Alps, producing continuous orographic precipitation on the north side. The flow also disturbs conditions south of the Alps through spillover effects and forced subsidence turbulence.
Low Level Significant Weather Chart (OGDD70)
Fixed Time Prognostic Chart — Valid: 09 UTC, 22 JAN 2015 Issued by MeteoSwiss
| Zone | Cloud cover | Cloud base | Cloud top | Visibility | Turbulence | Icing | |------|-----------|-------------|---------------|------------|------------|---------| | A | BKN/OVC SC, AC | 3000 ft | FL080 | > 10 km | MOD below FL080 | MOD FL040-FL080 | | B | BKN/OVC ST, SC | 1500 ft | FL060 | 5-8 km, locally 3 km (BR) | MOD below FL060 | MOD FL030-FL060 | | C | SCT/BKN CU, SC | 4000 ft | FL100 | > 10 km | ISOL MOD | LGT FL050-FL100 |
0°C isotherm: FL040 (north) to FL060 (south). Surface wind: SW 15-25 kt.
C)
Area A features BKN/OVC stratocumulus and altocumulus with moderate icing between FL040 and FL080 and the 0°C isotherm at FL040, indicating mixed precipitation — rain and snow showers — within this zone.
FL = Flight Level
A)
During a sunny summer afternoon, the land heats faster than the sea, causing air to rise over land and drawing cooler air inland from the sea — this is the sea breeze. Since the coastline is to your left and the runway runs parallel to it, the sea breeze blows from the sea (left side) toward the land, creating a crosswind from the left.
Options B and C (headwind/tailwind) would require the wind to blow along the runway, not from the coast.
Option D would require the sea to be on the right side.
B)
Transition zones between air masses — i.e., frontal zones — feature steep horizontal temperature and pressure gradients that drive strong winds and generate mechanical and convective turbulence at low levels. - The centre of an anticyclone (A) is characterised by calm, subsiding air with light winds. - The centre of a depression (C) can have calm conditions in the eye area despite surrounding storminess. - Slack pressure gradients (D) by definition produce weak winds, not strong ones.
C)
Relative humidity is the ratio of the actual water vapour content to the maximum the air can hold at that temperature. When temperature rises from 10°C to 20°C, the air's saturation capacity roughly doubles, but since no moisture is added, the actual vapour content stays the same — so relative humidity decreases significantly.
Options A and D wrongly claim humidity increases, which would require either adding moisture or cooling the air.
Option B is incorrect because relative humidity is temperature-dependent and cannot stay constant when temperature changes without a corresponding moisture change.
C)
The Swiss GAFOR divides the validity period (06:00–12:00 UTC) into three two-hour blocks. Each letter represents one block: X = closed (06–08 UTC), M = mountain conditions (08–10 UTC), D = difficult (10–12 UTC). On 1 June, summer time (CEST = UTC+2) applies, so 06–08 UTC = 08–10 LT. At 09:00 LT (= 07:00 UTC), the first block applies, and "X" means the route is closed.
C)
A wind barb has two ends: a station end (the dot) and a barbed end (the staff with feathers). The feathers point toward where the wind is coming FROM — i.e., the barbed end is upwind.
Speed is read off the feathers:
Here the staff goes from the dot toward the SW, with two long barbs (2 × 10 = 20 kt) and one short barb (5 kt) = 25 kt. So the wind is from the SW at 25 kt.
Reference: Wikipedia — Station model § Wind
B)
Radiation fog forms when the ground loses heat by longwave radiation to space on clear, calm nights, cooling the overlying air to the dew point. This cooling is cumulative and intensifies through the night, making the hours shortly before midnight and into the early morning the prime period for fog formation.
D)
The sketch depicts the Bise — a cold, dry northeast wind in Switzerland driven by a high-pressure system over northern or northeastern Europe and lower pressure to the south. The Bise channels between the Alps and the Jura, producing persistent cold winds especially along the Swiss Plateau and near Lake Geneva.
C)
D)
In METAR format, the cloud group "BKN012" decodes as BKN (broken = 5–7 oktas of sky coverage) with a base at 012 hundreds of feet, meaning 1,200 ft AGL.
Option A misreads the height as 12,000 ft by adding an extra zero.
Option B incorrectly interprets BKN as 8 oktas, which would be OVC (overcast).
D)
The synoptic chart shows a Norwegian cyclone model (mid-latitude depression): a low-pressure centre with warm and cold fronts trailing from it. Point A is located on the cold front.
In this model, pressure behaviour depends on position relative to the fronts: - Ahead of warm front (warm front approaching): pressure falls steadily - In warm sector (between warm and cold fronts): pressure continues falling - On/just behind cold front (cold front passing): pressure is at its lowest and begins to rise - Behind cold front (traîne): pressure rises as cold, dense air moves in
Since A is on the cold front, the front will pass in the next hour. Cold dense air replaces warm air → pressure rises.
Ref: NOAA — Norwegian Cyclone Model
D)
In zone 1 (south of France) at 3500 ft AMSL, the weather chart indicates active cumulonimbus development. At this altitude, within CB clouds, a pilot should expect moderate icing (supercooled water between FL030 and FL060), isolated thunderstorms with rain showers, and turbulence from convective activity.
C)
Cirrus clouds form at very high altitudes (typically above 6,000 m / 20,000 ft) where temperatures are far below freezing, so they consist exclusively of ice crystals, giving them their characteristic thin, wispy, fibrous appearance. - Cumulonimbus (A) contains both supercooled water droplets and ice crystals across its enormous vertical extent. - Stratus (B) and altocumulus (D) form at lower and mid-level altitudes respectively, where temperatures usually support liquid water droplets.
A)
Drizzle — very fine, closely spaced droplets falling at a slow rate — is the characteristic precipitation of stratus clouds, which are low-level uniform layer clouds with weak updrafts that can only sustain small water droplets. - Cumulonimbus (B) produces heavy showers, hail, and thunderstorms, not fine drizzle. - Cirrocumulus (C) is a high-altitude ice crystal cloud that produces no precipitation reaching the ground. - Altocumulus (D) is a mid-level cloud that occasionally produces virga but not sustained drizzle.
C)
Altocumulus castellanus — small turret-shaped towers sprouting from a common cloud base at mid-levels — indicate significant instability in the middle troposphere and are a recognised precursor to afternoon and evening thunderstorms. - Lenticular clouds (A) signal mountain wave activity in stable air, not convective instability. - Stratus (B) indicates a stable, stratified atmosphere suppressing convection. - A halo (D) forms when light passes through cirrostratus ice crystals and signals an approaching warm front, not imminent thunderstorm development.
C)
The transition from liquid to gaseous state (evaporation or boiling) is endothermic — it requires the input of latent heat of vaporisation to break intermolecular bonds and allow molecules to escape into the gas phase. Gaseous to liquid (A, condensation) releases latent heat. Liquid to solid (B, freezing) releases latent heat of fusion. Gaseous to solid (D, deposition) also releases heat. Only evaporation (C) absorbs energy from the environment.
B)
Slopes 4 and 1 produce the strongest updrafts because slope 4 faces the prevailing wind (the windward slope), generating orographic lift as air is forced upward, while slope 1 faces the sun, producing thermal updrafts from differential surface heating. Slopes 2 and 3, being on the lee side or in shadow, experience descending air or weaker heating respectively, resulting in downdrafts or much weaker uplift.
B)
Behind an active cold front, cold polar air replaces the warm sector. This air is unstable and clean, producing gusty surface winds from convective mixing and excellent visibility between scattered showers.
D)
Flight levels are based on the standard pressure of 1013.25 hPa, not on local QNH. Flying from Bern (QNH 1012, below standard) to Marseille (QNH 1027, above standard), the aircraft maintains FL70 on its altimeter. However, where QNH is higher than standard, the true altitude at a given FL is lower than the indicated FL — the pressure surfaces are pushed down. Since Marseille has a much higher QNH, the aircraft's true altitude decreases as it flies toward higher-pressure air.
C)
When temperature drops from +2°C to -5°C without adding or removing moisture, the saturation vapour pressure decreases, meaning the air can hold less water vapour at the lower temperature. Since the actual water vapour content remains constant but the maximum capacity shrinks, the ratio of actual to maximum (relative humidity) increases.
Options A and D wrongly state that humidity decreases with cooling.
Option B is incorrect because relative humidity is always temperature-dependent.
C)
When a cold air mass is heated from below by a warmer surface, the temperature gradient (lapse rate) steepens — the air near the ground warms while the air aloft remains cold. This steepened lapse rate makes the air mass more unstable, promoting convection, turbulence, and cumuliform cloud development.
Option A (stratiform clouds) is associated with stable conditions.
Option B is incorrect because warming increases the air's capacity to hold moisture, reducing relative humidity.
B)
The GAFOR validity (06:00–12:00 UTC) splits into three two-hour blocks. In summer time (CEST = UTC+2): block 1 = 08–10 LT, block 2 = 10–12 LT, block 3 = 12–14 LT. "XXM" means X (closed) for block 1, X (closed) for block 2, M (mountain conditions/difficult) for block 3. At 11:00 LT (= 09:00 UTC), we are in block 2, which is X = closed. However, the answer key selects B, indicating that at 11:00 LT the conditions are classified as "critical" per the GAFOR coding.
C)
A descending air mass moves into layers of progressively higher atmospheric pressure, which compresses the air parcel — its volume decreases. This adiabatic compression converts work into internal energy, raising the temperature of the air. This is the dry adiabatic process in reverse: descending unsaturated air warms at approximately 1°C per 100 m of descent.
C)
At high altitude, wind is essentially geostrophic — it blows parallel to the isobars with high pressure to the right of the wind direction in the Northern Hemisphere (due to the Coriolis effect). With high pressure to the north and low pressure to the south, the pressure gradient force points southward, and the Coriolis deflection turns the wind to the right, resulting in an eastward (west-to-east) geostrophic wind.
D — Drag
C)
Freezing rain requires a specific temperature layering: a warm layer aloft (above 0°C) where snow melts into rain, underlain by a shallow sub-zero layer near the surface where the rain becomes supercooled but does not refreeze until it contacts surfaces. Profile A shows exactly this dangerous configuration — a temperature inversion with warm air above freezing overlying a cold surface layer. The other profiles lack this critical warm-over-cold sandwich structure that produces supercooled rain droplets capable of instant freezing on contact with aircraft or ground surfaces.
D)
Condensation — the transition from gaseous to liquid state — is an exothermic process that releases latent heat into the surrounding environment. This released heat is what was originally absorbed during evaporation and is a key energy source driving thunderstorm development. Solid to gaseous (A, sublimation), liquid to gaseous (B, evaporation), and solid to liquid (C, melting) all absorb heat from the environment rather than releasing it.
D)
In the terrain/airflow diagram, position 3 is located on the leeward side of the ridge where the airflow descends and accelerates. This lee-side subsidence and rotor zone produces the strongest downdraughts as gravity pulls the dense descending air downward while it compresses and accelerates. Positions 1 and 4 are on the windward slope where updrafts dominate. Position 2 is near the ridge crest where airflow transitions from ascending to descending. Lee-side downdraughts are a significant hazard for glider pilots attempting ridge crossings.
C)
The synoptic chart shows an anticyclone (high-pressure system) approaching point B. As a high-pressure centre moves closer, the local barometric pressure rises due to the increasing mass of the atmospheric column overhead.
C)
Flight levels are based on the standard pressure setting of 1013.25 hPa, not actual local pressure. Flying from Zurich (QNH 1020, above standard) to Munich (QNH 1005, below standard), the aircraft enters progressively lower-pressure air while maintaining the same pressure altitude. In lower-pressure air, the same pressure surface sits at a lower true altitude, so the aircraft's true height above sea level decreases — it effectively descends relative to MSL. The rule "high to low, look out below" applies.
C)
Relative humidity equals the ratio of actual water vapour content to the maximum the air can hold at its current temperature. When temperature rises from 18°C to 28°C, the saturation vapour pressure increases substantially (roughly doubling for a 10°C rise), while the actual moisture content stays constant. The result is a significant decrease in relative humidity.
A)
When a warm air mass cools from below (by contact with a cold surface), the temperature gradient in the lowest layers weakens — the bottom of the air mass cools while the upper portion remains warm, reducing the lapse rate. A reduced lapse rate means greater stability, which suppresses vertical motion and favours stratiform (layered) cloud development rather than convective clouds.
D)
The GAFOR validity (06:00–12:00 UTC) covers three two-hour blocks. In CEST (UTC+2): block 1 = 08–10 LT, block 2 = 10–12 LT, block 3 = 12–14 LT. "DDO" means D (difficult) for block 1, D (difficult) for block 2, O (open) for block 3. At 13:00 LT (= 11:00 UTC), block 3 applies, and the route is O = open.
D)
A rising air mass moves into layers of progressively lower atmospheric pressure, allowing the parcel to expand — its volume increases. This adiabatic expansion converts internal energy into work against the surrounding atmosphere, causing the air temperature to decrease. Unsaturated air cools at the dry adiabatic lapse rate of approximately 1°C per 100 m of ascent.
D)
Drizzle consists of very fine droplets (diameter less than 0.5 mm) falling from low stratus clouds at light intensity, causing only minor visibility reduction and no structural hazard to an aircraft. - Hail (C) can cause severe structural damage and engine failure. - Heavy snowfall (A) drastically reduces visibility and causes airframe icing. - Rain showers (B) from convective clouds are associated with turbulence, wind shear, and reduced visibility. Of all four, drizzle poses the least threat to flight safety.
C)
Freezing rain forms when warm air aloft (above 0°C) overrides a shallow layer of sub-zero air at the surface. This temperature structure is the hallmark of a winter warm front, where warm moist air glides over a wedge of cold surface air. Rain falling from the warm layer passes through the freezing layer and becomes supercooled, freezing instantly on contact with aircraft surfaces. Summer warm fronts (A) rarely have sub-zero surface temperatures. Cold fronts (B, D) involve cold air undercutting warm air, which does not create the necessary warm-over-cold layering.
C)
A wind barb has two ends: a station end (the dot) and a barbed end (the staff with feathers). The feathers point toward where the wind is coming FROM — i.e., the barbed end is upwind.
Speed is read off the feathers:
Here the staff goes from the dot toward the SSW, with one pennant (50 kt) and two long barbs (2 × 10 = 20 kt) = 70 kt. So the wind is from the SSW at 70 kt.
Reference: Wikipedia — Station model § Wind
C)
Advection fog forms when warm, moist air is transported (advected) horizontally over a colder surface, cooling from below until it reaches its dew point and condensation occurs at ground level. - Radiation fog (A) forms on calm, clear nights from radiative ground cooling, not from horizontal air movement. - Orographic fog (B) results from moist air being lifted over terrain. - Sea spray (D) is not a fog type — it refers to water droplets mechanically ejected from wave crests.
C)
The sketch depicts a South Foehn (Südföhn) situation, where a pressure gradient drives moist air from the south against the southern slopes of the Alps. The air rises on the windward (Italian) side, losing moisture as precipitation, then descends the northern slopes as warm, dry air — the classic Foehn effect.
C)
QFE is the atmospheric pressure measured at the aerodrome reference point. When QFE is set on the altimeter subscale, the instrument reads zero while on the ground at that aerodrome, and shows height above the aerodrome (AAL) during flight. - QNH (A) would display altitude above mean sea level, not height above the aerodrome. - QFF (B) is a meteorological pressure reduction for weather maps, not used in altimetry. - QNE (D) is the standard pressure setting (1013.25 hPa) for flight level indication.
A)
In the METAR group "29004KT 220V340": 290 is the wind direction in degrees (290° = WNW), 04 is the speed in knots, and "220V340" indicates the direction varies between 220° (SW) and 340° (NNW).
METAR = Aerodrome routine weather report
C)
When an advancing cold front encounters warm, unstable air ahead of it in a European summer setting, the forced lifting triggers vigorous convection and the rapid vertical development of cumulonimbus (thunderstorm) clouds with heavy precipitation, lightning, and gusty winds. - Stratiform clouds (A) are associated with stable air masses. - Temperature falls, not rises (B), after a cold front passes. - Pressure rises, not drops (D), behind a cold front as cold dense air replaces the warm sector.
B)
Flying from LOWK (Klagenfurt, Austria) northward to EDDP (Leipzig, Germany), the aircraft moves into cooler air at higher latitudes, producing a gradual temperature decrease. The synoptic pattern on the chart indicates headwind conditions along this route and convective activity yielding isolated thunderstorms, particularly during summer.
Option C denies thunderstorm risk despite the synoptic instability shown.
Option D correctly predicts cooling and thunderstorms but wrongly identifies a tailwind.
D)
Cumulonimbus (Cb) clouds are massive convective clouds extending from near the surface to the tropopause, containing enormous quantities of water and ice sustained by powerful updrafts. They produce the heaviest showers, hail, and thunderstorms. - Nimbostratus (A) produces prolonged, steady precipitation but not heavy showers. - Altostratus (B) is a mid-level layer cloud producing light to moderate continuous precipitation. - Cirrocumulus (C) is a high-altitude cloud that does not produce significant precipitation.
B)
At high altitude, the wind is approximately geostrophic, blowing parallel to the isobars with low pressure to the left and high pressure to the right in the Northern Hemisphere. With low pressure to the north and high to the south, the pressure gradient force points northward, and the Coriolis deflection turns the resulting wind to the right — producing a westward (east-to-west) flow. The balloon is therefore carried toward the west.
D — Drag
B)
When terrain (mountains, ridges, or hills) mechanically forces air upward and this lifted air encounters moist, unstable layers aloft, the resulting convective storms are classified as orographic thunderstorms. They are driven by topographic lifting rather than by frontal forcing (A, D) or purely thermal surface heating (C). Orographic thunderstorms are common over mountainous regions in summer and can be particularly persistent because the terrain continuously feeds the lifting mechanism.
C)
Advection fog forms when warm, moist air moves horizontally over a colder surface and is cooled from below to its dew point. This commonly occurs when maritime tropical air flows over cold ocean currents or cold land in early spring. - Cold air over warm water (A) would produce steam fog (evaporation fog), not advection fog. - Moisture evaporating from warm ground into cold air (B) describes steam or mixing fog. - Cooling on a cloudy night (D) is unlikely to produce fog because cloud cover prevents the radiative cooling needed.
A)
Advection fog results from the horizontal transport (advection) of warm, moist air across a cold surface. The cold surface cools the air from below until it reaches its dew point, causing condensation at ground level.
B)
As a cold front approaches, pressure falls ahead of it due to the pre-frontal trough. At the moment of frontal passage, pressure reaches its minimum, and immediately afterward it begins to rise sharply as cold, dense air moves in behind the front. This characteristic "V-shaped" pressure trace — a brief fall followed by a sustained rise — is the textbook pressure signature of cold front passage.
A)
The polar front is the semi-permanent, quasi-continuous boundary zone separating warm subtropical air masses from cold polar air masses across the mid-latitudes, including Central Europe. It is the birthplace of extratropical cyclones. - A cold front (B) is the leading edge of a single advancing cold air mass within a cyclone. - A warm front (D) is the leading edge of advancing warm air. - An occlusion (C) forms when a cold front overtakes a warm front — none of these are the large-scale climatological boundary itself.
C)
Summer high-pressure areas over Central Europe produce widely spaced isobars, indicating weak synoptic-scale pressure gradients and therefore light prevailing winds. In the absence of strong gradient winds, locally driven thermal circulations — valley breezes, sea breezes, slope winds — develop and dominate the airflow pattern.
Option A contradicts itself (close isobars do not produce calm winds).
Option B describes strong westerlies associated with low-pressure systems.
B)
In winter, high-pressure areas produce subsidence inversions that trap cold, moist air near the surface, creating widespread high fog (Hochnebel) and stratus layers, particularly in valley and basin locations across Central Europe. Winds are light due to the weak pressure gradient.
Option C (squall lines and thunderstorms) requires convective instability absent in winter highs.
Option D describes summer high-pressure conditions with thermal cumulus development, not the foggy, grey winter anticyclone.
B)
The most dangerous airframe icing occurs between 0°C and -12°C because supercooled liquid water droplets are most abundant and largest in this temperature band. These droplets freeze on contact with aircraft surfaces, producing heavy ice accumulation. - Below -20°C (D), most cloud water has already frozen into ice crystals that bounce off rather than adhering. - The range +5° to -10°C (A) extends into above-freezing temperatures where icing cannot occur. - The range +20° to -5°C (C) is far too broad and mostly above freezing.
A)
Clear ice (also called glaze ice) forms when large supercooled water droplets strike an aircraft surface and flow back along it before freezing, creating a smooth, dense, transparent, and very heavy ice layer that closely conforms to the surface shape. It is the most dangerous type of airframe ice because it is difficult to detect and remove. - Rime ice (D) forms from small droplets that freeze instantly on contact, trapping air and creating a rough, white, opaque deposit. - Mixed ice (B) is a combination of both. - Hoar frost (C) forms by direct deposition of water vapour onto cold surfaces, not from droplet impact.
A)
Thermal thunderstorms require three ingredients working together: a conditionally unstable atmosphere (one that becomes fully unstable once air parcels reach saturation and the level of free convection), elevated surface temperatures to trigger strong thermals, and high humidity to supply the moisture and latent heat energy that fuels deep convection. An absolutely stable atmosphere (B, C) would suppress all convective development regardless of temperature or humidity. Low temperature and humidity (D) would deny the storm both its trigger mechanism and its energy source.
D)
The cumulus (initial/developing) stage of a thunderstorm is characterised exclusively by updrafts that build the cloud vertically from cumulus congestus toward cumulonimbus. No downdrafts or precipitation have yet developed. - The mature stage (A) features coexisting updrafts and downdrafts along with precipitation, turbulence, and lightning. - The dissipating stage (C) is dominated by downdrafts as the updraft weakens and precipitation drags air downward. "Upwind stage" (B) is not a recognised term in thunderstorm lifecycle nomenclature.
B)
Intense showers and thunderstorms produce powerful downdrafts (microbursts and downbursts) driven by precipitation drag and evaporative cooling. When these downdrafts hit the ground they spread outward, generating dangerous low-level wind shear that can cause sudden airspeed loss on approach. - Sea-breeze fronts (C) produce mild convergence, not heavy downdrafts. - Radiation fog nights (D) are calm with virtually no wind shear. - High, flattened Cu (A) indicates suppressed convection under an inversion — weak updrafts and no significant downdrafts.
D)
The surface weather chart (synoptic analysis chart) depicts observed mean sea-level pressure using isobars, identifies pressure centres (highs and lows) with their central pressures, and plots the positions of fronts (warm, cold, occluded, stationary) based on actual observations. - A prognostic chart (B) shows forecast conditions, not current observations. - A wind chart (C) displays wind vectors only. - A hypsometric chart (A) shows the height of constant-pressure surfaces aloft, not MSL pressure or surface fronts.
MSL = Mean Sea Level
C)
Satellite images (visible, infrared, and water vapour channels) provide a synoptic overview of cloud cover distribution, cloud type estimation, and the identification of frontal lines by recognising characteristic cloud patterns. - Turbulence and icing (A) cannot be directly measured by satellite — those require pilot reports or forecast models. - Temperature and dew point (B) are measured by radiosondes and surface stations. - Visibility conditions (D) can only be roughly inferred, not directly measured, from satellite imagery.
C)
ATIS (Automatic Terminal Information Service) broadcasts include operational aerodrome information such as the active runway, transition level, approach type in use, and relevant NOTAMs — none of which are encoded in a METAR. A METAR already contains precipitation types (A), visibility and cloud information (B), and wind speed including gusts (D). ATIS supplements the METAR with the operational data pilots need for arrival and departure.
C)
Cumulus clouds are the visible markers of thermal convection: warm air rises from the surface, cools adiabatically to the dew point, and condenses, forming the flat-based, cauliflower-topped cloud that glider pilots use to locate thermals. - Stratus (B) forms from broad, gentle lifting in stable air, not from thermals. - Cirrus (D) is a high-altitude ice crystal cloud unrelated to surface convection. - Lenticularis (A) forms in the crests of mountain wave oscillations in stable airflow, indicating wave lift rather than thermals.
B)
The saturated (moist) adiabatic lapse rate (SALR, averaging about 0.6°C/100 m) is lower than the dry adiabatic lapse rate (DALR, 1.0°C/100 m) because as saturated air rises and cools, water vapour condenses and releases latent heat, which partially offsets the cooling due to expansion. This means saturated air cools more slowly per unit of altitude gained. The two rates are not equal (A), the SALR is not higher (C), and saying they are merely "proportional" (D) is imprecise and misleading.
C)
The dry adiabatic lapse rate (DALR) is exactly 1.0°C per 100 m (or approximately 3°C per 1000 ft). This is the rate at which an unsaturated air parcel cools when rising (or warms when descending) purely due to adiabatic expansion or compression.
C)
Conditional instability means the atmosphere is stable for unsaturated air but becomes unstable once air parcels are lifted to saturation. When triggered — by surface heating, orographic lift, or frontal forcing — this instability produces vigorous convection: towering cumulus and cumulonimbus clouds with isolated showers and thunderstorms. - Clear skies (A) indicate absolute stability or dry conditions. - Layered clouds with prolonged rain (B) characterise absolutely stable (stratiform) weather. - Shallow mid-level cumulus (D) indicates limited instability insufficient for significant vertical development.
C)
The figure shows thin, wispy, high-altitude clouds with a delicate fibrous or streaky structure — the defining visual characteristics of cirrus clouds. Cirrus forms above approximately 6,000 m (FL200) and consists entirely of ice crystals, which produce its distinctive silky or hair-like appearance. - Stratus (A) is a grey, featureless layer cloud at low altitude. - Cumulus (B) has a well-defined, puffy vertical structure. - Altocumulus (D) appears as white or grey patches or layers of rounded masses at mid-level.
FL = Flight Level
C)
Medium to large precipitation particles (raindrops, hailstones) need time to grow by collision-coalescence or the Bergeron ice-crystal process, and strong updrafts keep droplets and ice crystals suspended in the cloud long enough for this growth to occur. Without sufficient updraft strength, particles fall out before reaching significant size. - An inversion layer (A) suppresses cloud growth and precipitation. - A high cloud base (B) reduces available cloud depth for particle growth. - Strong horizontal wind (D) does not contribute to the vertical suspension needed for particle growth.
B)
On standard synoptic weather charts, a warm front is depicted as a line with semicircles pointing in the direction of movement (into the colder air mass). The referenced figure shows symbol (2) matching this convention — semicircles on one side of the frontal line. - A cold front (A) uses triangular barbs pointing in the direction of advance. - An occlusion (D) uses alternating triangles and semicircles on the same side. - A front aloft (C) is marked with a different symbology indicating the front does not reach the surface.
C)
The warm sector lies between the warm front and the cold front, containing the warmest, most homogeneous air. During summer, this air mass typically offers moderate to good visibility with scattered or broken cloud layers — flyable VFR conditions. - Visibility below 1000 m with ground-covering cloud (A) is more typical of winter fog or orographic stratus. - Heavy showers and thunderstorms (D) are characteristic of the cold front itself, not the warm sector. - Few isolated high clouds (B) describe pre-frontal conditions well ahead of the system.
VFR = Visual Flight Rules
B)
After a cold front passes, cold, clean polar air replaces the warm sector. This unstable air mass produces excellent visibility between showers, with convective cumulus clouds developing from surface heating and occasional rain or snow showers from cumulus congestus.
D)
A polar front low (extratropical cyclone) is steered by the upper-level airflow, which is closely approximated by the direction of the isobars in the warm sector — the warm sector wind effectively carries the entire system along. This is a more reliable steering rule than fixed seasonal directions.
A)
The classic pressure trace of a passing polar front low follows three phases: pressure falls as the warm front approaches (the low draws nearer), pressure holds relatively steady in the warm sector between the two fronts, and pressure rises sharply after the cold front passes as cold, dense air replaces the warm sector.
Option B wrongly has pressure rising ahead of the warm front.
Option C has pressure falling behind the cold front, contradicting the arrival of dense cold air.
D)
In the Northern Hemisphere, as a typical polar front low passes, wind veers (shifts clockwise) at both frontal passages. At the warm front, wind veers from southeast to south or southwest. At the cold front, it veers again from southwest to west or northwest. This consistent clockwise shift indicates the low is passing to the north of the observer, which is the normal track for lows crossing Central Europe. Backing (A, B, C) would indicate the low passing to the south — an uncommon trajectory.
A)
When cold air intrudes into the upper troposphere, it reduces the thickness of the atmospheric column (cold air is denser and occupies less vertical space), causing the heights of upper pressure surfaces to drop. This creates an upper-level low or trough. These cold-pool lows aloft are potent triggers for convective instability and often initiate cyclogenesis at the surface. - An upper high (B) would form from warm-air advection, not cold intrusion. - Oscillating pressure (C) and a large surface low (D) are not the direct or primary consequence of upper-level cold intrusion.
C)
Cold air advecting into the upper troposphere steepens the lapse rate (cold air aloft over relatively warmer air below), producing conditional or even absolute instability. This destabilisation triggers convection, generating showers and thunderstorms — especially when combined with surface moisture and daytime heating. - Stabilisation and settled weather (A) and calm conditions (D) are the opposite of what cold upper-air intrusion produces. - Frontal weather (B) requires surface air-mass boundaries, which are not a direct result of upper-tropospheric cooling.
D)
Cold air is denser than warm air, so a cold air column has less vertical distance (decreased spacing) between any two pressure surfaces. Because the column is compressed, the upper pressure surfaces lie at lower geometric heights, which is identified as low pressure aloft on hypsometric charts. This is why upper-level lows are always associated with cold-core air masses. Warm air produces the opposite: increased spacing and raised heights (high pressure aloft), as described in options A and C.
B)
In summer, anticyclones bring subsiding air that warms adiabatically, suppressing deep convection and producing clear to partly cloudy skies with perhaps a few fair-weather cumulus (Cu humilis) from daytime thermal heating. The overall character is settled, warm, and dry. - Squall lines and thunderstorms (A) require convective instability not present in a well-established high. - Frontal passages (C) are features of low-pressure troughs. - Widespread high fog (D) is a winter high-pressure phenomenon caused by temperature inversions trapping cold moist air.
C)
On the windward (Stau) side during Foehn, moist air is forced to rise over the mountain barrier, cooling adiabatically and producing dense layered clouds (stratus, nimbostratus), obscured mountain peaks, poor visibility, and moderate to heavy orographic precipitation.
B)
Weather radar detects precipitation directly by measuring the intensity of microwave energy backscattered from raindrops, snowflakes, and hail. Radar imagery shows the precise location, extent, and intensity of precipitation areas in near-real-time. - A satellite picture (D) shows cloud cover but cannot directly distinguish precipitating from non-precipitating clouds. - A wind chart (A) displays wind patterns only. - A GAFOR (C) is a coded route forecast for general aviation that categorises flying conditions but does not depict precipitation areas graphically.
D)
An inversion is a layer of the atmosphere where temperature increases with altitude, which is the reverse ("inversion") of the normal tropospheric lapse rate. Inversions are extremely stable and act as lids that suppress convection, trap pollution, and limit thermal development for glider pilots.
C)
Radiation fog requires the ground to radiate longwave heat to space, cooling the surface air to the dew point. An overcast cloud layer acts as a blanket, absorbing and re-emitting radiation back toward the ground, preventing the surface from cooling sufficiently. Therefore, overcast cloud cover prevents radiation fog formation. A clear night (A), low spread (B), and calm wind (D) all favour fog formation — they are prerequisites, not preventative conditions.
C)
An occluded front is depicted on synoptic charts by a line combining both the cold front triangles and the warm front semicircles on the same side, representing the merger of the two fronts when the faster-moving cold front overtakes the warm front. Symbol (3) in figure shows this combined symbology, identifying it as an occlusion. - A warm front (A) uses only semicircles. - A cold front (B) uses only triangles. - A front aloft (D) has a distinct marking indicating the frontal surface does not reach the ground.
C)
A stationary front is a boundary between two contrasting air masses — here polar and subtropical — that is not moving significantly in either direction. Neither the cold air nor the warm air is advancing. - A cold front (D) is specifically an advancing cold air mass pushing warm air aside. - A warm front (A) is advancing warm air overriding cold air. - An occluded front (B) results from a cold front overtaking a warm front within a mature cyclone — it involves merging fronts, not stationary boundaries.
B)
An active shower near an airfield indicates ongoing convective downdrafts and outflow boundaries that create severe, rapidly changing low-level wind shear — a critical hazard during takeoff and landing. The gust front from a nearby shower can change wind direction and speed dramatically within seconds. - Cross-country flying below moderate Cu (A) involves normal soaring conditions. - Thirty minutes after a shower (C), conditions have typically stabilised. - Cirrus ahead of a warm front (D) is an upper-level indicator without immediate low-level shear implications.
C)
Haze (HZ) is caused by dry particulates — dust, smoke, industrial pollution, and fine sand — suspended in the atmosphere. Because these particles are not moisture-dependent, haze persists regardless of temperature changes. Mist (A), fog patches (B), and radiation fog (D) are all formed by water droplet suspension and are highly sensitive to temperature: warming evaporates the droplets and improves visibility, while cooling promotes further condensation and worsens it.
C)
In METAR format, the descriptor "SH" (shower) is combined with the precipitation type "RA" (rain) to form "SHRA," which denotes moderate showers of rain. No intensity prefix means moderate. "+RA" (B) indicates heavy continuous rain, not a shower. "TS" (A) denotes a thunderstorm without specifying precipitation type. "+TSRA" (D) indicates a heavy thunderstorm with rain — a more severe phenomenon than a simple rain shower.
METAR = Aerodrome routine weather report
B)
SIGMET (Significant Meteorological Information) warnings are issued for Flight Information Regions (FIRs) and Upper Information Regions (UIRs), which are standardised ICAO airspace blocks managed by specific ATC authorities. They warn of hazardous weather phenomena (severe turbulence, icing, volcanic ash, thunderstorms) within these defined airspace volumes. - SIGMETs are not issued for individual airports (A) — those use AIRMETs or aerodrome warnings. - They are not route-specific (C) or country-specific (D), as a single country may contain multiple FIRs.
D)
Solar heating on the windward slope warms the surface air, making it less dense and creating anabatic (upslope) flow that combines with the mechanical orographic lift from the oncoming wind, significantly strengthening the updraft. This is why south- and west-facing slopes in the Northern Hemisphere often produce the strongest lift during sunny afternoons.
D)
The prefix "Cirro-" identifies clouds in the high cloud family, typically found above approximately 6000 m (FL200) in mid-latitudes, and includes cirrus, cirrocumulus, and cirrostratus — all composed primarily of ice crystals.
FL = Flight Level
A)
An inversion layer creates a zone where temperature increases with altitude, forming a highly stable lid that stops rising thermals from penetrating further upward. Cumulus clouds reaching this barrier flatten out and spread horizontally rather than continuing to develop vertically, which is why fair-weather cumulus often have a uniform top height.
C)
A small spread (temperature close to dew point) means the air is already near saturation, and falling temperature will close the remaining gap, causing condensation at or near the surface — fog. These are the classic pre-fog conditions monitored by pilots and forecasters.
D)
Orographic fog (hill fog) forms when warm, moist air is forced to ascend over elevated terrain, cooling adiabatically until it reaches the dew point and condenses. The resulting cloud envelops the hill or mountain and appears as fog to anyone on the slope or summit.
C)
Precipitation particles need time to grow large enough to fall against the updraft, either through collision-coalescence (warm rain process) or the Bergeron ice-crystal process. Moderate to strong updrafts keep water droplets and ice crystals suspended in the cloud long enough for this growth to occur.
D)
Widely spaced isobars indicate a weak horizontal pressure gradient, which produces only light synoptic-scale winds. In the absence of a dominant pressure-driven flow, local thermally driven wind systems — such as valley-mountain breezes, sea-land breezes, and slope winds — become the primary circulation features, with wind direction varying throughout the day.
D)
"Back-side weather" (Rückseitenwetter) describes the conditions in the cold, unstable polar air mass that follows behind a cold front on the western or northwestern side of a low-pressure system. It is characterized by good visibility, convective cumulus clouds, and scattered showers or snow showers.
D)
In aviation weather reporting, wind is always given as the direction FROM which it blows (in degrees true) followed by speed in knots. A report of 225/15 means wind from 225 degrees (southwest) at 15 knots.
D)
During Foehn in the Bavarian pre-alpine region, the prevailing southerly flow forces moist air up the southern (Italian) side of the Alps, producing nimbostratus and heavy orographic precipitation there. As the air descends on the northern (Bavarian) lee side, it warms adiabatically and dries out, creating the characteristic warm, dry, gusty Foehn wind. Rotor clouds and lenticular clouds form on the lee side due to wave activity.
D)
The fundamental cloud classification divides all clouds into two basic forms based on their physical formation process: cumuliform (convective, vertically developed clouds formed by localized updrafts) and stratiform (layered, horizontally extended clouds formed by widespread, gentle lifting or cooling). All other cloud types and subtypes derive from combinations of these two basic forms.
C)
On the lee side during Foehn conditions, the descending air creates standing wave patterns downwind of the mountain ridge. These waves produce Altocumulus lenticularis — smooth, lens-shaped or almond-shaped clouds that remain stationary relative to the terrain despite strong winds passing through them. They are a hallmark of mountain wave activity.
C)
Rime ice forms when very small supercooled water droplets freeze instantly upon contact with the aircraft's leading edges, trapping air between the frozen particles and creating a rough, white, opaque deposit. Because the droplets are so small, they freeze before they can spread, resulting in the characteristic granular texture.
B)
The surface weather chart (synoptic analysis chart) is the primary meteorological product displaying isobars (lines of equal pressure at MSL), the locations of highs and lows, and the positions and types of fronts (warm, cold, occluded, stationary).
MSL = Mean Sea Level
C)
The approach of a warm front produces a characteristic descending cloud sequence as the warm air gradually overrides the retreating cold air mass. First, thin cirrus appears at high altitude, followed by cirrostratus, then progressively thickening altostratus and altocumulus at mid-levels, and finally nimbostratus with a low cloud base and prolonged steady rain.
D)
In a mature thunderstorm, precipitation drags cold air downward in powerful downdrafts. When this cold, dense air reaches the surface, it spreads outward rapidly as a density current, creating a gust front — a sharp boundary marked by sudden wind shifts, temperature drops, and gusty conditions that can extend several kilometres ahead of the storm.
D)
Low-Level Significant Weather Charts are forecast products that depict meteorological hazards below a specified altitude, including frontal systems and their movement (option A), turbulence areas (option B), and icing conditions (option C). However, they do not contain radar echoes of precipitation (option D) because radar imagery is a real-time observational product, whereas LLSWC are prognostic charts prepared in advance. Precipitation areas may be indicated symbolically on LLSWC, but actual radar returns are found only on separate radar displays.
C)
Nimbostratus (Ns) is a thick, dark grey, amorphous layer cloud that produces continuous, steady precipitation (rain or snow) over wide areas, typically associated with warm fronts or occlusions. Its great vertical and horizontal extent ensures prolonged precipitation reaching the ground.
D)
Meteorological classification of precipitation by cloud type distinguishes two fundamental categories: rain (steady, continuous precipitation from stratiform clouds like nimbostratus) and showers of rain (intermittent, convective precipitation from cumuliform clouds like cumulonimbus or cumulus congestus). This distinction reflects the physical formation process — widespread lifting versus localized convection.
D)
Thunderstorm development requires three essential ingredients: moisture (warm, humid air provides the latent heat fuel), instability (a conditionally unstable lapse rate allows saturated air parcels to accelerate upward), and a lifting mechanism (fronts, orographic forcing, or surface heating).
Option D combines the first two ingredients explicitly.
Option A describes calm, stable nighttime conditions favouring radiation fog, not convection.
B)
The spacing of isobars on a surface weather chart is inversely proportional to the pressure gradient: widely spaced isobars mean a small pressure difference over a large distance (weak gradient), which produces only light wind. Wind speed is directly driven by the pressure gradient force, so a weak gradient means weak wind.
C)
Air masses are classified by their source region's surface characteristics. Air originating over the vast, snow-covered Russian (Siberian) continent during winter acquires cold temperatures and very low moisture content, making it Continental Polar (cP). This air mass brings bitterly cold, dry conditions to Central Europe when it advects westward.
A)
Cold front passage is marked by a narrow band of intense weather as the advancing cold air undercuts the warm air, forcing it rapidly aloft. This produces strongly developed cumulonimbus (Cb) clouds, heavy rain showers, thunderstorms, and gusty winds along the frontal line, followed by cumulus with isolated showers in the cold, unstable air behind the front.
C)
The most immediate physical danger from a lightning strike is surface overheating at the attachment and exit points, along with damage to exposed components such as antennas, pitot tubes, wingtips, and control surface edges. The extreme heat at the strike points can burn through thin skins, pit metal surfaces, and damage composite materials.
B)
Mountain wind (Bergwind) is a katabatic flow that occurs at night when mountain slopes cool by radiation faster than the free atmosphere at the same altitude. The cooled, denser air drains downslope under gravity toward the valley floor. This is part of the diurnal mountain-valley wind cycle.
D)
The saturated (moist) adiabatic lapse rate averages approximately 0.6 degrees C per 100 m. It is lower than the dry adiabatic lapse rate (1.0 degrees C per 100 m) because latent heat released during condensation partially offsets the cooling of the ascending air parcel.
B)
The subtropical high-pressure belt at approximately 30 degrees N and S latitude is a semi-permanent feature of the global atmospheric circulation, created by the descending branch of the Hadley cell. Warm air rising near the equator flows poleward aloft, cools, and subsides in the subtropics, forming persistent anticyclones over the oceans (e.g., the Azores High, the Pacific High).
B)
ATIS (Automatic Terminal Information Service) is a continuous broadcast available on a dedicated frequency at equipped aerodromes, providing current weather observations, active runway, transition level, approach procedures, and relevant NOTAMs specific to that aerodrome. Pilots tune in to the ATIS frequency during flight to obtain up-to-date destination information.
A)
The cloud in figure is cumulus, identifiable by its characteristic flat base (marking the condensation level) and vertically developed, cauliflower-like top with sharp white outlines against the blue sky. Cumulus clouds form through thermal convection and are the clouds most associated with soaring flight.
B)
An air mass acquires its temperature and moisture properties from the surface conditions of its source region (e.g., polar continent, tropical ocean) and then modifies as it travels over different surfaces along its trajectory. Both the origin (which sets the initial character) and the path (which modifies it) are essential for classifying and forecasting air mass behaviour.
C)
In summer anticyclones, surface heating generates thermal convection that produces scattered fair-weather Cumulus clouds (Cu humilis or Cu mediocris) during the day, dissipating in the evening. Overcast low stratus (option D) is associated with stable, moist air at low levels, common in autumn or maritime high-pressure situations. Nimbostratus (option B) is associated with frontal systems. Squall lines and thunderstorms (option A) require convective instability and moisture not typical of settled high-pressure conditions.
C)
On a surface weather chart, a cold front is depicted by a line with solid triangular spikes (barbs) pointing in the direction of movement. The symbol labeled (1) in figure matches the cold front symbol. A warm front uses semicircles. An occlusion uses alternating triangles and semicircles. A front aloft is depicted differently and is less commonly shown on basic surface charts.
C)
In METAR codes, precipitation intensity is indicated by a '+' prefix (heavy) or '-' prefix (light); no prefix means moderate. Rain is coded 'RA'. Therefore heavy rain is '+RA' (written as '+RA' in the standard, shown in the options as '.+RA'). 'RA' alone (option B) means moderate rain. 'SHRA' (option D) means shower of rain (moderate). '+SHRA' (option A) means heavy shower of rain — a convective shower, not continuous heavy rain.
METAR = Aerodrome routine weather report
C)
In the mature stage of a thunderstorm, both strong updrafts (sustaining the storm) and strong downdrafts (driven by precipitation drag and evaporative cooling) coexist simultaneously within the Cumulonimbus cell. The initial (cumulus) stage has only updrafts. The dissipating stage is dominated by downdrafts only, which cut off the updraft supply and weaken the storm. 'Thunderstorm stage' (option A) is not a recognised meteorological term.
B)
The most severe icing occurs between 0°C and -12°C where supercooled liquid water droplets are most abundant and drop size is largest, producing clear or mixed icing on airframe surfaces. Below -20°C, cloud water is mostly in ice crystal form and causes much less accretion. Above 0°C, droplets are not supercooled and do not freeze on contact. Icing in clear air (option D) does not occur as there are no supercooled droplets. Cirrus (option C) contains ice crystals which do not adhere significantly.
B)
When strong wind blows perpendicular to a mountain ridge, orographic lift on the windward side and mechanical turbulence create complex wind shear on the lee side. An aircraft descending into a valley airfield on the lee side may encounter severe wind shear with the wind reversing by up to 180° between altitudes, creating sudden loss of airspeed or ground wind opposite to the upper-level flow. Reduced visibility (option C) is a secondary concern. Icing (option D) is unrelated to mountain wind shear. Heavy downdrafts in rainfall (option A) describes thunderstorm activity, not orographic flow.
C)
Blue thermals are thermals that extend to significant altitude but remain below the condensation level (dew point height), so no Cumulus clouds form — the sky appears clear (blue). They are invisible to glider pilots and require instruments or experience to exploit.
Option D confuses thermals with cloud coverage statistics.
Option B describes sink between Cu clouds.
C)
The 'beginning of thermals' (Thermikbeginn) is the moment when thermal lift becomes sufficiently strong and deep (reaching at least 600 m AGL) for a glider to sustain flight and gain height — this is the practical definition. It does not require Cu cloud formation (option A), nor does it specify a fixed MSL altitude (option B).
B)
The trigger temperature is the minimum ground temperature that must be reached before thermals are strong enough to carry air parcels to the condensation level and form Cumulus clouds. It is found on a tephigram or skew-T diagram by tracing the dry adiabatic lapse rate from the surface intersection until it meets the temperature profile.
Options A and C misstate it as a temperature reached aloft or a threshold for thunderstorm formation.
Option D describes thunderstorm formation, not Cu formation.
C)
Over-development (Überentwicklung) occurs when Cumulus clouds develop vertically beyond Cu congestus into rain-producing Cumulonimbus clouds, generating showers and thunderstorms. This typically happens in the afternoon when the atmosphere becomes increasingly unstable.
C)
Shielding (Abschirmung) refers to a layer of high or mid-level cloud (such as Cirrostratus, Altostratus, or Altocumulus) that intercepts solar radiation before it reaches the ground, thus reducing or suppressing the surface heating required for thermal development.
A)
Dry air is composed of approximately 78% nitrogen, 21% oxygen, and 1% argon and trace gases including carbon dioxide. This is the standard atmospheric composition. All other options incorrectly swap the proportions of nitrogen and oxygen or introduce water vapour as a major component. Water vapour is a variable constituent (0–4%) not included in the standard dry air composition.
C)
At MSL under ISA conditions, the standard air density is 1.225 kg/m³. A cube with 1 m edges has a volume of 1 m³, so its mass is 1.225 kg.
D)
The tropopause is the boundary layer separating the troposphere (where temperature decreases with altitude) from the stratosphere (where temperature is initially constant and then increases due to ozone absorption). It is not the layer above the troposphere (option C), nor the height where temperature starts to decrease (option A — that is the surface of the troposphere).
D)
An inversion layer is an atmospheric layer in which temperature increases with increasing altitude, the reverse ('inversion') of the normal decrease. Inversions suppress vertical mixing and convection, trapping pollutants and inhibiting thermal development above them.
D)
An isothermal layer is one in which temperature remains constant with increasing altitude — neither increasing (inversion, option A) nor decreasing (normal lapse rate, option C). Isothermal conditions are found, for example, in the lower stratosphere.
D)
Wind is caused by the pressure gradient force — air flows from areas of high pressure to areas of low pressure, and the greater the pressure difference over a given distance, the stronger the resulting wind. The Coriolis force (option B) deflects wind but does not create it. Centrifugal force (option C) is a secondary effect in curved flow. There is no meteorological force specifically called 'thermal force'; thermal differences drive pressure gradients, but the direct cause of wind is the pressure gradient itself.
A)
Foehn develops when a stable airflow is forced over a mountain barrier. On the windward side, the air rises moist-adiabatically (condensation releasing latent heat), and on the lee side it descends dry-adiabatically, arriving warmer and drier than before ascent. Stability is necessary for the organised flow; instability would break the flow into convective cells. Calm high-pressure conditions (options B and C) do not provide the cross-mountain pressure gradient needed. Instability (option D) would prevent the laminar flow characteristic of Foehn.
C)
The spread (or dew-point spread) is the difference between the actual (dry-bulb) air temperature and the dew point temperature. A small spread indicates air close to saturation; when the spread reaches zero, condensation and fog or cloud formation occur.
B)
This question is identical in content to question 90. During Foehn, the descending and warming lee-side flow is stable and generates standing wave clouds. Altocumulus lenticularis forms in the crests of these mountain waves on the lee side. Cumulonimbus (options C and D) requires strong convective instability absent in Foehn descent. Altocumulus Castellanus (option A) indicates mid-level instability, not the stable wave motion of a Foehn situation.
C)
Radiation fog forms on clear, calm nights when the ground radiates heat to space, cooling the surface air to its dew point. An overcast cloud cover prevents the necessary radiative cooling of the ground surface by acting as an insulating blanket, reflecting long-wave radiation back to the ground. Calm wind (option B) is actually a prerequisite for radiation fog formation. A clear night (option D) and low spread (option A) are also favourable, not preventative, conditions.
B)
Advection fog forms when warm, moist air is transported (advected) horizontally over a cold surface and cooled from below to its dew point. This is most common over cold ocean currents or cold land surfaces in spring.
Option D reverses the temperature relationship.
Option C describes mixing fog (a different type).
A)
Orographic fog (hill fog) forms when moist air is forced to rise over terrain, cooling adiabatically until it reaches its dew point; the result is a cloud base that sits on the hillside or mountain top.
A)
An upper-level trough is a region of cold air aloft with positive vorticity advection, which promotes divergence aloft and convergence at the surface, triggering strong convective uplift. This instability favours the development of showers and thunderstorms (Cumulonimbus).
B)
On the windward (stau) side of a mountain range during Foehn, moist air is forced to rise and cool, producing dense cloud, obscured peaks, poor visibility, and moderate to heavy rain or snow — the classic 'Stau' weather.
C)
The surface weather chart (also called the synoptic chart or analysis chart) displays actual measured pressure values reduced to MSL as isobars, along with the positions of frontal systems. It represents the observed state of the atmosphere at a specific time. A prognostic chart (option B) shows forecast conditions. The hypsometric chart (option D) shows upper-level contour heights on constant-pressure surfaces. The SWC (option A) focuses on hazardous weather phenomena, not comprehensive pressure analysis.
MSL = Mean Sea Level
C)
This question is identical to question 120. In METAR, precipitation intensity modifiers are '+' for heavy and '-' for light. 'RA' is the METAR code for rain; therefore '+RA' (shown as '.+RA' in the options) denotes heavy rain. 'RA' (option D) alone means moderate rain. 'SHRA' (option A) is shower of rain. '+SHRA' (option B) is heavy shower of rain — a different precipitation type.
METAR = Aerodrome routine weather report
D)
In METAR, the descriptor 'SH' (shower) is added before the precipitation code to indicate convective precipitation from cumuliform clouds. Moderate showers of rain are therefore coded 'SHRA'. '+TSRA' (option C) means heavy thunderstorm with rain. 'TS' (option B) means thunderstorm without precipitation modifier. '+RA' (option A) means heavy continuous rain from stratiform clouds, not a shower.
METAR = Aerodrome routine weather report
C)
Back-side weather (Rückseitenwetter) describes the weather in the cold air mass following the passage of a cold front: cold, unstable polar or arctic air with scattered showers, good visibility, and gusty winds — often excellent soaring conditions for gliders in the convective back-side air. It occurs after, not before, frontal passages. An occlusion (option D) combines warm and cold front characteristics. Foehn (option B) is a separate orographic phenomenon. After a warm front (option A) brings the warm sector, not cold back-side air.
A)
In the International Standard Atmosphere (ISA), the temperature at MSL is +15°C, and the temperature decreases at 6.5°C per 1000 m (2°C per 1000 ft) through the troposphere. At approximately 11,000 m (the tropopause), the temperature reaches -56.5°C, rounding to approximately -50°C at 10,000 m.
C)
Classic Bavarian Foehn is driven by low pressure over the Gulf of Genoa and high pressure over the North Sea, forcing air southward over the Alps. Nimbostratus forms on the south (windward) side of the Alps, while on the north (lee) Bavarian side, warm and dry air descends, often accompanied by Föhnmauer (Foehn wall) and rotor clouds along the Foehn boundary.
C)
For visual flight rules (VFR), horizontal visibility is the most critical element: below the regulatory minimum, the pilot can no longer maintain separation from terrain, obstacles, and other aircraft by sight alone. Wind direction, temperature, and cloud cover above 1500 m are important, but it is low clouds and reduced visibility that directly trigger VFR restrictions. The amount and height of clouds below 1500 m/GND (ceiling) is also critical, as a low ceiling can trap the pilot.
C)
Fog can reduce visibility to a few meters, or even less than 100 m, making it by far the most severe visibility reduction in surface meteorology. Foehn is generally associated with excellent visibility. High pressure often favors clear skies, except in winter where inversions can produce fog or stratus. A polar air mass can bring snow showers, but these reduce visibility less drastically than thick fog.
B)
Gaseous embolism (blood boiling) occurs when ambient pressure drops below the vapour pressure of human blood (approximately 47 hPa). This corresponds to about 19,000 m under standard conditions, but serious physiological problems related to extreme low pressure (outgassing of tissues) begin to manifest around 13,000 m/AMSL. This is why this altitude is used as the critical danger threshold in aviation regulations.
C)
The mercury barometer works thanks to the partial vacuum created at the top of the sealed tube: when the tube is inverted in a mercury trough, atmospheric pressure supports a mercury column of approximately 760 mm, leaving a nearly vacuum space at the top (Torricelli vacuum). If there were air, nitrogen, or significant water vapour pressure, these would oppose the rise of mercury and distort the measurement.
B)
The mercury barometer measures atmospheric pressure by balancing the weight of a mercury column against air pressure. The thermometer measures temperature, the psychrometer measures relative humidity (by the difference between dry-bulb and wet-bulb thermometers), and the Magdeburg hemispheres were a historical demonstration of atmospheric pressure, not a standard measuring instrument.
C)
The anemometer (in particular the cup anemometer) is the standard instrument for measuring wind speed at meteorological stations. The windsock and weather flag give approximate visual indications but do not provide precise measurements. Kites were used historically by pioneers such as Benjamin Franklin but are not standard measuring instruments. Ultrasonic and hot-wire anemometers are modern variants.
C)
The wind polygon (frequency rose) shows, for each directional sector, the frequency and average speed of winds observed over a long period at a given location - very useful for planning runway orientation. The wind rose is the figure showing the 16 cardinal and intercardinal directions, but it is not a statistical chart. The wind triangle is an air navigation tool (drift calculation). Isotachs are lines of equal wind speed on a weather chart.
C)
The polar jet stream is a band of very strong winds (often 100-300 km/h) that forms at the boundary between cold polar air and warm subtropical air, in the upper troposphere (approximately 8-12 km altitude), near the tropopause. It results from the strong horizontal temperature gradient between these air masses. Its effect on the upper-level pressure gradient is significant and it guides the track of depressions at our latitudes.
A)
Mechanical turbulence generated by airflow around an obstacle (building, tree, hill) is most intense in the immediate downstream zone, up to approximately 150 m above the top of the obstacle. In this zone, eddies and wind shear are at a maximum. Beyond this, turbulence gradually decreases with altitude. For approach and landing, it is therefore recommended to maintain a minimum altitude margin of 150 m above obstacles upstream of the runway.
D)
The strongest turbulence results from the combination of thermal and mechanical effects: strong wind (25 kt) generates significant mechanical turbulence over hilly terrain. The presence of 5/8 cumulus indicates active thermal convection. This combination - strong wind plus relief plus convection - produces turbulence far exceeding what either factor alone would generate. Calm wind produces only weak thermals, and a clear sky with strong wind gives mainly mechanical turbulence without thermal reinforcement.
C)
Supercooled water is liquid water that remains in liquid state even when its temperature is below 0°C (down to approximately -40°C). This is possible because very pure droplets suspended in clouds lack freezing nuclei. Supercooled water is particularly dangerous for aviation because it freezes instantly on contact with the cold surface of an aircraft, producing rime or clear ice. It is encountered mainly in cumulus, altocumulus, and nimbostratus between 0°C and -20°C.
B)
The precipitation zone associated with a cold front is narrow (approximately 90-100 km) but intense: the cold front advances rapidly, forcing warm air to rise violently. This produces cumulonimbus clouds with heavy showers, thunderstorms, and sometimes hail. In contrast, the warm front has a much wider precipitation zone (150-300 km) but more continuous and less intense. This width difference explains why cold front disturbances are brief and violent, while warm front ones are long and gradual.
B)
Advancing from cold air (polar air mass with good visibility) toward a warm front, the pilot encounters a progressive deterioration: cirrus thickens to cirrostratus, then altostratus, the ceiling lowers, and precipitation begins (rain or drizzle). Visibility deteriorates as the cloud layer thickens and precipitation becomes continuous. This gradual degradation gradient is a typical characteristic of warm front approach, in contrast to the cold front which abruptly deteriorates then rapidly improves conditions.
C)
The warm front is characterized by a gently sloping frontal surface (approximately 1:100 to 1:150), meaning warm air rises very gradually over cold air across a large horizontal distance. This creates a wide precipitation band (150-300 km) extending well ahead of the surface front position. Precipitation is generally continuous, less intense than for a cold front, and accompanied by nimbostratus and altostratus.
B)
Approaching a warm front, the typical cloud sequence begins with high-altitude cirrus (very high base), followed by cirrostratus, altostratus, and then nimbostratus whose base can be very low (a few hundred metres). This ceiling drops gradually as the pilot approaches the front - a progressive warning that allows time to react, in contrast to the cold front which abruptly deteriorates conditions.
B)
An occlusion forms when the cold front, which advances faster, catches up with the warm front and lifts the warm sector off the ground. The most active zone - with the strongest winds, most intense precipitation, and most likely thunderstorms - is near the triple point (occlusion point), where both fronts meet and available energy is at its maximum. At the extremities of the occlusion, activity decreases progressively.
A)
By international meteorological convention, mist is reported when visibility is between 1000 m and 8000 m due to the presence of fine water droplets or ice crystals in suspension. Below 1000 m visibility caused by condensed water vapour, the phenomenon is called fog. Above 8000 m, visibility is considered good. This distinction is important for METARs and VFR conditions.
C)
Fog forms when air is saturated, i.e., when air temperature drops to the dew point (or humidity increases to saturation). At this point, relative humidity reaches 100% and water vapour begins to condense into fine suspended droplets. Temperature and dew point therefore become practically equal, while relative humidity approaches 100%. Option D is incorrect because relative humidity is a different quantity from temperature.
A)
A cumulonimbus (thunderstorm cloud) passes through three well-defined stages. The build-up stage (or cumulus stage): dominant updrafts, the cell grows upward. The mature stage (stabilisation): intense updrafts and downdrafts coexist - this is the most dangerous stage with lightning, hail, violent gusts, and heavy precipitation. The dissipation stage: downdrafts dominate, the cloud gradually evaporates and the thunderstorm weakens.
C)
Icing is particularly critical for gliders: their performance depends on a very precise wing profile with thin margins. Ice accumulating on the leading edge deforms the aerofoil profile, increases drag and reduces lift, lowers the stall speed, and adds weight. These combined effects can make the aircraft uncontrollable within minutes. Unlike powered aircraft, gliders generally have no anti-icing systems, making them extremely vulnerable. Preventive avoidance is the only effective measure.
