Source: exam.quizvds.it (EASA ECQB-SPL) | 150 questions
Correct: A)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: B)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: B)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: D)
Explanation: Advection fog forms when warm, humid air moves horizontally over a cold surface (land or sea), cooling the air to its dew point. Option A describes radiation fog (not advection), option B is incorrect because cold air over a warm ocean would create evaporation/steam fog, not advection fog, and option C describes steam or evaporation fog.
Correct: D)
Explanation: Advection fog results from the horizontal movement of warm, moist air over a cold surface, which cools the air from below until it reaches its dew point. Option A reverses the temperature relationship (cold air over warm ground would not produce fog this way), option B describes mixing fog, and option C describes radiation fog caused by nocturnal cooling.
Correct: B)
Explanation: As a cold front approaches, pressure falls ahead of it due to the preceding low-pressure trough; once the front passes, colder, denser air causes pressure to rise again. Option A (continually increasing) would indicate persistent high pressure building, option C (continually decreasing) describes a deepening low without frontal passage, and option D (constant) is inconsistent with dynamic frontal systems.
Correct: D)
Explanation: The polar front is the semi-permanent boundary separating cold polar air masses from warmer subtropical air, and it is the birthplace of mid-latitude cyclones affecting Central Europe. A warm front is the leading edge of an advancing warm air mass, a cold front is the leading edge of an advancing cold air mass, and an occlusion is a later stage where these fronts merge — none of these are the primary climatological boundary itself.
Correct: A)
Explanation: In summer, high pressure areas over Central Europe produce widely spaced isobars, meaning weak pressure gradients and calm synoptic winds; this allows local thermally driven wind systems (valley breezes, sea breezes) to develop. Option B is wrong because small isobar spacing means strong winds, not calm. Options C and D describe conditions more typical of strong synoptic flow associated with low-pressure systems.
Correct: A)
Explanation: In winter, high pressure areas favour calm winds and surface-based temperature inversions that trap moisture near the ground, leading to widespread high fog (Hochnebel) or stratus. Option B (frontal weather) is associated with lows, option C (thunderstorms) requires instability absent in winter highs, and option D describes summer high-pressure conditions.
Correct: D)
Explanation: The most dangerous icing temperatures are 0°C to −12°C because liquid water droplets remain supercooled and in large quantities at these temperatures, maximising ice accretion on airframes. Above +5°C ice cannot form, and below −20°C to −40°C most water has already frozen into ice crystals which do not adhere as readily to surfaces.
Correct: B)
Explanation: Clear ice (glaze ice) forms when large supercooled water droplets strike an aircraft, flow back before freezing, and solidify into a dense, smooth, heavy layer that is very difficult to remove. Hoar frost forms from deposition of water vapour on cold surfaces. Rime ice forms from small supercooled droplets that freeze on contact, trapping air and producing a white, opaque, brittle deposit. Mixed ice combines both rime and clear ice characteristics but is not the primary type formed from large droplets.
Correct: C)
Explanation: Thermal (air mass) thunderstorms require a conditionally unstable atmosphere — one that becomes unstable once convection is triggered — combined with high temperatures to drive strong surface heating and high humidity to provide the latent heat energy needed to sustain deep convection. An absolutely stable atmosphere suppresses convection regardless of temperature or humidity, and low humidity limits latent heat release needed to fuel the storm.
Correct: C)
Explanation: The cumulus stage is characterised entirely by updrafts that build the storm upward; no downdrafts have yet developed. The mature stage features both strong updrafts and downdrafts along with precipitation. The dissipating stage is dominated by downdrafts as the updraft cuts off. There is no meteorological stage called the 'upwind stage'.
Correct: A)
Explanation: Precipitation falling from heavy showers or thunderstorms creates strong downdrafts (microbursts or downbursts) that spread outward near the ground, generating intense low-level wind shear. A sea-breeze front can cause some shear but not 'heavy' downdrafts. Radiation fog nights are associated with calm conditions. Flat cumulus clouds on warm days indicate weak convection without significant downdrafts.
Correct: B)
Explanation: A surface weather chart (synoptic chart) depicts mean sea-level pressure via isobars, identifies pressure centres (highs and lows), and shows the positions of weather fronts derived from actual observations. A wind chart shows wind data only, a prognostic chart shows forecast conditions, and a hypsometric chart shows terrain elevation.
Correct: A)
Explanation: Satellite imagery shows cloud cover distribution, cloud patterns, and derived front line positions across large areas. It cannot directly measure turbulence, icing, temperature/dew point profiles (those come from soundings), or quantify ground visibility — those require other observational systems.
Correct: A)
Explanation: ATIS (Automatic Terminal Information Service) includes operational airport information such as the runway in use, transition level, approach type, and NOTAMs relevant to the aerodrome, which are not encoded in a METAR. A METAR does report current weather phenomena (precipitation types), visibility, cloud base, wind mean and gust speeds — so options B, C, and D are all available in METARs.
Correct: C)
Explanation: Cumulus clouds form as a result of thermal convection: rising air parcels cool to the dew point and condensation begins, marking the cloud base. Stratus is a layered cloud formed by broad lifting or fog, not thermals. Cirrus is high-altitude ice crystal cloud unrelated to surface thermals. Lenticularis (lenticular clouds) form in wave lift over mountains, not thermals.
Correct: B)
Explanation: 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.
Correct: B)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: B)
Explanation: 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.
Correct: A)
Explanation: 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).
Correct: D)
Explanation: The saturated (moist) adiabatic lapse rate (SALR, ~0.6°C/100 m on average) is lower than the dry adiabatic lapse rate (DALR, 1.0°C/100 m) because the condensation of water vapour releases latent heat, partially offsetting the cooling of the rising air parcel. The two rates are not equal (option A), not proportional in the way option C implies, and the SALR is definitely not higher than the DALR (option B).
Correct: B)
Explanation: The dry adiabatic lapse rate (DALR) is 1.0°C per 100 m (or approximately 3°F per 1000 ft). An unsaturated air parcel rising adiabatically cools at exactly this rate. Option A (0.65°C/100 m) is the standard atmosphere environmental lapse rate, option C (2°/1000 ft) is incorrect, and option D (0.6°C/100 m) approximates the saturated adiabatic lapse rate.
Correct: A)
Explanation: In a conditionally unstable atmosphere, air is stable when unsaturated but becomes unstable once lifted to saturation (the level of free convection). This triggers vigorous convection producing towering cumulus, cumulonimbus, isolated showers and thunderstorms. Layered clouds and prolonged rain characterise stable (stratiform) conditions, clear skies indicate absolutely stable or dry conditions, and shallow mid-level cumulus does not match the vertical extent of conditional instability.
Correct: B)
Explanation: Cirrus clouds are thin, wispy, high-altitude ice crystal clouds, typically above FL200. Their characteristic streaky or fibrous appearance is shown in the referenced figure MET-004. Altocumulus is a mid-level cloud in patches or layers, cumulus is a heap cloud at lower levels, and stratus is a grey featureless layer cloud.
Correct: A)
Explanation: Formation of medium to large precipitation particles requires strong updrafts to keep droplets or ice particles suspended long enough to grow by collision-coalescence or the Bergeron process. Weak updrafts allow small particles to fall before they grow significantly. An inversion layer suppresses growth, a high cloud base reduces available cloud depth, and strong wind alone does not sustain particles in the cloud.
Correct: D)
Explanation: On synoptic weather charts, a warm front is depicted by a line with semicircles pointing in the direction of movement (into the cooler air). The referenced figure MET-005 shows symbol (2) as a warm front. Cold fronts use triangular barbs, occlusions combine both symbols, and a front aloft is marked differently.
Correct: B)
Explanation: Within the warm sector of a polar front low, the air is relatively warm and moist but the dominant cloud cover is not severe; conditions typically offer moderate to good visibility with scattered or broken cloud layers. Visibility less than 1 km with ground-covering cloud is more typical of fog or orographic stratus in the cold sector. Heavy showers and thunderstorms are post-cold-front back-side weather. Good visibility with only high cirrus is more characteristic of the pre-warm-front region far ahead.
Correct: A)
Explanation: After a cold front passes, cold, unstable polar air replaces the warm sector air; this instability produces good visibility (clean polar air) with convective cumulus clouds and showery precipitation. Poor visibility with stratus and snow is more typical of a warm occlusion or the cold sector aloft. Options C and D describe intermediate or pre-frontal conditions.
Correct: A)
Explanation: A polar front low moves in the direction of and roughly parallel to the isobars in its warm sector, because the warm sector winds steer the system. Seasonal directional rules (northeast/southeast or northwest/southwest) are oversimplified and not a reliable principle. Movement parallel to the warm front line southward is inconsistent with the observed eastward to northeastward tracks of North Atlantic lows over Europe.
Correct: C)
Explanation: Ahead of an approaching warm front, pressure falls as the low approaches. Within the warm sector, pressure remains relatively steady (though slightly falling). After the cold front passes, cold dense air causes pressure to rise sharply. Options A and B incorrectly place rising pressure ahead of the warm front, and option D has pressure falling behind the cold front.
Correct: B)
Explanation: In the Northern Hemisphere, as a polar front low passes, the wind veers (shifts clockwise, e.g., from south to southwest) with the warm front passage and veers again (e.g., from southwest to northwest) with the cold front passage. Backing (anti-clockwise shift) would indicate the low passing to the south of the observer, which is less common in Central Europe.
Correct: D)
Explanation: When cold air advects into the upper troposphere, it contracts the air column (cold air is denser), reducing the thickness between pressure levels; this lowers pressure aloft and produces an upper-level trough or low. Upper lows associated with cold-air pools are a key trigger for convective instability. A surface high results from upper-level divergence, not cold-air inflow aloft.
Correct: A)
Explanation: Cold air intruding into the upper troposphere destabilises the atmosphere by creating a steep lapse rate (cold air above, potentially warmer air below). This conditional instability, when combined with moisture, generates convective activity including showers and thunderstorms. It does not produce frontal weather (which requires air mass boundaries at the surface), nor does it cause calm weather or cloud dissipation.
Correct: C)
Explanation: Cold air is denser, so a column of cold air has shorter vertical distances between pressure surfaces (closer isobars aloft) and pressure surfaces lie at lower heights — indicating low pressure aloft. This is why upper-level cold pools are associated with upper troughs. Warm air has the opposite effect: greater thickness and higher pressure surfaces.
Correct: A)
Explanation: In summer, high pressure areas bring calm synoptic winds (weak pressure gradient) and subsidence suppresses deep convection, resulting in sunny skies with possible development of small fair-weather cumulus (few Cu). Frontal weather is associated with lows, squall lines and thunderstorms require instability and moisture not found in subsiding high-pressure air, and fog is typical of winter or overnight conditions in continental highs.
Correct: A)
Explanation: On the windward (luv) side of a mountain range during Foehn conditions, moist air is forced to rise, cools at the DALR then SALR, and precipitates much of its moisture as heavy orographic rain or snow with layered cloud and poor visibility — this is the 'Stauseite' effect. The warm, dry and gusty descending Foehn wind occurs on the lee (downwind) side, not the windward side.
Correct: C)
Explanation: Weather radar detects the intensity and location of precipitation by measuring backscattered microwave energy from raindrops and other hydrometeors; it is the primary tool for showing precipitation areas. Satellite images show cloud cover, not precipitation directly. Wind charts show wind patterns. GAFOR is a general aviation route forecast in text/coded format.
Correct: C)
Explanation: An inversion is an anomalous condition where temperature increases with altitude instead of the normal decrease; it is highly stable and acts as a lid on convection. Option A describes an isothermal layer (constant temperature), option B misidentifies pressure (which always decreases with height), and option D describes the normal lapse rate — the opposite of an inversion.
Correct: D)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: A)
Explanation: 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).
Correct: D)
Explanation: Overcast cloud cover prevents the ground from radiating heat to space at night (the greenhouse/blanket effect), so the surface does not cool sufficiently to reach the dew point, and radiation fog cannot form. Calm wind, clear nights, and a low temperature–dew point spread (low spread) all favour fog formation, not prevent it.
Correct: D)
Explanation: On standard synoptic weather charts, an occlusion is depicted by a line combining both cold-front triangles and warm-front semicircles on the same side, representing a front where the cold front has caught up with the warm front. The referenced figure MET-005 shows symbol (3) as an occlusion. Cold fronts show only triangles, warm fronts only semicircles, and fronts aloft are marked differently.
Correct: C)
Explanation: A stationary front is a boundary between two contrasting air masses (here polar and subtropical) with no significant horizontal movement in either direction. A cold front moves toward the warm air, a warm front moves toward the cold air, and an occluded front is the result of a cold front overtaking a warm front.
Correct: D)
Explanation: A shower that is visible close to the airfield is producing active downdrafts and outflow boundaries right now; these create severe, rapidly shifting low-level wind shear that is an immediate threat during approach or departure. Flying ahead of a warm front involves gradually deteriorating conditions but not severe shear. Cross-country flying below moderate Cu is normal gliding activity. Thirty minutes after a shower has passed, conditions have typically normalised.
Correct: D)
Explanation: Haze (HZ) is caused by dry particles (dust, smoke, pollution) suspended in the atmosphere and is not dependent on temperature or moisture; it persists regardless of temperature changes. Radiation fog, mist, and patches of fog are all moisture-dependent phenomena that form, thicken, or dissipate in direct response to temperature changes relative to the dew point.
Correct: B)
Explanation: In METAR coding, the descriptor 'SH' (shower) combined with the precipitation type 'RA' (rain) gives 'SHRA' for moderate showers of rain. '+TSRA' denotes heavy thunderstorm with rain, 'TS' alone indicates thunderstorm without precipitation reported separately, and '+RA' denotes heavy continuous rain (not a shower).
Correct: C)
Explanation: SIGMETs (Significant Meteorological Information) are issued for Flight Information Regions (FIRs) or Upper Information Regions (UIRs), which are defined blocks of airspace managed by specific ATC authorities. They are not issued for specific routes, individual countries (which may contain multiple FIRs), or individual airports (which use AIRMETs or terminal forecasts).
Correct: C)
Explanation: Solar irradiation (insolation) heating the windward slope warms the surface air, reducing its density and creating anabatic (upslope) flow that adds to the orographic lifting already occurring; this intensifies updrafts on the windward side. The lee side experiences descending air, night-time cooling suppresses thermals, and warming of upper layers would increase stability and suppress convection.
Correct: B)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: A)
Explanation: Isobars (lines of equal pressure) on surface charts indicate both wind direction and speed. Above the friction layer, wind flows parallel to isobars (geostrophic wind); close to the surface it crosses them at an angle toward lower pressure. Closely spaced isobars indicate a strong pressure gradient force and therefore strong winds; widely spaced isobars indicate light winds. Wind direction in the Northern Hemisphere is anticlockwise around lows and clockwise around highs (Buys-Ballot's Law).
Correct: D)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: A)
Explanation: The prefix 'Cirro-' denotes clouds in the high cloud family (above approximately 6,000 m / FL200), including cirrus, cirrocumulus, and cirrostratus. 'Strato-' refers to layer-type clouds at low to mid levels, 'Nimbo-' refers to rain-producing clouds (e.g., nimbostratus), and 'Alto-' denotes mid-level clouds (approximately 2,000–6,000 m).
Correct: D)
Explanation: An inversion layer acts as a lid that limits the vertical extent of cumulus cloud growth; thermals and updrafts lose buoyancy at the inversion, causing clouds to spread out and flatten at that level rather than growing into towering cumulus. The spread (temperature minus dew point) controls cloud base height, relative and absolute humidity affect cloud formation likelihood, but none of these cap the cloud top as directly as an inversion.
Correct: B)
Explanation: A low spread (temperature close to dew point) means the air is near saturation, and decreasing temperature (e.g., nocturnal cooling or advection of cold air) will bring the temperature down to the dew point, causing condensation and fog. Strong winds promote mixing that prevents fog. Low pressure is associated with ascending air, not fog formation. Increasing temperature widens the spread and dissipates fog.
Correct: B)
Explanation: Orographic (hill) fog forms when warm, moist air is forced to rise over elevated terrain, cools adiabatically to the dew point, and saturates; the resulting cloud envelops the hill or mountain as fog. Prolonged radiation cooling describes radiation fog, evaporation into cold air describes steam fog, and mixing of air masses describes mixing fog.
Correct: B)
Explanation: Precipitation forms in clouds when updrafts are strong enough to keep water droplets or ice crystals suspended long enough to grow — through collision-coalescence (warm clouds) or the Bergeron–Findeisen process (cold clouds). Without sufficient updrafts, particles fall before reaching precipitation size. An inversion prevents cloud growth, calm winds and sunshine are surface conditions not directly responsible for in-cloud precipitation, and high humidity/temperature alone do not create precipitation without dynamic lifting.
Correct: D)
Explanation: Large spacing between isobars indicates a weak pressure gradient and therefore weak synoptic-scale winds. In the absence of strong pressure-gradient forcing, local thermally driven wind systems (valley-mountain winds, sea-land breezes) dominate the local circulation. Strong prevailing westerly or easterly winds require close isobar spacing.
Correct: A)
Explanation: 'Back-side weather' (Rückseitenwetter) refers to the cold, unstable, showery conditions in the polar air mass on the back (west/northwest) side of a low-pressure system, experienced after a cold front has passed. It is not associated with occlusions (which bring a different cloud and precipitation pattern), Foehn (a thermodynamic lee-side phenomenon), or warm fronts.
Correct: B)
Explanation: Wind is reported in aviation as direction FROM and speed; '225' is the bearing 225° true (southwest), and '15' is the speed in knots. Wind direction is always the direction from which the wind is blowing, so 225° means the wind blows from the southwest. Speed in METARs and standard reports is in knots unless explicitly stated otherwise.
Correct: B)
Explanation: During Foehn in the Bavarian pre-alpine region, the classic pattern involves nimbostratus and heavy precipitation on the southern (windward) Italian side of the Alps, a Foehn wall of cloud at the ridge, and on the northern (lee) side a warm, dry, gusty wind with possible rotor turbulence and lenticular clouds. Option A incorrectly places the Nimbostratus on the northern side and the rotor on the windward side. Options A and D have the cloud and rotor positions reversed.
Correct: D)
Explanation: "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.
Correct: C)
Explanation: 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.
Correct: B)
Explanation: QNH is the altimeter setting adjusted to make the instrument read the elevation above mean sea level at the station. It is calculated by reducing the airfield QFE to sea level using the ISA temperature gradient. With QNH set, the altimeter reads the airfield elevation on the ground and true altitude above MSL in the air (assuming ISA conditions). Note that "true altitude" (answer A) accounts for actual temperature deviations from ISA — QNH gives indicated altitude, which may differ from true altitude in non-ISA conditions.
Correct: C)
Explanation: 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.
Correct: B)
Explanation: Clouds are fundamentally divided into two basic types: cumulus (convective, vertically developed) and stratiform (layered, horizontally extended). Cumulus clouds result from convective uplift, while stratus clouds form from large-scale lifting or cooling of air layers. Options A and C mix sub-categories with the basic classification, and option D uses non-standard terminology ('layered and lifted') rather than the correct scientific distinction.
Correct: C)
Explanation: During Foehn conditions, the air descends on the lee side and warms adiabatically, causing any remaining moisture to produce characteristic standing wave clouds. Altocumulus lenticularis (lens-shaped wave clouds) forms in the stable wave patterns downstream of a mountain ridge during Foehn. Cumulonimbus (options A and B) is associated with strong convection, not the stable descending flow of Foehn, and Altocumulus Castellanus (option D) indicates convective instability in the mid-levels, not lee-side wave activity.
Correct: A)
Explanation: Rime ice forms when small supercooled water droplets and ice crystals strike the airframe and freeze instantly on contact, creating a white, opaque, brittle deposit typically on leading edges. Clear ice (option B) forms from large supercooled water droplets that spread before freezing, producing a smooth, dense, clear coating. Mixed ice (option C) is a combination of both. Hoar frost (option D) forms from water vapour depositing directly as ice crystals on cold surfaces, not from droplet impact.
Correct: D)
Explanation: The surface weather chart (synoptic chart) displays isobars, high and low pressure centres, and frontal systems such as warm, cold, and occluded fronts at mean sea level. A Significant Weather Chart (SWC, option A) focuses on hazardous weather phenomena for flight, not the overall pressure pattern. A wind chart (option B) shows only wind vectors. A hypsometric chart (option C) depicts constant-pressure surfaces (contour heights), not surface fronts.
Correct: B)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: D)
Explanation: 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.
Correct: A)
Explanation: 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.
Correct: C)
Explanation: As a warm front approaches, the first sign is high-level Cirrus, which gradually thickens into Cirrostratus, then Altostratus and Altocumulus at mid-levels, finally transitioning to Nimbostratus with prolonged rain and a lowering cloud base. Option A describes a high-pressure or thermal anticyclone scenario. Option B describes the passage of a cold front (squall line, Cb, gusty winds). Option D describes a coastal sea-breeze pattern unrelated to frontal meteorology.
Correct: C)
Explanation: During a fully developed (mature stage) thunderstorm, cold precipitation-laden air descends rapidly beneath the Cumulonimbus and spreads outward upon reaching the surface, creating a gust front — a sharp boundary of cold gusty air that can precede the visible storm by several kilometres. Electrical discharge (option A) is a separate thunderstorm hazard. The anvil top (option B) is a structural feature caused by upper-level winds, not downdrafts. Freezing rain (option D) results from a temperature inversion aloft, not directly from Cb downdrafts.
Correct: C)
Explanation: Low-Level Significant Weather Charts (LLSWC) depict meteorological hazards relevant to low-altitude flight, including turbulence areas, icing conditions, and frontal systems with their movement. They do not contain radar echo data of precipitation, which is a real-time product displayed on weather radar imagery. Options A, B, and D are all standard items found on LLSWC; only radar echoes (option C) are absent because LLSWC are forecast charts, not real-time radar products.
Correct: B)
Explanation: 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.
Correct: C)
Explanation: Nimbostratus (Ns) is a thick, dark grey layer cloud specifically associated with prolonged, steady rain or snow falling uniformly over a wide area, typically along warm fronts. Altocumulus (option A) is a mid-level cloud that does not produce significant precipitation. Cumulonimbus (option B) produces heavy showers and thunderstorms, not continuous prolonged rain. Cirrostratus (option D) is a high-level ice cloud that does not produce precipitation reaching the ground.
Correct: C)
Explanation: Meteorologically, precipitation is classified by its cloud type of origin: rain (continuous precipitation from stratiform clouds such as Nimbostratus) and showers of rain (convective precipitation from cumuliform clouds such as Cumulonimbus or Cumulus congestus). Options A, B, and D describe precipitation by intensity or type of precipitation (snow vs. rain, light vs. heavy), which are separate classification systems not based on cloud type.
Correct: C)
Explanation: Thunderstorms require three key ingredients: moisture (warm humid air provides latent energy), lift (to trigger convection), and instability (a conditionally unstable environmental lapse rate means rising saturated air becomes warmer than its surroundings and accelerates upward). Option A describes stable, overcast conditions unfavourable for convection. Option B's strong inversion layer would suppress convective development. Option D describes radiation fog conditions with stable cold air.
Correct: A)
Explanation: Widely spaced isobars on a surface weather chart indicate a small pressure gradient (small pressure difference over a large distance), resulting in a weak pressure gradient force and therefore light winds. The wind speed is directly proportional to the pressure gradient. Options B and C incorrectly state that wide isobar spacing means a strong gradient, and option D incorrectly reverses the relationship between gradient strength and wind speed.
Correct: A)
Explanation: 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.
Correct: B)
Explanation: An air mass originating over the cold Russian or Siberian continent during winter acquires characteristics of its source region: cold temperatures and low humidity, classifying it as Continental Polar (cP) air. Maritime air masses (options A and C) originate over ocean areas and carry higher moisture content. Continental Tropical (option D) air originates over warm, dry continental areas such as the Sahara, not over polar continental regions.
Correct: D)
Explanation: Cold fronts are characterised by active convective weather: rapidly developing Cumulonimbus clouds producing heavy showers and thunderstorms, accompanied by squall-line activity, strong gusty winds, and followed by scattered cumulus with isolated showers in the cold air behind the front. Option B (cirrus thickening to nimbostratus) describes a warm front. Options A and C describe anticyclonic or sea-breeze patterns respectively.
Correct: B)
Explanation: The most immediate physical danger when an aircraft is struck by lightning is surface overheat and structural damage to exposed parts — lightning can burn through fairings, damage antennas, pit metal surfaces, and in extreme cases damage control surfaces. Avionics may be affected, but explosion of cockpit equipment (option A) is not a primary risk in certified aircraft. Depressurisation (option C) applies only to pressurised aircraft. Radio static noise (option D), while possible, is not the most imminent danger.
Correct: A)
Explanation: Mountain wind (Bergwind or katabatic wind) is the nocturnal downslope flow: at night, air in contact with the mountain slopes radiates heat, cools, becomes denser than the surrounding free air, and drains downhill under gravity. Valley wind (Talwind) is the daytime upslope flow caused by solar heating (option C). Options B and D confuse the direction or the time of day.
Correct: D)
Explanation: 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.
Correct: B)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: B)
Explanation: The saturated (moist) adiabatic lapse rate (SALR) averages approximately 0.6°C per 100 m (6°C per 1000 m), because latent heat released by condensation partially offsets the dry adiabatic cooling rate. The dry adiabatic lapse rate (DALR) is 1.0°C/100 m (option A), not the saturated rate. Option C (2°C/1000 ft) converts to approximately 0.66°C/100 m and is a rough approximation but not the standard stated value. Option D (0°C/100 m) would imply no temperature change with altitude.
Correct: C)
Explanation: The subtropical high-pressure belt forms near 30°N and 30°S latitudes as a result of the Hadley cell circulation: warm air rising at the equator moves poleward, cools, and descends in these subtropical zones, creating semi-permanent anticyclones over oceanic areas (e.g., Azores High, Pacific High). The equatorial belt (option A) is dominated by the ITCZ with low pressure. Option B describes areas of lifting, which generate low pressure. Mid-latitudes (option D) are where the polar front and cyclonic activity are found.
Correct: C)
Explanation: ATIS (Automatic Terminal Information Service) is a continuous broadcast of recorded aerodrome information including current weather, active runway, and NOTAMs at destination aerodromes, and can be received by radio during flight. PIREP (option A) is pilot-reported weather en-route, not destination-specific. SIGMET (option B) covers significant meteorological hazards over a wide area. VOLMET (option D) broadcasts meteorological information for multiple aerodromes but is less aerodrome-specific than ATIS.
Correct: D)
Explanation: The cloud shown in figure MET-002 is Cumulus — a convective cloud with a flat base and cauliflower-like vertical development, characteristically white with sharp outlines in good visibility. Stratus (option A) forms as a flat, featureless grey layer. Cirrus (option B) appears as thin, wispy filaments at high altitude. 'Altus' (option C) is not a recognised cloud genus in the ICAO classification.
Correct: C)
Explanation: An air mass is defined by the temperature and humidity properties it acquires in its source region, and how those properties are modified as it moves. Both the region of origin (polar, tropical, equatorial) and the path it travels (maritime or continental) determine whether the air is warm or cold, moist or dry. Wind speed (option A) is not a defining characteristic. Environmental lapse rate at origin (option B) is a consequence, not the defining property. Temperatures at origin and present region (option D) alone do not capture the moisture dimension.
Correct: B)
Explanation: 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 A) is associated with stable, moist air at low levels, common in autumn or maritime high-pressure situations. Nimbostratus (option C) is associated with frontal systems. Squall lines and thunderstorms (option D) require convective instability and moisture not typical of settled high-pressure conditions.
Correct: B)
Explanation: 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 MET-005 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.
Correct: B)
Explanation: 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 A) means moderate rain. 'SHRA' (option C) means shower of rain (moderate). '+SHRA' (option D) means heavy shower of rain — a convective shower, not continuous heavy rain.
Correct: B)
Explanation: 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.
Correct: C)
Explanation: 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.
Correct: A)
Explanation: 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 D) is not a recognised meteorological term.
Correct: A)
Explanation: 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 B) does not occur as there are no supercooled droplets. Cirrus (option C) contains ice crystals which do not adhere significantly.
Correct: B)
Explanation: 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 A) is a secondary concern. Icing (option C) is unrelated to mountain wind shear. Heavy downdrafts in rainfall (option D) describes thunderstorm activity, not orographic flow.
Correct: D)
Explanation: 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 A confuses thermals with cloud coverage statistics. Option B describes sink between Cu clouds. Option C describes clear-air turbulence (CAT) near thunderstorms, a different phenomenon.
Correct: D)
Explanation: 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). Option C adds an unnecessary cloud formation criterion to what is fundamentally an altitude threshold.
Correct: D)
Explanation: 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 B misstate it as a temperature reached aloft or a threshold for thunderstorm formation. Option C describes thunderstorm formation, not Cu formation.
Correct: C)
Explanation: 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. Option A describes a change in thermal visibility. Option B refers to synoptic-scale deepening of depressions. Option D describes the spreading of Cu under an inversion (which is actually 'street' or 'cover' formation, a separate phenomenon).
Correct: B)
Explanation: 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. Option A describes cloud cover on a windward mountain slope. Option C describes the anvil of a Cb, not shielding. Option D describes sky coverage in oktas, which is unrelated.
Correct: B)
Explanation: 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.
Correct: D)
Explanation: 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. Option A (0.01225 kg) is off by a factor of 100, option B (0.1225 kg) by a factor of 10, and option C (12.25 kg) by a factor of 10 in the opposite direction. These represent common decimal-point errors.
Correct: C)
Explanation: 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 A), nor the height where temperature starts to decrease (option B — that is the surface of the troposphere). Option D confuses the tropopause with the stratopause.
Correct: A)
Explanation: 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. Option B describes normal atmospheric conditions. Option C describes an isothermal layer. Option D describes a generic boundary without specifying the temperature gradient direction.
Correct: B)
Explanation: An isothermal layer is one in which temperature remains constant with increasing altitude — neither increasing (inversion, option D) nor decreasing (normal lapse rate, option A). Isothermal conditions are found, for example, in the lower stratosphere. Option C describes a generic atmospheric boundary layer, not a layer of constant temperature.
Correct: B)
Explanation: 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 C) deflects wind but does not create it. Centrifugal force (option A) 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.
Correct: C)
Explanation: 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 A and B) do not provide the cross-mountain pressure gradient needed. Instability (option D) would prevent the laminar flow characteristic of Foehn.
Correct: A)
Explanation: 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. Option B is incorrect because dew point and condensation point are effectively the same. Option C describes relative humidity. Option D describes the saturation mixing ratio or absolute humidity capacity.
Correct: C)
Explanation: 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 A and B) requires strong convective instability absent in Foehn descent. Altocumulus Castellanus (option D) indicates mid-level instability, not the stable wave motion of a Foehn situation.
Correct: D)
Explanation: 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 A) is actually a prerequisite for radiation fog formation. A clear night (option B) and low spread (option C) are also favourable, not preventative, conditions.
Correct: D)
Explanation: 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 A reverses the temperature relationship. Option B describes mixing fog (a different type). Option C describes radiation fog. The defining factor in advection fog is the movement of warm moist air over cold ground.
Correct: B)
Explanation: 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. Option A describes radiation fog. Option C describes steam fog (evaporation/mixing fog). Option D describes mixing fog. The key process is forced lifting of moist air over elevated terrain.
Correct: C)
Explanation: 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). Options A and B describe stable, anticyclonic conditions. Option D (high stratus) would require stable, moist conditions near the surface, not the convective instability associated with a cold upper trough.
Correct: A)
Explanation: 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. Option B describes the lee side of the Foehn (warm, dry, gusty). Option C describes stable, fog-prone conditions unrelated to Foehn. Option D describes conditions more typical of frontal convective activity.
Correct: C)
Explanation: 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 A) shows upper-level contour heights on constant-pressure surfaces. The SWC (option D) focuses on hazardous weather phenomena, not comprehensive pressure analysis.
Correct: B)
Explanation: 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 A) alone means moderate rain. 'SHRA' (option C) is shower of rain. '+SHRA' (option D) is heavy shower of rain — a different precipitation type.
Correct: B)
Explanation: 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 A) means heavy thunderstorm with rain. 'TS' (option C) means thunderstorm without precipitation modifier. '+RA' (option D) means heavy continuous rain from stratiform clouds, not a shower.
Correct: A)
Explanation: 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 B) combines warm and cold front characteristics. Foehn (option C) is a separate orographic phenomenon. After a warm front (option D) brings the warm sector, not cold back-side air.
Correct: D)
Explanation: 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. Options A and B give incorrect MSL starting values (+30°C and +20°C). Option C reverses the sign convention, implying temperature increases with altitude.
Correct: B)
Explanation: 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. Option A incorrectly describes the lee-side wind as cold and humid and places the Ns on the wrong side. Option C describes the synoptic pressure setup only partially. Option D places the Ns on the north (lee) side, which is incorrect.
