Meteorology Flashcards
What is the Dry Adiabatic Lapse Rate (DALR)?
The DALR is 3°C per 1,000 feet (9.8°C/km), the rate at which unsaturated air cools when rising or warms when descending due to pressure changes without heat exchange.
Example: Air at 15°C rising 2,000 feet cools to 9°C (15 - (3 × 2)).
What is the Saturated Adiabatic Lapse Rate (SALR)?
The SALR is about 1.5°C per 1,000 feet (5-6°C/km), the rate at which saturated air cools when rising, reduced by latent heat release from condensation.
Example: Saturated air at 15°C rising 2,000 feet cools to 12°C (15 - (1.5 × 2)).
How does the DALR affect atmospheric stability?
If the environmental lapse rate (ELR) is less than 3°C per 1,000 feet (e.g., 2°C), dry air is stable and resists rising. If ELR exceeds 3°C, it’s unstable, promoting convection.
Explanation: Stability depends on comparing ELR to DALR for dry air.
How does the SALR affect atmospheric stability?
If the ELR exceeds 1.5°C per 1,000 feet (e.g., 2°C), saturated air is unstable, leading to cloud formation and potential thunderstorms. If less, it’s stable.
Explanation: Latent heat release makes moist air more buoyant.
What happens when unsaturated air becomes saturated while rising?
It transitions from DALR (3°C/1,000 ft) to SALR (1.5°C/1,000 ft).
Example: Air at 20°C rises 1,000 feet to 17°C (DALR), saturates, then rises another 1,000 feet to 15.5°C (SALR).
How does the DALR apply to descending air?
Unsaturated air warms at 3°C per 1,000 feet when descending.
Example: Air at 5°C at 5,000 feet warms to 20°C at sea level (5 + (3 × 5)).
Why is the SALR less than the DALR?
Condensation releases latent heat, reducing the cooling rate from 3°C to 1.5°C per 1,000 feet.
Explanation: This heat offsets expansion cooling.
What are the height classifications of clouds?
Low: Below 6,500 feet (e.g., stratus, cumulus).
Medium: 6,500–20,000 feet (e.g., altostratus, altocumulus).
High: Above 20,000 feet (e.g., cirrus, cirrostratus).
What are the form classifications of clouds?
Stratiform: Layered, stable air (e.g., stratus, nimbostratus).
Cumuliform: Heaped, unstable air (e.g., cumulus, cumulonimbus).
What weather is associated with stratus clouds?
Overcast, drizzle or light rain.
Aviation Impact: Poor visibility, stable conditions.
What weather is associated with cumulus clouds?
Fair weather if small; heavy showers or thunderstorms if large and unstable.
Aviation Impact: Turbulence risk if towering.
What weather is associated with altostratus clouds?
Steady rain or snow (2–5 mm/hr), overcast, often ahead of warm fronts.
Aviation Impact: Icing and visibility reduction.
What weather is associated with altocumulus clouds?
Scattered, may signal thunderstorms or a front within 24 hours.
Aviation Impact: Indicates instability aloft.
What weather is associated with cirrus clouds?
Fair weather, thin and wispy, but may precede rain in 12–24 hours.
Aviation Impact: Early warning of frontal systems.
What weather is associated with cumulonimbus clouds?
Heavy rain (>10 mm/hr), hail, lightning, severe turbulence.
Aviation Impact: Avoid due to extreme hazards.
What weather is associated with nimbostratus clouds?
Continuous rain or snow (2–5 mm/hr), thick overcast, low visibility.
Aviation Impact: Prolonged poor conditions.
What is clear ice?
Dense, transparent ice from large supercooled droplets (>0.5 mm) freezing slowly, common in warm fronts or cumulonimbus.
Hazard: Reduces lift (e.g., 25% with 1 mm buildup), increases drag.
What is rime ice?
Opaque, brittle ice from small supercooled droplets.
Hazard: Blocks sensors, alters aerodynamics.
What is mixed ice?
Combines clear and rime ice from varying droplet sizes (0.1–0.5 mm), in transitional zones.
Hazard: Weight and adhesion issues, risks engine failure.
What conditions favor clear ice formation?
Temperatures near 0°C to -10°C, large supercooled droplets in nimbostratus or cumulonimbus.
Explanation: Slow freezing allows dense buildup.
What conditions favor rime ice formation?
Colder temperatures (-10°C to -20°C), small supercooled droplets in cumulus or freezing fog.
Explanation: Instant freezing creates a porous structure.
What are the hazards of icing to aircraft?
Reduces lift, increases drag and weight, alters aerodynamics, blocks sensors or intakes, risking engine failure and control loss.
Aviation Impact: Severe for helicopters due to rotor imbalance.
What does WHISTLE stand for in thunderstorm hazards?
Weather, Hail, Icing, Squalls, Turbulence, Lightning, Electricity.
What is the Weather hazard in WHISTLE?
Severe conditions (e.g., heavy rain >10 mm/hr, wind shifts) reducing visibility.
Aviation Impact: Disrupts navigation.
What is the Hail hazard in WHISTLE?
Hailstones (>2 cm) damage surfaces, engines, and windscreens in cumulonimbus cores.
Aviation Impact: Structural failure risk.
What is the Icing hazard in WHISTLE?
Rapid clear or mixed ice buildup in updrafts with supercooled water, reducing lift and increasing weight.
Aviation Impact: Control loss potential.
What are Squalls in WHISTLE?
Sudden wind gusts (>20 kt increase) near the ground, often from downdrafts.
Aviation Impact: Risks control loss during takeoff/landing.
What is the Turbulence hazard in WHISTLE?
Severe updrafts/downdrafts (>2,000 ft/min) in cumulonimbus, stressing airframes.
Aviation Impact: Structural damage or passenger injury.
What is the Lightning hazard in WHISTLE?
Strikes (>100,000 volts) damaging electronics, composites, or fuel systems.
Aviation Impact: Critical for helicopters with exposed components.
What is the Electricity hazard in WHISTLE?
Static discharges (e.g., St. Elmo’s fire) disrupting radio and navigation systems (interference >10 dB).
Aviation Impact: Communication loss.
What is radiation fog?
Forms on clear, calm nights when ground cools, condensing near-surface moisture.
Aviation Impact: Delays morning operations.
What is advection fog?
Warm, moist air cools over a cold surface (e.g., sea fog).
Aviation Impact: Persistent, affects coastal airfields.
What is frontal fog?
Rain from fronts saturates near-surface air.
Aviation Impact: Linked to prolonged weather systems.
What is steam fog?
Cold air over warm water causes evaporation and condensation.
Aviation Impact: Localized, affects inland water areas.
What conditions favor radiation fog formation?
Clear skies, light winds.
Explanation: Ground loses heat, cooling air to dew point.
What is a katabatic wind?
Cold, dense air flows downslope (5–10 kt) due to gravity, often at night.
Weather: Frost, valley fog.
What is an anabatic wind?
Warm air rises upslope (5–10 kt) due to daytime heating.
Weather: Clears fog, improves visibility.
What is a sea breeze?
Cool sea air moves inland to replace rising warm land air.
Weather: Moist, cooler conditions.
What are trade winds?
Steady winds (10–20 kt) from subtropical highs to the equator.
Weather: Stable, dry conditions.
What are westerly winds?
Mid-latitude synoptic winds (20–40 kt) driven by pressure gradients.
Weather: Variable, fronts, depressions.
What conditions favor katabatic winds?
Cold, stable air over elevated terrain at night, with clear skies enhancing cooling.
Explanation: Gravity drives downslope flow.
What is the source region of Arctic Maritime (Am) air?
Arctic Ocean.
What weather is associated with Arctic Maritime (Am) air?
Cold (10 km).
Aviation Impact: Turbulence, icing risk.
What is the source region of Polar Maritime (Pm) air?
North Atlantic or Pacific.
What weather is associated with Polar Maritime (Pm) air?
Cool (5–10°C), moist, unstable.
Weather: Showery, gusty, cumuliform clouds.
What is the source region of Polar Continental (Pc) air?
Northern landmasses (e.g., Siberia).
What weather is associated with Polar Continental (Pc) air?
Very cold (-10°C), dry, stable.
Weather: Clear or light snow if moistened over sea.
What is the source region of Tropical Maritime (Tm) air?
Subtropical oceans (e.g., Azores).
What weather is associated with Tropical Maritime (Tm) air?
Mild (15–20°C), moist, stable.
Weather: Foggy, drizzly, stratus clouds.
What is the source region of Tropical Continental (Tc) air?
Subtropical land (e.g., North Africa).
What weather is associated with Tropical Continental (Tc) air?
Hot (>25°C), dry, stable.
Weather: Hazy, dusty, clear skies.
What is a warm front?
Warm air advances over colder air with a shallow slope (~1:150), causing gradual ascent.
What weather is associated with a warm front?
Before: Cirrus to altostratus, falling pressure (2 hPa/hr), light rain.
During: Nimbostratus, steady rain (2–5 mm/hr), fog, visibility.
After: Warmer, humid air, drizzle.
What is a cold front?
Cold air undercuts warm air with a steep slope (~1:50), forcing rapid ascent.
What weather is associated with a cold front?
Before: Warm, humid air, building cumulus, falling pressure.
During: Squalls, heavy showers/thunderstorms, temperature drop (5–10°C).
After: Cooler, drier air, good visibility (>10 km).
What is an occluded front?
Cold front overtakes warm front, lifting warm air aloft.
What weather is associated with an occluded front?
Before: Cirrus and altostratus, like a warm front.
During: Mixed rain/snow (1–3 mm/hr), less intense.
After: Gradual clearing.
What conditions favor warm front development?
Warm, moist air (e.g., Tm) meeting colder, denser air (e.g., Pc), with a depression driving ascent.
Explanation: Shallow slope prolongs weather.
What does the Blue colour state indicate?
Visibility ≥8 km, cloud base ≥2,500 ft AGL. No operational restrictions.
What does the White colour state indicate?
Visibility 5–8 km, cloud base 1,500–2,500 ft AGL. Minor restrictions.
What does the Green colour state indicate?
Visibility ≥5 km, cloud base ≥500 ft AGL. Normal operations, light weather (e.g., drizzle).
What does the Yellow 1 colour state indicate?
Visibility 1,600–5,000 m, cloud base 200–500 ft AGL. Caution needed.
What does the Yellow 2 colour state indicate?
Visibility 800–1,600 m, cloud base 100–200 ft AGL. Significant restrictions.
What does the Red colour state indicate?
Visibility <800 m, cloud base <100 ft AGL. Possible airfield closure.
How do you calculate pressure altitude (PA)?
PA = elevation + (1013 - QNH) × 30 ft/hPa.
Example: Elevation 500 ft, QNH 990 hPa → PA = 500 + (1013 - 990) × 30 = 1,190 ft.
How do you calculate density altitude (DA)?
DA = PA + 120 × (actual temp - ISA temp).
Example: PA 2,000 ft, actual temp 25°C, ISA temp 11°C → DA = 2,000 +
How do you calculate density altitude (DA)?
DA = PA + 120 × (actual temp - ISA temp).
Example: PA 2,000 ft, actual temp 25°C, ISA temp 11°C → DA = 2,000 + 120 × (25 - 11) = 3,680 ft.
How do you calculate relative humidity (RH)?
RH = (actual vapour / saturation vapour) × 100.
Example: At 20°C, actual vapour 10 g/m³, saturation 17 g/m³ → RH = (10 / 17) × 100 ≈ 58.8%.
How do you calculate temperature change using DALR?
3°C per 1,000 ft for unsaturated air.
Example: Air at 15°C rises 2,000 ft → 15 - (3 × 2) = 9°C.
How do you calculate temperature change using SALR?
1.5°C per 1,000 ft for saturated air.
Example: Air at 15°C rises 2,000 ft → 15 - (1.5 × 2) = 12°C.
What is the ISA temperature at 2,000 feet?
ISA temp at sea level is 15°C, decreasing 1.98°C per 1,000 ft.
At 2,000 ft: 15 - (1.98 × 2) ≈ 11°C.
How are warm fronts depicted on synoptic charts?
Red semi-circles pointing in the direction of movement.
Aviation Impact: Expect prolonged rain, icing.
How are cold fronts depicted on synoptic charts?
Blue triangles pointing in the direction of movement.
Aviation Impact: Sudden weather changes, turbulence.
How are occluded fronts depicted on synoptic charts?
Purple alternating semi-circles and triangles.
Aviation Impact: Mixed precipitation, clearing soon.
What do isobars indicate on a synoptic chart?
Lines of equal pressure (e.g., 1000 hPa).
Tight spacing means strong winds (>30 kt). Aviation Impact: Turbulence risk.
What does the 528 line represent on a synoptic chart?
On a 500 hPa chart, 528 dam (5,280 meters) is a threshold where snow is likely below if surface temperatures are near or below 0°C.
Indicates a cold upper atmosphere supporting snow.
What does the 546 line represent on a synoptic chart?
On a 500 hPa chart, 546 dam (5,460 meters) is a transitional zone; below this, mixed precipitation or snow is likely if surface temperatures are 0–5°C.
Above, rain is favored.
What does the 564 line represent on a synoptic chart?
On a 500 hPa chart, 564 dam (5,640 meters) indicates warmer air aloft; above this, rain is typical, below it, snow or mixed precipitation increases in winter.
Marks a warmer, often tropical air mass.
What does a trough indicate on a synoptic chart?
An elongated low-pressure area, shown as a dashed line, linked to showers or thunderstorms.
Aviation Impact: Expect instability, turbulence.
How is wind depicted on a synoptic chart?
Wind barbs show direction and speed: each full barb = 10 kt, half barb = 5 kt.
Example: Two full barbs + half barb = 25 kt.
What conditions favor snow below the 528 line?
Surface temperatures near or below 0°C, cold air mass (e.g., Pc or Am), and 500 hPa height ≤528 dam.
Cold aloft ensures snow reaches the ground.
How does DALR influence cloud base height?
Cloud base occurs where air cools to its dew point at 3°C/1,000 ft.
Example: Air at 20°C with dew point 14°C forms clouds at 2,000 ft (20 - 14 = 6°C ÷ 3°C/1,000 ft).
What weather is associated with cirrostratus clouds?
Thin, high clouds with a halo effect around the sun/moon, indicating rain within 12–24 hours.
Aviation Impact: Early frontal warning.
What are the hazards of clear ice to helicopters?
Heavy buildup (e.g., 10 mm/min) on rotors reduces lift, increases drag, and risks imbalance.
Aviation Impact: Lethal control loss.
What are the hazards of squalls in thunderstorms?
Sudden gusts (>20 kt) from downdrafts risk control loss near the ground.
Example: Wind shifts from 10 kt to 35 kt in seconds.
What conditions favor advection fog formation?
Warm, moist air moves over a cooler surface.
