Meteorology

Question 1

What is true about the temperature lapse rate at the tropopause

Answer 1

The temperature lapse rate changes abruptly, becoming nearly zero - Temperature stops decreasing with height

Question 2

What does the amount of water vapour air can hold depend on

Answer 2

Air temperature

Question 3

In the troposphere, how does the rate of pressure decrease differ between lower and higher altitudes

Answer 3

Pressure decreases rapidly at lower altitudes and more slowly at higher altitudes

Question 4

What is the approximate height and temperature of the tropopause at:
1. The equator
2. The poles

Answer 4

1. Height: ~55,000 - 60,000 ft
   Temperature: ~ -80 °C
2. Height: ~25,000 - 30,000 ft
   Temperature: ~ -50 °C

Question 5

How does low air density adversely affect both turbine and reciprocating engines

Answer 5

Low air density causes:
-Reduced mass of air entering the engine
-Less oxygen available for combustion
-Reduced power output
-Longer takeoff roll and poorer climb performance

Question 6

What surface weather conditions are associated with:
1. Upper-air divergence
2. Upper-air convergence

Answer 6

1. Upper-air divergence leads to:
   Rising air
   Surface low pressure
   Cloud formation
   Unsettled or deteriorating weather
2. Upper-air convergence leads to:
   Descending air
   High surface pressure
   Clear skies
   Stable weather conditions

Question 7

What weather conditions are generally associated with:
1. Easterly winds
2. Westerly winds

Answer 7

1. -In the tropics (trade winds): stable, dry, anticyclonic air
   -In mid-latitudes: usually associated with air moving from high-pressure regions; can bring stable, clear weather
   -Easterly winds alone don’t define weather it’s the pressure systems they originate from that determine stability and precipitation
2. -In mid-latitudes: westerlies dominate, bringing unstable air, frontal systems, clouds, and precipitation
   -In the tropics: westerlies are less common; weather depends on local pressure patterns
   -Westerly winds often signal changing or unsettled weather, especially when associated with low-pressure systems

Question 8

When are surface-based temperature inversions most common

Answer 8

Most common during clear nights/early mornings with calm or light winds, especially in winter, because radiational cooling of the ground cools the air near the surface while a lack of mixing allows warmer air to remain above

Question 9

Where is the greatest annual temperature range usually found

Answer 9

Continental interiors, far from oceans

Question 10

What is usually recorded in a weather hut

Answer 10

Temperature
Atmospheric pressure
Humidity
Wind speed and direction
Rainfall / precipitation

Question 11

What is the atmosphere primarily heated by

Answer 11

Long wave radiation from the Earth’s surface

Question 12

What does the amount of heat absorbed from the sun depend on

Answer 12

Solar angle (altitude of the sun)
Duration of daylight
Surface albedo (reflectivity)
Atmospheric conditions (clouds, dust, etc.)
Elevation

Question 13

What are the following:
1. stable layer
2. absolutely stable
3. unstable layer
4. conditionally unstable layer

Answer 13

1. layer where air resists vertical motion; displaced air tends to return to its original position
2. A layer where air, if lifted, is always cooler than its surroundings and will sink back, regardless of moisture content
3. layer where air, if lifted, is warmer than its surroundings and will continue to rise
4. layer where dry air is stable but moist air becomes unstable if lifted beyond its lifting condensation level (LCL)

Question 14

What atmospheric conditions can be expected when flying through or near a temperature inversion

Answer 14

Flying through an inversion: turbulence is usually light; visibility may be poor near the surface due to haze or fog

Climbing above an inversion: air becomes more unstable, possible turbulence

Descending below an inversion: air is stable, smoother flight

Seasonal differences:
Winter: stronger inversions, especially near the surface - poor visibility, smooth air above inversion

Summer: inversions weaker, may be broken by solar heating; performance effects less pronounced

Question 15

What effect do oceans have on weather in terms of:
Temperature
Humidity
Cloud
Stability
Heating/cooling

Answer 15

Moderate temperature (smaller daily and annual temperature range)

Increase humidity

Promote cloud, fog, and precipitation

Produce more stable air than land

Delay heating and cooling due to high heat capacity

Question 16

When is terrestrial (longwave) radiation at a daily, seasonal, geographical, and surface type maximum

Answer 16

Daily Maximum: Peaks in afternoon (2–4 PM), shortly after maximum surface temperature

Seasonal Maximum: Occurs during summer months due to higher ground surface and air temperatures

Geographical Maximum: Highest values in hot, dry, low-cloud-cover regions like subtropical deserts

Surface Type: Bare soil and dry land surfaces emit higher amounts of longwave radiation than cooler, moist, or heavily vegetated areas

Question 17

What happens when air is cooled to, and then below its dew point

Answer 17

At dew point: Air becomes 100% saturated

Below dew point: Excess water vapour condenses and freezes if temp is below 0°C

Question 18

What is the mixing ratio

Answer 18

The mass of water vapour per unit mass of dry air, usually expressed in grams per kilogram (g/kg)

Mixing ratio does not change unless condensation or evaporation occurs

Question 19

What happens to relative humidity and mixing ratio as:
1. An unsaturated parcel of air rises
2. A saturated parcel of air rises

Answer 19

1. Relative humidity increases
   Mixing ratio remains constant
   Why: Cooling reduces the air’s capacity to hold water vapour, but no condensation occurs yet
2. Relative humidity remains at ~100%
   Mixing ratio decreases
   Why: Cooling causes condensation, removing water vapour from the air

Question 20

In terms of SALR, DALR and ELR:
When is an air mass Stable,
Absolutely Stable,
Unstable
Conditionally Unstable

Answer 20

Stable: ELR < SALR < DALR

Absolutely Stable: ELR < DALR (Unsaturated Air)

Unstable: SALR < DALR < ELR

Conditionally Unstable: SALR < ELR < DALR
If air Unsaturated - Stable
If air Saturated - Unstable

Question 21

What main information can be derived from the stability of the atmosphere

Answer 21

Likelihood of cloud formation

Type of clouds (layered vs convective)

Probability of turbulence

Potential for thunderstorms

Expected visibility

General weather severity

Question 22

What is required for the release or absorption of latent heat

Answer 22

change of state of water without a temperature or pressure change

Question 23

What are supercooled droplets, where are they mostly encountered, and what temperature range are they found

Answer 23

Liquid water droplets at temperatures below 0°C that haven’t frozen yet

Commonly Found In:
Cu, Cb and St clouds
Mountainous terrain(orographic induced updrafts)
Near frontal systems(rain falling from a warm front through a cold front)

Most common between 0°C and -15°C
Can be found up to -40°C with a mixture of ice crystals, and supercooled water droplets
Below -40°C supercooled water droplets freeze automatically

Question 24

In moving air masses, under what conditions are condensation and evaporation likely to occur

Answer 24

Condensation: when air is cooled (usually by ascent) to its dew point

Evaporation: when air is warmed or moves into drier air, lowering relative humidity

Question 25

What happens to the amount of water vapour in a saturated parcel of air when the temperature increases

Answer 25

The actual water vapour stays the same, but the air becomes unsaturated because its capacity to hold vapour increases

Question 26

How does vapour pressure compare between a supercooled water surface, a water surface, and an ice surface

Answer 26

Highest over supercooled water, then liquid water, and lowest over ice Because water molecules escape more easily from liquid (even when supercooled) than from a crystalline ice lattice

Question 27

What happens when air reaches its saturation vapour pressure and why How does vapour pressure vary with temperature

Answer 27

Water vapour in the air condenses Cooling air lowers the equilibrium vapor pressure, leading to condensation if the air was near saturation Vapor pressure decreases as temperature decreases

Question 28

What precipitation/turbulence is associated with the following cloud types: 1. Stratus 2. Stratocumulus 3. Nimbostratus 4. fair-weather Cumulus 5. Cumulonimbus 6. Cirrus / Cirrostratus

Answer 28

1. Light drizzle, poor visibility, smooth air, possible icing if below 0°C 2. Little or no precipitation, light turbulence, possible icing 3. Continuous rain/snow, poor visibility, moderate icing, generally smooth air 4. Light turbulence, little or no precipitation, icing if supercooled 5. Heavy rain, hail, severe turbulence, severe icing, wind shear, thunderstorms 6. No precipitation reaching ground, jet-stream turbulence

Question 29

What conditions contribute to the formation of frontal fog

Answer 29

When rain falls from relatively warm air aloft through a layer of cold, stable air at the surface, causing the cold air to become saturated Type of fog is most commonly associated with warm fronts, where the warm, moist air overruns the cold air, but it can also occur in advance of, or behind, slow-moving cold fronts

Question 30

When do the following types of precipitation occur: 1. Rain 2. Snow 3. Freezing Rain 4. Sleet / Ice Pellets 5. Hail 6. Drizzle 7. Graupel

Answer 30

1. Entire column above 0°C 2. Entire column below 0°C 3. Snow melts in warm layer aloft, falls through shallow sub-zero layer, freezes on contact with surfaces 4. Snow melts, then refreezes before reaching ground 5. Cumulonimbus only Strong updrafts Repeated lifting through freezing level 6. Stratus/Nimbostratus Small droplets, low intensity 7. Soft hail Supercooled droplets freeze onto snowflakes

Question 31

What type of air movement leads to fog formation

Answer 31

Cooling of air near the surface Usually via horizontal movement (advection fog) or radiation cooling Little vertical motion

Question 32

At what temperatures are the following found in clouds: 1. Supercooled water droplets 2. Freezing rain 3. Ice crystals

Answer 32

1. 0°C to about -15°C 2. Liquid drops below 0°C to -5°C, formed aloft, freeze on impact 3. Primarily below -15°C, dominant below -40°C

Question 33

What clouds/weather can be associated with warm and cold fronts in south africa

Answer 33

- Warm Front Cloud sequence: -Cirrus - Cirrostratus - Altostratus - Nimbostratus Weather: -Widespread layered cloud -Steady rain -Poor visibility -Frontal fog Slow, widespread, wet - Cold Front Clouds: -Cumulonimbus - mainly along front if unstable air, heavy rain/thunderstorms -Cu/Sc behind the front (post-frontal clearing) Weather: -Heavy showers -Thunderstorms -Gusty winds -Severe turbulence -Snow on high ground (Cape winter) Fast, violent, unstable

Question 34

What temperature is ice most likely to form on an aircraft

Answer 34

0 to -15°C

Question 35

What is the definition of the following types of icing: 1. Trace 2. Light 3. Moderate 4. Severe

Answer 35

1. Ice becomes perceptible. Rate of accumulation is slightly greater than sublimation. No de-icing required 2. Rate of accumulation may create a problem if flight continues longer than 1 hour. De-icing occasionally required 3. Accumulation rate is such that even short encounters become hazardous. De-icing required 4. Accumulation is so rapid that de-icing systems fail to reduce or control it. Immediate exit required

Question 36

What are the following and when do they occur 1. Hoar Frost 2. Rime Ice 3. Clear Ice 4. What is mixed ice

Answer 36

1. Ice crystals formed by deposition when moist air contacts a surface below 0°C, usually overnight in clear, calm conditions Cloud: None Temp: Below 0°C 2. Forms from small supercooled droplets freezing immediately on impact, creating a rough, milky, porous surface Cloud: Stratus / stratocumulus Temp: ~0°C to –15°C 3. Forms from large supercooled droplets that spread before freezing, creating smooth, dense, heavy ice. Cloud: Cumulonimbus, Ns, freezing rain Temp: ~0°C to –10°C 4. Combination of rime and clear ice, caused by varying droplet sizes.

Question 37

What type of ice is formed from small and large supercooled water droplets

Answer 37

Small - Rime ice Large - Clear ice

Question 38

When is icing most likely to occur(seasons, front type, cloud type)

Answer 38

Most common in winter but occur any time of year Warm fronts and occluded fronts Warm, moist air is lifted over colder air Produces widespread cloud, precipitation, and supercooled droplets Icing often occurs ahead of the surface front and within the frontal cloud mass Cumuliform clouds Strong vertical motion High liquid water content Stratus / Cumulus / Cumulonimbus Widespread, persistent cloud Produces moderate but prolonged icing

Question 39

In which regions are thunderstorms mostly encountered, and why

Answer 39

**Regions Thunderstorms are mostly encountered** - Tropical regions (most frequent and intense) - Subtropical regions - Also mid-latitudes during warmer seasons, though less frequently **Why thunderstorms are most common there** - Strong surface heating - High solar angles cause intense convection - Abundant low-level moisture - Warm oceans and evaporation supply moisture - High atmospheric instability - Steep lapse rates allow vigorous vertical development - Trigger mechanisms - ITCZ convergence, sea-breeze fronts, terrain, and frontal lifting

Question 40

Jet Streams 1. Where are jetstreams found 2. What are the main types of jetstreams 3. What hazards are associated with jetstreams 4. Where is CAT most likely relative to the jet

Answer 40

1. -Near the tropopause - At boundaries of strong horizontal temperature gradients - Typically above frontal zones, especially polar fronts 2. -Polar Jet Stream: ~ 60° N/S - associated with the polar front and is generally stronger, especially in winter - Subtropical Jet Stream: 30° N/S) - typically higher in altitude and more stable in position than polar jet - Tropical Easterly Jet - active in summer over Africa and India - Polar Night Jet - found in the stratosphere during winter 3. -Clear Air Turbulence (CAT) due to strong wind shear -Severe wind shear (vertical and horizontal) -Rapid weather development and intensification of frontal systems -Significant headwind / tailwind effects affecting fuel and timing 4. -Near the jet core - On the cold air (polar) side

Question 41

What is the formula for: 1. Temperature error 2. Pressure altitude 3. Density altitude

Answer 41

1. Height Error ≈ 4 ft × (height in 1000 ft) × (ISA deviation in °C) Cold = lower than indicated 2. Pressure Altitude = Indicated Altitude + (1013 - QNH) × 30 3. Density Altitude = Pressure Altitude + [120 × (OAT - ISA)]

Question 42

In the Southern Hemisphere, when flying north/south with easterly/westerly drift, will the altimeter over- or under-read

Answer 42

Flying South: Westerly drift: drifting toward higher pressure - altimeter under-reads Easterly drift: drifting toward lower pressure - altimeter over-reads Flying North: Westerly drift: drifting toward lower pressure - altimeter over-reads Easterly drift: drifting toward higher pressure - altimeter under-reads

Question 43

What are characteristics of the Polar Front Jet (PFJ) and Subtropical Jet (STJ)

Answer 43

Polar Front Jet (PFJ) -Forms along the polar front - the boundary between cold polar air and warmer mid-latitude air ~ 60°, near the tropopause -Cold air side of the front has the strongest wind speeds -Driven by strong horizontal temperature gradients (thermal wind) -Most pronounced in winter, weaker in summer Subtropical Jet (STJ) -Forms near the tropopause at ~30° latitude -Related to Hadley cell descending air and conservation of angular momentum -Usually on the poleward side of the subtropical high, not along a frontal boundary -Clear air turbulence often occurs on the equator side of the jet

Question 44

What are the following and what weather is associated with: 1. Polar front 2. Arctic front

Answer 44

1. The boundary between cold polar air and warm tropical (or mid-latitude) air Associated weather: - Frontal depressions / cyclones often develop along this boundary - Jetstreams (polar jet) are aligned roughly along it - Widespread cloud and rain due to overrunning of warm air over cold air 2. The boundary between very cold arctic air and the less cold polar air Associated weather: - Sharp temperature drops when the front passes - Snow and squalls in winter - Strong, gusty winds due to tight pressure gradients

Question 45

What weather is associated with the following 1. Cut-off Low 2. Col 3. Trough 4. Ridge

Answer 45

1. Prolonged rain Thunderstorms Cold, unstable air Poor flying conditions 2. Light winds Poor visibility Fog / haze 3. Unstable air Showers Thunderstorms 4. Generally stable conditions Light to moderate winds Low cloud, fog or haze possible near the surface (especially at night/morning)

Question 46

How do isobars typically appear around a/an: 1. Cyclone 2. Anti-Cyclone

Answer 46

1. Closed circles Tightly spaced Pressure decreases toward centre 2. Closed circles Widely spaced Pressure increases toward centre

Question 47

How do cyclones and anti-cyclones differ in pressure gradient and duration

Answer 47

Cyclones(low pressure): Steep gradient Strong winds Shorter duration Anti-cyclones(high pressure): Gentle gradient Light winds Longer lasting

Question 48

In the Southern Hemisphere, what happens to wind with the passage of a: 1. Warm front 2. Cold front

Answer 48

Warm front: - Ahead of the front (cold sector): Winds are typically from the south or southeast, carrying cooler air - At the moment of passage: Winds veer clockwise gradually (e.g., SE - S - SW), bringing warmer air - After the front (warm sector): Winds settle into northwesterly or northerly flow - Wind gradually increases Cold front: - Before cold front: Winds may back slightly (NE - N) as front approaches - During cold front passage: Winds veer clockwise sharply (e.g., N - NW - W) - After cold front: Winds settle into southerly / southwesterly post-frontal flow - Wind sharply increases

Question 49

What is the following: 1. Pressure gradient force 2. Coriolis force 3. Which direction does the Coriolis force act in the Southern and Northern Hemisphere

Answer 49

1. The force caused by pressure differences, accelerating air from high pressure toward low pressure 2. An apparent force caused by Earth’s rotation that deflects moving air: 3. To the left in the Southern Hemisphere To the right in the Northern Hemisphere

Question 50

What are the following and where do they occur: 1. geostrophic wind 2. trade winds 3. westerlies 4. polar easterlies

Answer 50

1. Wind where PGF and Coriolis force balance, causing airflow parallel to isobars. Where: Above the friction layer (~2000–3000 ft AGL) 2. Persistent N/S easterly winds blowing from subtropical highs toward the equator Where: Between ~30°S and the equator 3. Prevailing winds blowing from west to east in the mid-latitudes Where: ~30° to 60° latitude 4. Cold winds blowing from east to west near the polar regions Where: Pole to ~60°

Question 51

What happens to wind direction and speed at sunrise vs sunset in the Southern vs Northern hemisphere and why

Answer 51

- At sunrise: Surface warms Stability decreases Mixing increases Surface wind speed increases Coriolis Force strengthens (because CF ∝ wind speed) SH - Wind Backs and Increases NH - Wind Veers and Increases - At sunset: Surface cools Stability increases Mixing decreases Surface wind speed drops Coriolis force weakens (because CF ∝ wind speed) SH - Wind Veers and Decreases NH - Wind Backs and Decreases

Question 52

What happens to surface wind during the day vs at night in the Southern Hemisphere

Answer 52

Day: Wind Backs Wind Increases Night: Wind Veers Wind Decreases

Question 53

What are the 3 jet streams and what are their characteristics

Answer 53

Polar Front Jet (PFJ) Present year-round Flows West → East Avg height: ~30 000-39 000ft SACAA exam answer: 40 000ft Strongest in winter hemisphere Subtropical (Tropical) Jet (STJ) Present year-round Flows West → East Avg height: ~35 000-45 000ft Weaker than Polar Jet Forms near the subtropical high-pressure belt Equatorial Easterly Jet (EEJ) Seasonal, mainly in summer hemisphere Flows East → West Avg height: ~45 000-50 000ft Formed due to strong temperature gradients (monsoon effect)

Question 54

During which phase of a cumulonimbus can a microburst occur

Answer 54

During the mature stage

Question 55

What are the three stages of a thunderstorm and what occurs in each

Answer 55

Cumulus stage - Updrafts only, cloud building, no precipitation at surface Mature stage - Updrafts and downdrafts, heavy rain, hail, turbulence, lightning, possible microbursts Dissipating stage - Downdrafts dominate, precipitation decreases, storm weakens

Question 56

What are the different types of fog and how do they form

Answer 56

Radiation fog – Cooling of air near the ground by radiation at night Advection fog – Warm moist air moving over a cold surface Upslope (orographic) fog – Moist air forced up sloping terrain and cooled Frontal fog – Rain evaporating into colder air near a frontal zone Steam (evaporation) fog – Cold air moving over warm water

Question 57

What wind changes are associated with the passage of different fronts (backing/veering, increase/decrease)

Answer 57

Cold front (SH): Wind veers Wind speed often increases at passage, then stabilises Warm front (SH): Wind backs on approach, then veers after passing Wind speed usually increases gradually Occluded front: Wind change depends on dominant front type Often veering with moderate increase Stationary front: Little or no wind direction change Wind speed generally steady Back/Veer reversed for NH

Question 58

How does a sea breeze compare to a land breeze in terms of strength

Answer 58

Sea breeze: Stronger Greater temperature contrast (land heats faster than sea) Land breeze: Weaker Smaller temperature gradient (land cools faster at night)

Question 59

What Q-code is used to indicate isobars on a surface weather chart

Answer 59

QFF

Question 60

What is the difference between a sideslip and a forward slip, and from which direction does the relative airflow come

Answer 60

Sideslip Purpose: Lateral control / crosswind correction made to land with wheels aligned with runway Aircraft attitude: Bank into the wind Rudder applied opposite the bank Result: Aircraft moves sideways relative to the air Relative airflow: Comes from the opposite side to the direction of slip ie. Right sideslip, RAF from the left Forward Slip Purpose: Increase drag / steepen descent Aircraft attitude: Bank into wind Rudder applied opposite the bank Result: Aircraft maintains track but descends rapidly Relative airflow: Comes from the opposite side to the slip direction

Question 61

When travelling from A to B, QNH increases but true altitude remains the same. What can be said about the air temperature at B

Answer 61

Because true altitude is unchanged while QNH increases, the air at B must be colder to contract the air column and offset the effect of higher pressure

Question 62

What type of weather can be expected near the ITCZ

Answer 62

Frequent thunderstorms (CB) Heavy rain and showers High humidity Light and variable surface winds Strong updraughts and downdraughts Severe turbulence and icing in CBs

Question 63

What winds are found at the following latitudes: 0-10° 10-30° 30-60° 60-90°

Answer 63

0-10°: Light and variable winds (Doldrums / ITCZ) 10-30°: Trade winds Northern Hemisphere: NE trades Southern Hemisphere: SE trades 30-60°: Westerlies 60-90°: Polar easterlies

Question 64

What is the minimum wind velocity for a jet stream

Answer 64

60 knots

Question 65

What does the amount of water vapour air can hold depend on

Answer 65

Air temperature only. Warmer air can hold more water vapour Colder air can hold less water vapour

Question 66

What is the relationship between ELR and DALR and SALR in: Stable air Conditionally unstable air Unstable air

Answer 66

Stable: ELR

Question 67

Why does dry air enhance cooling at night

Answer 67

Less water vapour = less absorption of outgoing longwave radiation

Question 68

Why do clouds reduce night-time cooling

Answer 68

Clouds absorb and re-radiate long wave radiation emitted by the Earth's surface

Question 69

Why does the surface cool faster than the air above it at night

Answer 69

The surface loses heat directly by longwave radiation The air above is cooled mainly by conduction from the surface, so it cools more slowly and only after the surface temperature drops

Question 70

Why is wind shear generally stronger at night

Answer 70

Surface cools, and a stable inversion forms Friction slows surface wind Above the inversion, wind remains strong Large vertical wind gradient forms, and creates strong vertical wind shear

Question 71

At what altitude is pressure approximately 50% of MSL in ISA

Answer 71

18 000 ft

Question 72

What is the fundamental difference in formation mechanism between advection fog and radiation fog

Answer 72

Radiation fog - surface cooling (nighttime radiational heat loss) Advection fog - Warm moist air moving over a colder surface

Question 73

What wind conditions favour advection fog and radiation fog

Answer 73

Radiation fog - Light winds - stronger winds dissipate it Advection fog - Moderate winds - too weak = no transport - too strong = mixing lifts it into stratus