Meteorology

Question 1

How is Atmospheric Pressure measured?

Answer 1

Hectopascals

Question 2

What are Geostrophic winds?

Answer 2

As the air mass starts to move, it is deflected to the right by the Coriolis force. The deflection increases until the Coriolis force is balanced by the pressure gradient force. At this point, the wind will be blowing parallel to the isobars.

Question 3

What are Isobars?

Answer 3

Lines of equal pressure and usually depicted at 4 hPa intervals. They indicate the rate of pressure change over a horizontal distance; the closer together higher-pressure gradient

Question 4

What is a Pressure Gradient?

Answer 4

The air pressure difference between the two locations is called the pressure gradient, and the force that actually drives the air from high pressure areas to low pressure areas is called the pressure gradient force

Question 5

What is a trough?

Answer 5

Pressure is lower in the trough than at the two sides, indicated by isobars extending outwards from an area of low pressure. The isobars often appear in a sharp ‘V’ shape.

Question 6

What is a ridge?

Answer 6

A spur of higher-pressure extending form the high-pressure area. The associated isobars are always rounded, never V-shaped.

Question 7

What is a COL?

Answer 7

A region of almost uniform pressure between two highs and two lows.

Question 8

What are the effects of warmer air?

Answer 8

Air moving upward results in a low at the surface converges toward the centre of the low, producing wind. It spirals inwards towards low pressure is associated with cloud formation

Question 9

What are the effects of colder air?

Answer 9

Air moving downwards results in a high-pressure system on the surface spreads out and diverges, producing wind. The air spirals outwards from high-pressure and is associated with clear skies

Question 10

What are the ISA Conditions?

Answer 10

Surface pressure = 1013.2 hPa (29.92 in Hg)
Surface temperature = 15 °C
Up to 11 km (approx. 36 000 ft) the temperature decreases at 6.5 °C/km (approx. 1.98 °C/1000 ft)
Above 11 km (approx. 36 000 ft) the temperature remains constant at -56.5 °C
At sea level the density (ρ) is 1.225 kg/m³

Question 11

What is the Tropopause height?

Answer 11

On average the height of the tropopause is about 5 miles (25 000 ft) over the poles, 7 miles (35 000 ft) over the UK and 11 miles (55 000 ft) over the equator

Question 12

What is the temperature of the Tropopause?

Answer 12

The temperature at the tropopause will be higher at the poles than at the equator. Over the UK the average tropopause temperature is -56 °C but can be as warm as -40 °C in the winter, and as cold as -80 °C in tropical air in the summer.

Question 13

What is the significance of the Tropopause?

Answer 13

Jet streams occur just below
Clouds rarely occur at/above the tropopause
Clear Air Turbulence
Contrails
Gas Turbines are more efficient

Question 14

What are the trigger actions?

Answer 14

Convections
Orographic Uplift
Turbulence
Convergence
Mass Ascent

Question 15

What are the Icing Conditions for Temperature?

Answer 15

Almost all icing occurs in air temperatures between 0°C and -20 °C, however, it can occur above 0 °C if the aircraft surface temperature is below 0°C. Below -20 °C icing is rare (the air is dry), though physical limit extends to -40 °C.

Question 16

What are Super Cooled Water Droplets?

Answer 16

Water droplets that have remained liquid although they are below freezing point until they have a condensation nuclei (particles in the air such as dust, pollution, etc.) which attract and condense ambient water vapour in clouds.

Question 17

What are the general icing rules for convective clouds?

Answer 17

Below -40 °C: chance of icing is small

-40 °C to -20 °C: light icing possible; severe unlikely except in newly developed clouds

-20 °C to 0 °C: rate of icing may be severe over substantial depth of cloud

Question 18

What are ice severity levels?

Answer 18

Trace : Ice becomes perceptible.

Light: Rate of accumulation is about 0.5 cm in 15-60 minutes.

Moderate: The rate of accumulation is about 0.5 cm in 5-15 minutes.

Severe The rate of accumulation exceeds 0.5 cm in 5 minutes.

Question 19

What are the hazards of icing?

Answer 19

Aerodynamic Effects
Weight
Visibility
Engine Intake
Undercarriage
Pitot Tubes and antenna
Vibration
Communications
Control Surfaces

Question 20

What are the Global Air Masses?

Answer 20

Tropical Maritime (Tm)
Tropical Continental (Tc)
Polar Continental (Pc)
Arctic Maritime (Am)
Polar Maritime (Pm)
Equatorial Maritime (Em)
Arctic Continental (Ac)
Antarctic Continental (AAc)

Question 21

What is a METAR?

Answer 21

METAR (Meteorological Airfield Report) is a message (issued hourly or half-hourly) giving the observed weather conditions at an airfield

Question 22

What is a TAF?

Answer 22

Forecast of conditions and significant changes expected during a specified period. The weather report covers 5 miles radius around an airport and uses the same descriptors and abbreviations as a METAR report. It is issued every 3 hours for military airfields and some civil airfields

Question 23

What is an Air Mass?

Answer 23

Air masses are large bodies of air having broadly uniform characteristics of moisture and temperature.

Question 24

What is a Weather Front?

Answer 24

A front is the division between two air masses of differing temperatures (and hence density).

Question 25

What are the two types of fronts?

Answer 25

Warm
Cold

Question 26

How does a Warm front occur?

Answer 26

A warm front occurs when a warm mass of air advances and replaces a body of colder air.
The fronts move slowly, typically 8 to 20 kts, with a slope of the advancing front slides over the top of the cooler air and gradually pushes it out of the area.

The warm air mass has very high humidity, and as is lifted over the denser cold air, the temperature drops and condensation occurs.

Question 27

What is the gradient of a warm front?

Answer 27

Typically shallow, of the order 1:100, but can be as steep as 1:50 or as shallow as 1:200. The warmer air is seen to ride over the colder air and advance warning of an approaching warm front is clearly evidenced by high altitude cloud formation.

Question 28

What cloud formations are you likely to see with a warm front?

Answer 28

Initially Cirrus ahead of the front (Approx 30,000 ft and 900 km ahead.

As the height reduces you will see Cirrostratus and Altostratus then eventually nimbostratus.

Question 29

What weather will be seen with a warm front?

Answer 29

Altostratus in the region of 20 000 ft may give rain or snow but is likely to be slight and will evaporate before reaching the surface.

The lower, thicker cloud will inevitably bring precipitation heavy enough to reach the surface and this is typically 200-300 km ahead of the front. Persistent rain is likely until the passage of the front whereby it will stop or at least ease and then only intermittent precipitation is likely.

Question 30

What pressure will you see with a warm front?

Answer 30

As the front approaches the proportion of warm to cold air vertically above the observer increases and therefore the pressure will drop.

The isobars are refracted toward the low pressure and this gives rise to the understanding that as the front approaches the pressure will fall steadily; this fall is arrested on the passage of the front and from then on the pressure will be steady.

Question 31

How does a cold front occur?

Answer 31

A cold front occurs when a mass of cold, dense and stable air advances and replaces a body of warmer air. The front moves more rapidly than warm fronts, progressing at a rate of 20 to 27 kts which typically moves in the opposite direction of a warm front

Question 32

Describe the slope of a cold front.

Answer 32

The slope is more pronounced and the air mass is so dense, it stays close to the ground, sliding under the warmer air and forcing the less dense air aloft. The rapidly ascending air causes the temperature to decrease suddenly, causing the creation of clouds.

Question 33

What is the cold front gradient?

Answer 33

Characteristically steeper than a warm front, typically 1:50.

The leading edge of the frontal surface commonly exhibits an overhanging nose caused by frictional retardation of the surface air.

This feature is transitory; formed by the over-running air above and then broken down by convective mixing, only for the process to re-occur.

This gives rise to a staggered progress which can cause severe gusts.

Question 34

What cloud and precipitation can you expect to see with a cold front?

Answer 34

If the warm air mass is convectively unstable then towering cumulus and cumulonimbus will readily form giving heavy rain of short duration, perhaps hail and thunder also.

In these conditions the precipitation may straddle the frontal surface and altocumulus will extend in advance of the front due to increased winds at that level.

Altostratus may also be present but a marked feature of the passage of the front is the rapid break-up of the cloud mass.

Question 35

What pressure will be seen with a cold front?

Answer 35

A cold front will also display a refraction of the isobars towards the low pressure and as a consequence, commonly, a fall of pressure in advance of the front is followed by a sharp rise on the front’s passage and thereafter a slower rise.

Question 36

What will the temperature be on a cold front?

Answer 36

There will be little change in advance of the front except where the temperature is lowered by associated precipitation.

The front’s passage will cause a sharp fall in temperature, associated with the changing air mass.

Thereafter the temperature will only vary with precipitation where a reduction can be anticipated.

Question 37

What is the wind associated with a Cold Front?

Answer 37

Ahead of the front the tendency will be for the wind to back and increase.

There will be a definite veering of the wind at the passage with squalls common.

After the passage the wind direction will be determined by the presence of squalls with the wind veering then backing as the squalls come through.

Question 38

What is an Occluded front?

Answer 38

Occluded fronts occur when a fast-moving cold front catches up with a slow-moving warm front.

Question 39

What is frontogenesis?

Answer 39

Frontogenesis is the formation or development of a front through the meeting of air or water masses from different origins.

Question 40

What is Frontolysis?

Answer 40

Frontolysis is the dissipation or weakening of an atmospheric front.

Question 41

What is a split front?

Answer 41

A split front is accompanied by a cyclonically curved cloud band, which, contrary to a classical Cold Front, contains a distinct double banded structure with cold cloud top temperatures at the leading edge and warmer cloud top temperatures at the rear edge.

Question 42

What is a stationary front?

Answer 42

A stationary front is a pair of air masses, neither of which is strong enough to replace the other.

Question 43

What weather will you likely see with a stationary front?

Answer 43

A wide variety of weather can be found along a stationary front, but usually clouds, prolonged precipitation, and storm trains are found there. When there is a lot of water vapor in the warmer air mass, significant amounts of rain or freezing rain can occur.

Question 44

What is a convergence line?

Answer 44

A convergence line is a band of cloud that remains stationary and can produce large amounts of rain across a relatively small area.

Question 45

Which way does the Earth’s rotation affect the circulation currents?

Answer 45

To the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Question 46

What are the three global cells?

Answer 46

Polar Cell
Ferrel (Mid Latitude) Cell
Hadley (Tropical) Cell

Question 47

What is the Polar Cell?

Answer 47

The cell is a closed circulation loop from about 60° to 90° latitude. It is within this cell that: Air rises, diverges and travels toward the poles. Once over the poles, the air sinks, forming the polar highs. At the surface air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies)

Question 48

What is the Ferrel (mid-latitude) cell.

Answer 48

The Ferrel cell is a mixing zone between the Hadley and Polar cells from about 30° to 60° latitude. This circulation cell (named by Ferrel in the C19th) is characterised by the air flows towards the relevant pole and eastward near the surface and towards the Equator and westward at higher levels

Question 49

What is the Hadley (tropical) cell.

Answer 49

The largest closed circulation cell, covering the equatorial region, the Hadley cell extending from the Equator (0°) to about 30° latitude. Low latitude air movement toward the Equator becomes heated, rises vertically and moves poleward in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates

Question 50

What are the four climatic controls that largely determine the climate of every ocean and continental region?

Answer 50

latitude, land and water distribution, topography and ocean currents.

Question 51

What are the 6 climate regions?

Answer 51

Polar
Temperate
Arid
Mediterranean
Tropical
Mountainous

Question 52

What are the trade winds?

Answer 52

Trade winds are the steady winds which blow on the equatorial side of the high pressure regions in both hemispheres.

Question 53

What are the three types of tropical storms?

Answer 53

Cyclones: Southwest Pacific Ocean west of 160° E and Indian Ocean

Typhoons: Northwest Pacific Ocean west of the dateline

Hurricanes: North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160° E

Question 54

What are the formation factors for tropical storms?

Answer 54

Warm, moist air and sea surface temperature generally greater than 26 °C

Winds near sea surface converging causing air to rise to form clouds

Low wind shear allowing allows the storm clouds to rise vertically to high levels

Sufficient distance from Equator for Coriolis force to impart spin (300 miles/480 km)