Meteorology

Question 1

What is troposphere

Answer 1

It is the first layer of the atmosphere. It extends up to 48,000 feet (14.5 km) over the equatorial regions. The vast majority of weather, clouds, storms, and temperature variances occur within this first layer of the atmosphere. Inside the troposphere, the average temperature decreases at a rate of about 2 °Celsius (C) every 1,000 feet of altitude gain, and the pressure decreases at a rate of about one inch per 1,000 feet of altitude gain.

Question 2

What is tropopause

Answer 2

It is a boundary at the top of troposphere. It traps moisture and the associated weather in the troposphere. The altitude of the tropopause varies with latitude and with the season of the year; therefore, it takes on an elliptical shape as opposed to round. Location of the tropopause is important because it is commonly associated with the location of the jet stream and possible clear air turbulence.

Question 3

What is coriolis force

Answer 3

The force created by the rotation of the Earth is known as the Coriolis force. In the northern hemisphere, the coriolis force deflects the airflow to the right (I.e. Westerly wind), and in the Southern Hemisphere, wind is deflected to the left.

Question 4

What is jet stream

Answer 4

Jet stream is a strong, narrow current in the upper tropopause or stratosphere. The wind speed must be greater than 60 knots to be classified as a jet stream.

Question 5

Why jet streams are westerlies?

Answer 5

STJ
On a global scale, surplus heating in the tropics creates north-south upper level temperature
gradients, which, in turn, creates upper-level high pressure at the equator. The resulting pressure gradient force causes upper air flow from the equator to the poles, which turns
eastward due to Coriolis Effect. So the winds in the upper troposphere are westerly at
midlatitudes.
PJ
The polar front jet forms in the region of strong temperature gradients between cold, polar air
and warmer air masses. The gradients increase with altitude because the warmer air columns
have a larger cumulative expansion than the colder air columns. The consequent pressure
difference in the upper troposphere will increase with altitude and cause strong winds.

Question 6

Pressure lapse rate

Answer 6

with every 1,000 feet of increase in altitude, the atmospheric pressure decreases 1 “Hg.

-reduces quicker with height in cold air

Question 7

ISA sea level pressure

Answer 7

1013. 2 mb

29. 92 “Hg

Question 8

ISA air temperature at sea level

Answer 8

15C

Question 9

Temperature lapse rate

Answer 9

1.98C per 1000ft

Question 10

ISA temperature above 36090ft

Answer 10

Constant at -56.5C

Question 11

How altitudes affect flight

Answer 11

• higher altitudes, thin air, more lift obtained by increasing speed, thus increasing takeoff and landing distance
• thin air, less efficient aircraft, thus decreasing climb rate

Question 12

Isobar

Answer 12

Isobars are lines drawn on the chart to depict lines of equal pressure.

Question 13

Anticyclone “high”

Answer 13

Greatest pressure in the centre

NH: wind rotates clockwise

Good weather

Question 14

Depression “low”

Answer 14

Lowest pressure in the centre

NH: wind rotates counterclockwise around a low

Bad weather

Question 15

QNH

Answer 15

Observed barometric pressure reduced to msl assuming ISA condition

-altimeter reads its height above sea level

Question 16

QFE

Answer 16

Pressure at a given datum

Altimeter reads vertical distance above datum

With aerodrome QFE set in the subscale, it will read 0 after landing

Question 17

QNE

Answer 17

Height indicated in the altimeter on landing at an aerodrome when the altimeter subscale is set to 1013.25mb

Used above FL150

Question 18

Wind pattern

Answer 18

In the Northern Hemisphere, the flow of air from areas of high to low pressure is deflected to the right and produces a clockwise circulation around an area of high pressure. This is known as anticyclonic circulation. The opposite is true of low-pressure areas

Question 19

Factors that affect wind

Answer 19

1. Pressure gradient force
2. Coriolis force
3. Friction

Question 20

Interrelation of coriolis force and pressure gradient

Answer 20

• when pgf=cf, wind blows on straight path along isobars
• cf>pgf, curved flow is around high pressure, wind curves clockwise around a high
• When the pressure gradient force is greater than the Coriolis force, the flow follows a curved path around low pressure. In the southern hemisphere this flow around a low pressure is in a clockwise direction.
• These relationships break down in the equatorial region when Coriolis force becomes so small that its influence is negligible. At the equator Coriolis force is zero, and is negligible from there to about 15 degrees latitude.

Question 21

Geostrophic wind

Answer 21

• In the atmosphere above the friction layer, only PGF and Coriolis force affect the horizontal motion of air
• Wind blows parallel to isobars when two forces in balance

Question 22

Gradient wind

Answer 22

At the surface of the Earth, all three forces come into play. As frictional force slows the wind speed, Coriolis force decreases. However, friction does not affect PGF. PGF and Coriolis force are no longer in balance. The stronger PGF turns the wind at an angle across the isobars toward lower pressure until the three forces balance.

Question 23

Friction layer

Answer 23

Friction between the wind and the terrain surface slows the wind. The rougher the terrain, the greater the frictional effect. Also, the stronger the wind speed, the greater the friction. it is always acting opposite to wind direction.
The frictional drag of the ground normally decreases with height and becomes insignificant above the lowest few thousand feet.

Question 24

Wind shear

Answer 24

Wind shear is a sudden, drastic change in wind speed and/or direction over a very small area. Wind shear can subject an aircraft to violent updrafts and downdrafts, as well as abrupt changes to the horizontal movement of the aircraft. While wind shear can occur at any altitude, low-level wind shear is especially hazardous due to the proximity of an aircraft to the ground. Low-level wind shear is commonly associated with passing frontal systems, thunderstorms, temperature inversions, and strong upper level winds (greater than 25 knots).
- the lighter the aircraft and its airspeed, the more vulnerable it is to wind shear

Question 25

Microburst

Answer 25

The most severe type of low-level wind shear, a microburst, is associated with convective precipitation into dry air at cloud base. Microburst activity may be indicated by an intense rain shaft at the surface but virga at cloud base and a ring of blowing dust is often the only visible clue. A typical microburst has a horizontal diameter of 1–2 miles and a nominal depth of 1,000 feet. The lifespan of a microburst is about 5–15 minutes during which time it can produce downdrafts of up to 6,000 feet per minute (fpm)and headwind losses of 30–90 knots, seriously degrading performance. It can also produce strong turbulence and hazardous wind direction changes

Question 26

Potential hazards of wind shear

Answer 26

- Turbulence - Violent air movement (up- or down-draughts or swirling or rotating air patterns) - Sudden increase or reduction of airspeed - Sudden increase or decrease of groundspeed and/or drift. - Clear Air Turbulence (CAT), which may be very severe, is often associated with jet streams. - Rotor action or down-draughts in the lee of mountain waves can create difficult flying conditions and may even lead to loss of control.

Question 27

When meeting a shear zone on approach to land

Answer 27

Angle of descent steepens as indicated airspeed reduces

Question 28

Most common situations where low level wind shear can be expected

Answer 28

- descending into a dense friction layer - descending into a cold zone - descending into the lee of sand dunes when a sea breeze blows - descending where the reported wind is lighter and blowing from a different direction than above that level - descending or ascending through a sea breeze boundary

Question 29

Sea breeze

Answer 29

During the day, land heats faster than water, so the air over the land becomes warmer and less dense. It rises and is replaced by cooler, denser air flowing in from over the water. This causes an onshore wind called a sea breeze. -10-15 kts

Question 30

Land breeze

Answer 30

at night land cools faster than water, as does the corresponding air. In this case, the warmer air over the water rises and is replaced by the cooler, denser air from the land, creating an offshore wind called a land breeze. 3-4 kts

Question 31

Sea breeze cloud

Answer 31

Cumulus cloud

Question 32

Sea breeze time

Answer 32

Sets in around 10am Peaks at 3pm Cease before sunset

Question 33

Mountain and valley breezes

Answer 33

- during the day the air above the mountain is heated and rises creating a valley breeze - at night air above the mountain cools more rapidly and sinks creating a mountain breeze

Question 34

Katabatic and anabatic winds

Answer 34

At night, When air over sloped terrain is cooled by conduction it becomes denser than near free air and drains to lower levels. The winds generated are known as katabatic winds. The reverse effect occurs on slopes on sunny days. Air in contact with a slope warms by conduction and ascends (not necessarily following the slope). Such ascending winds are called anabatic winds. The upward flow will be strongest in the early afternoon and over sun facing slopes. -anabatic wind is weaker because it has to work against gravity

Question 35

Factors affecting Katabatic and anabatic winds

Answer 35

1. the degree of cooling along the slope (the colder the surface, the greater the potential for the generation of very dense air and hence greater wind speed); 2. the roughness of the slope (the smoother the slope the greater the potential for uninterrupted and thus stronger flow); 3. the steepness of the slope (gentle slopes are more favorable for katabatic development because steep slopes cause the wind to become turbulent, resulting in mixing with surrounding air and the consequential breakdown of continual downward movement of cold air).

Question 36

Downslope wind

Answer 36

While the wind flows smoothly up the windward side of the mountain and the upward currents help to carry an aircraft over the peak of the mountain, the wind on the leeward side does not act in a similar manner. As the air flows down the leeward side of the mountain, the air follows the contour of the terrain and is increasingly turbulent. This tends to push an aircraft into the side of a mountain. The stronger the wind, the greater the downward pressure and turbulence become.

Question 37

Mountain waves

Answer 37

Airflow over a ridge or mountain range may disturb flow downstream to a great height. The flow upwind of the ridge is smooth and horizontal. At the ridge line the airflow is lifted and follows the shape of the ridge. On the other side a dramatic change in the flow takes place. The flow does not return to horizontal flow but continues as a wave that may be smooth or may contain dangerous turbulent zones. If the air stream is sufficiently moist at any level, cloud may form in the ascending sections and produce almond or lens-shaped clouds called lenticular clouds. However if the air is dry the first indication of wave motion for a pilot may be a rapidly increasing or decreasing altimeter reading.

Question 38

Föhn wind

Answer 38

1. lower cloud base and precipitation on windward slopes; 2. higher cloud base on lee slopes; 3. higher temperatures and hence lower density at low levels in the lee of the mountain.

Question 39

The conditions required for mountain waves

Answer 39

1. wind perpendicular or near perpendicular to the mountain; 2. wind strength of at least 25 to 30 knots near the mountain top; 3. wind speed increasing with height; 4. a stable layer.

Question 40

Define stability

Answer 40

Atmospheric stability tells you how likely it is air will rise and form clouds and precipitation.

Question 41

Stable air

Answer 41

if, because of the vertical temperature distribution, a lifted parcel is cooler and therefore denser than the surrounding air, the parcel will tend to sink. Thus the environment is defined as being stable;

Question 42

Unstable air

Answer 42

if, because of the vertical temperature distribution, a lifted parcel is warmer and less dense than the surrounding air, the lifted parcel will continue to rise. In this case the environment is defined as being unstable;

Question 43

Neutral air

Answer 43

because of the vertical temperature distribution, a lifted parcel is the same temperature as the surrounding air, conditions are said to be neutral;

Question 44

conditional instability

Answer 44

in some situations the atmosphere is stable for unsaturated parcels of air but unstable if saturated

Question 45

Adiabatically process

Answer 45

Air changes temperature due to change of pressure No exchange of heat with surroundings

Question 47

Temperature lapse rate

Answer 47

The rate of decrease of temperature per unit increase of height I.e. C per 1000ft

Question 48

DALR

Answer 48

Dry Adiabatic Lapse Rate (DALR) is the rate of cooling of unsaturated air 3C/1000ft

Question 49

SALR

Answer 49

saturated adiabatic lapse rate (SALR) is the rate at which the temperature of a parcel of air saturated with water vapour changes as the parcel ascends. - cooling is partly offset by the latent heat of condensation - 1.5°C/1000 feet

Question 50

ELR

Answer 50

The environmental lapse rate (ELR), is the rate of decrease of temperature with altitude in the stationary atmosphere at a given time and location. ISA: 1.98 °C/1,000 ft from sea level to 11 km (36,090 ft or 6.8 mi). From 11 km up to 20 km (65,620 ft or 12.4 mi), the constant temperature is −56.5 °C (−69.7 °F)

Question 51

ELR

Answer 51

Stable

Question 52

DALR,SALR < ELR

Answer 52

Unstable

Question 53

DALR>ELR>SALR

Answer 53

Conditional unstable

Question 54

Inversion

Answer 54

- negative lapse rate (temp increase with altitude) - enhance stability(limit vertical movement) - visibility below is fair and above is clear(weather and pollutants kept below the layer)

Question 55

Below inversion layer

Answer 55

Risk of carburettor icing

Question 56

Surface-based temperature inversions

Answer 56

occur on clear, cool nights when the air close to the ground is cooled by the lowering temperature of the ground. The air within a few hundred feet of the surface becomes cooler than the air above it.

Question 57

Subsidence inversions

Answer 57

occur with high-pressure systems that cause air in the upper levels to sink and thus warm. When the upper layer warms at a greater rate, an inversion is formed

Question 58

Frontal inversion

Answer 58

- occur when warm air spreads over a layer of cooler air, - or cooler air is forced under a layer of warmer air.

Question 59

Fog

Answer 59

Fog is a cloud that is on the surface. It typically occurs when the temperature of air near the ground is cooled to the air’s dew point. At this point, water vapor in the air condenses and becomes visible in the form of fog. - visibility less than 1000m - air must be stable

Question 60

Conditions required for fog

Answer 60

- cooling - adequate supply of moisture - availability of condensation nuclei

Question 61

Radiation fog

Answer 61

On clear nights, with relatively little to no wind present, radiation fog may develop. Usually, it forms in low-lying areas like mountain valleys. This type of fog occurs when the ground cools rapidly due to terrestrial radiation, and the surrounding air temperature reaches its dew point. As the sun rises and the temperature increases, radiation fog lifts and eventually burns off. Any increase in wind also speeds the dissipation of radiation fog. If radiation fog is less than 20 feet thick, it is known as ground fog.

Question 62

Conditions for radiation fog

Answer 62

1. Anticyclones and long clear night (clear sky for terrestrial radiation to escape) 2. Light wind for mixing of surface air 3. Land

Question 63

Dispersal of radiation fog

Answer 63

When solar radiation is introduced, relative humidity is reduced

Question 64

Advection fog

Answer 64

When a layer of warm, moist air moves over a cold surface, advection fog is likely to occur. Unlike radiation fog, wind is required to form advection fog. Winds of up to 15 knots allow the fog to form and intensify; above a speed of 15 knots, the fog usually lifts and forms low stratus clouds. Advection fog is common in coastal areas where sea breezes can blow the air over cooler landmasses.

Question 65

Difference between radiation fog and advection fog

Answer 65

advection fog : - can form over sea - requires a surface that is already cold rather than one that is cooling - can persist throughput the day - require wind

Question 66

Dispersal of advection fog

Answer 66

- decrease in moisture content of the moving air | - change in wind direction

Question 67

Upslope fog

Answer 67

Upslope fog occurs when moist, stable air is forced up sloping land features like a mountain range. This type of fog also requires wind for formation and continued existence. Upslope and advection fog, unlike radiation fog, may not burn off with the morning sun but instead can persist for days. They can also extend to greater heights than radiation fog

Question 68

Steam fog

Answer 68

Steam fog, or sea smoke, forms when cold, dry air moves over warm water. As the water evaporates, it rises and resembles smoke. This type of fog is common over bodies of water during the coldest times of the year. Low-level turbulence and icing are commonly associated with steam fog.

Question 69

Ice fog

Answer 69

Ice fog occurs in cold weather when the temperature is much below freezing and water vapor forms directly into ice crystals. Conditions favorable for its formation are the same as for radiation fog except for cold temperature, usually –25 °F or colder. It occurs mostly in the arctic regions but is not unknown in middle latitudes during the cold season.

Question 70

What's the fog at Golden Gate Bridge

Answer 70

Advection fog forms when humid air from the Pacific Ocean swoops over the chilly California current flowing parallel to the coast. The fog hugs the ground and then the warm, moist air condenses as it moves across the bay or land. This is common near any coastline. Sometimes, high pressure squashes it close to the ground. By the way, the color of the Bridge is International Orange and was chosen in part because of its visibility in the fog. -common in summer

Question 71

How does cloud form

Answer 71

When the air cools and reaches its saturation point, the invisible water vapor changes into a visible state. Through the processes of sublimation and condensation, moisture condenses or sublimates onto matter like dust, salt, and smoke known as condensation nuclei.

Question 72

Types of cloud

Answer 72

1. Cumulus-type | 2. Stratus-type

Question 73

Cumulus-type clouds

Answer 73

- vertical extend | - indicate unstable weather

Question 74

Stratus-type clouds

Answer 74

- horizontal extend | - stable weather

Question 75

Types of cloud formation

Answer 75

1. Orographic 2. Convection 3. Turbulence 4. Frontal lifting

Question 76

Cloud classification

Answer 76

1. Low cloud - below 6500 ft - Stratus, cumulus, stratocumulus, cumulonimbus 2. Medium cloud - 6500 to 23000ft - altocumulus , altostratus, nimbostratus 3. High cloud - 16500-45000ft - cirrus, cirrocumulus, cirrostratus

Question 77

Orographic lifting

Answer 77

Orographic ascent is the forced vertical motion of air by mountains or raised terrain - stratiform: air is moist and stable - cumulus: air is moist and unstable

Question 78

Convection cloud

Answer 78

Air will rise from the surface by convection when surface air are heated Suitable conditions commonly occur when: strong surface heating occurs during the day; or a relatively cold air stream moves over a warmer surface. Cumuliform clouds form if the surface air is moist enough and the rising air is cooled to saturation at the condensation level. The depth of convection is determined by the moisture content of the rising air and the temperature distribution of the environmental air.

Question 79

Frontal lifting

Answer 79

- general ascent of air over a wide area - cold front: when cold air stream bumps into a warm one. Warm air forced to rise; creates cumulus - warm front: warm air overtakes a cold one, warm air forced to rise; creating stratiform cloud

Question 80

Turbulent cloud

Answer 80

Turbulent mixing between atmospheric layers above and below the level of the dew-point temperature -st and sc are usual

Question 81

Cirrus

Answer 81

Nil precipitation Dry ice crystal Light-moderate turbulence in jet stream

Question 82

Cirrostratus

Answer 82

Nil precipitation Dry ice crystal Negligible turbulence

Question 83

Cirrocumulus

Answer 83

Nil precipitation Dry ice crystal Light-moderate turbulence in jet stream

Question 84

Altostratus

Answer 84

Rain, snow, sleet Can cause severe rime or glaze icing Turbulence not common

Question 85

Altocumulus

Answer 85

Precipitation not common Light to moderate icing Light to moderate turbulence

Question 86

Stratus

Answer 86

Light drizzle Very light time ice Turbulent if amy inversion is present

Question 87

Stratocumulus

Answer 87

Light rain or drizzle Light to moderate rime ice Light turbulence

Question 88

Cumulonimbus

Answer 88

``` Can occur at any level Light to heavy showers Hail in CB severe glaze and rime ice in CB Moderate to severe turbulence in CB ```

Question 89

Nimbostratus

Answer 89

Persistent steady rain or drizzle Moderate rime ice and possible glaze icing Generally no turbulence

Question 90

Cumulus

Answer 90

Low cloud

Question 91

Warm front

Answer 91

- warm air advances towards cold air - gentle slope - predominantly stratiform clouds - cb is possible if unstable - speed 10-15 kts - distance to 1000km

Question 92

Cold front

Answer 92

A cold front occurs when a mass of cold, dense, and stable air advances and replaces a body of warmer air. It 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, forcing the creation of clouds. The type of clouds that form depends on the stability of the warmer air mass. A cold front in the Northern Hemisphere is normally oriented in a northeast to southwest manner and can be several hundred miles long, encompassing a large area of land.

Question 93

Effects of Cb

Answer 93

-thunderstorm - Turbulence. Vertical movement within a Cb can be as much as 50kt. The interaction between strong updrafts and strong downdrafts causes wind shear and severe turbulence within the cloud. Strong surface winds, variable in direction and strength, are common at surface level in the vicinity of the Cb. These can be particularly hazardous to aircraft on take-off or landing. - In-Flight Icing. Moderate to Severe icing can be expected, especially in the higher levels of the cloud. - Electrical disturbance. Aircraft flying in the vicinity of Cb clouds may experience electrical disturbances effecting communications and navigation systems. The electrical phenomenon known as St Elmo's Fire, while not a threat to safe flight, is an indication of nearby Cb activity. Aircraft in the vicinity of a Cb are at risk of being hit by Lightning. - Precipitation. Hail can cause significant structural damage to an aircraft. Other precipitation, such as snow, sleet, or rain, can contaminate airfield and runway surfaces creating a hazard to aircraft attempting to take-off or land. - Extreme weather. Severe downdrafts, microbursts and funnel clouds such as Tornados are also features of cumulonimbus clouds.

Question 94

What type of ice would you encounter when flying through CB?

Answer 94

Structural icing? | Hail?

Question 95

How many miles above the CB?

Answer 95

beware of flying through or just under the anvil. Although the turbulence levels are low, often severe-icing conditions exist, including super cooled ‘liquid’ water. Generally the advice is to avoid cbs by a minimum of 5nm; however, to provide a margin for errors in detection (different radar systems and their responses in these conditions), rapid cloud formation and movement, anvil conditions, and misjudgment, then my experience suggests that aiming for a 15nm miss distance is safer.

Question 96

Crosswind landing

Answer 96

pilots will either use "crabbing" (by pointing the aircraft towards the wind so that the aircraft heading forms an angle with the runway alignment) or use "wing-low" (adding a small rolling angle such that the two wings are not on the same levels) to counter balance the effect of crosswinds. As the first technique could potentially damage the landing gear, whereas the second technique may cause wing tip or engine to hit the ground when landing, the stronger the crosswinds, the larger the potential hazard to safe landing.