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Weather > Weather > Flashcards

Weather Flashcards

1
Q

What is the composition of the earth’s atmosphere?

A

Nitrogen 78%, Oxygen 21%, Argon, Carbon Dioxide, and traces of other gases 1% Also a small amount of water vapor which is responsible for major changes in the weather.

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2
Q

Describe the first layer of the earth’s atmosphere.

A

The troposphere extends from 4 to 12 miles over the northern and southern poles and up to 48,000 feet over the equatorial regions,

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3
Q

What is the significance of the troposphere in terms of weather?

A

The vast majority of weather, clouds, storms, and temperature variances occur within this first layer of the atmosphere.

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4
Q

Describe temperature and pressure variations within the troposphere.

A

The average temperature decreases at a rate of about 2 degrees celsius every 1,000 feet of altitude gain. The pressure decreases at a rate of about one inch per 1,000 feet of altitude gain.

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5
Q

What is the tropopause?

A

The tropopause is a boundary layer at the top of the troposhpere which traps moisture and the associated weather in the troposphere.

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6
Q

What is the altitude of the tropopause?

A

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.

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7
Q

Why is the location of the tropopause important to pilots?

A

The tropopause is commonly associated witht the location of the jet stream and possible clear air turbulence.

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8
Q

What is the stratosphere?

A

The stratosphere extends from the tropopause to a height of about 160,000 feet. Little weather existes in this layer and the air remains stable, although certain types of clouds occasionally extend into it.

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9
Q

What layers of the atmosphere lie above the stratosphere? Are they important in terms of weather?

A

The mesosphere and thermosphere lie above the stratosphere. They have little influence over weather.

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10
Q

What causes vertical circulation of the earth’s atmosphere?

A

The earth is wamed by energy radiating from the sun. The process causes a circular motion tht results when warm air rises and is replaced by cooler air.

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11
Q

Why does warm air rise?

A

Heat causes the air molecules to spread apart. As the air expands, it becomes less dense and lighter than the surrounding air.

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12
Q

Why does cool air sink?

A

As air cools, the molecules pack together more closely, becoming denser and heavier than warm air. As a result, cool, heavy air tends to sink and replace warmer rising air.

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13
Q

What is coriolis force?

A

The force caused by the earth’s rotation.

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14
Q

How does the coriolis force affect the circulation of the atomosphere?

A

Air is deflected to the right in the Northern Hemisphere causing it to follow a curved path instead of a straight line.

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15
Q

What causes the prevailing upper level westerly winds in the conterminous United States?

A

See PHAK pages 12-3 and 12-4.

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16
Q

Why are surface winds generally slower than winds at altitude?

A

Within 2,000 feet of the ground, friction between the surface and the atmosphere slows the moving air. It also changes the direction of the air flow.

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17
Q

What are standard sea level pressure and temperature?

A

29.92 inches of mercury and 59 degrees farenheit.

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18
Q

What does a pattern of rising pressure at a single weather station indicate?

A

This generally indicates the approach of fair weather.

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19
Q

What does a pattern of decreasing or rapidly falling pressure indicate?

A

This generally indicates approaching bad weather and possibly severe storms.

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20
Q

As altitude increases, what happens to pressure?

A

As altitude increases, pressure decreases an average of 1 inch per 1,000 feet.

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21
Q

What is the definition of Density Altitude?

A

Density Altitude is pressure altitude corrected for non-standard temperture.

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22
Q

How does Density Altitude affect the performance of an aircraft?

A

At higher altitudes, with a decreased atmospheric pressure, takeoff and landing distances are increased, while climb rates decrease.

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23
Q

Why does a higher Density Altitude increase takeoff performance?

A

If the air is thin, more speed is required to obtain enough lift for takeoff; therefore, the ground run is longer. Also, aircraft engines and propellers are less efficient. This leads to reduced rates of climb and a greater groud run for obstacle clearance.

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24
Q

At what altitude does the average person become impaired by reduced oxygen in the atmosphere?

A

The reactions of an average person become impaired at an altitude of around 10,000 feet, but for some people impairment can occur at an altitude as low as 5,000 feet.

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25
Q

What are some symptoms of Hypoxia?

A

Symptoms range from mild disorientation to total incapacitation, depending on body tolerance and altitude. PHAK page 2-7.

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26
Q

What causes wind?

A

Air flows from areas of high pressure into areas of low pressure because air always seeks out lower pressure.

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27
Q

What are two types of motion in the atmosphere?

A

Convection (vertical motion) and wind (horizontal motion).

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28
Q

Describe the flow of air around a High pressure area in the Northern Hemisphere.

A

Clockwise circulation of dry, descending air spreading outward.

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29
Q

Descrive the flow of air around a Low pressure area in the Northern Hemisphere.

A

Counter-clockwise circulation of air moving inward.

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30
Q

What type of weather is normally associated with a High pressure system?

A

Good weather is typically associated with high-pressure systems.

31
Q

What type of weather is normally associated with a Low pressure system?

A

Bad weather - increasing cloudiness and precipitation.

32
Q

In the Northern Hemisphere, when planning a flight from west to east where would you find favorable winds?

A

On the North side of a High pressure system or the South side of a Low pressure system.

33
Q

In the Northern Hemisphere, when planning a flight from east to west where would you find favorable winds?

A

On the Sorth side of a High pressure system or the North side of a Low pressure system.

34
Q

What causes convective currents?

A

Uneven heating of the air.

35
Q

Generally, how can you avoid turbulent conditions caused by updrafts and downdrafts?

A

Flying at higher altitudes, even above cumulus cloud layers.

36
Q

Cooler, denser air flowing in from over a large body of water is called a ___ ______?

A

Sea breeze.

37
Q

When cooler, denser air flows out from land over a large body of water it is called a ____ ______?

A

Land breeze.

38
Q

Which side of a mountain is the greatest and most dangerous turbulence located? (Windward or leeward)

A

Leeward (downwind). As the air flows down the leeward side of the mountain, the wind follows the contour of the terrain and is increasingly turbulent. This tends to push an sircraft into the side of a mountain.

39
Q

What is windshear?

A

A sudden, drastic change in wind speed and/or direction over a very small area.

40
Q

At what altitudes does windshear occur?

A

Any altitude.

41
Q

Where could a pilot expect to encounter windshear?

A

Windshear can affect any flight and any pilot at any altitude. It often remains undetected and is a silent danger to aviation.

42
Q

When should a pilot be especially alert to the possibilioty of windshear?

A

When flying in and around thunderstorms and frontal systems.

43
Q

What type of weather systems is low level wind shear commonly associated with?

A

Passing frontal systems, thurderstorms, temperature inversions, and strong upper level winds (greater than 25 knots).

44
Q

What is the most severe type of low level windshear?

A

Microburst

45
Q

What weather conditions are conducive to microbursts?

A

Convective precipitation into dry air at the cloud base.

46
Q

What are some visual indications of a microburst?

A

An intense rain shaft at the surface but virga at the cloud base and a ring of blowing dust.

47
Q

What are the typical dimensions of a microburst?

A

Horizontal diameter of 1-2 miles and a niminal depth of 1,000 feet.

48
Q

What is the lifespan of a microburst?

A

About 5-15 minutes.

49
Q

How strong are the effects of a microburst?

A

Can produce downdrafts of up to 6,000 feet per minute and headwind losses of 30-90 knots, seriously degrading performance. Can also produce strong turbulence and hazardous wind direction changes.

50
Q

What hazards can occur during an inadvertent takeoff into a microburst?

A

A performance-increasing headwind, followed by performance-decreasing downdrafts, followed by a rapidly increasing tailwind. This can result in terrain impact or flight dangerously close to the ground.

51
Q

What hazards can occur if a microburst is encountered during an approach?

A

A performance-increasing headwind, followed by performance-decreasing downdrafts, followed by a rapidly increasing tailwind. This can result in terrain impact or flight dangerously close to the ground.

52
Q

What symbols are used on weather maps to indicate wind speed?

A

A barb equals 10 knots, half a barb equals 5 knots, a pennant equals 50 knots.

53
Q

What is an isobar?

A

Lines drawn on a chart to depict lines of equal pressure.

54
Q

What is the significance of isobars that are closely spaced on a weather map?

A

Isobars that are closely spaced indicate a steep pressure gradient and strong winds.

55
Q

What is a high?

A

An area of high pressure surrounded by lower pressure.

56
Q

What is a low?

A

An area of low pressure surrounded by higher pressure.

57
Q

What is a ridge?

A

An elongated area of high pressure.

58
Q

What is a trough?

A

An elongated area of low pressure.

59
Q

How can a pilot predict the wind direction and speed at 2,000 feet above the surface?

A

Generaly, the wind 2,000 feet above ground level is 20 to 40 degrees to the right of surface winds, and the wind speed is greater.

60
Q

What are the characteristics of rising air?

A

Rising air expands and cools. (adiabatic cooling)

61
Q

What are the characteristics of descending air?

A

As atmospheric pressure increases, the temperature of descending air increases as it is compressed. (“adiabatic heating.”)

62
Q

What changes take place as a parcel of air rises?

A

Pressure decreases, volume increases, temperature decreases.

63
Q

What changes take place as a parcel of air descends?

A

Pressure increases, voume decreases, temperature increases.

64
Q

What is the average rate of temperature change as air ascends through the atmosphere?

A

Average rate is 2 degrees Celsius (3.5 degrees Farenheit) per 1,000 feet. (“lapse rate”)

65
Q

What effect does water vapor have on the atmosphere?

A

Since water vapor is lighter than air, moisture decreases air density, causing it to rise. Conversely, as moisture decreases, air becomes denser and tends to sink.

66
Q

Which is more stable, moist air or dry air?

A

Since moist air cools at a slower rate, it is generally less stable than dry air since the moist air must rise higher before its temperature cools to that of the sourrounding air.

67
Q

What determines the stability of the air and the resulting weather?

A

The combination of moisture and temperature.

68
Q

What are the characteristics of stable air?

A

Cool, dry air is very stable and resists vertical movement, which leads to good and generally clear weather.

69
Q

What are the characteristics of unstable air?

A

The greatest instability occurs when the air is moist and warm, as it is in the tropical regions in the summer.

70
Q

What is a temperature inversion?

A

When the tempreature of the air rises with altitude, a temperature inversion exists.

71
Q

What happens to visibility when the relative humidity is high in an inversion layer?

A

It can contribute to the formation of clouds, fog, haze, or smoke resulting in diminshed visibility in the inversion layer.

72
Q

When do surface based inversion layers occur?

A

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

73
Q

When do frontal inversions occur?

A

When warm air spreads over a layer of cooler air, or cooler air is forced under a layer of warmer air.

Weather (1 decks)

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