Weather Theory Flashcards
Test on Weather Theory (132 cards)
1
Q
What percentage of the Earth’s Atmosphere is made up of Oxygen?
A
21
2
Q
True/False. The Anvil of a thunderstorm indicates the direction of storm movement.
A
True
3
Q
rue/False. Airflow circulates clockwise (anti-cyclonic) around a Low Pressure System.
A
False
4
Q
What are the different types of icing an aircraft can encounter in-flight.
A
Clear Ice, Rime Ice, Mixed.
5
Q
True/False. An Occluded Front typically develops when a faster moving cold front catches up to a slower moving warm front.
A
True
6
Q
Downdrafts in a microburst can be as strong as…
A
6,000 FPM and cause headwind losses of 30-90 knots.
7
Q
What are the different cloud classification types.
A
High (Cirrus), Middle (Alto), Low (Stratus), and Clouds with Vertical Development.
8
Q
True/False. In an Inversion, temperature increases with altitude to a certain point.
A
True
9
Q
True/False. Coriolis Force is caused by the rotation of the Earth and it deflects airflow to the right in the Northern Hemisphere.
A
True
10
Q
Where is Advection Fog most commonly found?
A
Coastal Areas
11
Q
True/False. Standard Pressure at Sea Level = 29.92 and Standard Temperature = 15C.
A
True
12
Q
What are the stages of a thunderstorm.
A
Cumulus, Mature, and Dissipating Stage
13
Q
rue/False. A Squall Line is a narrow band of active thunderstorms.
A
True
14
Q
In which layer of the atmosphere do most aircraft operate?
A
Troposhere
15
Q
True/False. The Standard Adiabatic Lapse Rate = -2C per Thousand Feet of Altitude gain.
A
True
16
Q
What is the Earth’s atmosphere made of and what is the percentage of each.
A
Nitrogen 78%
Oxygen 21%
Argon, carbon dioxide and traces of other gases 1%
17
Q
How does air flow in a low pressure system?
A
Counter clockwise (cyclonic) and up. Hint: Right hand thumbs up: Makes a backwards L for Low pressure, fingers show counter clock wise and thumb points up.
18
Q
How does air flow in a high pressure system?
A
Clockwise (anticyclonic) down and out.
Hint: Right hand thumbs down: Fingers point clockwise, thumb pointed down for down flow.
19
Q
What is an Occluded Front?
A
A faster moving cold front catches up to a slower moving warm front.
20
Q
What is a microburst?
A
Low level wind shear.
21
Q
What is Coriolis Force caused by?
A
The rotation of the Earth.
22
Q
What direction(s) does Coriolis Force deflect airflow?
A
Right in the Northern Hemisphere. Left in the Southern Hemisphere.
23
Q
Name the Standard Pressure and temperature at sea level.
A
Standard pressure at seal level is 29.92 (1,013.2 mb)
Standard temperature is 15C or 59F
24
Q
What is a squall line?
A
A narrow band of active thunderstorms.
25
The Standard Adiabatic Lapse Rate is equal to what?
-2c per thousand feet of altitude gain. (In the Troposphere)
26
What is above the Troposphere?
The Tropopause.
27
What is weather?
It is the state of the atmosphere at a given time and place with respect to variables, such as temperature, moisture, wind velocity, visibility, and barometric pressure.
28
What is the atmosphere?
A blanket of air made up of a mixture of gases (in constant motion) that surrounds the Earth.
29
How far does the atmosphere reach?
Almost 350 miles from the surface of the Earth.
30
How high does the troposphere extend.
(0-12 KM) 7 Miles. Can change seasonally and reach as far as 4-12 miles over the northern and southern poles and up to 48000ft over equatorial regions.
31
How does the temperature change in the Tropopause?
It stays fairly constant.
32
What is the purpose of the Tropopause?
It is a boundary that traps moisture and associated weather in the troposphere.
33
What is the height of the Tropopause?
It varies depending on height of the Troposphere.
34
Areas of low pressure exist over the equatorial regions and areas of high pressure exist over the polar regions due to what?
Due to difference in temperature.
35
High pressure air likes to flow where?
Into low pressure areas.
36
Within how many feet of the ground does friction between the surface and the atmosphere slow moving air?
2,000 FT
37
Can wind direction on the surface vary from a few thousand feet above and why?
Yes. Wind is diverted from its path because of the friction between the surface and atmosphere.
38
Atmospheric pressure can also be reported in what?
Millibars. 1 Hg is equal to approximately 34 mb
39
1 Hg is equal to what?
Approximately 34 mb
40
Standard seal level pressure in millibars is what?
1,013.2 mb
41
How does atmospheric pressure change as altitude increases?
On average, with every 1,000 ft of increase in altitude, the atmospheric pressure decreases 1"Hg (34mb)
42
What is the typical mb pressure readings range?
950.0 to 1,040.0
43
Does density altitude effect aircraft performance and if so, how?
Yes. High density altitude means worse performance. This is because the aircraft thinks it is working at a higher altitude than it actually is. Low density altitude causes the aircraft to preform better as it thinks that it is operating at a lower altitude.
44
What is convection/ convective currents?
Upward and downward motion of air.
45
What is wind?
Horizontal motion.
46
How do Sea and Land Breezes work?
Day: Cool air over the water sinks (higher pressure) flows toward low pressure warm air over land, and rises. Air continues in that pattern. This is the same idea for Night breezes, only the water would be warmer and the land cooler.
47
Can convective Currents create turbulence?
Yes.
48
How is turbulence created?
Uneven heating (areas of rock, sand, barren land vs areas of green and water) creates small areas of local circulation called convective currents. Convective currents cause bumpy turbulent air when flying at lower altitudes during warmer weather.
49
How does wind flow on each side of the the mountain?
Nice and smooth on the windward side but turbulent on the lea-word side.
50
What is wind shear?
Drastic change in wind speed and or direction in a very small area. Windshear can subject an aircraft to violent up and down drafts as well as horizontal movement.
51
What type of windshear is the most hazardous?
Low-level windshear.
52
What is Low-level wind shear commonly associated with?
Passing frontal systems, thunderstorms, temperature inversions, and strong upper level winds.
53
Microburst activity may be indicated by?
An intense rain shaft at the surface but virga at cloud base and a ring of blowing dust.
54
What is the size of a typical microburst?
Diameter: 1-2 miles and a nominal depth of 1,000 ft.
55
What is Virga?
Rain that has not reached the surface.
56
What is the lifespan of a microburst.
About 5-15 Minutes.
57
The stability of the atmosphere depends on?
Its ability to resist vertical (up and down) motion.
58
A stable atmosphere makes vertical movement difficult and small vertical disturbances dampen out and disappear. True/False?
True.
59
In an unstable atmosphere, small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity. True/False?
True.
60
What can atmospheric instability lead to?
Significant turbulence, extensive vertical clouds, and severe weather.
61
What happens to rising air?
It expands to a larger volume. As the molecules of air expand the temperature of the air lowers. As a result, when a parcel of air rises, pressure decreases, volume increases, and temperature decreases.
62
What happens to descending air?
As atmospheric pressure increases, the temperature of descending air increases as it is compressed.
63
The adiabatic process takes place in all air that moves?
Up and down.
64
The rate at which temperature decreases with an increase in altitude is referred to as its?
Lapse rate. (adiabatic lapse rate)
65
What are the moist, standard, and dry adiabatic lapse rates?
Moist: -1.1C - -2.8C per thousand feet climbed.
Standard: -2C (3.5F) per thousand feet climbed.
Dry: -3C per thousand feet climbed.
66
Is water vapor lighter than air?
Yes.
67
Humid air is less dense than dry air and tends to rise. True/False?
True
68
As moisture decreases, air becomes denser and tends to sink. True/False?
True
69
Moist air is generally less stable than dry air because?
It cools at a slower rate than dry air. Moist air must rise higher before its temperature cools to that of the surrounding air.
70
What is an inversion?
An atmospheric anomaly where temperature rises with altitude to a certain point-the top of the inversion. The top of the layer acts as a lid, keeping weather and pollutants trapped below. If the relative humidity of the air is high it can contribute to cloud formation, fog, haze, or smoke resulting in diminished visibility in the layer.
71
Humidity refers to what?
The amount of water vapor present in the atmosphere at a given time.
72
Relative humidity is what?
The actual amount of moisture in the air compared to the total amount of moisture the air could hold at that temperature. If relative humidity is 65% that means the air is holding 65% of the total amount of moisture it is capable of holding at that temperature and pressure.
73
How do you determine cloud bases? (Where the cloud starts)
Find the OAT (outside air temperature), the dew point at the surface, and the dew point. EX: Temp 85F and dew point 71F equals a spread of 14F. Divide spread by 4.4. 14/4.4=3.18. Times this by 1,000. 3.18x1000=3,180.
The cloud base is 3,180 AGL. (This is a close estimate)
74
What is fog and when does it occur?
Fog is a cloud 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.
75
How is fog classified?
According to how it forms and what it is dependent upon the current temperature and the amount of water vapor in the air.
76
Radiation Fog:
Forms on clear nights with relatively little to no wind present. Usually 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.
77
This type of fog forms in low-lying areas like mountain valleys.
Radiation Fog.
78
This type of fog occurs when the ground cools rapidly due to terrestrial radiation, and the surrounding air temperature reaches its dew point.
Radiation Fog.
79
Advection Fog
When a layer of warm, moist air moves over a cold surface, advection fog is likely to occur. 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. Is common in coastal areas where sea breezes can blow the air over cooler landmasses.
80
When a layer of warm, moist air moves over a cold surface what kind of fog is likely to occur?
Advection Fog.
81
Is wind required to form Advection fog? If so, how much?
Yes. Winds up to 15 knots allow the fog to form and intensify. Wind over 15 knots causes the fog to lift and form low stratus clouds.
82
Where is Advection Fog commonly found?
Coastal areas where sea breezes can blow air over cooler landmasses.
83
Upslope Fog
Upslope fog occurs when moist, stable air is forced up sloping land features like mountain ranges. This type of fog requires wind for the formation and continued existence. Upslope and advection, unlike radiation fog, may not burn off with the morning sun but instead can persist for days. They can also exted to greater heights than radiation fog.
84
This type of fog requires wind and sloping land features.
Upslope Fog
85
These types of fog may not burn off with the morning sun and may persist for days.
Advection and upslope fog.
86
These types of fog may exted to greater heights than radiation fog.
Advection and upslope fog.
87
Steam Fog (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.
88
Low-level turbulence and icing are commonly associated with what kind of fog?
Steam fog.
89
This type of fog is formed when cold, dry air moves over warm water.
Steam fog.
90
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 radiatin fog ecept for cold temperature, usually -25F or colder. It occurs mostly in the arctic regions but is not unknown in middle latitudes during cold seasons.
91
Conditions favorable for this type of fogs formation are the same as radiation fog, except for the cold temperature, usually -25F.
Ice Fog
92
Water vapor forms directly into ice crystals to form this type of fog.
Ice Fog.
93
This type of fog most commonly forms in arctic regions.
Ice Fog.
94
Clouds are visible indicators and are often indicative of future weather. True/False?
True.
95
How are clouds formed?
For clouds to form, there must be adequate water vapor and condensation nuclei, as well as a method by which the air can be cooled. When the air cools and reaches its saturation point, the invisible water vapor changes into a visible state.
96
Clouds are determined by?
Height, shape, and characteristics.
97
Low clouds consist of?
Stratus clouds; clouds up to 6500ft AGL. Stratus, Stratocumulous, Nimbostratus.
Primarily made of water droplets, can include supercooled water droplets that induce hazardous aircraft icing. Thin, form in layers.
98
Middle clouds consist of
Alto clouds; height from 6500ft agl to 20,000ft agl. Alto stratus and altocumulus.
Composed of water, ice crystals, and supercooled water droplets.
99
High clouds consist of?
Cirrus clouds; above 20,000 ft agl. Cirrostratus, cirrocumulus, and cirrus. Composed of ice crystals and pose no real threat of turbulence or aircraft icing. Ringlet, fibrous.
100
Clouds with vertical development:
Cumulus into cumulonimbus.
These are thunderstorm clouds. Indicate areas of instability and turbulence. They are moist and unstable and produce hazardous weather such as lightning , hail, tornadoes, and gusty winds.
101
Castellanus Clouds:
Common base with separate vertical development.
102
Lenticular Clouds:
Lens-shaped, form over mountains in strong winds.
| Indicative of very strong turbulence.
103
Nimbus clouds:
Rain-bearing clouds. Cumulonimbus means cumulus clouds that are raining.
104
Fracto Clouds:
Ragged or broken.
105
Cumulonimbus Cloud:
Thunderstorm cloud.
106
What are air masses?
They are large bodies of air that take on the characteristics of the surrounding area or source region.
107
How are air masses classified?
According to the regions where they originate.
108
What is a source region? (Air masses)
A source region is typically an area in which the air remains relatively stagnant for a period of days or longer.
During this time of stagnation, the air mass takes on the temperature and moisture characteristics of the source region.
109
Air mass passing over a warmer surface:
An air mass passing over a warmer surface is warmed from below, and convective currents form, causing the air to rise. This creates an unstable air mass with good surface visibility. Moist, unstable air causes cumulus clouds, showers, and turbulence to form.
110
Air mass passing over a colder surface:
An air mass passing over a colder surface does not form convective currents but instead creates a stable air mass with poor surface visibility. The poor surface visibility is due to the fact that smoke, dust, and other particles cannot rise.
111
Name some air masses
A (arctic) cP (continentalpolar) mP (maritime polar) cT (continental tropic, and mT (Maritime tropic)
112
As an air mass moves accross bodies of water and land, it eventually comes in contact with another air mass with different characteristics. What is the boundary layer between two types of air masses known as?
A front. It could be a Warm, Cold, Stationary, or Occluded front.
113
Name tthe different types of fronts
Warm, Cold, Stationary, Occluded.
114
Warm front
Occurs when a warm mass of air advances and replaces a body of colder air. Move slower than cold fronts: typically 10-25mph. The slope of the advancing front slides over the top of the cooler air and gradually pushes it out of the area. Contains warm air that often has very high humidity. As the warm air is lifted, the temperature drops and condensation occurs. Generally, Prior to the passage of a warm front, cirriform or stratiform cloud, along with fog can be expected to form along the frontal boundary. In the summer months, cumulonibus clouds (thunderstorms) are likely to develop. Weather forms along the front boundary. You will experience the weather ahead of the front.
115
Cold front
Occurs when a cold mass of dense stab air advances and replaces a body of warm air. Cold fronts move more rapidly than warm fronts, progressing at a rate of 25-30mph; however, extreme cold fronts have been recorded moving at speeds of up to 60mph. A typical cold front moves in amanner opposite that of a warm front. It is so dense it stays close to the ground and acts like a snowplow, 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. As the cold front passes, towering cumulus or cumulonimbus cloud continue to dominate the sky. The front will proceed the weather or meet at the same time.
116
Stationary front
When the forces of two air masses are relatively equal the boundary or front that separates them remains stationary and influences the local weather for days. The weather associated with a stationary front is typically a mixture that can be found in both warm and cold fronts.
117
Occluded front
An occluded front occurs when a fast-moving cold front catches up with a slow- moving warm front. As the occluded front approaches, warm front weather prevails but is immediately followed by cold front weather. (They move together.
118
Cumulus Stage of thunderstorms:
Lifting action of the air begins. If sufficient moisture and instability are present, the clouds continue to increase vertical height. Continuous, strong updrafts prohibit moisture from falling.
119
Mature Stage of thunderstorms:
Within approximately 15 min, the thunderstorm reaches the mature stage, which is the most violent time period of the thunderstorm's life cycle. At this point, drops of moisture, whether rain or ice, are too heavy for the cloud to support and begin falling from the cloud in the form of rain or hail. This creates a downward motion of the air. Warm, rising air; cool, precipitation-induced descending air; and violent turbulence all exist within and near the cloud.
120
Dissapaiting stage of thunderstorms:
Once the vertical motion near the top of the cloud slows down, the top of the cloud spreads out and takes on an anvil-like shape. At this point, the storm enters the dissipating stage. This is when the downdrafts spread out and replace the updrafts needed to sustain the storm.
121
How far should you circumnavigate thunderstorms identified as severe or giving an extreme radar echo and why?
20 Nautical miles since hail may fall for miles outside the clouds. If flying around is not an option, stay on the ground.
122
When flying around thunderstorms we should divert which direction?
Away from the anvil. The anvil indicates the direction of storm movement. The anvil is the nose of the storm.
123
Squall lines often develop when?
On or ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front. The line may be to long to detour easily and too wide and severe to penetrate. It often contains stead-state thunderstorms and presents the single most intense weather hazard to aircraft. It usually forms rapidly, generally reaching maximum intensity during the late afternoon and the first few hours of darkness.
124
Tornadoes:
Can occur with both isolated and squall line thunderstorms. Reports for forcasts of tornadoes indicate that atmospheric conditions are favorable for violent turbulence. An aircraft entering a tornado vortex is almost certain to suffer loss of control and structural damage. Since the vortex exteds well into the cloud, any pilot inadvertently caught on instruments in a severe thunderstorm could encounter a hidden vortex.
125
Turulence
Potentially hazardous turbulence is present in all thunderstorms; a severe thunderstorm can destroy an aircraft. Strongest turbulence within the cloud occurs with shear between updrafts and downdrafts. Outside the cloud, shear turbulence has been encountered several thousand feet above and 20 miles latteraly from a severe storm. A low level turbulent area is the shear zone associated witht he gust front. Often a "roll cloud" on the leading edge of a storm marks the top of the eddies in this shear and it signifies an extremely turbulent zone.
126
Icing
Updrafts in a thunderstorm support abundant liquid water with relatively large droplet sizes. When carried above the freezing level, the water becomes supercooled. Super cooled water freezes on impact with an aircraft. Clear icing can occur at any altitude above the freezing level, but at high levels, icing from smaller droplets may be rime or mixed rime and clear ice. the abundance of larce, supercooled water droplets makes clear icing very rapid. pilots be alert for icing anytime the temps approach 0C and visible moisture is present.
127
Name the 3 types of Icing.
Clear, Rime, and mixed.
128
Clear Ice:
Clear in color, Mostly develops from large water droplets. Freezes like an icicle as it runs back along the wing. Hard to de-ice. Sticky and thick.
129
Rime Ice:
Milky in color. Mostly develops from smaller water droplets. Water droplets freeze on impact with the aircraft. Usually builds up on the leading edge of the wing. Easier to remove.
130
Mixed
A mixture of clear and rime ice.
131
Hail
Hail may be encountered in clear air several miles from thunderstorm clouds. As hailstones fall through air whose temp is above 0C they begin to melt and precipitation may reach the ground ans either hail or rain. Rain at the surface does not mean the absence of ail aloft.Possible hail should be anticipated with any thunderstorm, especially beneath the anvil of a large cumulonimbus. Hailstones larger than one-half inch in diameter can significantly damage an aircraft in a few seconds.
132
Lightning
Can puncture the skin of an aircraft and damage communications and electronic navigational equipment. Nearby lightning can blind a pilot rendering him or her momentarily unable to navigate either by instrument or visual reverence. Can also induce permanent errors in the magnetic compass. even distant discharges can disrupt radio communications on low and medium frequencies.
