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33 Cards in this Set
- Front
- Back
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Every physical process of weather is the result of __ |
Heat transfer |
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Composition of the atmosphere |
78% nitrogen 21% oxygen 1% trace gases |
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Layers in the atmosphere |
0~36,000 feet -- troposphere ~36,000 feet -- tropopause ~36,000-160,000 feet -- stratosphere 160,000-280,000 feet -- mesosphere 280,000 feet-350 miles -- theromsphere |
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North/south air currents |
Generally from pole (high pressure) to equator (low pressure) |
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Northern hemisphere Coriolis force
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Bends trajectories to the right |
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Airflow around high-pressure regions in Northern hemisphere |
Away from high-pressure region, clockwise (anticyclonic) |
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Airflow around low-pressure regions in Northern hemisphere |
Toward low-pressure region, counterclockwise (cyclonic) |
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Direction of winds aloft
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2,000 feet AGL, winds 20-40 degrees to right of winds on surface This is due to friction, not the Coriolis force |
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Dry and moist adiabatic lapse rate |
Unsaturated, dry: -3 degrees C per 1000 feet -5.4 degrees F per 1000 feet Moist: -1.1 degrees C to -2.8 degrees C per 1000 feet -2 degrees F to -5 degrees F per 1000 feet |
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Which air is more / less stable? |
Cool, dry air is stable (resists vertical movement)
Moist, warm air is unstable |
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Temperature inversion typically occurs... |
When cool air near the ground (overnight) sits below a layer of warmer air
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Moisture carrying capacity of air varies... |
Doubles with every 11 degree C (20 degree F) increase in temperature |
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Temperature convergence rate for clouds |
-2.5 degrees C (-4.4 degrees F) per 1000 feet |
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The most frequent type of surface-based temperature inversion is that which is produced by |
Terrestrial radiation on a clear, relatively still night |
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Stable air mass is likely to have what kind of visibility? |
Poor surface visibility |
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Unstable air mass is likely to have what kind of surface visibility? |
Good surface visibility |
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How can we determine the stability of an air mass? |
Measure the ambient lapse rate and compare with dry adiabatic lapse rate. |
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Are temperature inversions stable or unstable? |
Generally stable |
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A pilot can be relatively certain of a wind-shear zone in a temperature inversion whenever the windspeed between 2,000 and 4,000 feet AGL is at least |
25 knots |
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Ice pellets indicate |
Freezing rain at higher altitude |
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Structural ice will accumulate most quickly from: A - cumulus clouds with below-freezing temperatures B - freezing drizzle C - freezing rain |
C - freezing rain |
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Can radiation fog occur over water? |
No. Only over land. |
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What conditions commonly create advection fog? |
Warm, moist air forms advection fog offshore over cold water and is moved inland by wind |
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When can hazardous wind shear be expected? |
Can encounter at any time, but especially near: * Temperature inversion * Thunderstorms * Frontal zones |
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When may hazardous wind shear be expected? A - When stable air crosses a mountain barrier where it tends to flow in layers forming lenticular clouds. B - In areas of low-level temperature inversion, frontal zones, and clear air turbulence. C - Following frontal passage when stratocumulus clouds form indicating mechanical mixing. |
B - In areas of low-level temperature inversion, frontal zones, and clear air turbulence. |
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Clouds forming in stable air have which characteristics? |
Stratified, horizontal development |
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Clouds forming in unstable air have which characteristics? |
Extensive vertical development |
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What are the four families of clouds? |
High Middle Low Extensive vertical development (cumuloform) |
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Is icing likely to occur in high clouds? |
No. High clouds are already ice crystals and are unlikely to stick to an aircraft. |
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How long do microbursts last? |
Up to 15 minutes |
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What is the maximum downdraft rate within a microburst? |
6,000 fpm |
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What is the maximum wind shear expected within a microburst? |
90 knots, 45 knot gain due to headwind followed by 45 knot loss due to tailwind |
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A predictive factor for low-level wind shear is... |
A low-level temperature inversion where wind speeds from 2,000-4,000 feet AGL are > 25 knots |
