Unit 7 Flashcards
What is the primary cause of weather?
unequal surface heating → causes diff in pressure
Coriolis force
deflects winds to the right in the N Hemisphere (caused by Earth’s rotation)
Air parcel
imaginary volume of air where all basic properties of atmospheric air may be assigned
Structure Atmosphere
Troposphere
layer from surface → 7 mi
altitude increase = temp decrease
Structure Atmosphere
Tropopause
transition zone between troposphere & stratosphere
altitude increases = wind & temp decrease
Structure Atmosphere
Stratosphere
4 -12 mi
Disadvantage flying: more fuel consumption (b/c warmer temp), more radiation, more ozone
Dew point
temp air must be cooled to become saturated by water vapor already present
What happens when temperature & dew point converge?
fog, clouds, rain form
Stable atmosphere
resists any upward/downward displacement
Stable air
stratiform clouds & fog
continuous precipitation
Unstable air
cumuliform clouds
showery precipitation
Adiabatic
changes where no heat is removed/added to air
Convective currents
localized vertical air movements
Cause turbulence (low altitudes)
Fronts
temp, humidity, wind often change rapidly over short distances across a frontal zone
Requirements in air for thunderstorm to form:
- Sufficient water vapor
- Unstable lapse rate
- Initial lifting to start strom process motion
Thunderstorm stages: Cumuls
building stage when there are (continuous updrafts)
Thunderstorm stages: Mature
greatest intensity (both updrafts & downdrafts)
severe wind shear/turbulence, precipitation begins
Thunderstorm stages: Dissipating
storm raining itself out (only downdraft)
Squall-line thunderstorms
most severe conditions (hail, destructive winds, tornadoes…)
Narrow thunderstorm usually ahead of a cold front
Clear ice
water droplets touch plane & flow across surface before freezing (smooth sheet)
Rime ice
water droplets are small & freeze without spreading (rough shape)
Less lift, more drag
Mountain wave
stable air crosses mountain barrier → air flowing up wind side (smooth) & wind across barrier (layers)
Wind shear
generates whirls of air (eddies) between 2 wind currents of diff velocities
Hazards: low-level temp inversions, frontal zones, clear air turbulence
When air temp within 5ºF of dew point & spread decreasing expect…
fog or low clouds
Greatest turbulence is in what type of cloud?
cumulonimbus clouds
Characteristics of stable air:
- Startform clouds
- Smooth air
- Fair/poor visibility in haze & smoke
- Continuous precipitation
- Cool
- Dry
Characteristics of unstable air:
- Cumuliform clouds
- Turbulent air
- Good visibility
- Showery precipitation
- Warm
- Humid
The wind at 5,000 feet AGL is southwesterly while the surface wind is southerly.
This difference in direction is primarily due to friction between wind & surface
You are avoiding a thunderstorm that is in your flightpath. You are over 20 miles from the cell; however, you are under the anvil of the cell. Is this a hazard?
Yes, hail can be discharged from the anvil.
The presence of ice pellets at the surface is evidence that there
is a temperature inversion with freezing rain at higher altitudes
Which conditions result in the formation of frost?
The temperature of the collecting surface is at or below the dewpoint of the adjacent air and the dew point is below freezing.
Low-level turbulence can occur and icing can become hazardous in which type of fog?
Steam fog
In which situation is advection fog most likely to form?
Air moving inland from the coast in winter
The stability of an air mass can usually be determined by
cloud types & types of precipitation
Temperature and radiation variations over land with a clear sky typically lead to
minimum temperature occurring after sunrise
At approximately what altitude above the surface would the pilot expect the base of cumuliform clouds if the surface air temperature is 82°F and the dewpoint is 38°F?
10,000 ft AGL
