Chapter 2 - Weather Flashcards
State the general characteristics in regard to the flow of air around high and low pressure systems in the Northern Hemisphere?
Low Pressure - inward, upward, and counterclockwise
High Pressure - outward, downward, and clockwise
What is a “trough”?
is an elongated area of realtively low atmospheric pressure.
What is a “ridge”?
is an elongated area of relatively high atmospheric pressure.
What are standard temperature and pressure values at sea level?
15 degrees C, 29.92” Hg
What are “isobars”?
line on a weather chart which connects areas of equal or constant barometric pressure.
What does the separation of the isobars on a weather map mean?
When isobars are close together the change in pressure is steeper, likewise the further apart they are the shallower the change is.
What causes the winds aloft to flow parallel to the isobars?
the coriolis force
Why do surface winds generally flow across the isobars at an angle?
surface friction
At what rate does atmospheric pressure decrease with an increase in altitude?
1” Hg per 1,000 ft
What does “dew point” mean?
Dew point is the temperature to which a sample of air must be cooled to attain a state of saturation.
When temperature and dew point are close together (within 5 degrees), what type of weather is likely?
Visible moisture in the form of clouds, dew, or fog.
What factor primarily determines the type and vertical extent of clouds?
The stability of the atmosphere.
How do you determine the stability of the atmosphere?
Unstable air - temperature decreases uniformly and rapidly as you climb. Likely to be around moist warm air.
Stable air - temperature remains unchanged or decreases only slightly.
List the effects of stable and unstable air on clouds, turbulence, precipitation, and visibility.
Stable Unstable
Clouds Stratiform Cumuliform
Turbulence Smooth Rough
Precipitation Steady Showery
Visibility Fair to Poor Good
At what altitude above the surface would a pilot expect the bases of cumuliform clouds if the surface temp is 82 degrees and the dew point is 62 degrees?
temperature - dew point ------------------------------ x 1,000 = base 4 Ex: 82-62=20 20/4=5 5 x 1,000= 5,000 ft AGL
What type of wx info should you be aware of with respect to icing?
a. Location of fronts - type, speed, direction
b. Cloud Layers - bases and tops, PIREP’s
c. Freezing level(s)
d. Air Temp and Pressure - low pressure temps at and around freezing are bad
What is “freezing level”?
A altitude at which the temperature reaches 0 degrees C.
How can a pilot determine the freezing level?
Current Icing Product, Forecast Icing Products, freezing level graphics.
What conditions are necessary for structural icing?
Visible moisture and below freezing temperatures at the point the moisture strikes the a/c.
Name the main types of icing an a/c may encounter in-flight?
Structural, induction systems, and instruments icing.
Name the three types of structural icing that may occur.
Clear Ice - forms after initial impact when the remaining liquid portions of the drop flows out over the a/c surface, gradually freezing as a smooth sheet of solid ice.
Rime Ice - forms when drops are small, such as those in stratified clouds or light drizzle. The liquid freezes before it can spread out.
Mixed Ice - Forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become imbedded in clear ice, building a very rough surface.
What action is recommended if you inadvertently encounter icing conditions?
Climb or descend to warmer air or dryer air.
Is frost considered to be hazardous to flight?
Yes, because frost does not change the aerodynamics of the wing but it creates air separation from the surface spoiling lift.