Temperature changes cause variations in air pressure and density. Because the earth’s surface is heated unevenly, altimeter settings will be different between weather stations.
Variation of terrain elevation
Unequal heating of the Earth’s surface
Above 2,000 feet AGL, wind flows along isobars. Below that altitude, friction with the earth’s surface deflects the wind.
stronger Coriolis force at the surface.
stronger pressure gradient at higher altitudes.
friction between the wind and the surface.
During the day, land surfaces become warmer than the adjacent water surfaces. This warms the air above the land causing the air to rise. The rising air is replaced by the inland flow of cooler, denser air located over the water. As the warm air flows over
water absorbing and radiating heat faster than the land
cool, dense air moving inland from over the water
warm, dense air moving inland from over the water
Frost disrupts the smooth airflow over the wing and can cause early separation of the airflow, resulting in a loss of lift.
Frost will disrupt the smooth flow of air over the wing, adversely affecting its lifting capability.
Frost will change the camber of the wing, increasing its lifting capability.
Frost will cause the airplane to become airborne with a higher angle of attack, decreasing the stall speed.
Every physical process of weather such as heating, cooling, evaporation, and condensation, is caused by or is the result of, a heat exchange.
movement of air.
Normally, temperature decreases with altitude. During an inversion, cooler air is trapped beneath a warmer layer of air. Therefore, temperature increases with altitude.
Clouds with extensive vertical development above an inversion aloft.
An increase in temperature as altitude is increased.
Good visibility in the lower levels of the atmosphere and poor visibility above an inversion aloft.
An inversion commonly forms on clear, cool nights when the ground radiates heat and cools faster than the overlying air.
terrestrial radiation on a clear, relatively still night.
the movement of colder air under warm air, or the movement of warm air over cold air.
warm air being lifted rapidly aloft in the vicinity of mountainous terrain.
Low-level temperature inversions normally occur in stable, smooth air, with poor visibility due to trapped pollutants which are commonly referred to as condensation nuclei. In addition, high humidity tends to cause formation of fog and low clouds.
Smooth air, poor visibility, fog, haze, or low clouds.
Light wind shear, poor visibility, haze, and light rain.
Turbulent air, poor visibility, fog, low stratus type clouds, and showery precipitation.
When air is cooled to its dewpoint, it can hold no more moisture, and is said to be saturated.
The temperature to which air must be cooled to become saturated.
The temperature at which dew will always form.
The temperature at which condensation and evaporation are equal
The amount of moisture in the air primarily depends on the temperature. For example, warm air can hold more moisture than cool air.
stability of the air.
Condensation occurs when water vapor changes to liquid form. Examples are when vapor changes to clouds, fog, or dew.
water vapor condenses
relative humidity reaches 100 percent
water vapor is present.
Evaporation occurs when liquid water changes to water vapor. Sublimation is the changing of ice directly to water vapor. Both processes add moisture to the air.
Heating and condensation.
Evaporation and sublimation.
Supersaturation and evaporation.
When the dewpoint of the surrounding air is below freezing, and the collecting surface is at or below the dewpoint, water vapor sublimates directly into ice crystals or frost instead of condensing into dew.
The temperature of the collecting surface is at or below freezing when small droplets of moisture fall on the surface.
The temperature of the surrounding air is at or below freezing when small drops of moisture fall on the collecting surface.
The temperature of the collecting surface is at or below the dewpoint of the adjacent air and the dewpoint is below freezing.
Due to a temperature inversion, a warm layer of air is aloft and keeps the rain in liquid forms. As the rain falls through colder air, it begins to freeze, finally turning into ice pellets. Ice pellets always indicate freezing rain at a higher altitude. I
is a temperature inversion with freezing rain at a higher altitude.
are thunderstorms in the area
has been cold frontal passage
The stability of air refers to its resistance to displacement upward or downward; it is determined by the actual lapse rate. Lapse rate generally refers to the decrease in temperature with an increase in altitude. A high lapse rate tends to indicate unsta
Actual lapse rate
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