GEOG 1101 Lecture Notes - Lecture 4: Fluid Parcel, Dew Point

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GEOG LESSON FOUR
RESULT:
** rising air in the atmosphere expands and cools
** sinking air in the atmosphere is compressed and warmed
The Rate of Adiabatic Temperature Change varies with the humidity
condition (water vapor content) of the air, is it Dry (unsaturated) or
Wet (saturated). Unsaturated air will change T° at a faster rate than
will saturated air.
Dry Adiabatic Rate (Dry Adiabatic Lapse Rate): (DAR or DALR)
When a parcel of air is unsaturated its air Tº > dew point Tº and
thus its RH < 100%.
* The DAR of unsaturated air is a constant rate of
1ºC / 100 m or 10ºC / 1000m.
Thus: rising air cools at 1ºC/100 m (10ºC / 1000m)
sinking air warms at 1ºC/100 m (10ºC / 1000m).
Saturated Adiabatic Rate (Saturated Adiabatic Lapse Rate):
(SAR or SALR)
(May also see this as WAR, Wet Adiabatic Rate; or MAR, Moist Adiabatic Rate)
When the air parcel is saturated its air Tº = d.p.Tº and thus its
RH = 100%.
* The SAR is not a constant rate but a variable rate of
.5º - .9ºC / 100 m or 5º - 9ºC / 1000m
* It is dependent on the moisture content of the air. The more water vapor
condensing to liquid there is in the air, the slower the rate of decline.
(closer to 5°C / 1000m).
* this is because condensation releases latent heat energy, this slowing the rate of cooling (or
warming)
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