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Author Topic: What is the lapse rate (temperature drop at altitude) for deserts?  (Read 1148 times)

Offline arumalpra

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The lapse rate calculator found in the internet shows 10c decrease at 1000 m altitude.
Is this same in a desert?

Appreciate help.
« Last Edit: 17/07/2016 09:25:28 by chris »


 

Offline Colin2B

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Re: Lapse rate in a desert
« Reply #1 on: 14/07/2016 08:30:17 »
Most calculators use dry lapse rate so should be ok. Remember that this only works for stable air and any atmospheric effects eg inversion layers, katabatic winds will change temperatures.
 

Offline Alan McDougall

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Re: Lapse rate in a desert
« Reply #2 on: 14/07/2016 09:12:43 »
The lapse rate calculator found in the internet shows 10c decrease at 1000 m altitude.
Is this same in a desert?

Appreciate help.

http://en.citizendium.org/wiki/Atmospheric_lapse_rate


Dry adiabatic lapse rate

Since the atmospheric pressure decreases with altitude (see Earth's atmosphere), the volume of an air parcel expands as it rises. Conversely, if a parcel of air sinks from a higher altitude to a lower altitude, its volume is compressed by the higher pressure at the lower altitude. An adiabatic lapse rate is the rate at which the temperature of an air parcel changes in response to the expansion or compression process associated with a change in altitude, under the assumption that the process is adiabatic (meaning that no heat is added or lost during the process).[6][7]

Earth's atmospheric air is rarely completely dry. It usually contains some water vapor and when it contains as much water vapor as it is capable of, it is referred to as saturated air (i.e., it has a relative humidity of 100%). The dry adiabatic lapse rate refers to the lapse rate of unsaturated air (i.e., air with a relative humidity of less than 100%). It is also often referred to as the dry adiabat, DALR or unsaturated lapse rate. It should be noted that the word dry in this context simply means that no liquid water (i.e., moisture) is present in the air ... water vapor may be and usually is present.

The dry adiabatic lapse rate can be mathematically expressed as:[8][9]


where:
   = the dry adiabatic lapse rate, 0.0098 K/m (equivalent to 9.8 K/kilometre or 5.4 F/1000 feet)
   = Earth's gravitational acceleration, 9.8076 m/s2
   = the specific heat of dry air at constant pressure, 1004.64 J/(kg  K)
The troposphere is the lowest layer of the Earth's atmosphere. Since  and  vary little with altitude, the dry adiabatic lapse rate is approximately constant in the troposphere.
 

Offline alancalverd

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Re: Lapse rate in a desert
« Reply #3 on: 15/07/2016 23:44:37 »
The lapse rate calculator found in the internet shows 10c decrease at 1000 m altitude.
Is this same in a desert?

Appreciate help.

Yes, up to about 10 km altitude.
 

Offline arumalpra

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Is this mean that the top of the world tallest building's (Burj khalifa in Dubai - 828m) temperature is 10c or 8 c lower than that of the ground floor?

Other aspect, Sun heats the earth. can somebody tell me the effect of this to the lapse rate?
 

Offline Colin2B

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Other aspect, Sun heats the earth. can somebody tell me the effect of this to the lapse rate?
It determines the ground temperature, but doesn't affect the lapse rate.
 

Offline arumalpra

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Say during the day time temperature at each km 30 20 10....
In the night                  25 15 15.... I understand the rate is the same.
If the above is correct, the temperatur at the  1km level depends on the heat generatey by the sun light.
Heat transfered up has effect. not just the pressure factor.
 

Offline chris

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Does this mean that the top of the world tallest building's (Burj khalifa in Dubai - 828m) temperature is 10c or 8 c lower than that of the ground floor?

Not quite, because that formula applies to free air. But the top of the building will be absorbing - and re-radiating - solar energy, so the "local" temperature will be higher. The building will also affect local air flow including potentially channelling warmer air from the ground, which may also influence the local temperature.
 

Offline alancalverd

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There is always a difference between the outside  air temperature and the surface temperature of an object at altitude. With the sun shining on a helicopter hovering at 10,000 ft, the skin temperature might be + 10 C and the OAT -10C. Once the aircraft starts moving, the ST drops towards the OAT.
 

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