Thursday, September 18, 2008

Burj Dubai and the adiabatic lapse rate

The amount of decrease is governed by the dry adiabatic lapse rate. The reason for this decrease is as follows. When a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air parcel expands, it pushes on the air around it, doing work; but generally it does not gain heat in exchange from its environment, because its thermal conductivity is low (such a process is called adiabatic). Since the parcel does work and gains no heat, it loses energy, and so its temperature decreases.

The formula is the following:
dT/dz = -9.8 C/Km which means approximately 1 degree Celsius drop each 100 meters of height.

However the above calculation is valid for dry atmosphere. In dubai, though sometimes in the winter it really gets dry - especially after heavy rain showers, the usual case is near 100% humidity. In this case we use the saturated adiabatic lapse rate. To save your time, here is the difference:
dT/dz = -6.5 C/Km which means 0.65 degree Celsius drop each 100 meters

In the case of Burj Dubai, at 819, the drop in temperature will be at 6-8 degrees.

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