Calculate the temperature of the parcel at the following elevations as it rises

Question

Calculate the temperature of the parcel at the following elevations as it rises up the windward side of a mountain.The mountain is 8000 feet high in elevation. A 40 degree F parcel of air at sea level begins to rise up the mountain. The Lifting Condensation Level is 2000 feet. The DALR is 5.5 F/1000’ and the SALR is 3.0 F/ 1000 ft. The surrounding air is 40 degrees F at sea level on the windward side of the mountain, and the Environmental Lapse Rate (lapse rate of the surrounding air) is 4 degrees F.

Question 1 Part A

At sea level on the windward side of the mountain, is the parcel of air stable or unstable?

Part B

At what elevation does the parcel of air become conditionally unstable?

A) 2,000 feet, B) 3,000 feet, C)  5,000 feet, D) 6,000 feet

Explanation / Answer

D. Answer-6000 feet:Initially the air is unsaturated. The parcel of air will rise with 5.5 degree F per 1000 ft rise in elevation. Starting from 0 ft, its initial temperature is 40 degree F. At about lifting condensation level the temperature of rising air will be 29 degree F. After that it will rise with saturated adiabatic lapse rate which is 3F per 1000m. At about 6000 feet its temperature will be 17 degree F.

Whereas the temperature of surrounding will rise with 4 degree F per 1000 feet in elevation. At the lifting condensation level the temperature of the surrounding air will be 28 degree F more than the temperature of air parcel. The temperature of surrounding air will be 16 degree F at 6000 feet. Since at this elevation the temperature of surrounding air is less or the air is cooler than the rising parcel of air. So the rising air parcel becomes conditionally unstable at 6000 m elevation when an otherwise stable air is forced to rise and becomes unstable.

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