4. Cloud seldom forms in the stratosphere because air there is very dry. Excepti

Question

4. Cloud seldom forms in the stratosphere because air there is very dry. Exceptional is Polar Stratospheric Cloud (PSC), which forms over the Antarctic and, less fre- quently, over the Arctic. The thicker form of such cloud (Type II PSC), which is still quite tenuous compared with tropospheric cloud, is composed of ice. (a) For a mixing ratio at 80 hPa of 3 ppmv, representative of water vapor in the lower stratosphere (cf. Fig. 18.8), calculate the temperature at which ice cloud forms. (b) Referring to Fig. 1.7 and to the discussion in Sec 18.3.2, where is such cloud likely to form?

Explanation / Answer

(a) In the stratosphere ice clouds starts to form at a temperature of around -22 degree centriate which lies in the middle stratosphere.The above temperation is less than the calculated temperature for water vapour in the lower stratosphere by the Gibb's Dalton law.

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