During our overview of the course on Monday, I mentioned that cloud droplets can

Question

During our overview of the course on Monday, I mentioned that cloud droplets cannot grow into rain-sized drops (radius of about 1 mm) through condensation alone. We do not need to derive the equations for condensational growth to see that this is indeed the case. (a) Imagine a parcel of air lofted upwards in a deep convective thunderstorm in the tropics. Assume cloud base has a temperature of 30°C, a pressure of 900 hPa, and that the number of aerosol particles that become water droplets is 100 cm3. If these droplets were lofted to the top of a tropical storm (around 200 hPa), how large would the drops become? All that is wanted here is an estimate, one that you can arrive at quickly if you recall what you learned about the thermodynamics of cloudy air. (b) Why did I choose the tropics for my initial parcel conditions

Explanation / Answer

(a) Since the temperature of the cloud base is 300C , the size of the droplets will be

Pcloud base/Ptropical storm = 900/200 = 4.5 , which means the droplets in the tropical storm will be 4.5 times the previous size.

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