Monday, July 24, 2017
Drought in Cape Town, etc
Drought in Cape Town, West Coast, etc. Contrary to what many believe, there is a lot of moisture in hot fairly dry desert air. The weather report says that at 17h00 Monday 24 July the humidity in Cairo will be 30% and the temperature will be 37 deg C. This air will hold about 13 grams of water vapour in each cubic metre. If the temperature was 15 deg C and the relative humidity was 95% the air would hold only about 12 grams of water vapour per cubic metre. When air cools the relative humidity increases and the weather report says that at 23h00 on Monday 24 July the relative humidity in Cairo will be 65% and the temperature will be 29 deg C. Now if you heat air with a high relative humidity it does not have to rise far before clouds form. If you heat low relative humidity air, it has to rise high before clouds form and you have to heat it a lot to get it to rise so far. So here is the idea: Wait until the air cools and RH is high and then heat air a little to get it to rise and form clouds. My method to heat it is to have pipes with heated water containers at the ends and with holes in the pipes to let steam out. This will humidify and heat the air.
Example. The weather report says that in Cairo on 28 July 2017 at 04h00 the RH will be 86% and the temperature will be 26 deg C. Using Espy's equation, if this 26 deg C air is heated to 28 deg C it only needs to rise 321 metres for clouds to form. By virtue of its temperature (T=28 deg C) it could rise 606 metres. So it can easily reach the height needed for clouds to form (used general sorts of lapse rates).