Naked Science Forum
Life Sciences => The Environment => Topic started by: Souffle on 05/08/2009 11:48:54
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I was on holiday on the south coast of Portugal last week and while sweating in the heat I was wondering why there weren't any clouds to protect me with their shady goodness. It was 35 deg and we were right by the sea but not a cloud all week! With all that sun shining on all that water surely there must be some evaporation going on to produce clouds? Where does the water vapour go?
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Clouds form when the water vapour condenses into droplets. This usually means that the warm water carrying air needs to meet cooler air for the water to chill and condense out to form clouds. Also, if the wind was predominantly blowing from the ocean towards the land there would have probably also have been relatively little dust in it, which supply the nuclii for the water droplets form upon.
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The Southeren region is dominated by subtropical anticyclones that allow the temper\aature to rise to those you observed and greater. Not only that but during the summer months portugal has around 29 days without any precipitation and that many days with 11 hours or more of continuous sunshine. With this sort of climate the afternoon levels of RH will be in the mid ranges and too low to produce cloud. as these graphics show.
Air temp for the last 24 hours:
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RH for the last 24 hours:
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If I get the time later I will search the archeives for last weeks data.
As it happens I am currently reading a paper about the "Relationship between the Subtropical Anticyclone and Diabatic Heating"
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High temperatures and summer high pressure systems produce little or no cloud. If you look at the current UK weather you will notice that we are having temperatures in the 20C range and have a stationary high pressure system above us with lower pressure systems skirting around the edges. This is producing little or no cloud over the country except around the coast where the lower pressure is.