Can we have an answer where the access of 15 W/m2 in the Sahara is coming from? Asked on this session on Tuesday.
If we suppose a disk of 1000 km radius over the Sahara, we get an imbalance of
pi * R² * (-15 W/m²) = ~ 47 TW (Tera Watt)
which is about 3 times the total power consumption by human beings, e.g. see:
http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)
http://en.wikipedia.org/wiki/Orders_of_magnitude_%28power%29
This power, which is leaving the Sahara to space, should come from advection on the borders of the domain. Let suppose the atmosphere of 20km height, the advection surface is then 2 * pi * R * 20km = 125 10^9 m² and thus the average lateral input of energy is a flux of 376 W/m²!!!
I guess this energy comes from the Hadley (and ferret) cels: the wet air ascension in the ITCZ produces precipitaion and dry the air. The subsidence of this dry air over the desert is an efficient way of energy transport (Foehn effect).
Very interesting! Altough the numbers are aproximately computed are very astounding..
I think that your explanation of it is very elegant,
at the moment I can not imagine other possible sources of incoming
energy.
It is also funny to think that this "advected" energy flux is of the same order of magnitude as the global average of the incoming radiation (1361W/m²/4 = 340.25 W/m²) and that this energy is extracted from entry of "cool" air in the upper part of the atmosphere and output of much warmer air in the lower part of the atmosphere. The -15 W/m² energy should be delivered by the compression of the air mass during its subsidence. could someone confirm it is realistic?