Passatin version
The Passatin version is a permanent, large-scale, stable descent inversion from the tropics ( subtropical high pressure belt ) to the ITC ( innertropical convergence zone ), where it is in turn broken by the increasing temperature and the absorption of water vapor.
Origin and expression
At an altitude of around 1000 to 1500 m, the rising air masses from the Passat ground layer are cooler than the descending air from the Passat upper layer (whereby the descending air heats up dry adiabatically, while the ascending air cools down moist adiabatically). In the Passatin version, in contrast to the normal decrease in temperature, the temperature increases with altitude. It is only a few hundred meters high.
The temperature inversion is amazing, because the rising air has just been warmed up by intense radiation on the ground, while the falling air has been on the move for a long time since it was warmed up and was able to cool down. That it is still warmer can only be explained by its origin. In the ITC, the air was not only warmed up on the surface of the earth, but also enriched with latent heat (heat of evaporation contained in the air humidity ), which was released again during condensation at altitude.
consequences
The inversion prevents the air of the Passat ground layer from rising further, because air masses rise i. A. only open when they are warmer (and thus have a lower density) than the surrounding air (or when they are forced to do so by wind and relief). But that is precisely not the case in the inversion.
This prevents high clouds from forming, which would be the prerequisite for rain. The consequence of the Passatin version are therefore cloud-free areas or areas with only low level cloud formation, the so-called trade wind clouds , and only extremely rare rainfall.
The formation of the largest sandy desert on earth, the Sahara , is therefore a. a consequence of the Passatin version.