9 March 2011 [Publications]
Condensation, hurricanes, forests and history of meteorology

While Napoleon's Grande Armée was experiencing the severe weather of Russian Winter of the year 1812, an outstanding Swiss physicist Jean-André Deluc mused over the causes of rain and wind. He wrote (Deluc, 1812, Gilberts Ann. d. Phys., 41, 162-194):

"if it [the rain] falls locally, (...), it is accompanied by more or less heavy gusts, which come into existence, (...) that where the water vapour turns into rain a kind of airfree space originates. This is the reason for sudden changes in wind direction which cease again when the air has reached its original density." (translation by Dr. Stefan Emeis).

The famous scholar (aged then 85) thus described one of the two key elements of condensation-induced atmospheric dynamics: when water vapor condenses, it is being ‘packed’ into a thousand of times smaller specific volume of the liquid. This results in partial 'rarification’ of the condensation area and turns the latter into the area of low pressure.

However, this is not the whole story. The second key element is the positive feedback between condensation and air motion. Indeed, atmospheric condensation is an unusual reaction that depends on air motion in a particular direction! It occurs when the moist air rises and cools. The larger the vertical air velocity, the greater the condensation intensity and, hence, the stronger the winds.

199 years after Deluc’s work we are glad to present a new study on condensation-induced dynamics of hurricanes. It is shown that considering the dynamics of the vapor sink it is possible to obtain, from basic atmospheric constants, realistic profiles of both radial and tangential velocities in hurricanes of varying intensity. It is also possible to estimate the size of the hurricane eye. Furthermore, the obtained radial profiles of hurricane pressure agree well with empirical observations. The previous order of magnitude estimates of pressure and velocity are confirmed. An extended summary can be found here.

Current approaches treat the radial and vertical wind as "secondary circulation". The notion reflects not only the lower magnitude of vertical and radial velocities as compared to tangential (rotational) velocity but also the relatively little attention that is paid to this circulation in hurricane theory. According to our results, the so-called "secondary" circulation is in fact the primary dynamic driver of atmospheric vortexes, both hurricanes and tornadoes.

This work is aimed by us to add one more brick to the physical foundations of the biotic pump theory. The statement that winds are driven by phase transitions of water vapor assigns the key role in the maintenance of the water cycle and moisture transport on land to natural forests — due to the huge evaporative/condensational potential of the latter. Deforestation causes first loss of stability and later a major continental dessication. A recent overview of the theory, "Biotic pump, condensation, atmospheric dynamics and climate", appeared in a special issue of the International Journal of Water "Water and the Complexities of Climate".

The discussion of these propositions by the meteorological community appears to be gradually gaining momentum. We are glad to report that following our appeal the second referee was ultimately found to assess the on-going work by our group on condensation-induced dynamics that is currently under open discussion in the Atmospheric Chemistry and Physics Discussion:

Where do winds come from? A new theory on how water vapor condensation influences atmospheric pressure and dynamics

The discussion has been extended from the original deadline of December 20th, 2010 to at least April 7th, 2011. We welcome comments, criticisms and suggestions.