http://www.bioticregulation.ru/pump/pump4-2.phpFeel the Pump Physics
Biotic pump of atmospheric moisture functions like this. Water vapor from the forest canopy undergoes condensation in the atmosphere and disappears from the gas phase. For this reason, the air rarifies and its pressure drops. In the result, air is sucked from below to compensate for this pressure drop. This, in its turn, leads to the drop of pressure at the surface, so that surface air is drawn from the neighboring areas to the area of the upwelling. If there is ocean in the neighborhood, then the air which is drawn to the continent will be enriched by evaporated moisture.
Pump physics is simple. One needs to have an idea of what ideal gas is, what diffusion is and how it differs from the dynamic flow of gases and, finally, how water vapor pressure depends on temperature (Clausius-Clapeyron law). All these phenomena can be vividly illustrated with use of interactive Flash models. You can change and monitor gas pressure, make water evaporate, make gas mixtures diffuse or flow dynamically. You can also get an idea of the major components of atmospheric circulation over forests, clear-cuts or deserts, by switching the circulation on and off yourself. All models were created for our website by S.K. Buruchenko.
Diffusion and dynamic flow of gases is not the same!
If you have problems with viewing the Flash object, click here for free installation of the latest version of Flash Player.
If a slide starts moving in an uncontrolled fashion, click on it, this will bring it to order.
Scene I. Dynamic gas flow (wind)
Suggested parameters to set: Na = 45; Na = 1; T = 5 K.
Dynamic gas flow arises if only there is a pressure difference (spatial pressure gradient). Molecules collide with each other and, meeting less resistance in the area of lower pressure, accelerate towards this area. Gas pressure is proportional to its concentration (number of molecules in a given volume) and temperature.
Set the suggested values for the numbers of molecules, press the star "Apply settings" to the left of the copyright button, then set temperature using the red slide. Now press the star to the right of the copyright. The partition will be removed. Gas will start rapidly propagating from the left to the right part of the vessel. Check the time when there are as many as 22 blue molecules in the right part of the vessel. This time will be about half a minute. Then go to Scene II and compare this time with the characteristic time of the (much slower) diffusion process.
When water vapor condenses in the atmosphere, air pressure drops and there appears a dynamic flow (wind) towards the area where condensation has occurred.
Scene II. Diffusion of gases
Suggested parameters to set: Na = 45; Nb = 45, T = 5 K.
Diffusion, i.e. mixing of different gases, occurs in the absence of pressure difference. This is a slow process. Try to record the time when the first 22 blue molecules arrive to the right part of the vessel. With suggested settings this can take ten minutes or even longer, compared to but half a minute for the dynamic flow. To speed up the process, try setting a higher value of temperature.
In this model we observe molecular diffusion. In the atmosphere the diffusion is of turbulent nature: chaotic atmospheric eddies (vortices) mix up atmospheric gases much more rapidly than do molecular collisions. However, the estimated turbulent diffusional fluxes for the major air constituents appear to be many times smaller compared to the dynamic fluxes generated by the evaporative force.
If you have any questions, you are welcome to ask them here.
These slides regulate the number of molecules in the two parts of the vessel.
Move the slides down to the utmost, then click on the star
to the left of the copyright. Current numbers of molecules are shown on the yellow scales.
Temperature slide and scales. One can change temperature from 1 to 101 degrees Kelvin.
Scales of gas pressure in the two parts of the vessel.
These scales indicate the current number of red and blue molecules in the right and left parts of the vessel.
This arrow indicates that a pressure difference is present. It appears when the number of molecules in one part of the vessel
is substantially larger than in the other, and disappears when the numbers of molecules in the two parts of the vessel
are approximately equal.
Current difference between the total number of molecules in the left a and right b parts of the vessel.
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