Question No. 23

TV news: Bill Gates is going to mix the offshore waters of the Atlantic Ocean, to pump deep cold waters upwards reducing evaporation, as a measure to tame the hurricanes that besiege the Atlantic coast of the U.S. But will the Gulf Stream persist then? Is it at all possible, after all?
Answered 19 July 2009.
Question author: Sergey.
Asked 19 July 2009.

Wind forms due to pressure drop that appears due to condensation of water vapor. Unlike the evaporation which rate is limited by solar radiation, condensation of water vapor can occur at an arbitrarily high rate. A vivid analogy: biomass production by green plants is limited by solar radiation, while biomass consumption by large animals can occur at an arbitrary rate.

It is easy to calculate that condensation rate (the rate of water vapor "consumption") in the hurricane exceeds the local rate of evaporation by many times. In other words, the hurricane does not live on water vapor that is evaporating from the warm sea right while the hurricane is developing. Instead, the hurricane relies on water vapor that has been accumulated in the atmosphere during prolonged periods of relative calmness that precede the hurricane. In this sense the hurricane can be compared to a big hungry animal who devours on its way all biomass that has been accumulating in the ecosystem for a long while. It is clear therefore that the decrease of local evaporation the might follow the proposed oceanic mixing cannot impact the hurricane energetics in a desirable way. On the contrary, surface temperature drop will cause the condensation to become more intense, so that the hurricane power can even increase in the end.

The only way to protect the continents against hurricanes is to restore the regular pulling power of the biotic pump of atmospheric moisture by a large scale forest restoration. In this case the condensation-related drop of atmospheric pressure will be re-distributed over thousands kilometers (not hundreds, as in the hurricane). In the result, the cumulative power of surface resistance that is proportional to distance traveled by the atmospheric masses, will grow by an order of magnitude. This prevents the development of hurricane wind speeds.

As for the Gulf Stream, a large scale anthropogenic mixing of the ocean can result in a complete destabilization of the existing oceanic circulation.

Water vapor accumulates in the atmosphere
Hurricane consumes water vapor that accumulates in the atmosphere during prolonged periods of calmness.

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