Increasing rainfall may affect winds: study

Feb 24, 2012 by Lin Edwards report
Image: Wikipedia.

(PhysOrg.com) -- Falling raindrops produce friction as they drop through the atmosphere to the ground, and this dissipates the kinetic energy, converting it into diffuse heat. Now researchers in the US have used recently-obtained satellite data to calculate the energy dissipation, and they have discovered it is a surprisingly major component of the atmosphere’s overall energy system.

Mathematicians Olivier Pauluis of New York University, and Juliana Dias of the National Oceanic and Atmospheric Administration (NOAA) in Colorado, USA, used radar data provided by the Tropical Rainfall Measurement Mission (TRMM) jointly run by the US National Aeronautics and Space Administration (NASA) and Japan’s counterpart, the Japan Aerospace Exploration Agency (JAXA). They used the data to compute the kinetic rate, which turns out to be on average 1.8 watts per square meter in the tropical regions between latitudes 30 degrees South and 30 degrees North.

They based their calculations on the energy a single raindrop dissipates, which was already known, and TRMM figures on total rainfall. The also provided height details, which were important because raindrops falling from a greater height dissipate more kinetic energy through .

The researchers found that energy dissipation produced by was around the same as dissipation caused by turbulence in the atmosphere, such as in storms and trade winds. Pauluis said that this result, despite seeming to be surprising, fits well with previous modeling.

Pauluis and Dias also calculated that rain-induced dissipation is stronger for continental convection than maritime convection. They conclude that changes in hydrologic (water) cycles could affect the amount of kinetic energy dissipated in the atmosphere and affect the amount of energy remaining to produce winds.

Hydrologic cycles are changing rapidly, and if these changes and increased evaporation result in greater rainfall (and rain falling from a greater height, as it does when the atmosphere is warmer), this would dissipate more and could thus result in slightly weaker air circulation by winds.

The paper was published in the journal Science. Climate scientist Dargan M.W. Frierson of the University of Washington, in a related Perspective, said that more research is needed to determine how likely a weakening of atmospheric circulation is, and what impact, if any, this effect would have on individual weather systems.

Any changes are unlikely to affect large storm systems such as hurricanes, since they are governed much more by sea temperatures than the energy available in the .

Explore further: Strong quake hits east Indonesia; no tsunami threat

More information: Satellite Estimates of Precipitation-Induced Dissipation in the Atmosphere, Science 24 February 2012: Vol. 335 no. 6071 pp. 953-956. DOI: 10.1126/science.1215869

ABSTRACT
A substantial amount of frictional dissipation in the atmosphere occurs in the microphysical shear zones surrounding falling precipitation. The dissipation rate is computed here from recently available satellite retrieval from the Tropical Rainfall Measurement Missions and is found to average 1.8 watts per square meter between 30°S and 30°N. The geographical distribution of the precipitation-induced dissipation is closely tied to that of precipitation but also reveals a stronger dissipation rate for continental convection than for maritime convection. Because the precipitation-induced dissipation is of the same magnitude as the turbulent dissipation of the kinetic energy in the atmosphere, changes in the hydrological cycle could potentially have a direct impact on the amount of kinetic energy generated and dissipated by the atmospheric circulation.

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julianpenrod
1 / 5 (4) Feb 25, 2012
Falling raindrops are credited with affecting winds across the globe, but, when I said that the giant turbines used for wind farms would affect climate because taking the energy from wind reduces the amount and speed of the wind, I am mocked. To be sure, the mechanisms and extent are different, but they represent an interaction between the preence of wind and the energy that gives rise to it. But, for all that wind turbines may not cover as large an area as storms, rememebr that storms last only a few hours, while the turbines will continue to rob moving air of its energy constantly.
rhapsodist
5 / 5 (3) Feb 27, 2012
Julian, if adding windfarms is going to decrease windspeed, should we first figure in what the effect of deforestation over the last 1,000 years has had?
TS1
not rated yet Feb 29, 2012
A question about below to anyone who might know:
"Falling raindrops produce friction as they drop through the atmosphere to the ground, and this dissipates the kinetic energy...a surprisingly major component of the atmospheres overall energy system.

The question is about the amount of cosmic dust that supposedly falls on earth from space daily, estimated at 30,000 metric tons per year by some. See eg:
http://www.thefre...20629998
http://www.astrob...mic-dust

So my question is, would this dust not also release kinetic energy and therefore affect the atmospheres overall energy system?
deepsand
3.4 / 5 (10) Feb 29, 2012
It does; but, it's miniscule.

Assuming that all of that dust were directly in the path of Earth's orbit, it would be impacting its atmosphere at a velocity of 28.783 kilometers/sec., with a total annual kinetic energy of 13.305 terajoules, or 36 gigajoules/day, roughly equivalent to the chemical energy released by burning 6 barrels of oil per day.

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