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The biotic pump physics is maturing to a novel theory of atmospheric circulation: Everybody’s invited!

Last modified October 13, 2009 09:34

Horizontal ocean-to-continent moisture transport is of vital importance to humanity, hence the recently proposed biotic pump theory, which suggests a major role for forests in this mechanism, has provoked widespread notice and debate. Here we address some criticisms and report on recent advances of the theory. A new field of research awaits capable newcomers from ecology, meteorology and physics.

Makarieva A.M., Gorshkov V.G.

Horizontal ocean-to-continent moisture transport is of vital importance to humanity, hence the recently proposed biotic pump theory, which suggests a major role for forests in this mechanism, has provoked widespread notice and debate. Here we address some criticisms and report on recent advances of the theory. A new field of research awaits capable newcomers from ecology, meteorology and physics.

 

In a recent publication Stigter and Meesters (2009), based on the results of Meesters et al. (2009), referred to the biotic pump theory of Makarieva and Gorshkov (2007), see also Sheil and Murdyarso (2009), Makarieva et al. (2009), as “completely discredited” due to “errors in basic atmospheric physics”. In doing so, Stigter and Meesters (2009) should also have mentioned the response to this critique published in the same journal (see Makarieva and Gorshkov 2009b). In our response we summarize why, far from being the last word implied by Stigter and Meesters (2009), the critique of Meesters et al. is itself riddled with errors and confusions. Here we highlight a few essential points.

 

The central point in the biotic pump theory is that condensation creates a local drop of air pressure driving winds in the lower atmosphere. Meesters et al. (2009) and Stigter and Meesters (2009) disagree based on their assertion that condensation leads to an air pressure rise due to the release of latent heat. This idea is in conflict with the fundamentals of thermodynamics, notably the Clausius-Clapeyron law. This law says that the saturated concentration of water vapor in an air parcel increases when the parcel’s temperature rises and decreases when the parcel’s temperature drops. Therefore, condensation (i.e. the decrease of vapor concentration) can only occur after the temperature drops and cannot be associated with any temperature rise. The well-known effect of the latent heat release consists only in the diminishment of the temperature drop that initiated condensation.

 

In considering the effect of condensation on air pressure, Meesters et al. (2009) and Stigter and Meesters (2009) fail to note that, since the atmosphere exists in the gravitational field of Earth, air pressure is approximately equal to the weight of the air column above the considered point. Thus, condensation by removing vapor from the gas phase reduces the air column weight and nearly instantaneously reduces air pressure at the surface (and elsewhere in the lower atmosphere) irrespective of the vertical temperature profile in the column. We note that other meteorologists recognize this relationship. For example, Trenberth (1991) is explicit on this point in his Eq. 6, see also Dool and Saha (1993), Lackmann and Yablonsky (2004). The contrasting statement of Stigter and Meesters (2009) regarding the effect of condensation on air pressure is incorrect.

 

An attentive observer will acknowledge that all the major weather events (large-scale cyclones, hurricanes, tornadoes) are accompanied by dense cloud formation and precipitation, i.e. by condensation of water vapor. Despite this common feature, the current meteorological paradigm accounts for the relevant phenomena by invoking a divergent range of mechanisms. In particular, it relies on horizontal differential heating to explain the moderate winds of the large-scale circulation patterns; it abandons this same concept of differential heating when describing hurricanes as a result of heat extraction from the isothermal oceanic surface; finally, it lacks any coherent theory to account for tornadoes.

 

All these phenomena can be explained by a single mechanism: condensation (Makarieva and Gorshkov, 2009b,c). This theory is new, so the details are still being clarified, but the theory has already offered progress in a number of areas. For example, sound numerical estimates of the wind wall and eye radius and wind velocity profiles for hurricanes and tornadoes using only a limited number of fundamental atmospheric parameters such as the circulation radius and land surface roughness (Makarieva and Gorshkov, 2009c)

 

When condensation occurs over a large area of the order of thousand kilometers in size, winds are generated but the cumulative impact of turbulent surface friction prevents them from achieving high velocities. Hence, an extensive forest cover ensures persistent, relatively mild winds. When, driven by random fluctuations, condensation occurs over an oceanic surface in the radius of only a few hundred kilometers, surface friction is too small to prevent formation of hurricane winds. Finally, extremely compact condensation events over deforested, heated land and over sea, lead to formation of tornadoes.

 

Thus, the new theory suggests natural vegetation not only guarantees a stable regional water cycle (Makarieva and Gorshkov, 2007), but also prevents tornado and hurricane formation both on the continent and on the adjacent oceanic area (Makarieva and Gorshkov, 2009b,c). Further investigations in these concepts promise further exciting advances. We believe a well founded discussion and debate of these concepts will contribute to our common understanding of our planet and our future.

 

References

 

  1. Dool H.M. van den, Saha S. (1993). Seasonal redistribution and conservation of atmospheric mass in a general circulation model. J. Climate, 6, 22-30.
  2. Lackmann G.M., Yablonsky R.M. (2004) The importance of the precipitation mass sink in tropical cyclones and other heavily precipitating systems. J. Atm. Sci., 61, 1674-1692.
  3. Gorshkov V.G., Makarieva A.M. (2007) Biotic pump of atmospheric moisture as driver of the hydrological cycle on land. Hydrology and Earth System Sciences, 11, 1013-1033. http://www.hydrol-earth-syst-sci-discuss.net/3/2621/2006/hessd-3-2621-2006.html
  4. Makarieva A.M., Gorshkov V.G. (2009a) Reply to A. G. C. A. Meesters et al.'s comment on "Biotic pump of atmospheric moisture as driver of the hydrological cycle on land". Hydrology and Earth System Sciences, 13, 1307-1311.
  5. http://www.hydrol-earth-syst-sci.net/13/1307/2009/hess-13-1307-2009.html
  6. Makarieva A.M., Gorshkov V.G. (2009b) Condensation-induced dynamic gas fluxes in a mixture of condensable and non-condensable gases. Physics Letters A, 373, 2801-2804.
  7. Makarieva A.M., Gorshkov V.G. (2009c) Condensation-induced kinematics and dynamics of cyclones, hurricanes and tornadoes. Physics Letters A, in press, doi:10.1016/j.physleta.2009.09.023.
  8. Makarieva A.M., Gorshkov V.G., Li B.-L. (2009) Precipitation on land versus distance from the ocean: Evidence for a forest pump of atmospheric moisture. Ecological Complexity, 6, 302-307.
  9. Meesters A.G.C.A., Dolman A.J., Bruijnzeel L.A. (2009) Comment on “Biotic pump of atmospheric moisture as driver of the hydrological cycle on land” by Makarieva AM, Gorshkov VG (2007). Hydrol. Earth Syst. Sci., 13, 1299-1305.
  10. Sheil D., Murdiyarso D. (2009) How forests attract rain: an examination of a new hypothesis. Bioscience 59: 341-347.
  11. Stigter K., Meesters A. (2009) A "Forests as biotic pump” hypothesis discredited due to errors in basic atmospheric physics. http://www.agrometeorology.org/topics/needs-for-agrometeorological-solutions-to-farming-problems/a-forest-as-biotic-pump201d-hypotesis-discredited-due-to-errors-in-basic-atmospheric-physics
  12. Trenberth K.E. (1991) Climate diagnostics from global analyses: conservation of mass in ECMWF analyses. J. Climate, 4, 707-722.

 

 

 

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