Maximum entropy production and the strength of boundary layer exchange in an atmospheric general circulation model
Axel Kleidon, Klaus Fraedrich, Edilbert Kirk and Frank Lunkeit
Boundary layer turbulence plays a central role in determining the strength of the overall atmospheric circulation by affecting the intensity of exchange of heat, mass, and momentum at the Earth’s surface. It is often parameterized using the bulk formula, in which the von-Karman parameter plays a critical role. Here we conducted a range of sensitivity simulations with an atmospheric general circulation model in which we modified the strength of boundary layer turbulence by varying the von-Karman parameter. These simulations show that the maximum of entropy production associated with boundary layer dissipation is consistent with the observed value of the von-Karman parameter of 0.4 and maximizes the planetary rate of entropy production with the global radiative temperature being close to its minimum value. Additional sensitivity simulations were conducted with an increased concentration of atmospheric carbon dioxide, which affects the relative radiative forcing of tropical vs. polar regions. We find that the global climate sensitivity is more-or-less independent of the assumed strength of boundary layer turbulence in our idealized setup. The difference in climate sensitivities of tropical and polar regions is at a minimum at a climatic state of MEP.
- Geophysical Research Letters, 33, L06706, doi:10.1029/2005GL025373.
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Figure 1: Sensitivity of globally averaged entropy production rates to different values of the von-Karman parameter. top: entropy production by poleward heat transport σaht (dotted line), sensible heat flux σsh (dashed line), and the sum of both σturb = σaht+σsh(i.e. entropy production by overall atmospheric turbulence, solid line). bottom: planetary entropy production σtot (solid line) and radiative temperature Trad (dotted line). The thin vertical line marks the value of the von-Karman parameter of the control simulation of k = 0.4.
Figure 2: Zonal averages of net radiative and sensible heat fluxes (top and bottom left respectively) and respective zonal surface temperatures (top right, difference to ”Control” simulation) and lapse rate (bottom right) for selected sensitivity simulations.
Figure 3: Sensitivity of global mean surface temperature (solid line), tropical surface temperature (dashed line) and polar temperature (dotted line) to an increase in pCO2 by a factor of 10. The vertical line marks the value of the von-Karman parameter of the control simulation of k = 0.4.