Vertical Heat Flux Components in the Northern Atmosphere

Micheal Hantel Geophysical Fluid Dynamics Program, Princeton University, Princeton, N.J. 08540

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Wolfgang Peyinghaus Geophysical Fluid Dynamics Program, Princeton University, Princeton, N.J. 08540

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Abstract

The large-scale atmospheric heat balance in zonally-averaged form is investigated for the northern atmosphere (50 mb≤p≤1000 mb; 10°S≤ϕ≤75°NN), both for annual and for summer and winter conditions. The basic equation is the conservation law for potential heat cpT+gz. The diabatic heating is written as a flux divergence, following van Mieghem. Only the vertical component of the corresponding flux is considered. It comprises radiation flux (HR) and precipitation flux (HC) and is combined with the convective potential heat flux into a generalized net vertical heat flux (Fp). Since the heat flux vector in the meridional-vertical plane is practically nondivergent, Fp can be calculated from the synoptic horizontal heat flux divergence by vertical integration, with the satellite-observed HR across the atmosphere's top as a boundary condition. The vertical pattern HR is separately calculated employing a model with 20 vertical layers for short-and longwave radiation, including 14 cloud layers. Its results compare favorably with independent estimates at the top and bottom of the atmosphere. HC is obtained as a residual. It is downward everywhere for the annual case and its surface values are in accord with observed precipitation. Northern atmosphere cross sections of Fp and its radiation, precipitation, and convective components are shown. The most important components of Fp are HR and HC. They nearly balance each other in the rain-belts of the inner tropics and mid-latitudes and represent the radiative-convective equilibrium of the atmosphere.

Abstract

The large-scale atmospheric heat balance in zonally-averaged form is investigated for the northern atmosphere (50 mb≤p≤1000 mb; 10°S≤ϕ≤75°NN), both for annual and for summer and winter conditions. The basic equation is the conservation law for potential heat cpT+gz. The diabatic heating is written as a flux divergence, following van Mieghem. Only the vertical component of the corresponding flux is considered. It comprises radiation flux (HR) and precipitation flux (HC) and is combined with the convective potential heat flux into a generalized net vertical heat flux (Fp). Since the heat flux vector in the meridional-vertical plane is practically nondivergent, Fp can be calculated from the synoptic horizontal heat flux divergence by vertical integration, with the satellite-observed HR across the atmosphere's top as a boundary condition. The vertical pattern HR is separately calculated employing a model with 20 vertical layers for short-and longwave radiation, including 14 cloud layers. Its results compare favorably with independent estimates at the top and bottom of the atmosphere. HC is obtained as a residual. It is downward everywhere for the annual case and its surface values are in accord with observed precipitation. Northern atmosphere cross sections of Fp and its radiation, precipitation, and convective components are shown. The most important components of Fp are HR and HC. They nearly balance each other in the rain-belts of the inner tropics and mid-latitudes and represent the radiative-convective equilibrium of the atmosphere.

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