Response of the Joint Ocean-Atmosphere Model to the Seasonal Variation of the Solar Radiation

RICHARD T. WETHERALD Geophysical Fluid Dynamics Laboratory, 1 NOAA, Princeton, N.J.

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SYUKURO MANABE Geophysical Fluid Dynamics Laboratory, 1 NOAA, Princeton, N.J.

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Abstract

The effect of the seasonal variation of solar radiation is incorporated into the joint ocean-atmosphere model developed at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration, and the resulting system is integrated for the 11/2-yr model time. The purpose of this study is to analyze the response of the joint air-sea model to seasonal changes in the solar zenith angle rather than to obtain a true equilibrium state. Comparisons are also made with results previously presented for the case of annual mean conditions.

The most important feature that emerges as a direct result of this seasonal variation is a significant warming of the lower troposphere in high latitudes. This warming is found to be caused by (1) the removal of the snowpack during the summer season, which decreases the earth's albedo there during this time, and (2) a net rise in the temperature of the ocean surface in high latitudes as a result of the seasonal variation of convective activity in the surface layer of the ocean. The present results indicate that the snow cover effect is the primary factor responsible for this warming trend whereas the ocean effect is of secondary importance.

The main consequences of this high latitude warming include a reduction of the mean atmospheric north–south temperature gradient (and, therefore, a reduction of baroclinic instability in middle latitudes), a reduction of the mean oceanic meridional circulation, and a reduction of the atmospheric and oceanic poleward heat energy transports.

Abstract

The effect of the seasonal variation of solar radiation is incorporated into the joint ocean-atmosphere model developed at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration, and the resulting system is integrated for the 11/2-yr model time. The purpose of this study is to analyze the response of the joint air-sea model to seasonal changes in the solar zenith angle rather than to obtain a true equilibrium state. Comparisons are also made with results previously presented for the case of annual mean conditions.

The most important feature that emerges as a direct result of this seasonal variation is a significant warming of the lower troposphere in high latitudes. This warming is found to be caused by (1) the removal of the snowpack during the summer season, which decreases the earth's albedo there during this time, and (2) a net rise in the temperature of the ocean surface in high latitudes as a result of the seasonal variation of convective activity in the surface layer of the ocean. The present results indicate that the snow cover effect is the primary factor responsible for this warming trend whereas the ocean effect is of secondary importance.

The main consequences of this high latitude warming include a reduction of the mean atmospheric north–south temperature gradient (and, therefore, a reduction of baroclinic instability in middle latitudes), a reduction of the mean oceanic meridional circulation, and a reduction of the atmospheric and oceanic poleward heat energy transports.

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