Climatological Effects of Orography and Land–Sea Heating Contrasts on the Gravity Wave–Driven Circulation of the Mesosphere

Abstract

On the basis of permanent January simulations performed with an idealized general circulation model for the troposphere and middle atmosphere, the sensibility of the general circulation to orographic and thermal forcing of large-scale stationary waves is assessed. Gravity waves are parameterized following Lindzen's saturation theory. Up to the stratopause, present model results coincide with earlier estimates, confirming that the boreal winter zonal-mean climate does crucially depend on the combined action of orography and land–sea heating contrasts. Since, in turn, the propagation and breakdown of internal gravity waves is strongly modulated by the background horizontal winds, the mesospheric response to stationary wave forcing turns out be substantial as well. It is found that in the climatological zonal mean, a warmer polar night stratosphere is accompanied by lower temperatures in the mesosphere up to about 80 km. The temperature signal induced by stationary wave forcing changes sign again in... Abstract On the basis of permanent January simulations performed with an idealized general circulation model for the troposphere and middle atmosphere, the sensibility of the general circulation to orographic and thermal forcing of large-scale stationary waves is assessed. Gravity waves are parameterized following Lindzen's saturation theory. Up to the stratopause, present model results coincide with earlier estimates, confirming that the boreal winter zonal-mean climate does crucially depend on the combined action of orography and land–sea heating contrasts. Since, in turn, the propagation and breakdown of internal gravity waves is strongly modulated by the background horizontal winds, the mesospheric response to stationary wave forcing turns out be substantial as well. It is found that in the climatological zonal mean, a warmer polar night stratosphere is accompanied by lower temperatures in the mesosphere up to about 80 km. The temperature signal induced by stationary wave forcing changes sign again in...