Space-Time Spectral Analysis of Mid-Latitude Disturbances Appearing in a GFDL General Circulation Model

Abstract

A space-time spectral analysis is applied to the Northern Hemisphere winter of an 11-layer GFDL general circulation model with seasonal variation. A statistical study is made of the stationary and transient ultra-long waves and transient long waves with respect to their wave characteristics, three-dimensional structure and energetics. The stratospheric stationary waves attain their maximum amplitude in geopotential at the latitudes of the stratospheric jet in agreement with observations and theories, although their amplitude is too large. The tropospheric stationary waves corresponding to the Siberian high and the Aleutian low are characterized by large eddy available potential energy which is mainly converted from zonal available potential energy. On the other hand, the tropospheric stationary wave corresponding to the local intensification of the subtropical jet is characterized by large eddy kinetic energy which is supplied by the energy flux from the region of large eddy energy conversion occurring to the north of the latitude of the Tibetan Plateau. The transient ultra-long waves are too weak in the troposphere and are associated with a more eastward moving component contrary to those observed in the troposphere. They are characterized by baroclinic energy conversion in the troposphere and barotropic conversion in the stratosphere. The transient long waves corresponding to cyclones are well simulated and their please relations agree with both observations and linear theories. Their kinetic energy is largest around 300 mb in agreement with observations, but contrary to linear theories. Their kinetic energy maxima occur over the Pacific and the Atlantic to the east of the maximum latitudinal gradient of the time mean temperature.