Tropical Intraseasonal Oscillations Appearing in a GFDL General Circulation Model and FGGE Data. Part II: Structure

Abstract

Space-time spectral and filter analyses are made of the structure of the tropical intraseasonal oscillations appearing in a GFDL 30-wavenumber spectral general circulation model and the FGGE IIIb data set. The model's tropical zonal velocity exhibits spectral peaks with periods of 40?50 and 25?30 days at wavenumber 1 for six individual years, although the 40?50 day peak is not as pronounced as that found in the FGGE dataset. Both the eastward moving 40?50 and 25?30 day oscillations take the form of a Kelvin?Rossby wave pattern in the upper troposphere and a Rossby mode in the lower troposphere. They also take the form of a latitudinally tilted Walker cell which is modified by a meridional convergence in the boundary layer.