Planetary-Scale Characteristics of the Atmospheric Circulation During January and February 1979

Abstract

The vertical and temporal Structure of the global scale flow in the Goddard Laboratory for Atmospheric Sciences analyses of data from the First GARP Global Experiment are presented. The fields are represented in terms of spherical harmonic expansions of the streamfunction, velocity potential and geopotential. The global scale patterns are obtained from triangular truncations of such series, neglecting terms past the fourth degree. Some modes display prominent high frequency oscillations in the velocity potential and geopotential height that may be related to diurnal cycles of cumulus convection. Such oscillations are not apparent in the streamfunction. Low-order harmonics with nodes only along latitude circles are nearly equivalent barotropic. However, those harmonics that have no nodes between the poles reverse phase with height. The following conclusions are drawn regarding the global scale patterns: 1) Since the divergent component of the meridional flow is not much smaller than the rotational part, the global scale pattern resembles forced modes of linear tidal theory more closely than it resembles free modes. 2) Because the vertical structure reverses, longitudinal heating gradients are probably important to the forcing. 3) The high frequency oscillations of the velocity potential and height field imply high frequency components in the forcing due to heating. 4) Monthly and weekly averages display suggestive teleconnection patterns.