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Roland A. Madden and Peter Speth

Abstract

The average structure of westward traveling disturbances that contribute to relative maxima found in space-time spectra from 13–32 days at northern latitudes is determined for each season. A compositing method used employs a minimum of space and time filtering in order to avoid biasing the results. The average latitudinal structure is “global” in that it is discernible in the Southern Hemisphere during December–February and September–November. It is primarily confined to northern latitudes during March–August. In all seasons the disturbance is out of phase between northern high latitudes and subtropical and tropical latitudes. The longitudinal structure is primarily zonal wavenumber 1 in all seasons. Further work is suggested to confirm the structures determined here and to learn if they reflect the superposition of a number of occasionally excited Rossby normal modes.

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Peter Speth and Roland A. Madden

Abstract

A space-time spectral analysis of a long time series of observed geopotential heights for each season at several levels and latitudes of the Northern Hemisphere was performed as part of a continuing investigation of large-scale traveling waves. The data set that is analyzed consists of the first six zonal wavenumbers. A discussion emphasizes westward traveling wave 1 with periods near 16 and 5 days which we argue are consistent with external Rossby warm. An additional outstanding feature is an eastward propagating wave 6 which may result from baroclinic instability.

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