A Planetary-Wave Climatology

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  • 1 Department of Atmospheric Science, Colorado State University, Fort Collins 80523
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Abstract

Ultralong and long planetary waves are analyzed at the 500 mb level in terms of their amplitudes, phases and stationarity characteristics, the latter described in terms of a stationarity index SIn. This index consists of the ratio between planetary-wave amplitudes computed from time-averaged 500 mb height patterns, and the wave amplitudes computed on a daily basis and averaged for the same time interval irrespective of their phase angles. The index assumes the value 1 for completely stationary waves and 0 for randomly variable waves.

Mean 500 mb height and planetary wave characteristics have been developed by calendar day. using NMC data between the years 1946 and 1979. Various significant singularities (i.e., departures from a low-order harmonic seasonal trend) in planetary-wave behavior are described. An index, SIn(d), computed by calendar day, was developed as a measure of probability that a certain planetary wave with number n would achieve its long-term mean phase angle on a certain date. This index, too, shows significant patterns with latitude and season, suggesting the presence of relatively short periods within the seasonal cycles of planetary-wave behavior, during which these waves may be extra sensitive to anomalies in their forcing parameters.

It is suggested that perturbation statistics derived from numerical general circulation models should be compared with the results presented in this study to permit an improved judgement on the veracity of such models.

Abstract

Ultralong and long planetary waves are analyzed at the 500 mb level in terms of their amplitudes, phases and stationarity characteristics, the latter described in terms of a stationarity index SIn. This index consists of the ratio between planetary-wave amplitudes computed from time-averaged 500 mb height patterns, and the wave amplitudes computed on a daily basis and averaged for the same time interval irrespective of their phase angles. The index assumes the value 1 for completely stationary waves and 0 for randomly variable waves.

Mean 500 mb height and planetary wave characteristics have been developed by calendar day. using NMC data between the years 1946 and 1979. Various significant singularities (i.e., departures from a low-order harmonic seasonal trend) in planetary-wave behavior are described. An index, SIn(d), computed by calendar day, was developed as a measure of probability that a certain planetary wave with number n would achieve its long-term mean phase angle on a certain date. This index, too, shows significant patterns with latitude and season, suggesting the presence of relatively short periods within the seasonal cycles of planetary-wave behavior, during which these waves may be extra sensitive to anomalies in their forcing parameters.

It is suggested that perturbation statistics derived from numerical general circulation models should be compared with the results presented in this study to permit an improved judgement on the veracity of such models.

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