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Climatology of Normal Mode Rossby Waves

Jon E. AhlquistDepartment of Meteorology, Florida State University, Tallahassee, Fl 32303

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Abstract

Three years of twice-daily NMC global operational analyses were projected onto normal mode Rossby waves to produce a climatology of these waves. For zonal wavenumbers. 1 through 4, annual average geopotential amplitudes at 50 kPa are about 5 gpm for the gravest symmetric meridional mode, and 10 and 20 gpm for the next two meridional model although the amplitude for a given time and latitude can greatly exceed the average. Seasonal average amplitudes differ by less than ±25% from the annual average. The modes’ frequencies drift during the course of a year, but this variation is not correlated with season.

Autocorrelations of Rossby wave time series become negligible for lags greater than approximately ten days, which is of the order of the wave period.

For all ten modes examined, geopotential fluctuations exist in both Northern and Southern Hemispheres.

Abstract

Three years of twice-daily NMC global operational analyses were projected onto normal mode Rossby waves to produce a climatology of these waves. For zonal wavenumbers. 1 through 4, annual average geopotential amplitudes at 50 kPa are about 5 gpm for the gravest symmetric meridional mode, and 10 and 20 gpm for the next two meridional model although the amplitude for a given time and latitude can greatly exceed the average. Seasonal average amplitudes differ by less than ±25% from the annual average. The modes’ frequencies drift during the course of a year, but this variation is not correlated with season.

Autocorrelations of Rossby wave time series become negligible for lags greater than approximately ten days, which is of the order of the wave period.

For all ten modes examined, geopotential fluctuations exist in both Northern and Southern Hemispheres.

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