On the Maintenance of Enstrophy in the Tropics during the FGGE Northern Summer

Abstract

The wind fields generated by the ECMWF FGGE III-b analyses at ten mandatory levels were used to examine the tropical enstrophy budget in the spectral domain during the 1979 northern summer (June?August). The seasonal mean analysis shows that the wave enstrophy has its maximum value in the upper troposphere and its major content in the low wavenumber regime. The wave enstrophy is nonlinearly transferred from the low to the large wavenumber regime. The wave enstrophy in the upper troposphere is supplied through the beta effect, while the upward transport of the wave enstrophy is generated by vortex stretching in the lower troposphere. The zonal enstrophy also has its maximum value in the upper troposphere and is supplied by the beta vortex stretching effects in the upper troposphere. Both wave and zonal enstrophies in the tropics exhibited a 40?50 day variation in the 1979 northern summer. The time series of various enstrophy variables suggests that the time variation of the wave enstrophy is maintained by the upward transport of this quantity generated in the lower troposphere. The time variation of the zonal enstrophy is supported by this quantity generated in the upper troposphere.