Space-time variations of equatorial Kelvin wave activity around the tropical tropopause region

Space-time variations of the temperature and the zonal wind around the tropical tropopause region are examined using the European Centre for Medium-Range Weather Forecasts(ECMWF)Re-Analysis data set(ERA-40)。The spectral analysis is performed to calculate power spectra in the zonal wavenumber and frequency domain for the zonal wind data。Two spectral peaks are found：one is in a region with frequency 0.035-0.25[1/day]and zonal wavenumber 1-10 for the Kelvin wave，and the other in a region with frequency 0.011-0.035[1/day]and zonal wavenumber 1-10 for the Intraseasonal Oscillation(ISO)。On the basis of these frequency-wavenumber domains the grid data are reconstructed to represent Kelvin wave and the ISO activities，and the variances are calculated from the gridded data to see space-time variations of the Kelvin wave and the ISO.The ISO activity is clearly related to the eastward propagating convections，though the Kelvin wave activity is organized around 60°E(The Western Indian Ocean)throughout the year。We selected Kelvin wave events from the reconstructed zonal wind data with a threshold of-2.938[m/s]to see the life cycle of the Kelvin waves.Kelvin waves with high activity around 60°E begin mostly around 30°W to 60°E and disappear around 60°E to 150°E.By performing the composite analysis for the Kelvin wave events we found that the Kelvin wave generation is closely coupled with the convective event，though the area of the Kelvin wave generation does not correspond to the active convective area such as in the western Pacific.

Space-time variations of the temperature and the zonal wind around the tropical tropopause region are examined using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis data set (ERA-40). The spectral analysis is performed to calculate power spectra in the zonal wavenumber and frequency domain for the zonal wind data. Two spectral peaks are found : one is in a region with frequency 0.035-0.25[1/day] and zonal wavenumber 1-10 for the Kelvin wave, and the other in a region with frequency 0.011-0.035[1/day] and zonal wavenumber 1-10 for the Intraseasonal Oscillation (ISO). On the basis of these frequency-wavenumber domains the grid data are reconstructed to represent Kelvin wave and the ISO activities, and the variances are calculated from the gridded data to see space-time variations of the Kelvin wave and the ISO. The ISO activity is clearly related to the eastward propagating convections, though the Kelvin wave activity is organized around 60゜E (the western Indian Ocean) throughout the year. We selected Kelvin wave events from the reconstructed zonal wind data with a threshold of -2.938 [m/s] to see the life cycle of the Kelvin waves. Kelvin waves with high activity around 60゜E begin mostly around 30゜W to 60゜E and disappear around 60゜E to 150゜E. By performing the composite analysis for the Kelvin wave events we found that the Kelvin wave generation is closely coupled with the convective event, though the area of the Kelvin wave generation does not correspond to the active convective area such as in the western Pacific.