Kelvin Waves in the Equatorial Middle Atmosphere Observed by the Nimbus 5. SCR

Abstract

The structure and behavior of Kelvin waves in the equatorial upper stratosphere and mesosphere are investigated by the use of infrared radiation measurements from the Selective Chopper Radiometer (SCR) on the Nimbus 5 satellite during the two years 1973?74. By making a combination of three upper channels of the SCR, Kelvin waves with vertical wavelengths of ?20 km are detected in the tropics. The long-term statistics indicate that zonal wavenumber 1 is prominent throughout the two-year period. The predominant period of the wave is determined by power spectrum analysis using the Doppler effect due to the wave migration. For wavenumber 1, the eastward moving Kelvin wave appears to have a period of 4?9 days. It is also found that the intrinsic (Doppler-shifted) phase velocity of the Kelvin wave is almost constant in time, regardless of the seasonal variation of the mean zonal wind. The dynamical significance of this wave is stressed in connection with the semiannual oscillation of the mean zonal wind in the equatorial middle atmosphere.