The 5-8-Day Kelvin and Rossby Waves in the Tropics as Revealed by Ground and Satellite-Based Observations

Abstract

An eastward propagating Kelvin wave of period near 7 days is observed in the radiosonde winds and temperature in the upper troposphere and lower stratosphere (UTLS) region and a wave of similar periodicity is observed simultaneously in the Mesosphere and Lower Thermosphere (MLT) winds acquired by MF radar at Pameungpeuk (7.5°S, 107.5°E) during the first Coupling Processes in the Equatorial Atmosphere (CPEA-1) Campaign (April 10-May 9, 2004). The horizontal and vertical characteristics of these waves are investigated using winds and temperature data acquired by TIDI (TIMED Doppler Interferometer) and Sounding of Atmosphere using Broadband Emission Radiometry (SABER) instruments respectively on TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite and European Centre for Medium-Range Weather Forecasts (ECMWF) winds and temperature. The wave observed in the MLT region has a dominant period of approximately 6.5 days and is found to propagate westward with zonal wave number 1. The horizontal structures of the wave in winds and the temperature indicate that the wave is of gravest symmetric wave number 1 Rossby wave. The downward phase propagation from the MLT region to tropopause indicates that the wave may have a source in the troposphere. The Kelvin wave observed in the UTLS region has zonal wave number 3. However, this wave becomes damped above 23 km, where the above mentioned westward propagating wave begins to amplify. During the observation period, the OLR distribution in the tropics shows similar periodicities, propagating eastward with zonal wave number 3 and westward with zonal wave number 1. These observations suggest that tropical convective heating may be a common source for these waves.