Characteristics of 10-day Kelvin Wave Observed with Radiosondes and CHAMP/GPS Occultation during the CPEA Campaign (April-May, 2004)

Abstract

As a part of the Coupling Processes in Equatorial Atmosphere (CPEA) program, an intensive radiosonde sounding was conducted for 30 days from April 10 to May 9, 2004, coinciding with the eastward phase of QBO, at seven stations over the Indonesian maritime-continent, including the Equatorial Atmosphere Radar (EAR) site at Koto Tabang (0.2°S, 100.32°E), west Sumatra. Using radiosonde profiles, we studied the behavior of equatorial Kelvin waves with periods of 10-12 days and vertical wavelengths of 6-7 km. The global feature of the Kelvin wave was also analyzed with simultaneous CHAMP/GPS (CHAllenging Mini satellite Payload/Global Positioning System) radio occultation (RO) data. The Kelvin wave characteristics delineated by the GPS RO analysis, assuming only zonal wave number 1 and 2 components, shows good agreement with radiosonde results in the stratosphere, although the wave amplitudes were estimated to be somewhat smaller for GPS RO. However, a discrepancy in the Kelvin wave characteristics was recognized around and below the tropopause. This discrepancy is likely due to higher zonal wave number (>2) components being dominant in the troposphere. The Kelvin wave amplitudes were enhanced around the tropopause and in the lower stratosphere between 17 and 25 km and dissipated above approximately 25 km, which is consistent with earlier results. GPS RO results show eastward phase propagation of wave number 1 during the first half of the CPEA campaign, while a mixture of wave numbers 1 and 2 appeared during the second half of the campaign. We also report the modulation of the tropopause structure by these Kelvin waves.