A Statistical Overview of Convection During the First CPEA Campaign

Abstract

Data from the Equatorial Atmosphere Radar (EAR) were analysed during the Coupling Processes in the Equatorial Atmosphere (CPEA) campaign of April-May 2004. Statistical averages of the daily perturbations of wind velocity, temperature and humidity were examined. In the lower stratosphere, horizontal wind variances of up to 1.5 m 2 s -2 were visible above the afternoon tropospheric convection. Vertical wind variances of up to 0.03 m 2 s -2 occurred at the same time. The average variances of temperature and humidity in the lower troposphere also increased in the afternoon. Estimates of average momentum flux were made. In the lower stratosphere (18.0-20.0 km), the average magnitudes were 0.7-0.9 m 2 s -2 for both |u'w'| and |u'w'|. These fluxes were observed above the convective cells and indicate the average momentum emitted by them. Residuals of the momentum flux components showed a small westward preference and very small northward directional preference for wave propagation during CPEA. Four individual convective events and three Super Cloud Clusters (SCCs) were examined in detail. Tropospheric horizontal and vertical wind variances increased by 5 to 10 times during intense convection. Directly above this convection, in the lower stratosphere, increases in variance were also recorded. Vertical wind velocity fluctuation amplitudes in the lower stratosphere increased from 0.05-0.1 ms -1 away from convection, to be 0.1-0.4 ms -1 during convection. The amplitudes decreased to their background levels as soon as the convection had passed the EAR site. In the lower troposphere, the virtual temperature perturbations increased to 1.0-2.0°C during convection, an increase from a background value of about 0.5°C. During two of the four individual events, the amplitude of the temperature perturbations stayed enhanced for several hours after the end of convection. This contrasts with the vertical velocities in the lower troposphere, which quickly decreased following the passage of the storms. Specific humidity profiles in most cases showed large increases in the amount of water vapour below 4 km during times of convection. At certain heights and times during intense convection, the specific humidity increased by up to 50% from its background level.