Diurnal Ocean Surface Warming Drives Convective Turbulence and Clouds in the Atmosphere

Abstract

Sunlight warms sea surface temperature (SST) under calm winds, increasing atmospheric surface buoyancy flux, turbulence, and mixed layer (ML) depth in the afternoon. The diurnal range of SST exceeded 1°C for 24% of days in the central tropical Indian Ocean during the Dynamics of the Madden Julian Oscillation experiment in October-December 2011. Doppler lidar shows enhancement of the strength and height of convective turbulence in the atmospheric ML over warm SST in the afternoon. The turbulent kinetic energy (TKE) dissipation rate of the marine atmospheric ML scales with surface buoyancy flux like previous measurements of convective MLs. The time of enhanced ML TKE dissipation rate is out of phase with the buoyancy flux generated by nocturnal net radiative cooling of the atmosphere. Diurnal atmospheric convective turbulence over the ocean mixes moisture from the ocean to the lifting condensation level and forms afternoon clouds.