Impact of convection on surface fluxes observed during LASP/DYNAMO 2011

Abstract

The NOAA WP-3D aircraft made extensive measurements over the tropical Indian Ocean during the Littoral Air-Sea Processes (LASP)/Dynamics of Madden-Julian Oscillation (DYNAMO) experiment. The low-level measurements from the WP-3D are analyzed here to examine the impact of tropical convection and its associated cold pool in modifying surface exchange of momentum and energy. Analysis of surface fluxes under convection and non-convection demonstrates the increased variability of surface fluxes under convection. Fluxes below convection are larger in magnitude, variable, and demonstrate no clear contribution from specific length scales. The lack of clear transport in the turbulence scales under convection highlights that additional processes beyond turbulence transport are occurring, which points to the role of precipitation evaporation below the cloud base. In contrast, surface fluxes under non-convective conditions are smaller and have a clear positive contribution throughout the turbulence region. Comparison of eddy correlation method with the COARE bulk surface flux parameterization indicates large scattering for the convective cases. Stress and latent heat flux from the COARE algorithm show good comparison with the eddy correlation fluxes, while the sensible heat flux seem to be consistently over-predicted, which may be a result of uncertainties in the measured sea surface temperature.