The ocean diurnal warm layer during CINDY–DYNAMO and its role in air–sea interaction and the Madden–Julian Oscillation

The development and variability of the diurnal upper ocean warm layer was studied during the CINDY-DYNAMO field experiment using an autonomous underwater SeaGlider. High spatial and temporal resolution in-situ observations were complemented by Meteosat7-derived OLR and shortwave fluxes. In addition OA Flux large scale wind conditions were assessed in our analysis. Based on data analysis we developed a simple linear regression model that provides an estimate of the strength of the diurnal warm layer based on environmental conditions: wind speed at the ocean surface and mean solar radiation. We defined three regimes: a warm layer regime, a warming regime and a cooling regime, each one interlinked to different environmental conditions. Furthermore we investigate the importance of the upper ocean warm layer development for the energy balance between the atmosphere and ocean. In particular we show how neglecting such phenomena leads to a systematic bias in the energy transfers (longwave radiative flux, latent heat flux, and sensible heat flux) from the ocean to the atmosphere. The intraseasonal transitions between these regimes coincide with different phases of the Madden-Julian Oscillation (MJO).