Oceanic response to Atmospheric Convectively Coupled Kelvin Wave events

Despite the recent progress in understanding the dynamics of MJO evolution, the prediction of its propagation over the MC remains a challenge for models. It is hypothesized that the propagation of the MJO envelope over the MC is dependent on the ability of atmospheric equatorial convectively coupled Kelvin waves (CCKWs) to cross this barrier. CCKWs are strongly influenced by ocean-atmospheric interactions and thus, feedbacks between precipitation, salt-stratified oceanic barrier layers and the upper ocean diurnal cycle are likely to play important roles in the multi-scale interactions between modes of atmospheric convection. This work provides the first direct assessment of these processes and their likely impact on the atmospheric convection over the MC region. The variability of the development and evolution of the warm layer and barrier layer as CCKWs approaches the land is investigated in a three-dimensional framework using the NEMO ocean model analysis with data assimilation. Using a Lagrangian database for CCKWs (Baranowski et al., 2016), a CCKW life cycle of the upper ocean layers and atmospheric boundary layer in the MC region is constructed for both “average” and “extreme” CCKW events. The NEMO composite fields present a distinctive signal before and after the passage of the CCKWs, showing an average decrease in the ocean surface temperature (observed down to 200m) and decrease in salinity (down to 140 m) after the passage of CCKWs. Upwelling is induced mainly by an increase in the curl of the wind stress (from ERA5) and stronger zonal winds, which excites an oceanic Kelvin wave, identified by positive anomalies in SSH and greater depth of the 20°C isotherm. CCKWs with precipitation anomalies above 7.7 mm day^-1 lead to an average increase in heat content of 5 x10⁸ J m^-2. In the Equatorial Line Observations (ELO) field campaign in early 2019, high resolution temperature and salinity profiles sampled by ocean gliders during two months provided an extensive dataset to further validate the model data and to investigate the impacts of the precipitation-induced barrier layers on the warm layer dynamics. These results will help elucidate how mainly locally driven processes can rectify onto the longer time scale of the MJO.