Tidal Mixing Effects on Sea Surface Temperatures, Diurnal Rainfall and the Madden-Julian Oscillation in the Maritime Continent

The Maritime Continent (MC) is known as Earth’s “boiler box” since a large amount of convective rainfall and latent heat release occurs here, affecting regional climate and midlatitude systems through atmospheric teleconnections. Convective precipitation over the MC is constrained by the seasonal progression of the Asian-Australian monsoon, the intraseasonal propagation of the Madden-Julian Oscillation (MJO) and diurnal convection triggered by sea-breeze circulations. Furthermore, the eastern MC region is known to have a strong tidal mixing signature that is reflected in cooler SSTs. We show that regional precipitation characteristics are sensitive to tidally-forced changes in the SST distribution.

A fully-coupled, regional WRF-ROMS model configuration is implemented at one-hour coupling frequency and using a 4-km, convection-resolving grid. The model integrations cover the three-month period of October, November and December 2011, which coincides with the DYNAMO field campaign. The model is forced with and without tides using the OSU tide model solutions applied as 2D boundary conditions.

Prescribing tidal forcing results in a spatially-averaged cooling of -0.27 °C in the eastern half of the MC, which is comparable to the intraseasonal SST anomalies associated with MJO. The largest SST cooling, greater than 1 °C, occurs near the Lesser Sunda Islands, the Flores Sea, the Banda Arc and the border of the Sulu and Celebes Seas. Areas with strong SST cooling exhibit a reduction in precipitation, especially over the water. Implications for how diurnal convection responds to these SST changes will be discussed.