MULTISCALE AIR-SEA INTERACTIONS DURING TOGA COARE

Two distinct intraseasonal oscillations (ISO) are found in the tropica l ocean atmosphere in the western Pacific region during Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). The ISO is characterized by cycles of dry-wet phases in the at mosphere due to the passage of Madden-Julian oscillations, and corresp onding warming/shoaling-cooling/deepening cycles in the ocean mixed la yer (OML). During the wet phase, 2-3-day disturbances and diurnal vari ations in the atmosphere are pronounced. During the dry phase, diurnal cycles in sea surface temperature (SST) is much enhanced while the OM L is shallow. These multiscale coupled air-sea variations are further investigated with an ocean mixed-layer model forced by the observed su rface heal, water, and momentum fluxes. The variations of ocean mixed layer are shown to be crucially dependent on the vertical distribution of solar radiation, that is, diurnal SST variability primarily determ ined by the absorbed solar radiation in the surface layer (similar to 1 m), and intraseasonal variations determined by penetrating solar rad iation below the surface layer. Results further reveal that the accumu lative effect of diurnal mixing cycles (solar hearing/nocturnal deepen ing) is essential to maintain a stable temperature stratification and a realistic evolution of mixed-layer depth and temperature at the intr aseasonal scale. The nonlinear response of the ocean mixed layer to th e surface heat and momentum fluxes indicates the need to resolve the h igh-frequency response including diurnal atmospheric radiative-convect ive processes and ocean mixing processes in a coupled model to simulat e the whole spectrum of multiscale variations within ISOs.