Atmosphere-ocean conditions jointly guide convection of the Boreal Summer Intraseasonal Oscillation: Satellite observations

The water-vapor and air-temperature profiles from the Atmospheric Infrared Sounder (AIRS), in combination with surface wind from Quick Scatterometer (QuikSCAT) and rainfall and sea surface temperature (SST) from Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI), are used to document surface conditions and vertical moist thermodynamic structures of the 2003-2006 Boreal Summer Intraseasonal Oscillation (BSISO) over the Indo-Pacific warm pool. The composite based on Wheeler and Hendon's intraseasonal oscillation index reveals that Convective Available Potential Energy (CAPE), SST, and surface convergence lead convection in both northward and eastward directions. The preconditioning of CAPE is much earlier than that of SST, implying that the atmosphere internal processes precondition CAPE. On the other hand, the ocean positively feeds back to the atmosphere from bottom up, forming a smooth transition from boundary layer moistening, shallow convection at lower or middle level, to the deep convection all through the troposphere. The preconditioning of the boundary layer moist (dry) anomalies to the subsequent positive (negative) rainfall maximum is as far as 60-90 degrees in longitude (15 degrees in latitude) and quarter-to-half cycle in time. In contrast, this boundary layer preconditioning is virtually undetected from conventional NCEP reanalysis. Finally, the implications of these new findings on the frictional "convective interaction with dynamics" (CID) theory of intraseasonal oscillation are also discussed.