MULTISCALE VARIABILITY OF DEEP CONVECTION IN RELATION TO LARGE-SCALE CIRCULATION IN TOGA COARE

Deep convection over the Indo-Pacific oceanic warm pool in the Tropica l Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) occurred in cloud clusters, which grouped together in re gions favoring their occurrence. These large groups of cloud clusters produced large-scale regions of satellite-observed cold cloud-top temp erature. This paper investigates the manner in which the cloud cluster s were organized on time and space scales ranging from the seasonal me an pattern over the whole warm-pool region to the scale of individual cloud clusters and their relationship to the large-scale circulation a nd sea surface temperature (SST). The dominant convective variability was associated with the intraseasonal oscillation (ISO). A large eastw ard propagating ensemble of cloud clusters marked the ISO's progress. The meridional structure of the ISO was strongly affected by the seaso nal cycle with a southward shift from the Northern Hemisphere in Octob er-November to the Southern Hemisphere in January-February. The SST ha d an intraseasonal signal in lagged quadrature with the cold cloudines s and rainfall in COARE. The SST increased (decreased) during the conv ectively suppressed (active) phases of the ISO, Enhanced low-level wes terly winds occurred toward the later stages of the enhanced-convectio n periods of the ISO, though not always centered at the equator. The s trongest westerlies tended to be located between two synoptic-scale cy clonic gyres, which were often not symmetric about the equator in the low-level. wind field. This asymmetry in the anomalous equatorial low- level westerlies may have different implications for the oceanic respo nse in the coupled atmosphere-ocean system than those centered on the equator. The cyclonic gyres contained highly concentrated deep convect ion, and, in four cases, the gyres developed into tropical cyclones. W ithin the envelope marking the convectively active phase of the ISO, c loud clusters were frequently concentrated into westward-propagating d isturbances with a local periodicity of similar to 2 days. These 2-day disturbances have been identified in earlier spectral studies and app ear to be related to westward propagating inertio-gravity waves. In CO ARE, they typically contained numerous cloud clusters, which underwent a distinct diurnal cycle. Most of the cloud clusters embedded in the 2-day disturbances moved westward, though some were stationary, and a few moved eastward. A cloud-duster tracking program identified groups of clusters (lime dusters) that exhibited continuity in time and space . In the most convectively active period of the ISO, the tracking prog ram identified almost the entire ISO cloud ensemble as a long-lasting, trackable superconvective system. This observation indicates the lack of a distinct scale-separation between convection and large-scale dis turbances during the most intense convective periods in COARE.