MULTISCALE ANALYSIS OF A SIMULATED OCEANIC MESOSCALE CONVECTIVE SYSTEM AND ITS ENVIRONMENTAL IMPACT

A case study is used to address unresolved issues in atmospheric deep convection, including how it organizes on the mesoscale in directional vertical shear, how its coupling with air-sea interaction processes can modify its evolution, and how its three-dimensional asymmetric structure can influence redistribution of horizontal momentum. A three-dimensional numerical model is used to simulate a mesoscale convective system (MCS) that occurred during the TOGA Coupled Atmosphere Ocean Response Experiment. A unique aspect of the simulations is a lower boundary condition where only surface fluxes and stresses that differ from those of the undisturbed environment are included, which enables isolation of the effect of internally-generated surface fluxes and stresses on MCS evolution.; A well-simulated aspect of the observed MCS is the evolution of its leading convective zone from a quasi-linear to a bow-shaped structure. This transition is accompanied by a mesoscale vortex along the northern edge of the 40-60-km long bow-shaped band of deep convection, elongated bands of weaker convective precipitation rearward and transverse to the leading edge near the southern end of the bow, and growth of a band of cellular deep convection northwest of the vortex center. The vertical wind shear that arises from the convectively-induced mesoscale flow is a critical factor influencing (1) development of the vortex, and (2) through its associated vertical pressure gradients, pronounced along-line variability of the convective updraft and precipitation structure within the MCS. The environmental wind profile is crucial to system organization since the orientation of its vertical shear relative to that of the incipient subcloud cold pool directly influences the onset of the convectively induced mesoscale flow.; The three-dimensional structure and asymmetry within the MCS influences how it modifies the environment. The differing convective band orientations and contrasting characteristics of horizontal accelerations among MCS subregions, where the relationship between convective band orientation and the environmental vertical shear differs, together can result in horizontal accelerations that strongly oppose each other. As a result, horizontal accelerations on the MCS-scale may differ significantly from those predicted by two-dimensional models.