Moist Absolutely Unstable Layer

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The theoretical characteristics of atmospheric convection have been studied for many years and the basic characteristics of different forms of convection are considered to be well-known. The Principal Investigator presents observational evidence that a phenomenon that he terms "moist absolutely unstable layers" (MAULs) occur in the atmosphere. It would be expected that such layers would dissipate quickly through turbulence, but the Principal Investigator hypothesizes that under certain conditions, these layers may be created faster than they can be dissipated. If MAULs indeed do persist over long time periods and spatial scales, this may have important implications for certain types of atmospheric convection. The main objectives of this proposal are to: (1) determine how MAULs are created and maintained; (2) determine the properties of MAULs and demonstrate that the lateral extent, depth and intensity of these layers play a fundamental role in establishing the organizational mode of moist convective overturning. The research methodology consists of three parts: (1) numerical simulations of existing observational cases that appear to exhibit MAULs; (2) numerical sensitivity experiments to determine the effects of varying model resolution and artificially changing the depth and strength of MAULs; (3) sensitivity experiments on idealized conditions generated from three-dimensional analytical initializations. It is expected that knowledge gained from this research will enhance fundamental understanding of the organizational and lifecycle processes of mesoscale convective systems. The results potentially will provide practical benefits, such as improvements in short-term (3 to 18 hour) weather forecasts and in the parameterization of convective processes in global climate models. The results also should provide a basis for theoretical studies of moist absolutely unstable layers.