Minimal Models for Investigating the Influence of Latent Heat Release on Midlatitude Dynamics

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This collaborative research will target some of the most scientifically interesting and operationally relevant problems in weather systems science of the midlatitudes. To isolate essential vs. non-essential processes of moist midlatitude dynamics, a set of geophysical fluid dynamics problems will be formulated and investigated by a research team of applied mathematicians and atmospheric scientists. The participants will use a minimal modeling approach coupled with comparison to observational data, and when appropriate, to the results of comprehensive-physics numerical computations. The goal is to isolate the essential physical mechanisms and the role of precipitating convection in shaping some of the canonical structures of the midlatitude atmosphere.Intellectual Merit: A minimal model will be used to study midlatitude dynamics with precipitating convection. Cloud microphysics is included in the limit that the time scales associated with condensation, auto-conversion and evaporation are small compared to all other relevant time scales in the problem (advection, buoyancy, rotation, and rainfall). The simplified thermodynamics is based on the following design principle: the conservation laws for momentum, energy, moist entropy, and total water should all be retained, but they should have the simplest nontrivial form possible. Under these assumptions, the fully three-dimensional model accounts for precipitating convection while vastly reducing the number of necessary closure models. Three main case studies will be conducted: (i) evolution of one or more baroclinically unstable mode(s) to investigate the role of latent heat release in the midlatitude occlusion process, (ii) the dynamics of a single-jet in the presence of low-altitude convection to elucidate the mechanisms responsible for the jet-convection feedback loop and its saturation, and (iii) double jet dynamics with convection as a simplified model for the occasional merger of the polar and subtropical jets and the subsequent possibility of extreme precipitation events.Broader Impacts: A primary goal of the project is cross training of junior researchers in atmospheric science and mathematical modeling. New developments in mathematical modeling will be brought to the atmospheric sciences community, and simultaneously junior mathematicians will be exposed to key open problems in atmospheric science. As one way of sharing new insights with both communities, the minimal model will be made publicly available as the UW Virtual Atmosphere, with educational/research modules to explore the effects of precipitating convection on the Eady baroclinic instability problem (UWVA:Eady), and nonlinear evolution of eddies and jets (UWVA:Jet). The research is likely to provide valuable insights into extreme weather associated with jet superposition, anticipated to be more frequent in a globally warming world. Slight increases in tropical sea-surface temperatures are expected to lead to a general northward displacement of the Northern Hemisphere subtropical jet, and thus to an increased likelihood of subtropical and polar jet superposition. Better understanding of the role of precipitating convection in the formation and evolution of midlatitude eddies and jets will likely lead to improved ability to predict high-impact weather in a warmer climate.