Roles of Convective Eddy Momentum Flux in Global Non-hydrostatic Models

Global non-hydrostatic models with explicit convection are here, at great cost. What new phenomena does this high resolution unlock, and how can the valuable information be extracted rather than averaged away? We argue that the eddy vertical transport of horizontal momentum by newly-resolved mesoscale convective processes are the best answer to this question. The technique involves coarse-graining product terms (fluxes) like wu and wv, as a way to account the effects of small scales on larger scales. Results from a first analysis indicate that the strongest effects arise from the preferential location of convection in certain sectors of low-level cyclones (like the downshear half, or downwind-of-downshear quadrant). This process is a powerful feedback on the larger-scale shear that induces that asymmetry in the first place. In this way, tropical cyclones (TCs) have a distinctive impact on the general circulation, a result that complements the better-studied interaction going the other way (the impact of shear on TCs). With the new DYAMOND initiative, a multi-model intercomparison allows the generality of this result to be considered, since our first analysis was in a model which may have had too much of its tropical convection organized into TCs.