"Closing The Budget": Evaluating the Use of the Circulation Budget for Practical Analysis of Tropical Dynamics

Circulation budgets are often used to analyse the physical processes of tropical cyclones, mesoscale convective vortices, and other meteorological features where there are dynamical interactions across scales. However, the question of how well these budgets practically close when calculated for standard model output data is unclear. The work undertaken here evaluates how friction, domain selection, and spatiotemporal model resolution affect the closure of the circulation budget. Circulation budget closure is closest at high output time interval resolution and on finer grid spacings. For the tropical convective examples evaluated here, column mean budget residuals increase by up to 50% as time output intervals increase from 5 minutes to 3 hours, with best closure at resolutions of 30 minutes and higher. Errors also increase dramatically with linear regridding to coarser horizontal grid spacing, and in the presence of convective processes on domain bounds. The results highlight, however, that on a model's native grid, the physical interpretation of the circulation budget terms remains the same, regardless of whether the budget closes accurately.