Physical mechanisms of the thermally driven cross-basin circulation



The physical mechanisms responsible for the formation of a thermally driven cross-basin circulation in a basin with asymmetric heating of opposite mountain sidewalls are investigated. A large-eddy simulation is performed with the Weather Research and Forecasting model for an idealized basin based on the topography of Arizona's Meteor Crater. The individual components of the horizontal momentum and thermodynamic balance equations are analyzed to determine their respective contributions in forcing the cross-basin circulation.

A cross-basin pressure gradient, with higher pressure on the less irradiated sidewall, leads to the development of a cross-basin flow near the basin floor. A weak opposing return flow develops above this cross-basin flow as a result of a reversed cross-basin pressure gradient. The reversed cross-basin pressure gradient is caused by cold-air advection by upslope winds in the stable morning atmosphere on the sunlit sidewall and warm-air advection by downslope winds on the still shaded sidewall, as this reverses the cross-basin temperature gradient, producing a higher temperature on the less sunlit sidewall.