LES of the thermally driven cross-basin circulation in an idealized basin - analysis of the momentum and thermodynamic budgets

The cross-basin circulation due to asymmetric irradiation of opposing sidewalls was found to be an important component of the daytime thermally driven wind circulation in the small basin of Arizona's Meteor Crater. The horizontal pressure gradient resulting from the asymmetric irradiation produces a flow near the basin floor that is directed from the shaded or less irradiated sidewall to the more strongly irradiated and thus warmer sidewall. An opposing return flow often forms on top of the near-surface cross-basin flow.

An LES simulation of the cross-basin circulation in an idealized basin, which is based on the topography of Arizona's Meteor Crater, was performed with WRF. We will discuss the formation mechanisms of the cross-basin flow near the basin floor and the opposing return flow by means of an analysis of the horizontal momentum and thermodynamic balance equations. The model is used to investigate (i) the respective role of thermodynamic and divergence effects in the formation of the cross-basin pressure gradient near the basin floor and (ii) the role of differential temperature advection along the basin sidewalls in reversing the local cross-basin temperature gradient and in the formation of the return flow.