The Impact of Diurnal Cycle on a Low-Froude Number Flow Observed during the PYREX Experiment

Abstract

The intensive observing period (IOP) 4 of the Pyrenees Experiment (PYREX) has been simulated with a hydrostatic three-dimensional model. The PYREX IOP 4 was devoted to the observation of the orographically generated flow above and around the Pyrenees Mountains located at the French?Spanish border. Two simulations, with or without surface thermal forcing, have been performed. Their results are described and compared with the PYREX observations. The influence of thermal forcing is assessed on the main characteristics of the flow, including the upwind flow reversal, the vertically propagating mountain wave, the regional winds created by the flow deviation around the mountain, and the lee vortices. Prominent alterations of the flow are found downwind of the mountain where the diurnal cooling induces the disappearance of the lee vortices and the heating significantly reduces the intensity of the low-level deviated flow.