T-REX EOPs: MESOSCALE VALLEY CIRCULATIONS AND SENSITIVITY TO SYNOPTIC CONDITIONS

Abstract: This paper analyzes the nighttime flow dynamics and heat budget in a deep valley, California’s Owens Valley, for varying synoptic conditions. Measurements from the Terrain-Induced Rotor Experiment (T-REX) reveal a pronounced valley-wind system with often non-classical flow structure. Examples include daytime down-valley winds despite clear skies and strong radiative heating, nighttime up-valley winds, or simultaneous down- and up-valley winds at different heights within the valley. Our analysis is based on the T-REX measurement data and the output of high-resolution nu-merical simulations using the Advanced Regional Prediction System (ARPS). Using horizontal grid resolutions of 1 km and 350 m, the model reproduces the observed event-to-event variability very well. This includes a layered structure with simultaneous down- and up-valley winds during Enhanced Observing Periods (EOPs) 1 and 2, a moderate down-valley flow during EOP 3, and strong down-valley winds during EOP 4 and 5. The analysis shows that the resulting valley wind structure and evolution is due to a subtle interaction between thermally-induced local circulations and the larger-scale synoptic forcings