High resolution simulations of boundary layer behavior in California's Owens Valley using the WRF-ARW model during T-REX 2006

The recent Terrain-induced Rotor Experiment (T-REX) field campaign, held during the spring of 2006 in Owens Valley of California, has provided researchers in a number of atmospheric science fields with a wealth of data that characterizes atmospheric boundary layer (ABL) structure and evolution in complex terrain regions. The primary focus of T-REX was to observe and study the highly perturbed Lee wave/boundary layer/rotor system common in the spring throughout the Owens Valley. The substantial volume of in-situ data obtained from the T-REX suite of meteorological instruments also afforded us the opportunity to study conditions that are unique to nocturnal stable atmospheric boundary layers that develop over rift valleys. The main goals of this paper are to: 1) examine the nocturnal low-level jet formation under quiescent boundary layer conditions within the Owens Valley; 2) characterize the role of surface heating/cooling and its effect on inversion layer variations within the Owens Valley; 3) evaluate planetary boundary layer parameterizations at high spatial resolution.

We employed the Weather Research and Forecasting (WRF) Advanced Research WRF (ARW) model run at high spatial and temporal resolutions to simulate ABL conditions associated with Enhanced Observation Periods (EOP) 4 & 5 (April 28-30) which were characterized by quiescent conditions and Intensive Observation Period (IOP) 13 (April 15-17, 2006) in which robust Lee wave/rotor activity over Owens Valley was observed. The interactions among inversion layer depths, near valley surface flows that intensified into nocturnal low level jets (LLJs), multi-layer wind structures above the valley, and synoptic systems are compared using WRF-ARW model ABL schemes involving local closure (Mellor-Yamada-Janjic) and non-local closure (Yonsei University) parameterizations. Surface and vertical sounding measurements used to validate our simulation results were derived from the Desert Research Institute's (DRI) Automated Weather Stations (AWS) and the National Center for Atmospheric Research (NCAR) Integrated Sounding System–Multiple Antenna Profiling Radar (ISS-MAPR).

The results of our forecast analyses were then compared with results obtained from other research groups modeling T-REX ABL structure and evolution during EOP and IOP phases, yielding a clearer picture of how model ABL parameterizations (along with other selectable configuration and namelist run-time options) impact the accuracy of high resolution simulations under the unique conditions of such rift valley environments.