A numerical study of a persistent cold air pool episode in the Salt Lake Valley, Utah. Issue 4 (25th February 2014) - Lu, Wei
Abstract The Weather Research and Forecasting (WRF) model is used to simulate a persistent cold air pool (CAP) episode observed in December 2010 during the Persistent Cold Air Pool Study (PCAPS) field campaign in Salt Lake Valley, Utah. The availability of intensive observations from PCAPS, especially the added vertical profiles, allows for an in‐depth analysis of CAP structure and evolution and model evaluation beyond what was done in similar work before. Comparisons of the WRF simulation with surface observations and upper air soundings indicate that WRF is capable of simulating the observed spatial and temporal variation of the valley atmosphere during the CAP episode. The model also successfully captures the formation and removal of the persistent temperature inversion. Process analysis helps quantify the contribution of various physical processes to the buildup and breakup of the inversion. The inversion developed due primarily to a rapid warming above the valley by synoptic subsidence and warm advection and to strong radiative cooling within the valley under clear sky conditions. The inversion was lifted when strong southerly winds entered the valley from the gap mixing out the cold air in the valley. Synoptic‐scale cold advection above the valley contributed to the inversion removal by weakening the inversion from aloft. Sensitivity experiments suggested that the WRF simulation of the CAP episode is more sensitive to large‐scale initialization fields with North American Mesoscale Model outperforming North American Regional Reanalysis and National Centers for Environmental Prediction (NCEP) Eta analysis than to the choice of boundary layer parameterizations and land surface models.