Using Doppler–Lidar Measurements of Recurrent Diurnal Marine Air Intrusion Flows into the Columbia River Basin to Characterize and Quantify HRRR Errors

The new generation of ground-based, Doppler-lidar instrumentation provides atmospheric wind data at dramatically improved accuracies and spatial/temporal resolutions. These upgraded capabilities have provided new insights into atmospheric flow systems, but they also should have a strong role in improving current NWP models. Besides using these capabilities directly for accurate and detailed model validation, new strategies and methodologies are being explored to exploit these advanced capabilities. It is here proposed and demonstrated that important insight into the nature of model errors can be gained by studying recurrent atmospheric flows, in this case a regional summertime diurnal sea breeze and subsequent marine-air intrusion into the arid interior of Oregon-Washington. The marine intrusions, not previously investigated in this region, were sampled by three scanning Doppler lidars deployed to the Columbia River Basin along a 71-km line as part of the Second Wind Forecast Improvement Project (WFIP2), using data from the summer 2016 segment of the 18-mo experiment. Lidar time-height cross sections of wind speed identified eight days when the diurnal-flow cycle, having peak wind speeds at midnight and minima in the afternoon, was obvious and strong. Eight-day composite time-height cross sections of lidar wind speeds, along with mean time series and composite wind profiles for each hour of the day, validated those generated by the operational NCEP-HRRR model. The HRRR simulated the diurnal wind cycle, but produced errors in the timing of onset and significant errors due to a premature nighttime demise of the intrusion flow, producing low-bias errors of 6 m s^-1. Day-to-day and in the composite, whenever a marine intrusion occurred, HRRR made these same errors. Warm-season and annual error statistics were traceable to this error signature. The errors occurred under a range of gradient wind conditions suggesting that they resulted from the misrepresentation of physical processes within a limited region around the measurement locations. Because of their occurrence in a limited geographical area, field-measurement programs can and should be designed to find and address the sources of these regionally generated errors.