Comparison of the Impacts of Momentum Control Variables on High Resolution Variational Data Assimilation and Precipitation Forecasting
AbstractThe momentum variables of streamfunction and velocity potential are used as control variables in a number of operational variational data assimilation systems. However, in this study it is shown that, for limited area high resolution data assimilation, the momentum control variables ps and kh (pskh) pose potential difficulties in background error modeling and, hence, may result in degraded analysis and forecast when compared with the direct use of x and y components of wind (UV) In this study, the characteristics of the modeled background error statistics, derived from an ensemble generated from Weather Research and Forecasting (WRF) Model real time forecasts of two summer months, are first compared between the two control variable options. Assimilation and forecast experiments are then conducted with both options for seven convective events in a domain that encompasses the Rocky Mountain Front Range using the three dimensional variational data assimilation (3DVar) system of the WRF Model. The impact.