Modification of the Unified Post Processor (UPP) Version 3 to Achieve Improved Accuracy for Model Verification

The Unified Post Processor (UPP) can be used to convert output from the Weather Research and Forecasting (WRF) model on raw model levels into pressure level output which can then be used by the Model Evaluation Tools (MET) for verifying WRF forecasts. The default UPP source code produces output on up to 46 pressure levels. However, the pressure space of the raw output from the WRF forecasts being produced by the Army Research Laboratory is significantly denser than the pressure space of the 46-level post-processed WRF output near the surface where the vertical gradients of the fields are strongest. This can result in MET pairing observations with model values which poorly represent what the model actually predicted at the observation location.

The UPP software was modified to increase the number of pressure levels from 46 to 70 and the configuration file was modified to produce output at all 70 levels. The result was an approximate doubling of the resolution of output pressure levels in the layer below 775 hPa and between approximately 200 and 500 hPa and an approximate quadrupling of the resolution in the layer between 500 and 725 hPa.