The effect of spaceborne microwave and ground-based continuous lightning measurements on forecasts of the 1998 Groundhog Day storm

This study seeks to evaluate the impact of several newly available sources of meteorological data on mesoscale model forecasts of the extratropical cy clone that struck Florida on 2 February 1998. Intermittent measurements of precipitation and integrated water vapor (IWV) distributions were obtained from Special Sensor Microwave/Imager (SSM/I) and Tropical Rainfall Measurin g Mission (TRMM) Microwave Imager (TMI) observations. The TMI also provided sea surface temperatures (SSTs) with structural detail of the Loop Current and Gulf Stream. Continuous lightning distributions were measured with a n etwork of very low frequency radio receivers. Lightning data were tuned wit h intermittent spaceborne microwave radiometer data through a probability m atching technique to continuously estimate convective rainfall rates. A series of experiments were undertaken to evaluate the effect of those dat a on mesoscale model forecasts produced after assimilating processed rainfa ll and IWV for 6 h. Assimilating processed rainfall, IWV, and SSTs from TMI measurements in the model yielded improved forecasts of precipitation dist ributions and vertical motion fields. Assimilating those data also produced an improved 9-h forecast of the radar reflectivity cross section that was validated with a coincident observation from the TRMM spaceborne precipitat ion radar. Sensitivity experiments showed that processed rainfall information had grea ter impact on the rainfall forecast than IWV and SST information. Assimilat ing latent heating in the correct location of the forecast model was found to be more important than an accurate determination of the rainfall intensi ty.