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Assimilating Moisture Information from Global Positioning System (GPS) Dropwindsondes into the NOAA Global Forecast System

Jason P. Dunion1 and Sim D. Aberson1 (Jason.Dunion@noaa.gov; Sim.Aberson@noaa.gov)

1NOAA/AOML/Hurricane Research Division

GPS dropwindsonde moisture data from G-IV hurricane synoptic surveillance and HRD research missions in 2005 and 2006 were assimilated into parallel (2005) and operational (2006) runs of the NCEP Global Forecasting System (GFS). The objectives of this study included: (i) assessing the impact of dropwindsonde moisture data from the 2005 G-IV missions on GFS forecasts of tropical cyclone track and intensity; (ii) assessing the impact of dropwindsonde data from the 2005/2006 G-IV missions on GFS analyses of humidity and how effectively the GFS represents dry layers such as the Saharan Air Layer; and (iii) evaluating the feasibility of performing targeted dropwindsonde humidity observations in the tropical cyclone to improve GFS forecasts. Efforts associated with the first goal showed that the dropwindsonde humidity data did not have a strong negative or positive impact on GFS forecasts of tropical cyclone track/intensity, though for some individual cases (e.g. 2005 Tropical Storm Irene and Hurricane Katrina), the dropwindsonde humidity information had a significant impact on the GFS track forecast. Based on these findings, the NOAA National Centers for Environmental Prediction approved the assimilation of dropwindsonde humidity data into the GFS model from all dropwindsondes launched from NOAA’s G-IV jet beginning on 22 August 2006. Preliminary findings associated with the first and second goals of this project (assessing GFS analyses of humidity and evaluating the feasibility of performing targeted dropwindsonde humidity observations in the tropical cyclone environment) will be presented.

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