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- Dropwindsondes are weather instruments that collect atmospheric data as they descend after being dropped from research aircraft. These dropwindsondes obtain vertical profiles of wind, temperature, and humidity from 400mb to the surface This data is then ingested by numerical numerical models to come up with hurricane track and intensity forecasts. These observations provide grid points of observations over the tropical oceans which are generally devoid of weather observations. Aberson and Franklin (1999) state that "accurate modeling of tropical cyclone motion and intensity requires both realistic numerical models and accurate representation of meteorological fields through the depth of the troposphere on a variety of scales." While models have greatly improved over the past 20 years, significant forecast improvements are still possible by decreasing the analysis error. This has been the primary goal of the Hurricane Research Division (HRD) branch of NOAA. This is wh! y NOAA has procured a new generation of dropwindsondes based on the Global Positioning System (GPS) as well a Gulfstream-IV jet aircraft (G-IV). A study of the impact of the new dropwindsondes' observations on hurricane forecast models was conducted by Aberson and Frankilin in 1997. In the 1997 study about 30 dropwindsondes were used during each mission. These observations were then put into the Geophysical Fluid Dynamics Laboratory (GFDL) and VICBAR hurricane models and the Global Spectral Model (GSM) using the National Center for Environmental Prediction (NCEP) Global Data Assimilation (GDAS). GDAS uses a quality control algorithm, synthetic data and analysis procedures, and the Global Spectral Model in its data assimilation. Further information about the data assimilation can be found in Aberson and Franklin (1999). For the study NCEP's GSM is run and is used as the boundary conditions for the HRD's barotropic model (VICBAR) and the GFDL model. The track forecasts of the GSM, VICBAR, and GFDL models were compared to the CLIPER model to calculate track errors and the SHIFOR model to calculate intensity errors. The CLIPER and SHIFOR models are statistical regression models which use only climatology and persistence in their forecasts More info at: "http://marine.rutgers.edu/mrs/education/spring2000/louisb/Results.html"
[Source: Reuters]
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