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Improvement of track and intensity forecasting through ensemble-based targeting techniques.Collaborating scientist(s):
Objective: Methods are evaluated to target aircraft and dropwindsonde observations to optimally improve tropical cyclone track forecasts. Background: Improved prediction of hurricane motion requires more information on the hurricane's large-scale environmental wind and height patterns than is typically available. While satellites can provide some wind data in the upper and lower troposphere, the middle levels are frequently almost void of observations. Operational models used for hurricane track forecasting need information from throughout the troposphere to be provide accurate TC track forecasts. As a result, operational models may fail to predict important changes of storm motion due to inadequate initial data, rather than inadequate physics of the prediction models. HRD's "Synoptic Flow" experiments use dropwindsondes to gather vertical profiles of wind, temperature, and humidity within 1,000 km of hurricanes. The experiment is typically conducted over the data-sparse oceanic regions of the western Atlantic or Gulf of Mexico roughly 48-72 hours before the projected landfall of a mature hurricane on the coast of the United States. The dropwindsondes define the hurricane's surrounding large-scale flow, particularly in the 300-700 mb middle tropospheric layer - the layer most directly related to tropical cyclone motion. From 1982-1996, HRD has completed a series of synoptic flow experiments in which dropwindsondes gather vertical profiles of wind, temperature, and humidity within about 1000 km of the center of potentially landfalling tropical cyclones in the North Atlantic Ocean. These observations have been shown to reduce errors by up to 30% on averge, an improvement equivalent to that obtained operationally during the last two decades. Since such observations have been shown to significantly impact track forecasts, a means to target such observations to optimally affect the forecasts is being developed. Method: The method of breeding the fastest growing modes in the operational global models used at the National Centers for Environmental Prediction (NCEP) and VICBAR provide information concerning locations of likely uncertainty in both initial conditions and forecasts. The ensemble ttransform technique will be used to find target locations from the models. By taking observations in these locations and outside of these locations, studies of the effectiveness of such a method are to be pursued. The NCEP global model is to be perturbed using different configurations of observations based upon information from the bred growing modes, and other operational models will be run based upon these global model runs. The overall impact of these observations will be assessed. Accomplishment: Results from 1997-2001 operational synoptic surveillance missions are similar and can be seen here. Targeting a few observations in particular regions in the TC environment has been shown to improve forecasts more than average throughout the environment. An automated operational system is being developed.
Key references: Toth, Z., and E. Kalnay, 1993: Ensemble forecasting at NMC: The generation of perturbations. Bull. Amer. Meteor. Soc., 74, 2317-2330. Bender, M. A., R. J. Ross, R. E. Tuleya, and Y. Kurihara: 1003: Improvements in tropical cyclone track and intensity forecasts using the GFDL initialization system. Mon. Wea. Rev., 121, 2046-2061. Lord, S. J., 1993: Recent developments in troical cyclone track forecasting with the NMC global analysis and forecasting system. Preprints of the 20th Conference on Hurricanes and Tropical Meteorology, San Antonio, Amer. Meteor. Soc., 290-291. Aberson, S. D., and M. DeMaria, 1994: Verification of a nested barotropic hurricane track forecast model (VICBAR). Mon. Wea. Rev., 122, 2804-2815. Bishop, C. H., and Z. Toth, 1999: Ensemble transformation and adaptive observations. Accepted by J. Atmos. Sci. Burpee, R. W., J. L. Franklin, S. J. Lord, R.E. Tuleya, and S.D. Aberson, 1996: "The impact of Omega dropwindsondes on operational hurricane track forecast models." Bull. Amer. Meteor. Soc., 77, 925-933. Franklin, J. L., and M. DeMaria, 1992: "The impact of Omega dropwindsonde observations on barotropic hurricane track forecasts." Mon. Wea. Rev., 120, 381-391. Bender, M. A., R. J. Ross, R. E. Tuleya, and Y. Kurihara, 1999: "Improvements in tropical cyclone track and intensity forecasts using the GFDL initialization system" Mon. Wea. Rev., 121, 2046-2061. Hock, T.F., and J.L.Franklin, 1999: "The NCAR GPS dropwindsonde." Bull. American Met. Soc.,80, 407-420. Aberson, S.D., and J.L.Franklin, 1999: "Impact on hurricane track and intensity forecasts of GPS dropwindsondes observations from the first-season fligs of the NOAA Gulfstream IV jet aircraft." Bull. American Met. Soc.,80, 421-428.
Last modified: 8/29/2002 |
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