ADAPTIVE OBSERVATIONS TO IMPROVE HURRICANE TRACK FORECASTS
Principal Investigator:
Sim D. Aberson
Collaborating
scientist(s):
Jimmy Franklin (NOAA/AOML/HRD)
Objective:
Evaluation of methods to target aircraft and dropsonde observations so
as to optimally affect tropical cyclone track forecasts.
Rationale:
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) provides information concerning locations of likely uncertainty
in both initial conditions and forecasts. 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:
Ensemble forecast information and dropwindsonde information for two
cases (Hurricane Felix - 16 August 1995, Hurricane Edouard - 31 August,
1996), have been archived. Sensitivity studies with the Geophysical
Fluid Dynamics Laboratory (GFDL) model and the NCEP Medium-Range
Forecast Model (MRF) have been completed. The western Atlantic Ocean is
shown to have no growing modes in the vicinity of the dropwindsondes in
the Hurricane Felix case (Fig.
1), and the entire set of data are shown
to have little impact on the ultimate track of the hurricane in the GFDL
model (Fig. 2).
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, 1997: Ensemble transformation and
adaptive observations. Submitted to J. Atmos. Sci.
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Last modified: 6/26/97