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Evaluate the impacts of higher resolution and alternate physical parameterizations on the performance of the GFDL hurricane model
GFDL 2002 second quarter milestone
Purpose:
Since the GFDL hurricane forecast system was implemented in 1995, the resolution of the NCEP global model (AVN) has been upgraded in both the horizontal and vertical. A number of changes have been made to the AVN convective and vertical parameterizations as well. Considering the recent improvements in the AVN tropical forecasts, it is important to implement improvements in both the resolution and physics of the GFDL model, since the GFDL model runs from the AVN initial fields.
Efforts:
The GFDL model has done an admirable job in helping reduce track errors. Since its implementation, the upgrades to its atmospheric physics packages and resolution have been rather minimal. This work represents an initiative to make significant changes to the GFDL forecast system.
Customers:
The GFDL coupled model forecasts of track, intensity and rainfall are run at NCEP and used as guidance at the National Hurricane Center.
Significance:
Increasing grid resolution, modifying the storm environment, and implementing a different convective parameterization scheme have resulted in significant improvements in hurricane track and intensity forecasts.
Success:
Two distinct upgraded versions of the GFDL hurricane system have been developed. Both upgrades described below include increasing the outer grid resolution from 1° to ½° and improving the filtering method to retain more relevant initial data near the storm. A re-running of the new "2002 GFDL" model for the 2001 season produced improvements in the skill of the track forecasts of ~ 10% for forecast periods from 24 to 72h. Skillful intensity forecasts were now achieved for the period of 24 to 60h compared to a period of 24 to 48h from the current operational model. This "2002 GFDL" model will go into NCEP operations for the upcoming Atlantic 2002 hurricane season. In the second version of the upgraded model, further model improvements include the successful AVN scheme convective parameterization together with increased vertical resolution from 18 to 42 levels. This version improved forecasts quite remarkably for the case of Hurricane Michelle shown in Figure1. Further tests of this model will be made during the coming summer.
Next steps:
As model resolution increases, explicitly resolving cloud scale structures becomes more scientifically appropriate. Recently, a cloud microphysics capability was installed in the GFDL model. The GFDL model can now predict various cloud properties including cloud water, rainwater and ice particles. Experiments will be run during this upcoming year.