Techniques to Assimilate SSM/I Observations of Marine Atmospheric Storms
Final rept. 30 Sep 96-30 Sep 98
ATMOSPHERIC AND ENVIRONMENTAL RESEARCH INC CAMBRIDGE MA
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This report describes the feature calibration and alignment FCA methodology and the results of applying FCA to the Navys COAMPS mesoscale weather forecast system. FCA quantifies different components of error by defining horizontal adjustment fields of displacements and amplifications to be applied to the forecast fields. The adjustment is determined by minimizing an objective function which constrains the distorted forecast field to closely fit the available observations, and ensures that the final adjustment produced by the minimization is relatively smooth and not too large. The methodology was applied to short-term 12-hour COAMPS model forecasts, which were compared against SSMI retrievals of integrated water vapor IWV. The adjusted forecasts were then used as the first guess fields of the COAMPS optimal interpolation data analysis cycle. Results from three case studies of marine storms over the North Pacific indicate that the adjustments to the first guess led to an improvement of the IWV forecasts. They also indicate that the adjustments are diminished during the data analysis steps of the COAMPS data assimilation system and during the first 12 hours of the forecast, suggesting the need for more effective ways of initializing the COAMPS model with the adjusted fields.