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SSM/I Observations of ERICA IOP 4 Marine Cyclone: A Comparison with In Situ Observations and Model Simulation

Simon W. ChangNaval Research Laboratory, Washington, D.C.

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Randall J. AllissDepartment of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

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Sethu RamanDepartment of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

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Jainn-Jong ShiScience Applications International Corporation, McLean, Virginia

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Abstract

Fields of rainfall rates, integrated water vapor (IWV), and marine surface wind speeds retrieved by the Special Sensor Microwave/Imager (SSM/I) during the intensive observational period 4 on 4 January 1989 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) were analyzed. Subjectively analyzed and model-simulated frontal structures were used to examine the spatial relationship of the SSM/I observed fields to the rapidly intensifying storm and the associated fronts. Qualitative and quantitative comparisons of SSM/I retrievals with GOES imagery, conventional observations, and results produced from the Naval Research Laboratory's (NRL) limited-area numerical model were also made.

SSM/I rainfall was found along the cold and warm fronts, with heavy precipitation within frontal bands. The spatial pattern and characteristics of SSM/I precipitation closely resembled those simulated by the model. Both the warm and the cold front were found to be located near the area of the strongest gradient in IWV. In the warm sector, areas of IWV greater than 40 mm were found, an amount supported by model simulations. Both SSM/I rain rate and IWV distribution were found to be useful in locating the cold and warm fronts. There was good agreement on the relationship of frontal locations to the precipitation patterns and IWV gradients. Most of the high-wind area near the storm center was obscured by clouds for marine surface wind retrieval. SSM/I-retrieved marine surface winds outside the cloud shield (flag 0) were compared to ship- and buoy-reported winds. It was found that the retrieved wind estimates were within 0–3 m s−1 of in situ observation over areas of slow wind shifts. The errors became larger in regions of rapid wind shifts.

Abstract

Fields of rainfall rates, integrated water vapor (IWV), and marine surface wind speeds retrieved by the Special Sensor Microwave/Imager (SSM/I) during the intensive observational period 4 on 4 January 1989 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) were analyzed. Subjectively analyzed and model-simulated frontal structures were used to examine the spatial relationship of the SSM/I observed fields to the rapidly intensifying storm and the associated fronts. Qualitative and quantitative comparisons of SSM/I retrievals with GOES imagery, conventional observations, and results produced from the Naval Research Laboratory's (NRL) limited-area numerical model were also made.

SSM/I rainfall was found along the cold and warm fronts, with heavy precipitation within frontal bands. The spatial pattern and characteristics of SSM/I precipitation closely resembled those simulated by the model. Both the warm and the cold front were found to be located near the area of the strongest gradient in IWV. In the warm sector, areas of IWV greater than 40 mm were found, an amount supported by model simulations. Both SSM/I rain rate and IWV distribution were found to be useful in locating the cold and warm fronts. There was good agreement on the relationship of frontal locations to the precipitation patterns and IWV gradients. Most of the high-wind area near the storm center was obscured by clouds for marine surface wind retrieval. SSM/I-retrieved marine surface winds outside the cloud shield (flag 0) were compared to ship- and buoy-reported winds. It was found that the retrieved wind estimates were within 0–3 m s−1 of in situ observation over areas of slow wind shifts. The errors became larger in regions of rapid wind shifts.

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