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A Dynamical Method for Building Continuity into the Deep-Layer Mean Wind

John LewisNOAA/NESDIS Systems Design and Applications Branch

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Andrew Van TuylSpace Science and Engineering Center, Madison, WI 53706

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Christopher VeldenSpace Science and Engineering Center, Madison, WI 53706

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Abstract

Deep-layer mean winds over the tropical Atlantic are routinely derived during the hurricane season at the Space Science and Engineering Center, Madison, Wisconsin, using imagery and soundings from the VISSR Atmospheric Sounder (VAS) aboard GOES. These analyses are 6–12 h apart and a method has been developed to build continuity into these winds. First, a static analysis is made at each time which vertically blends gradient wind shear derived from VAS temperatures with winds derived from tracking the visible and infrared imagery. The deep layer mean (DLM) winds that come from the static analyses are subsequently adjusted in time using the conservation of absolute vorticity as a constraint.

This methodology is used to derive the large-scale circulation that accompanied Hurricane Debby (1982) in the Atlantic Ocean. Dropwindsonde data collected around Debby and the National Meteorological Center's analyses are used to qualitatively verify the analyses. Results indicate dial the vertical blending process is especially valuable in reconstructing the synoptic flow when the track winds are sparse at midlevel. The temporal adjustment is applied to three analysis periods and acts like an averaging process that smooths the fields. Subjective verification of the time adjusted DLM winds indicates an improvement at the initial time, but a degradation at the final time.

Abstract

Deep-layer mean winds over the tropical Atlantic are routinely derived during the hurricane season at the Space Science and Engineering Center, Madison, Wisconsin, using imagery and soundings from the VISSR Atmospheric Sounder (VAS) aboard GOES. These analyses are 6–12 h apart and a method has been developed to build continuity into these winds. First, a static analysis is made at each time which vertically blends gradient wind shear derived from VAS temperatures with winds derived from tracking the visible and infrared imagery. The deep layer mean (DLM) winds that come from the static analyses are subsequently adjusted in time using the conservation of absolute vorticity as a constraint.

This methodology is used to derive the large-scale circulation that accompanied Hurricane Debby (1982) in the Atlantic Ocean. Dropwindsonde data collected around Debby and the National Meteorological Center's analyses are used to qualitatively verify the analyses. Results indicate dial the vertical blending process is especially valuable in reconstructing the synoptic flow when the track winds are sparse at midlevel. The temporal adjustment is applied to three analysis periods and acts like an averaging process that smooths the fields. Subjective verification of the time adjusted DLM winds indicates an improvement at the initial time, but a degradation at the final time.

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