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The Relationship Between Stability and Boundary Layer Winds in the Trades

Ellen J. SteinerCooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder 80309

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Abstract

Surface winds over the oceans are an essential component in the computation of wind stress and energy exchanges between the atmosphere and ocean. One technique to determine winds over large, uninstrumented oceanic regions is the tracking of the movement of cloud patterns from geosynchronous satellites. These low-level cloud drift vectors often correlate poorly with surface winds, partly because of wind shear in the boundary layer.

In this study, data from a small island station located in the southeast trade wind regime was used to show the influence of stability on the boundary layer winds. There was stronger low-level shear on stable days; thus on stable days cloud drift winds are likely to be poorer estimates of surface winds than on unstable days, when deep easterlies were found to characterize both the cloud and subcloud layers. It is shown that synoptic charts can be used to assess the low-level stability. By taking the stability into account, it should be possible to better extrapolate satellite winds to the surface.

Abstract

Surface winds over the oceans are an essential component in the computation of wind stress and energy exchanges between the atmosphere and ocean. One technique to determine winds over large, uninstrumented oceanic regions is the tracking of the movement of cloud patterns from geosynchronous satellites. These low-level cloud drift vectors often correlate poorly with surface winds, partly because of wind shear in the boundary layer.

In this study, data from a small island station located in the southeast trade wind regime was used to show the influence of stability on the boundary layer winds. There was stronger low-level shear on stable days; thus on stable days cloud drift winds are likely to be poorer estimates of surface winds than on unstable days, when deep easterlies were found to characterize both the cloud and subcloud layers. It is shown that synoptic charts can be used to assess the low-level stability. By taking the stability into account, it should be possible to better extrapolate satellite winds to the surface.

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