Application of the Bratseth Scheme for the Analysis Of GALF, Data Using a Mesoscale Model

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  • 1 Science Applications International Corporation, McLean, Virginia
  • | 2 Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina
  • | 3 Naval Research Laboratory, Washington, D.C.
  • | 4 Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina
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Abstract

The successive correction scheme of Bratseth, which converges to optimum interpolation, is applied for the numerical analysis of data collected during the Genesis of Atlantic Lows Experiment. A first guess for the analysis is provided by a 12-h forecast produced by integrating a limited-area model from a prior coarse operational analysis. Initially, univariate analyses of the mass and wind fields are produced. To achieve the coupling of the mass and wind fields, additional iterations on the geopotential are performed by extrapolating the geopotential to grid points, using improving estimates of the geostrophic wind. This improved geostrophic wind is then used to update the geostrophic component of the initial univariate wind analysis. Use of a background forecast produces much improved mesoscale structures in the analysis. Enhanced gradients of the geopotential and larger wind shears are the result of the coupling of the mass and wind fields, particularly in regions of lower data density. Application of the vertical mode initialization scheme of Bourke and McGregor is used to diagnose the divergent component of the mesoscale circulations produced with the analysis scheme.

Abstract

The successive correction scheme of Bratseth, which converges to optimum interpolation, is applied for the numerical analysis of data collected during the Genesis of Atlantic Lows Experiment. A first guess for the analysis is provided by a 12-h forecast produced by integrating a limited-area model from a prior coarse operational analysis. Initially, univariate analyses of the mass and wind fields are produced. To achieve the coupling of the mass and wind fields, additional iterations on the geopotential are performed by extrapolating the geopotential to grid points, using improving estimates of the geostrophic wind. This improved geostrophic wind is then used to update the geostrophic component of the initial univariate wind analysis. Use of a background forecast produces much improved mesoscale structures in the analysis. Enhanced gradients of the geopotential and larger wind shears are the result of the coupling of the mass and wind fields, particularly in regions of lower data density. Application of the vertical mode initialization scheme of Bourke and McGregor is used to diagnose the divergent component of the mesoscale circulations produced with the analysis scheme.

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