Summary
This study examined ECMWF operational analyses of the outflow layer of two tropical cyclones (Allen, 1980; Elena, 1985) during their passage across the Atlantic and Caribbean. Wind fields and related derived quantities were compared to those from objective analyses of specialized data sets. Errors in center position and storm motion from the ECMWF analyses were also evaluated.
Analyses of wind and angular momentum flux in 1985, subsequent to upgrading of the operational model, were superior to those from 1980. High-resolution, uninitialized analyses from 1985, however, provided no advantages over lower resolution, initialized analyses for the same time period. For all ECMWF analyses, azimuthally averaged (mean) tangential velocity, and thus mean vorticity, were well represented. Mean radial velocity and mean divergence were poorly represented. Problems with the latter arose primarily due to underestimation of outflow, especially in the 1980 analyses. Azimuthaleddy fluxes of angular momentum in the ECMWF analyses quantitatively differed from but qualitatively resembled, the control analyses.
Vorticity maxima at 850 mb in the operational analyses most accurately defined the center position of the storms, with a mean error less than or equal to one grid point. In contrast, surface pressure minima failed to provide reliable estimates. Over open ocean and at early stages of storms, analysis quality was uneven, with occasional large position errors and widely varying locations of vorticity maxima in the vertical.
Nevertheless, in regions surrounded by even a few rawinsondes, such as the Caribbean or Gulf of Mexico, ECMWF analyses contained sufficient information to allow individual case studies of the tropical cyclone environment. In the same regions, estimates of the eddy flux convergence of angular momentum were found to be accurate enough to aid in operational hurricane intensity prediction. Enhancements in resolution and model initialization at ECMWF since 1985 should further improve operational analyses of the tropical cyclone environment.
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Molinari, J., Vollaro, D. & Robasky, F. Use of ECMWF operational analyses for studies of the tropical cyclone environment. Meteorl. Atmos. Phys. 47, 127–144 (1992). https://doi.org/10.1007/BF01025613
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DOI: https://doi.org/10.1007/BF01025613