Diagnostic analysis of short-term hurricane vortex evolution in high-resolution ensemble Kalman Filter data assimilation
The results of case studies to date indicate considerable skill of the high-resolution analysis from HEDAS in terms of intensity and spatial patterns of circulation at vortex scales when compared to observation-based wind and surface pressure analysis. In the case of Hurricane Bill (2009), however, the deterministic forecasts from the high-resolution HEDAS analyses exhibited significant vortex spin-down during first 12 hours, unlike the observed storm. The track forecasts were consistent with the best-track estimates. A similar tendency for the vortex spin-down was also identified in 1-hour long, forecasts during cycling in HEDAS. This tendency was, as expected, systematically corrected by the observations in the analysis. To better understand the evolution of the modeled vortex and the associated errors in the analysis and in relation to the subsequent forecast errors, in the current study relationships between the primary and secondary circulation and thermodymamical fields were evaluated using the ensemble data from the analysis as well as the results of the subsequent deterministic and ensemble forecasts. The diagnostics include the ensemble-based multi-variate error correlations and wind-mass balance and principal wave analysis in a vortex-relative reference frame.