The Influence of Multi-Level Wind Shear on Tropical Cyclones

Typically, the influence of vertical wind shear on tropical cyclones is calculated using the vector difference between the winds at two levels (typically 850mb and 200mb). Correlations of different combinations of two-level measures of vertical wind shear with short term intensity changes and seasonal tropical cyclone statistics reveal broad structures that indicate using information at only two levels is not optimal. Two separate approaches are applied to attempt to improve the traditional shear metric. For seasonal statistics, a new formulation of vertical wind shear involving multiple levels, the root mean squared (RMS) shear, is presented as an alternative. The RMS shear compared with the traditional two-level shear correlates better with seasonal tropical cyclone statistics. For intensity, the Coupled Hurricane Intensity Prediction Scheme (CHIPS) is utilized to measure the influence of a multiple level shear parameterization on tropical cyclone intensity hindcasts. The results are compared to the same model using a two-level shear parameterization.