Upshear-downshear variations in tropical cyclones from dropsondes

Molinari and Vollaro (2007, in review) found a shear-related bias in helicity values calculated using troposphere-deep dropsondes in Hurricane Bonnie (1998). The exceptionally large helicity values found downshear-left were determined to result from strong vertical shear of the radial wind, associated with the shear-induced secondary circulation. Similarly, low helicity values were found upshear. Following on from this work, the present study focuses on shear-induced variations in other aspects of tropical cyclone structure using similar dropsonde data. In particular, the work considers the impact of shear on the azimuthal variation of temperature and dew point, equivalent potential temperature, and radial and tangential wind fields.

The goal of the study is to investigate whether there are any systematic upshear-downshear variations in tropical cyclone structure as revealed by dropsondes released from the upper-troposphere, and whether such features are dependent on the magnitude of the shear, the intensity of the system and the direction of the shear relative to the storm motion.