Analyzing the Thermodynamic Impact of Shear on Tropical Cyclones Using Dropsondes

Predicting changes in tropical cyclone intensity remains a difficult challenge. To improve intensity forecasts, a deeper understanding of the impacts of environmental vertical wind shear on tropical cyclones is required. This study addresses this issue using a dataset of 20,733 dropsondes from aircraft missions occurring between 1996 and 2016 in the Pacific and Atlantic Ocean basins. Analyses show that the lower tropospheric equivalent potential temperature (θ_e) differences between shear-rotated quadrants become greater as shear increases. Additionally, all quadrants within the storm have decreased lower tropospheric θ_e in high shear cases compared to low shear cases These results suggest that in high shear cases, lower θ_e air is advected into the lower troposphere by downdrafts compared to low shear cases. As shear increases, mid-level relative humidity in the upshear quadrants also decreases. Prior studies have speculated that the presence of this dry air upshear may be a result of the lateral advection of environmental dry air or local subsidence. Given these findings, it is hypothesized that lowering lower tropospheric θ_e and decreasing mid-level relative humidity in the upshear quadrants are detrimental to the production of upshear convection. Without the development of a more symmetric precipitation distribution, tropical cyclone intensification is less likely to occur as demonstrated by prior research.