Large-Scale Atmospheric Forcing of Vertical Wind Shear in the Tropics

It has been well-established that vertical wind shear (VWS) plays a key role in modulating tropical cyclone activity, but there are multiple large-scale processes that can produce VWS in the tropics and their interactions are not fully understood. One of the strongest inter-annual drivers of tropical VWS is the El-Nino Southern Oscillation (ENSO) which modulates shear through variations in the Walker circulation. VWS may be further modulated through midlatitude intrusions of high potential vorticity (PV) streamers and Rossby wave breaking into lower latitudes. In this study, we investigate how both ENSO and PV streamer activity influence the seasonal and spatial variations in tropical VWS. The relative contributions from sources of ‘tropical’ ENSO and ‘extra-tropical’ high PV shear will be discussed, along with potential relationships between the two sources of VWS. Furthermore, we look at how tropical cyclone activity in the Atlantic basin is influenced when VWS is driven by ENSO, PV streamers, or combinations of both sources.