Local and remote influences on vertical wind shear in the tropical Atlantic region

Climate variability in the Tropical Atlantic is affected by local factors as well as by the remote influence of the El Nino-Southern Oscillation (ENSO) phenomenon in the Tropical Pacific. An important manifestation of this remote influence is the strong correlation between ENSO and hurricanes in the Atlantic, with a warm ENSO event being associated with decreased hurricane activity. Vertical wind shear over the tropical Atlantic plays an important role in mediating this relationship. The vertical shear variability over the Main Development Region (MDR) for hurricanes is decomposed into local and remote components, using observational data as well as global climate model integrations. Model simulations of the ENSO-vertical shear relationship are compared to observations. It is shown that there is a significant interaction between the local and remote influences, because of the inherently nonlinear nature of vertical shear. In particular, the mean simulation of vertical shear over the Tropical Atlantic is shown to affect how the remote influence of ENSO modulates the shear. Implications of this nonlinear interaction for climate change projections are discussed.