A Stealth Thermal Control by El Niño on Intense Tropical Cyclones in the Central and Eastern Pacific

Abstract:

The El Niño Southern Oscillation (ENSO) phenomenon, which features strong oceanic surface warming over the equatorial eastern Pacific, has major climatic and societal impacts. In particular, it greatly influences the yearly variations of tropical cyclone (TC) activities in both the Pacific and Atlantic basins via atmospheric dynamical factors such as vertical wind shear and stability. Until recently the direct ocean thermal control of ENSO on TCs has not been taken into consideration because of a mismatch in both timing and location. ENSO peaks in winter and the warming occurs along the equator, a region without TC activity. Here, we present evidence that El Niño discharges its heat into the eastern north Pacific basin 2-3 seasons after it peaks. This basin is characterized by abundant TC activity and is the second most active TC region in the world. As a result, an “El Niño heat reservoir” underneath the ocean surface is delivered to this basin during the TC season (boreal summer/fall) following the winter time peak of El Niño. ENSO exerts a delayed and stealth ocean thermal control on the overlying TCs that can draw the heat out from below the ocean surface, which provides an additional ocean heat supply favorable for the formation of hurricanes with strong intensities. This thermal control on intense TC variability has significant implications for seasonal predictions and long-term projections of TC activity over the eastern north Pacific.