Ocean-Atmosphere Coupling in SST Hot Spot Regimes as a Function of ENSO: Local SST and Deep Convection Relationships, Larger-Scale Interactions With and Modulations on El Nino, and Remote Tropical and Extratropical Connections Using Multi-Satellite Observations and ERA-Interim Reanalysis

Using a novel, process-level approach, we explore sea-surface temperature (SST) and deep convection relationships in a region of the near-equatorial central South Pacific where domain mean SSTs frequently exceed 30°C from subseasonal to seasonal timescales mostly during the austral summer, and mostly during El Nino years. Composite analyses show that SSTs above 30°C are unstable, with subsequent deep convection formation and ocean cooling rates, but both the duration and spatial scale of the hot spots are a function of both the location of El Nino (Central versus East Pacific) and the intensity of El Nino. During La Nina events, anomalously strong easterlies preclude the widespread formation of SST hot spots in the central Pacific selection region. During the 12-year analysis period of 2002 - 2014, the moderate El Nino of 2009-2010 was exhibited by the strongest and most elongated deep convection in the hot spot selection region, the heaviest and most widspread precipitation, and greatest large-scale upward motion, and the most pronounced westerly wind bursts between 150° and 200°, but the quick switch in spring 2010 to easterly winds, and deep convection induced ocean cooling, coincided with a quick draw-down and retreat of that moderate El Nino. Using comprehensive observations from multisensors including MODIS cloud data, TRMM precipitation radar data, CERES surface, troposphere, and top-of-atmosphere cloud radiative forcing data, and profiles of large-scale forcing variables from ERA-Interim, we characterize the role of local versus remote forcing on both SST hot spots and deep convection during recent weak, moderate, and strong El Ninos, as well as the role of deep convection and local westerly wind anomalies on El Nino itself. We investigate the importance of the magnitude of the delay of atmosphere response, in the form of lagged deep convection to SST anomalies, on potentially prolonging and even intensifying El Nino events. Finally, we investigate the relative contributions of local hot spots versus domain-wide ENSO on mid-latitude teleconnections, with an emphasis on attempting to explain the unexpected poleward shift in the storm track off the West Coast of the United States relative to normal El Ninos during the recent 2015-2016 strong El Nino Event.