FORMATION AND LIMITING MECHANISMS FOR VERY HIGH SEA-SURFACE TEMPERATURE - LINKING THE DYNAMICS AND THE THERMODYNAMICS

The present study composites atmosphere and ocean conditions associate d with ocean hot spots. Ocean hot spots are defined as regions where S ST exceeds 29.75 degrees C and that have an area greater than 1 X 10(6 ) km(2). The composite atmosphere includes surface flux parameters, de ep convection and cloud amounts, cloud radiative forcing, and analysis fields from the National Meteorological Center (NMC) and European Cen tre for Medium-Range Weather Forecasts weather forecasting systems. Th e composite ocean includes sea level height and the temperature and ve locity structures down to 720 m from the NMC ocean forecasting system. These fields are composited for the months before, during, and after the appearance of hot spots in order to develop a four-dimensional pic ture of the atmosphere and ocean conditions that are associated with t he formation and the decay of these very high ocean surface temperatur es. The analysis indicates that the formation of these hot spots is la rgely confined to the region within the 28 degrees C isotherm of the l ong-term mean SST, with greatest concentrations occurring in the weste rn Pacific warm pool. Extended analysis of the warm-pool hot spots (0 degrees-10 degrees S, 156 degrees E-176 degrees W) indicates strong in fluences from interannual, annual, and 30-60 day timescales, with La N ina conditions appearing to inhibit formation, southern summer favorin g formation, and the descending (ascending) phase of the Madden-Julian oscillation (MJO) favoring formation (decay). This interaction with t he MJO indicates how internal, or remotely forced, atmospheric variabi lity, in addition to local feedbacks, may be playing a role to help li mit SST. Furthermore, the out-of-phase relationship between SST and de ep convection associated with this variability suggests the possibilit y of a positive feedback mechanism for the MJO. With respect to the su rface heat budget, the data indicate that during the hot spot evolutio n, the convective perturbations to the surface shortwave exceed those for evaporation by at least a factor of 2. The composite ocean conditi ons indicate that the rapidly varying atmospheric conditions associate d with the hot spot evolution induce significant changes below the sur face layer of the ocean as well. These changes appear to be primarily linked to the onset of westerly wind bursts associated with the enhanc ed deep convection. Removing the El Nino time periods from the composi tes indicates that the composite ocean is more dependent on the intera nnual state than the composite atmosphere. These results indicate that the ocean should not be rendered too simple with respect to understan ding the limiting mechanisms of high SST.