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      Spatial and Seasonal Variations of Sea Surface Temperature Threshold for Tropical Convection

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          Abstract

          Tropical rainfall variations are of direct societal relevance and drive climate variations worldwide via teleconnections. The convective rainfall tends to occur when sea surface temperature (SST) exceeds a threshold, SST thr, usually taken to be constant in time and space. We analyze 40-yr monthly observations and find that SST thr varies by up to 4°C in space and with season. Based on local convective instability, we develop a quantitative theory that largely explains the SST thr variations using the climatological state of the tropical atmosphere. Although it is often assumed that spatial variations of tropical upper-tropospheric temperature are small and can be neglected, it is shown that lower climatological values favor a lower SST thr. Similarly, a small increase in climatological surface relative humidity also leads to a decrease in SST thr, as does a lower climatological air–sea temperature difference. Consequently, efforts to understand and predict natural or forced variations in tropical rainfall must account for, in addition to SST, the temperatures aloft and the near-surface humidity and temperature and requires improved understanding of what controls their distribution in space and time.

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          Most cited references44

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          Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM

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            NCEP–DOE AMIP-II Reanalysis (R-2)

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              Sea Surface Temperature, Surface Wind Divergence, and Convection over Tropical Oceans.

              Large-scale convection over the warm tropical oceans provides an important portion of the driving energy for the general circulation of the atmosphere. Analysis of regional associations between ocean temperature, surface wind divergence, and convection produced two important results. First, over broad regions of the Indian and Pacific oceans, sea surface temperatures (SSTs) in excess of 27.5 degrees C are required for large-scale deep convection to occur. However, SSTs above that temperature are not a sufficient condition for convection and further increases in SST appear to have little effect on the intensity of convection. Second, when SSTs are above 27.5 degrees C, surface wind divergence is closely associated with the presence or absence of deep convection. Although this result could have been expected, it was also found that areas of persistent divergent surface flow coincide with regions where convection appears to be consistently suppressed even when SSTs are above 27.5 degrees C. Thus changes in atmospheric stability caused by remotely forced changes in subsidence aloft may play a major role in regulating convection over warm tropical oceans.
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                Author and article information

                Contributors
                Journal
                Journal of Climate
                American Meteorological Society
                0894-8755
                1520-0442
                August 01 2023
                August 01 2023
                : 36
                : 15
                : 4899-4912
                Affiliations
                [1 ]a Division of Earth and Climate Sciences, Nicholas School of the Environment, Duke University, Durham, North Carolina
                [2 ]b Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
                [3 ]c Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York
                Article
                10.1175/JCLI-D-22-0545.1
                73353bcd-db18-4c47-bf01-f5ce84b713ba
                © 2023
                History

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