Weakening Satellite Era and Future Tropical Atlantic Interannual Sea Surface Temperature Variability

Multidecadal changes in tropical Atlantic interannual sea surface temperature (SST) variability are investigated in this thesis during the satellite era and in future projections. In particular, two El Niño-like phenomena driving high interannual SST variability in the eastern tropical Atlantic have been examined, namely: (1) the Atlantic Niños centered in the eastern equatorial Atlantic (ATL3, 20˚W-0˚; 3˚S-3˚N) and (2) the Benguela Niños developing in the Angola-Benguela area (ABA, 8˚E-16˚E; 20˚S-10˚S). The interannual SST variability in these two regions is important as both climate modes impact the climate of the surrounding countries. 

Over the satellite era, multidecadal changes in interannual SST variability in these regions have been analyzed using observational data and reanalysis products. In the ATL3 region, the May-June-July interannual SST variability has weakened by 31% during 2000-2017, relative to 1982-1999. In the ABA, it is shown that relative to 1982-1999, during 2000-2017 the March-April-May interannual SST variability has reduced by 30.5%. 

Lastly, future projections of the ATL3 and ABA interannual SST variability under high CO2 emission scenarios were assessed. In the ATL3 region relative to 1950-1999, 80% of 40 CMIP5 and CMIP6 models agree on a reduction of the interannual SST in 2050-2099. The ATL3-averaged interannual SST variability change in CMIP5 and CMIP6 models can to a large part (61%) be related to the reduced thermocline feedback. In the ABA relative to 1970-1999, during 2070-2099 the interannual SST variability during the FOCI model peak season, May-June-July, decreases by about 24%. The reduction of the interannual SST and temperature variability in the ABA appears as a consequence of a smaller temperature response to thermocline depth variations.


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