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Weakened SST variability in the tropical Atlantic Ocean since 2000


A prominent weakening in equatorial Atlantic sea surface temperature (SST) variability, occurring around the year 2000, is investigated by means of observations, reanalysis products and the linear recharge oscillator (ReOsc) model. Compared to the time period 1982–1999, during 2000–2017 the May–June–July SST variability in the eastern equatorial Atlantic has decreased by more than 30%. Coupled air–sea feedbacks, namely the positive Bjerknes feedback and the negative net heat flux damping are important drivers for the equatorial Atlantic interannual SST variability. We find that the Bjerknes feedback weakened after 2000 while the net heat flux damping increased. The weakening of the Bjerknes feedback does not appear to be fully explainable by changes in the mean state of the tropical Atlantic. The increased net heat flux damping is related to an enhanced response of the latent heat flux to the SST anomalies (SSTa). Strengthened trade winds as well as warmer SSTs are suggested to increase the air–sea specific humidity difference and hence, enhancing the latent heat flux response to SSTa. A combined effect of those two processes is proposed to be responsible for the weakened SST variability in the eastern equatorial Atlantic. The ReOsc model supports the link between reduced SST variability, weaker Bjerknes feedback and stronger net heat flux damping.

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The authors would like to thank the anonymous reviewers for their constructive comments. This study was supported by the German Federal Ministry of Education and Research as part of the BANINO project (03F0795A) and the SFB 754 “Climate-Biochemistry Interactions in the tropical Ocean”. We acknowledge : the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, for providing NOAA High Resolution SST data and NCEP Reanalysis data, from their Web site at https://www.esrl.noaa.gov/psd/; the UK Met Office and ECMWF for providing datasets; the global ocean heat flux and evaporation products were provided by the WHOI OAFlux project (http://oaflux.whoi.edu) funded by the NOAA Climate Observations and Monitoring (COM) program; the Climate Data Guide: GPCP (Monthly): Global Precipitation Climatology Project. Retrieved from https://climatedataguide.ucar.edu/climate-data/gpcp-monthly-global-precipitation-climatology-project.

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Prigent, A., Lübbecke, J.F., Bayr, T. et al. Weakened SST variability in the tropical Atlantic Ocean since 2000. Clim Dyn (2020). https://doi.org/10.1007/s00382-020-05138-0

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  • Atlantic Niño
  • Ocean and atmosphere dynamics
  • Bjerknes feedback
  • Net heat flux damping