Preprints
https://doi.org/10.5194/esd-2021-46
https://doi.org/10.5194/esd-2021-46

  18 Aug 2021

18 Aug 2021

Review status: a revised version of this preprint is currently under review for the journal ESD.

Weakened impact of the Atlantic Niño on the future equatorial Atlantic and Guinean Coast rainfall

Koffi Worou1, Hugues Goosse1, Thierry Fichefet1, and Fred Kucharski2 Koffi Worou et al.
  • 1Georges Lemaître Centre for Earth and Climate Research (TECLIM), Earth and Life Institute (ELI), Université catholique de Louvain (UCLouvain), Louvain-la-Neuve, Belgium
  • 2Earth System Physics Section, Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

Abstract. The Guinea Coast is the southern part of the West African continent. Its summer rainfall variability mostly occurs on interannual timescales and is highly influenced by the sea surface temperature (SST) variability in the eastern equatorial Atlantic, which is known as the Atlantic Niño (ATL3). Using historical simulations from 31 General Circulation Models (GCMs) participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we first show that these models are able to simulate reasonably well the rainfall annual cycle in the Guinea Coast, with, however, a wet bias during boreal summer. This bias is associated with too high mean summer SSTs in the eastern equatorial and south Atlantic regions. Next, we analyze the near-term, mid-term and long-term changes of the Atlantic Niño mode relative to the present-day situation, in a climate with a high anthropogenic emission of greenhouse gases. We find a gradual decrease of the equatorial Atlantic SST anomalies associated with the Atlantic Niño in the three periods of the future. This result reflects a possible reduction of the Atlantic Niño variability in the future due to a weakening of the Bjerkness feedback over the equatorial Atlantic. In a warmer climate, an oceanic extension of the Saharan Heat Low over the North Atlantic and an anomalous higher sea level pressure in the western equatorial Atlantic relative to the eastern equatorial Atlantic weaken the climatological trade winds over the equatorial Atlantic. As a result, the eastern equatorial Atlantic thermocline is deeper and responds less to Atlantic Niño events. Among the models that simulate a realistic rainfall pattern associated with ATL3 in the present-day climate, there are 15 GCMs which project a decrease of the Guinean Coast rainfall response related to ATL3, and 9 GCMs which show no substantial change in the patterns associated with ATL3. In these 15 models, the zonal wind response to the ATL3 over the equatorial Atlantic is strongly attenuated in the future climate. Similar results are found when the analysis is focused on the rainfall response to ATL3 over the equatorial Atlantic. There is a higher confidence in the reduction of the rainfall associated with ATL3 over the Atlantic Ocean than over the Guinea Coast. We also found a decrease of the convection associated with ATL3 in the majority of the models.

Koffi Worou et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2021-46', Anonymous Referee #1, 14 Sep 2021
    • AC1: 'Reply on RC1', Koffi Worou, 18 Nov 2021
  • RC2: 'Comment on esd-2021-46', Anonymous Referee #2, 17 Sep 2021
    • AC2: 'Reply on RC2', Koffi Worou, 18 Nov 2021
  • RC3: 'Comment on esd-2021-46', Anonymous Referee #3, 17 Sep 2021
    • AC3: 'Reply on RC3', Koffi Worou, 18 Nov 2021
  • RC4: 'Comment on esd-2021-46', Anonymous Referee #4, 20 Sep 2021
    • AC4: 'Reply on RC4', Koffi Worou, 18 Nov 2021
  • RC5: 'Comment on esd-2021-46', Anonymous Referee #5, 01 Oct 2021
    • AC5: 'Reply on RC5', Koffi Worou, 18 Nov 2021

Koffi Worou et al.

Koffi Worou et al.

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Short summary
Over the Guinea Coast, the increased rainfall associated with warm phases of the Atlantic Niño is reasonably well simulated by 24 climate models out of 31, for the present-day conditions. In a warmer climate, general circulation models project a gradual decrease with time of the rainfall magnitude associated with the Atlantic Niño for the 2015–2039, 2040–2069 and 2070–2099 periods. There is a higher confidence in these changes over the equatorial Atlantic than over the Guinea Coast.
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