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Warm phase of AMV damps ENSO through weakened thermocline feedback
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  • Paloma Trascasa Castro,
  • Yohan Ruprich-Robert,
  • Frederic S. Castruccio,
  • Amanda Maycock
Paloma Trascasa Castro
University of Leeds, University of Leeds

Corresponding Author:[email protected]

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Yohan Ruprich-Robert
Barcelona Supercomputing Center, Barcelona Supercomputing Center
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Frederic S. Castruccio
National Center for Atmospheric Research (NCAR), National Center for Atmospheric Research (NCAR)
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Amanda Maycock
University of Leeds, University of Leeds
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Interactions between ocean basins affect El Niño Southern Oscillation (ENSO), altering its impacts on society. Here, we explore the effect of Atlantic Multidecadal Variability (AMV) on ENSO behaviour using idealized experiments performed with the NCAR-CESM1 model. Comparing warm (AMV+) to cold (AMV-) AMV conditions, we find that ENSO sea surface temperature (SST) anomalies are reduced by ~10% and ENSO precipitation anomalies are shifted to the west during El Niño and east during La Niña. Using the Bjerknes stability index, we attribute the reduction in ENSO variability to a weakened thermocline feedback in boreal autumn. In AMV+, the Walker circulation and trade winds strengthen over the Pacific, increasing the background zonal SST gradient. Those background changes shift ENSO anomalies westwards, with wind stress anomalies more confined to the West. We suggest the changes in ENSO-wind stress decrease the strength of the thermocline feedback in the East, eventually reducing ENSO growth rate.
16 Dec 2021Published in Geophysical Research Letters volume 48 issue 23. 10.1029/2021GL096149