Investigating the roles of external forcing and ocean circulation on the atlantic multidecadal SST variability in a large ensemble climate model hierarchy

Lisa N. Murphy, Jeremy M. Klavans, Amy C. Clement, Mark A. Cane

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

This paper attempts to enhance our understanding of the causes of Atlantic multidecadal variability (AMV). Following the literature, we define theAMVas the SST averaged over the North Atlantic basin, linearly detrended and lowpass filtered. There is an ongoing debate about the drivers of theAMV, which include internal variability generated from the ocean or atmosphere (or both) and external radiative forcing.We test the role of these factors in explaining the time history, variance, and spatial pattern of the AMV using a 41-member ensemble from a fully coupled version of CESM and a 10-member ensemble of the CESM atmosphere coupled to a slab ocean. The large ensemble allows us to isolate the role of external forcing versus internal variability, and the model differences allow us to isolate the role of coupled ocean circulation. Both with and without coupled ocean circulation, external forcing explains more than half of the variance of the observedAMVtime series, indicating its important role in simulating the twentieth-centuryAMVphases. In this model the net effect of ocean processes is to reduce the variance of the AMV. Dynamical ocean coupling also reduces the ability of the model to simulate the characteristic spatial pattern of the AMV, but forcing has little impact on the pattern. Historical forcing improves the time history and variance of the AMV simulation, while the more realistic ocean representation reduces the variance below that observed and lowers the correlation with observations.

Original languageEnglish (US)
Pages (from-to)4835-4849
Number of pages15
JournalJournal of Climate
Volume34
Issue number12
DOIs
StatePublished - Jun 15 2021
Externally publishedYes

Keywords

  • Atlantic Ocean
  • Climate variability
  • General circulation models
  • Multidecadal variability
  • Ocean circulation
  • Sea surface temperature

ASJC Scopus subject areas

  • Atmospheric Science

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