Climate Dynamics

, Volume 43, Issue 1–2, pp 103–117 | Cite as

Pacific Walker Circulation variability in coupled and uncoupled climate models

  • S. SandeepEmail author
  • Frode Stordal
  • Prashant D. Sardeshmukh
  • Gilbert P. Compo


There is still considerable uncertainty concerning twentieth century trends in the Pacific Walker Circulation (PWC). In this paper, observational datasets, coupled (CMIP5) and uncoupled (AGCM) model simulations, and additional numerical sensitivity experiments are analyzed to investigate twentieth century changes in the PWC and their physical mechanisms. The PWC weakens over the century in the CMIP5 simulations, but strengthens in the AGCM simulations and also in the observational twentieth century reanalysis (20CR) dataset. It is argued that the weakening in the CMIP5 simulations is not a consequence of a reduced global convective mass flux expected from simple considerations of the global hydrological response to global warming, but is rather due to a weakening of the zonal equatorial Pacific sea surface temperature (SST) gradient. Further clarification is provided by additional uncoupled atmospheric general circulation model simulations in which the ENSO-unrelated and ENSO-related portions of the observed SST changes are prescribed as lower boundary conditions. Both sets of SST forcing fields have a global warming trend, and both sets of simulations produce a weakening of the global convective mass flux. However, consistent with the strong role of the zonal SST gradient, the PWC strengthens in the simulations with the ENSO-unrelated SST forcing, which has a strengthening zonal SST gradient, despite the weakening of the global convective mass flux. Overall, our results suggest that the PWC strengthened during twentieth century global warming, but also that this strengthening was partly masked by a weakening trend associated with ENSO-related PWC variability.


Pacific Walker Circulation Hydrological cycle ENSO 



S.S. and F.S. acknowledge the financial support of the Research Council of Norway through the funding of the project SoCOCA (190159/V10). The Norwegian national supercomputing (NOTUR) resources of Hexagon (Project nn2345k) and Norstore (Project ns2806k) were extensively used in this work. The twentieth century reanalysis Project used resources of the National Energy Research Scientific Computing Center managed by Lawrence Berkeley National Laboratory and of the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory, which are supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and Contract No. DE-AC05-00OR22725, respectively. Support for the twentieth century reanalysis Project dataset is provided by the U.S. Department of Energy, Office of Science Innovative and Novel Computational Impact on Theory and Experiment (DOE INCITE) program, and Office of Science (BER), and by the National Oceanic and Atmospheric Administration Climate Program Office. The research of P.D.S. and G.P.C was supported by the Office of Science (BER), U.S. Department of Energy and by the NOAA Climate Program Office. The CMIP5 coupled model simulations were obtained from Program for Climate Modeling Inter-comparison (PCMDI), which is a part of World Climate Research Program, and we thank each modeling group for providing their data. The authors thank J. Hurrell of NCAR for help in understanding differences in SST datasets. For providing their SST data, we thank the Hadley Centre, N. Rayner, and BADC for HadISST, NOAA/NCDC and T. Smith for ERSST, and the JMA and M. Ishii for COBE.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • S. Sandeep
    • 1
    • 4
    Email author
  • Frode Stordal
    • 1
  • Prashant D. Sardeshmukh
    • 2
    • 3
  • Gilbert P. Compo
    • 2
    • 3
  1. 1.Section for Meteorology and Oceanography, Department of GeosciencesUniversity of OsloOsloNorway
  2. 2.Cooperative Institute for Research in the Environmental Sciences (CIRES)University of ColoradoBoulderUSA
  3. 3.Physical Sciences Division, Earth System Research LaboratoryNational Oceanic and Atmospheric AdministrationBoulderUSA
  4. 4.Center for Prototype Climate ModelingNew York University Abu DhabiAbu DhabiUAE

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