Seasonal southern hemisphere multi-variable reflection of the southern annular mode in atmosphere and ocean reanalyses
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Variations of southern hemisphere (SH) climate variables are often linked to the southern annular mode (SAM) variability. We examined such linkage by seasons using state-of-the-art atmosphere and ocean/sea-ice reanalyses. The associated SAM related anomaly (SRA) fields of the climate variables, denoting anomalies corresponding to the same variation in SAM, are overall consistent across the reanalyses. Among the atmospheric products, 20CRV2 differs from ERA-interim and CFSR in the sea-level pressure SRAs over the Amundsen Sea, resulting in less warming over the Antarctic Peninsula. Among the ocean reanalyses, ORAP5 and C-GLORS exhibit the largest consistency. The major difference between them and the lower-resolution CFSR and SODA reanalyses is deeper penetration of anomalous meridional currents. Compared to the other ocean reanalyses, CFSR exhibits stronger and spatially more coherent surface-current SRAs, resulting in greater SRAs of sea-ice motion and ice thickness along the ice edges. The SRAs of sensible and total surface heat fluxes are reduced in CFSR due to ocean–atmosphere coupling. Significant sea-ice concentration SRAs are present on the west side of peninsulas along the east Antarctica coast in spring and winter, most notably in ORAP5 and C-GLORS, implying changes in new-ice production and shelf-water formation. Most atmosphere and ocean variables manifest an annular SRA pattern in summer and a non-annular pattern in the other seasons, with a wavenumber-3 structure strongest in autumn and weakest in summer. The wavenumber-3 structure should be related to the zonal wave three pattern of the SH circulation, the relation of which to SAM needs further exploration.
KeywordsSouthern annular mode Climate anomaly Seasonal variation Reanalysis products Southern hemisphere
This work was funded by the National Natural Science Foundation of China (Grant No. 41406006). Y. Z was sponsored by Shanghai Sailling Program (Grant No. 15FY1406400), and P. U. and T.V. by the Academy of Finland (contracts 263918 and 264358). The ERA-interim product was obtained from ECMWF. The CFSR product was obtained through the NCAR/UCAR Research Data Archive. Support for the 20CRV2 product 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 Biological and Environmental Research (BER), and by the National Oceanic and Atmospheric Administration Climate Program Office. The ORAP5 reanalysis was obtained through Copernicus Environment Monitoring Service. CMCC is acknowledged for providing the C-GLORS reanalysis. The SODA Version 2.2.4 is retrieved from the NCAR/UVAR Climate Data Guild. We thank Hao Zuo from ECMWF, Andrea Storto from CMCC, Benjamin Giese from Texas A&M University, Robert Dattore from NCAR and Gilbert Compo from University of Colorado for their help in retrieving these data.
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