Influence of the preceding austral summer Southern Hemisphere annular mode on the amplitude of ENSO decay
There is increasing evidence of the possible role of extratropical forcing in the evolution of ENSO. The Southern Hemisphere Annular Mode (SAM) is the dominant mode of atmospheric circulation in the Southern Hemisphere extratropics. This study shows that the austral summer (December–January–February; DJF) SAM may also influence the amplitude of ENSO decay during austral autumn (March–April–May; MAM). The mechanisms associated with this SAM–ENSO relationship can be briefly summarized as follows: The SAM is positively (negatively) correlated with SST in the Southern Hemisphere middle (high) latitudes. This dipole-like SST anomaly pattern is referred to as the Southern Ocean Dipole (SOD). The DJF SOD, caused by the DJF SAM, could persist until MAM and then influence atmospheric circulation, including trade winds, over the Niño3.4 area. Anomalous trade winds and SST anomalies over the Niño3.4 area related to the DJF SAM are further developed through the Bjerkness feedback, which eventually results in a cooling (warming) over the Niño3.4 area followed by the positive (negative) DJF SAM.
Key wordsSouthern Hemisphere Annular Mode ENSO Southern Ocean Dipole
越来越多的证据表明热带外因子可以影响 ENSO 的发展. 南半球环状模是南半球热带外大气环流的主导模态. 本文分析结果表明, 南半球夏季(12-2月)的南半球环状模, 可以影响衰减期(3–5月)的 ENSO 振幅. 这种南半球环状模影响 ENSO 振幅的物理机制可以归纳如下: 南半球环状模与南半球中(高)纬度的海温呈现正(负)相关. 这种偶极子型的海温异常结构简称为南大洋偶极子. 12-2 月由南半球环状模导致的南大洋偶极子型海温异常, 持续到 3–5 月后可以进而影响大气环流, 包括 Niño3.4 区域的纬向风. 由南半球环状模导致的 Niño3.4 区域的纬向风和海温异常进而通过 Bjerkness 反馈发展起来. 当 12-2 月南半球环状模为正(负)位相时, 3–5月 Niño3.4区域海温偏冷(暖).
关键词南半球环状模 ENSO 南大洋偶极子
Unable to display preview. Download preview PDF.
The authors would like to thank the editor and the anonymous reviewers for their insightful comments and suggestions, which contributed greatly towards improving the manuscript. This work was jointly supported by the China Special Fund for Meteorological Research in the Public Interest (Grant No. GYHY201506032), an NSFC project (Grant No. 41405086), and a NationalKeyR&DProgram of China (Grant No. 2016YFA0601801). The datasets, including NCEP–NCAR, 20CR, CMAP, GPCP, and ERSST.v3b, were obtained from NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, via their website: http://www.esrl.noaa.gov/psd/. The HadISST dataset was provided by the Met Office Hadley Centre. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output.
- Fogt, R. L., J. Perlwitz, A. J. Monaghan, D. H. Bromwich, J. M. Jones, and G. J. Marshall, 2009a: Historical SAM variability. Part II: Twentieth-century variability and trends from reconstructions, observations, and the IPCC AR4 models. J. Climate, 22, 5346–5365, doi: 10.1175/2009JCLI2786.1.CrossRefGoogle Scholar
- Li, J. P., and J. X. L. Wang, 2003: A modified zonal index and its physical sense. Geophys. Res. Lett., 30, 1632, doi: 10.1029/2003GL017441.Google Scholar
- Li, J. P., and Coauthors, 2013: Progress in air–land–sea interactions in Asia and their role in global and Asian climate change. Chinese Journal of Atmospheric Sciences, 37, 518–538, doi: 10.3878/j.issn.1006-9895.2012.12322. (in Chinese)Google Scholar
- Wang, F., 2010a: Subtropical dipole mode in the Southern Hemisphere: A global view. Geophys. Res. Lett., 37, L10702, doi: 10.1029/2010GL042750.Google Scholar
- Wang, S.-Y., M. L. L’Heureux, and H. H. Chia, 2012a: ENSO prediction one year in advance using western North Pacific sea surface temperatures. Geophys. Res. Lett., 39, L05702, doi: 10.1029/2012GL050909.Google Scholar
- Wang, S. Y., M. L’Heureux, and J. H. Yoon, 2012b: Is global warming changing the ENSO precursor in the western north pacific? 37th NOAA Annual Climate Diagnostics and Prediction Workshop, Fort Collins, CO, NOAA, 115–120.Google Scholar
- Zheng, F., and J. P. Li, 2012: Impact of preceding boreal winter southern hemisphere annular mode on spring precipitation over south China and related mechanism. Chinese Journal of Geophysics, 55, 3542–3557, doi: 10.6038/j.issn.0001-5733.2012.11.004. (in Chinese)Google Scholar