Abstract:

Impacts of eastern Pacific and central Pacific El Niño–Southern Oscillation (ENSO) events on climate changes in the extratropical area of the Southern Hemisphere were investigated for two different periods (1979–1998 and 1999–2012) and four seasons using the Ocean Reanalysis Pilot 5 (ORAP5) ocean and sea-ice reanalysis product and the ERA-Interim atmospheric reanalysis product for 1979–2012. Results show that there was significant interdecadal variability in the response patterns of climate variables to ENSO variations before and after 1999. Between 1979 and 1998, correlation between the dominant empirical orthogonal function of Southern Hemisphere extratropical climate variables and responses of the climate variables to ENSO events were both higher for the Niño3 sea surface temperature anomaly index, indicating that Eastern Pacific-type ENSO events had larger influences on Southern Hemisphere extratropical climate changes. Between 1999 and 2012, there were no considerable differences between the response fields to the variations of different Niño indices. For both periods, the atmospheric variables, including sea-level pressure, surface wind and surface air temperature, showed the strongest and weakest responses to ENSO events in winter and summer, respectively, and they manifested a zonal wavenumber-3 structure in their response fields in austral autumn. For 1999–2012, unlike responses of sea-level pressure and surface wind, responses of surface air temperature over the Ross and Amundsen Seas to variations in the Niño4 index were stronger than those to variations in the Niño3 index. This feature was also found in the response fields of mixed layer temperature, indicating the presence of oceanic influences in surface air temperature anomalies. Responses of mixed layer depth and temperature were closely related to variations in Niño indices. Between 1979 and 1998, differences in the responses of sea-ice concentration to variations in different Niño indices mainly occurred during the freezing seasons, while differences in sea-ice thickness responses to variations in different Niño indices mainly occurred in summer. Interdecadal variability in sea-ice concentration and thickness responses to variations in the Niño3 index was large in autumn and winter, while variability in responses to variations in the Niño4 index was large in all non-summer months.

Key words: Southern Hemisphere extratropical climate, El Niño-Southern Oscillation (ENSO), Eastern Pacific- type, Central Pacific-type, Niño indices