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Keywords:

  • tropical cyclone;
  • ENSO;
  • Southern Oscillation Index;
  • Southern Annular Mode;
  • Antarctic Oscillation;
  • southwest Pacific;
  • SPEArTC

ABSTRACT

In this study, we focus on possible climatological relationships between southwest Pacific tropical cyclone (TC) activity and the Southern Annular Mode (SAM) and ENSO, at both interannual and synoptic time-scales. The investigation focuses on TC seasonal characteristics (e.g. cyclogenesis, track characteristics, extratropical transition, and intensity) as modulated according to the polarity of the SAM and ENSO. At synoptic time-scales, we also look at possible triggers of TC cyclogenesis in the SAM signal up to 20 days in advance. The physical basis for this relationship is assessed using a number of different gridded data fields. During seasons characterized by positive phases of SAM and both positive and negative Southern Oscillation Index (SOI) values, there is an increased frequency of TCs undergoing extratropical transition near New Zealand. At synoptic time-scales, we found an interesting yet inconclusive relationship between the SAM and tropical cyclogenesis during SOI positive seasons. While statistically significant, there is no clear physical mechanism linking the mid-latitude SAM phenomenon to the genesis of TCs. In summary, the results show a clear interannual climatological relationship between an increased frequency of TCs undergoing extratropical transition near New Zealand and the positive phase of SAM.