Historical trends in Southern Ocean storminess: Long-term variability of extreme wave heights at Cape Sorell, Tasmania

Abstract

Atmospheric re-analyses indicate increased Southern Ocean (SO) storminess over the past few decades. A southern Australia waverider record provides a 23-year record of storm waves generated in the SO. Statistical models to estimate long-term trends in frequency and intensity of severe storm waves, based on time-dependent versions of the Peak over Threshold model, are applied to investigate SO storminess trends. Significant increase in frequency of storm wave events observed in the corrected ERA-40 re-analysis significant wave height (HS) record is supported by increasing frequency of synoptic storms which drive large wave events at the site in both ERA-40 and NCEP-NCAR re-analyses. However buoy data show a small decrease in storm wave event frequency, consistent with previous studies investigating trends in SO mean HS from altimeter records. Re-analysis winds, with apparent increasing trend, may have influenced prior SO research conclusions, particularly related to weakening of the SO CO2 sink.