Mean Southern Hemisphere Extratropical Cyclone Behavior in the 40-Year NCEP–NCAR Reanalysis

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Abstract
This paper presents a new climatology of Southern Hemisphere (SH) extratropical cyclones. This has been compiled by applying a state-of-the-art cyclone tracking scheme to the 6-hourly National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) global reanalyses spanning the period 1958–97. The results show there to be, on average, between 35 and 38 cyclonic systems per analysis (depending on season), with the greatest density [exceeding 6 × 10−3 cyclones (deg lat)−2] found south of 60°S in all seasons and in the Indian and west Pacific Oceans in autumn and winter. For the most part, there is a net creation of cyclones (i.e., cyclogenesis exceeds cyclolysis) north of about 50°S, and a net destruction to the south of this latitude. Having said this, the most active cyclogenesis takes place south of 45°S. The NCEP–NCAR reanalyses indicate that most SH cyclogenesis occurs at very high latitudes, and the axis of the maximum lies on, or to the south of, 60°S. This... Abstract This paper presents a new climatology of Southern Hemisphere (SH) extratropical cyclones. This has been compiled by applying a state-of-the-art cyclone tracking scheme to the 6-hourly National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) global reanalyses spanning the period 1958–97. The results show there to be, on average, between 35 and 38 cyclonic systems per analysis (depending on season), with the greatest density [exceeding 6 × 10−3 cyclones (deg lat)−2] found south of 60°S in all seasons and in the Indian and west Pacific Oceans in autumn and winter. For the most part, there is a net creation of cyclones (i.e., cyclogenesis exceeds cyclolysis) north of about 50°S, and a net destruction to the south of this latitude. Having said this, the most active cyclogenesis takes place south of 45°S. The NCEP–NCAR reanalyses indicate that most SH cyclogenesis occurs at very high latitudes, and the axis of the maximum lies on, or to the south of, 60°S. This...

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