Interannual variations of storm tracks in the Southern Hemisphere and their connections with the Antarctic oscillation

Interannual variations of storm tracks in the Southern Hemisphere (SH) are studied. Large interannual variations are found in the enveloping function of meridional wind nu(c), and these suggest some dominant periodicities. Some of these periodicities are a quasi-biennial oscillation in the subtropical branch of the winter storm track and the midlatitude spring storm track. a 3 year period and a long period of 8 years. The Antarctic oscillation (AAO) seems to be connected to the interannual variation of storm tracks in the SH. A significant negative correlation between nu(e) and the AAO index in the high latitudes. a positive correlation in the midlatitudes and again a negative correlation in the subtropics are found throughout the year. During the high index phase of the AAO, the low-level zonal wind shear increases in the region of midlatitude storm tracks and the static stability decreases, increasing the growth rate of baroclinic eddies, i.e. increase of nu(e) (the opposite occurs during the negative phase). This explains the positive correlation in the midlatitudes between nu(c) and the AAO index. In the region of the subtropical storm track during the high index phase the wind shear decreases and the static stability increases. decreasing the growth rates, thus explaining the negative correlation between nu(c) and the AAO index. Copyright (C) 2003 Royal Meteorological Society.