Effect of air-sea-ice interaction on winter 1996 Southern Ocean subpolar storm distribution

Air-sea-ice interaction processes in the Southern Ocean are investigated ut ilizing space-observed surface winds, sea ice concentration, and sea surfac e temperature (SST) from September through December, 1996. The sea ice edge (SIE) shows three ice-extent maxima around the Antarctic during September and October when sea ice coverage is maximum. They are located in the centr al Indian Ocean, east of the Ross Sea, and in the eastern Weddell Gyre. Dur ing September and October, most of the strong and long lasting storms initi ate northeast of the three sea ice maxima. Such spatial distributions of st orms and sea ice reflect coupling processes of the air-sea-ice interaction. A relatively stable, wave number 3 atmospheric circulation pattern that is believed to be fixed by the land-ocean distribution prevails during the ic e maximum season. The ice-extent maxima coincide with strong southerlies an d divergent wind fields associated with this pattern, which suggests that t he mean atmospheric circulation determines the ice distribution. The ice-ex tent maxima can enhance the regional meridional surface pressure gradient a nd therefore strengthen the westerly winds north of the ice edge. The decre asing ice extent east of the ice maxima creates a local zonal thermal gradi ent which enhances local southerlies. This positive feedback between the wa ve pattern in the mean atmospheric circulation and ice distribution partial ly causes the eastward propagation of the ice maxima and also provides a fa vorable condition for cyclogenesis northeast of the ice-extent maxima. The mechanism of the cyclogenesis is the baroclinic instability caused by the c old air blown from the ice pack to the warm open-ocean waters. Where the SS T is warmest off the SIE and the southerlies are the strongest, the potenti al for cyclogenesis is most likely. This is consistent with the observation s.