Southern extratropical cyclone behavior in ECMWF analyses during the FROSTspecial observing periods

The data collected during the three special observing periods (SOPs) of the Antarctic First Regional Observing Study of the Troposphere project provid e an excellent base upon which re, study the behavior of cyclonic systems i n winter, spring, and summer in the Southern Hemisphere. This paper provide s a report on the behavior of these cyclonic systems during the three SOPs as revealed in the twice-daily ECMWF operational analyses. The study has been undertaken with an objective cyclone tracking algorithm applied to the digital analyses. The results revealed cyclone behavior gene rally in accord with long-term climatologies developed with this scheme. Ln the SOPs the authors observed many systems to be generated in the western part of the ocean basins and then to move east and, to a lesser extent, sou th. In the three periods they found a concentration of tracks just to the n orth of the Antarctic continent, being particularly noticeable in the India n Ocean. At the same time, they found significant differences in cyclone be havior between the climatology and the SOPs in specific regions. The monthl y mean sea level pressure (MSLP) anomalies during the SOPs were quite large (and exceeded 10 hPa in places), particularly in the Pacific and in the re gion to the south of Australia. It appears that the anomalous cyclone struc ture during the SOPs could be related to the anomalies of the MSLP. The aut hors suggest that the PP three SOPs cannot be regarded as typical of their time of year, but it could be argued that no specific period could be so re garded. The results obtained with these high quality analyses during the SOPs have confirmed the Antarctic coast as a region of high cyclone density and of ve ry active cyclogenesis. The identification of these high levels of coastal cyclogenesis appears to differ from early studies that suggested the greate st (winter) cyclogenetic activity to be much farther north in the 40 degree s-50 degrees S region. The results presented here, however, concur with rec ent studies undertaken with high-resolution satellite data and four-dimensi onal data analyses, and the theoretical consequences of the baroclinic stru cture of the Antarctic coastal region.