Climatic Characteristics Of Southern Ocean Cyclone And Its Relationship With AAO And ENSO

The extra tropical cyclones in the Southern Ocean or surrounding Antarctica continentare one of the most important synoptic weather systems in Southern Hemisphere. Thecyclone plays an important role in the general atmosphere circulation as well as in highlatitude atmosphere-sea ice-ocean interaction. A severe cyclone or cyclone sudden burstingwith rapid development may introduce potential risks for commercial navigation andlogistical support of the Chinese National Antarctic Research Expedition (CHINARE). Betterunderstanding the characteristics of temporal and spatial distribution of the Southern Oceancyclones and the relationship between cyclones and Southern Hemisphere atmospheric,oceanic and climate factors is of great significance to our knowledge of the weather andclimate in the Southern hemisphere. In this study, we investigate the extra tropical cyclonesthat have entered into35°S in Southern Hemisphere. The6-hour sea level pressure from theEuropean Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysisfor the period of1979-2013was studied using a automated cyclone detection and trackingalgorithm developed by the University of Reading. We focus on the cyclones that have lifetime longer than2days and at least1000km moving distance. We have identified variouscharacteristics of the cyclone, such as source (total numbers), distribution, intensity,frequency, life time, annual and seasonal variability. The relationship between cycloneanomalies with AAO, ENSO and the SST gradient were also investigated. Based on our study,the following conclusions can be drawn out:(1)Number of Cyclones had significant seasonal, inter-annual and multi-scale cyclecharacteristics. Total annual cyclone showed a significant growth trend (P<0.05). Intensity ofCyclones also showed a significant increasing trend at the end of1990. Cyclones mainly hadlifetime in7days, and the proportion of these cyclones were70-80%. The percent oflong-lived cyclone are larger in summer compared with those in winter. (2)The high-density cyclone activity areas was in60°S-70°S between southernAustralia and Antarctica. In spring and summer, there also had a cyclone high-density areawhich in Bellingshausen Sea. Most cyclones could explosive in the South Atlantic and SouthIndian Ocean mid-latitude regions and less in South Pacific, these cyclones were more inwinter and autumn, lesser in spring and summer. Zhongshan station of China in Prydz Baywhere cyclones could explosive growth, logistical support need to be vigilant.(3) Cyclone anomalies in the Southern Ocean were closely related to AAO, ENSO and50°S-70°S sea surface temperature gradient. Showed that when phase of AAO werepositive, cyclone activity and cyclogenesis overall southward migration, negative phaseopposite. Warm or cold ENSO events corresponded to different numbers of cyclones. Effectof ENSO on cyclones activity was more significant in some region of South Pacific and someregion near the Atlantic on the east coast of South America. When warm (El Nino) eventhappened in spring and winter, number of cyclones was more than La Nina events happened,but in summer and autumn the number of cyclones was more in La Nina. There were highsignificant negative correlation region between50°S-70°S SST gradient and cycloneactivity, but these regions were discontinuity. However, there were significant positivecorrelation region between50°S-70°S SST gradient and cyclogenesis.