南大洋夏季气旋的统计特征

Characteristics of Cyclones in Summer over the Southern Oceans

为增加对南半球气旋及爆发性气旋的理解,利用美国国家环境预报中心NCEP(National Centers for Environmental Prediction)提供的1(°)×1(°)FNL格点资料对南大洋2004~2007年3个夏季(12,1,2月)热带地区以外的气旋及爆发性气旋的位置及路径等特征进行统计分析,发现1月份为南大洋夏季气旋与爆发性气旋发生发展的高峰月,55°S^70°S为气旋分布最大值区,较多的气旋生成于南美洲东部、南极半岛附近,而爆发性气旋则大多生成于澳大利亚大陆西南50°S^60°S内,南极半岛东北部以及20°E,60°E附近,并且随着夏季向秋季过渡,南大洋气旋位置分布逐渐向高纬度集中。南大洋夏季气旋及爆发性气旋路径走向大多为东-东南走向,个别为东北走向。南大洋夏季气旋生命周期平均为2~6 d,水平尺度平均约为1000 km,爆发性气旋一般维持在1周左右,水平尺度平均约为3000 km。特殊的地理环境使得南大洋气旋具有发生频率高、中心气压值低、水平尺度大等特点。

Characteristics of cyclones and explosively developing cyclones （or＂bombs＂） over the Southern Oceans in summer （December, January, February） from 2004 to 2007 are analyzed by using the Final Analysis （FNL） data issued by the National Centers for Environmental Prediction （NCEP）. Statistical analyses suggest that cyclones and explosively developing cyclones frequently occurred in January, and most cyclones were concentrated in the latitude zone 55°S～70°S. From December to February, cyclones gradually concentrated near the Antarctic Continent. In general, cyclones and bombs move east-southeastward, while some exceptions move northeastwardly. In addition, we revealed other characteristics of cyclones and explosively developing cyclones over the southern oceans such as intensity, lifetime, and horizontal scale. Generally speaking, the lifetimes of cyclones over the southern oceans are around 2--6 days, and their horizontal scales are around 1 000 km. But for explosive cyclones, their lifetimes are about 1 week, and their horizontal scales are nearly 3 000 km. The special southern hemisphere geographical conditions may influence the cyclones over the southern oceans so that they have higher occurrence frequencies, lower central pressures and larger horizontal scales compared with their northern hemisphere counterparts.