中文摘要：

用澳洲850 hPa上空的变温和温度权重相结合的冷空气活动日数定义了澳洲冷空气活动指标（cold air index,CAI）,据CAI分析了澳洲冷空气活动的季节内和年际变化特征,结果表明：澳洲西南部地区是冷空气活动的关键区,5月其收缩于澳洲西南角,7月和8月其中心及影响范围均向北移动,主要分布区向澳洲东部伸展;整个冬季（6—8月）的澳洲冷空气活动没有显著的年际差异,而5—8月各月的冷空气活动却存在明显的年际变化特征。

英文摘要：

A cold air index（CAI） is defined as the cold air activity days weighted with respect to the temperature and 24 h temperature change at 850 hPa over Austrilia. The intraseasonal and interannual features of Australian cold air activity are studied using CAI. Results show that the key region of cold air activity is located in the southwest of Australia in May, and its center and influence range display a gradual northward shift in July and August with the main activity region expanding towards the east part of Australia. Australian cold air activity has no obvious interannual difference over the whole winter （JJA）, but it has distinct interannual variation in May ,June, July and August, respectively.