Influence Of Australian Cold Air Activity On West Pacific Subtropical High And Its Pertinent Weather In China.

Activities of Australian cold air affect the West Pacific Subtropical High(WPSH) through intensifying west-south airflow. The accuracy of WPSH forcasting is crucial to weather forecast of China, specially important to the rainfall predicting during flood seasons. Therefore, it is significant and practical to analyze the influences of the activity of Australian cold air on WPSH. The relationship between Australian cold air activities and change of lagging WPSH index is studied by using statistical methods of correlation and spectrum based on the re-analysis data of grid point of NCEP during 1948-2003 and the data of precipitation in the middle-lower reaches of Yangtze River. Meantime, remote correlation between Australian cold air activity and rainfall of the middle-lower reaches of Yangtze River is discussed. Some new research results have been obtained from this thesis. The main conclusions are summed up as follows:(1) In January, Australian mainland is under the control of warm and low pressure. WPSH moves back to sea. There is airflow obviously crossing the equator from north hemisphere to south hemisphere. In July, Australian mainland is controlled by cold high. Moving of WPSH towards north and west affects Asia mainland. There is strong crossing-equator airflow from south hemisphere to north hemisphere.(2) Australian cold air activities relatively have long periods of 10-15 days and short periods 7.5-8.6 days . There are primary periods of 7.5-8.6 days in both daily changes of WPSH intensity index and WPSH ridge line, which is coincident with the 7.5-8.6 days short periods of Australian cold air activities.(3) In June, there is a significantly negative correlation at lag=5 between the change of Australian temperature and WPSH ridge line, and positive correlation at lag=10 between change of Australian temperature and WPSH intensity index. In July, there is significantly negative correlation between the change of Australian temperature and 8-day lagging WPSH ridge to west, and 8-day lagging WPSH acreage index change, and 10-day lagging WPSH intensity index change, and 11-day lagging WPSH ridge to west change. In August, Australian temperature change has significantly negative correlation with the change of 5-day lagging WPSH acreage index, and positive correlation with the change of 10-day lagging WPSH ridge to west. The change of lagging WPSH index has linear correlation with Australian temperature.(4) When there is stronger cold air activities in Australian, crossing-equator airflow is intensifyed, which results in WPSH moving towards north consequently. Lagging time of WPSH moving northward to Australian cold air activities is about seven days.(5) There is a remote correlation of 7.7 days between the change of Australian temperature and rainfall of the middle-lower reaches of Yangtze River in waterlogging year and they have in-phase surging in the 7.7-day periods. Australian cold air activities affect rainfall of the middle-lower reaches of Yangtze River after spending 7.3 days . The affecting processes are: when Australian cold air activity is stronger, WPSH moves northward and the middle-lower reaches of Yangtze River is sunny and controlled by WPSH; when Australian cold air activity weakens, WPSH moves southward and the middle-lower reaches of Yangtze River locate on the edge of WPSH with rainy days.