Researches On The Onset Process Of Summer Somali Jet And The Relations Between Onset Dates And General Circulation (Precipitation) Anomaly

At first, the Summer Somali Jet (SSMJ) onset dates during the period from 1948 to 2002 are decided by a defined index for SSMJ onset in this paper. Then, the processes of SSMJ onset and the influence of anomalies of the winter land-sea surface temperature and the East Asia winter monsoon are analyzed. At last, the relations between onset dates and general circulation (precipitation) anomaly are studied. The main results show:(1) The onset of SSMJ is the earliest signal of the Asia summer monsoon's onset; and the onset of SSMJ is caused by the African-Indian Ocean System, which is including Mascarene High, Middle African Low and Arabian High; the developing Indian Low can force SSMJ eastward after crossing equator. The interannual anomaly of SSMJ onset dates reflects the interannual anomaly of prophase winter temperature difference of land with sea. When the winter monsoon is stronger (weaker), the onset of SSMJ is later (earlier) in the coming spring.(2) The studies of the possible Influenced mechanism of the SSMJ onset dates show :In stronger winter monsoon years, Tibetan Plateau obstruct from the southward of Siberian cold high, so, on the one hand, cold air comes round to East Asia area and makes the earth temperature of area around Mongolia Plateau colder; on the other hand, cold air is rounded to Iran Plateau and makes area around Iran Plateau colder. As result, temperature gradient from sea to land is greater and the onset of SSMJ is earlier in the spring and vice verse.(3) The interannual relation between SSMJ onset dates and summer monsoon inEaster Asia is evident. When the onset date of SSMJ is earlier (later), the summer monsoon is stronger (weaker).(4) In lately twenty years, SSMJ onset dates has positive correlation with precipitation of South Asian and Changjiang- Huaihe River Basin in summer However, onset dates has negative correlation with precipitation of South China Sea in summer. The interannual correlation between SSMJ onset dates and summer rain in China is evident. When the onset date of SSMJ is earlier (later), the summer rain of Changjiang- Huaihe River Basin is heaver (lighter) ,and the rainfall of summer in the South China, the North-east China and the Huanghe River is lighter (heaver).(5) After mid-1970s, the relations between SSMJ onset dates and the rain in Changjiang- Huaihe River Basin and South China Sea in summer are notable, which is because the relation between subtropical anticyclone and SSMJ onset is evident in lately twenty years.