Variation of Cold Air Frequency in Spring and Its Diagnostic Analysis in the Northeast of Tibet Plateau

Yang Zhaoming;Shi Shengbo;Duan Lijun;Zhang Tiaofeng;Climate Center of Qinghai Province;Qinghai Key Laboratory of Disaster Preventing and Reducing;

cold air frequency;;variation;;diagnostic and analysis;;the northeast of Tibet Plateau;;circulation factor;;cold air activity;;Tibet Plateau

Using 68 stations' ground temperature observation data in the northeast of Tibet Plateau from 1961 to 2015, we studied the strength index I(including frequency) sequence of cold air process in spring months,analyzed the characteristics of regional cooling air frequency and its origins by using climate diagnostic method. The results showed that: the tendency rate of climate change of cold air process frequency in spring from 1961 to 2015 was decreasing and the decrease rate was-0.290 per 10 years, this process was not significant. The decreasing trend in Qaidam and the southern part was in accordance with that in the northeast of Tibet Plateau, but the increasing trend in the eastern part was opposite to it. In terms of periodic variation,the quasi-periodic around 3, 5, 7, 8 years' frequency was relatively high but the 25 years and other quasiperiodic frequency were relatively low. The continuing spring height value on the high(low) side at 500 hPa in Baikal Lake region was one of the main factors causing less(more) cold air process in the northeast of Tibet Plateau from 1991 to 2015(from 1961 to 1980). In spring, the continuing strong high-pressure ridge of Uralf Mountain, low-pressure trough from Balkhash Lake to Baikal Lake and high-pressure ridge from Caspian Lake to Aral Sea could easily lead the northern cold air to influence China by northwestern and northern paths.The northeast of Tibet Plateau was on the passage of cold air southward, so the cold air process tended to be more frequent; on the contrary, the cold air process frequency tended to be less.