关键词: 西北地区中部, 异常多雨, 大气环流, 海冰面积, 海温, 协同影响

Abstract:

Located at the hinterland of East Asia and the edge of Qinghai-Tibet Plateau, the central part of northwest China has complex terrain and diverse climate types. Most of the areas are rain-fed agriculture, which is also the most vulnerable area of the ecological environment. June is the critical period for summer grain crop growth, which has a great influence on climate. In June 2019, the amount and days of precipitation in most of the central part of northwest China were more accompanied by frequent heavy rainfall. At the same time, there was a rare continuous low temperature and rainy weather. Thus, based on the monthly average height field, wind field reanalysis data of the National Centers for Environmental Prediction (NCEP), NOAA reconstructed sea surface temperature since 1961, the daily precipitation data of 54 weather stations in the central part of northwest China in June, and the sea ice area of ten regions in the Arctic since 1979, the causes of precipitation anomaly in the central part of northwest China in June 2019 was analyzed. The key sea ice areas and period, the key periods of the North Atlantic Triple (NAT) that have a significant impact on the precipitation in June were investigated. Furthermore, the synergistic effect and influence mechanism between the sea ice areas and the NAT with ENSO event were analyzed. The results showed that the correlation between precipitation and altitude field in the central part of northwest China changed significantly in June. Also, the precipitation was abnormal more when the distribution of height anomaly field in middle and high latitudes was the Eurasian 2 pattern (EU2) teleconnection pattern (i.e., summer EU (Eurasian) teleconnection type) since the 1990s. The precipitation was more when the EU2 is positive phase “+ - + -”, and vice versa. The influence of the sea ice area in the Chukchi Sea from March to April and the NAT in spring on 500 hPa altitude field changed significantly since 1990 and 1992, respectively. It had a significant influence on the EU2 teleconnection pattern, but the influence of NAT is less than that of the Chukchi Sea ice area. When the sea ice area was less and NAT positive phase (sea ice area more and NAT negative phase), the probability of more (less) precipitation in the central part of northwest China increased obviously. ENSO events had no obvious direct impact on the precipitation, but the subtropical high was anomaly stronger and westward in the next year of the El Nino event. The Chukchi Sea ice area was abnormally small with a strong positive phase NAT in spring in 2019, which made the EU2 teleconnection positive anomaly. El Nino event transported water vapor from the Western Pacific Ocean to the North Pacific Ocean, which cooperated with EU2 teleconnection made the cold air and water vapor were enough to make abnormal precipitation in the central part of northwest China. The research results could provide a basis for short-term climate prediction. While all the relationship between the precipitation in June, sea ice area from March to April, NAT in spring, and altitude field in the central part of northwest China had changed since the 1990s, then the interaction of them (air-ice-sea) needs further study.

Key words: the central part of northwest China, precipitation anomaly, atmospheric circulation, sea ice area, sea surface temperature, synergistic impact