Abstract:

This study was conducted to reveal the impact and mechanism of the North Atlantic sea surface temperature anomaly (SSTA) associated with Ningxia precipitation and to improve the accuracy of precipitation prediction ability in Ningxia. Based on the monthly precipitation data of 20 meteorological stations in Ningxia, NCEP/NCAR atmospheric data, Hadley center sea surface temperature data, and utilizing empirical orthogonal decomposition, composite, and correlation methods, we studied the relationships and their decadal changes between the North Atlantic SSTA and Ningxia precipitation anomaly from late spring to early summer (April-June). It was found that the relationship had continuously increased since 1961 but nonsignificantly until the 1980s. Since then, the North Atlantic Ocean “triple type” (NAT) SSTA in early winter and spring has caused precipitation anomalies in Ningxia from April to June but it differs each month. Corresponding to the positive (negative) phase NAT, Ningxia precipitation is more (less) in April, less(more) in May, and less northerly and more southerly (more northerly and less southerly) in June. Furthermore, the mechanism is revealed of NAT affecting Ningxia precipitation anomaly by inducing an atmosphere anomaly wave train in the area from Europe to the Asia-Pacific. The positivephase NAT can induce a wave train with atmosphere circulation anomaly pattern of geopotential height “west lower and east higher” at 500 hPa around Ningxia in April, which is the typical atmosphere anomaly pattern of more precipitation in Ningxia in April. Additionally, at the low layer of 850 hPa, the southerly wind anomalies transform warmer and humid air into Ningxia, contributing to more precipitation. In May and June, with the transition from spring to summer, the abnormal wave train polar shifts. In May, Ningxia is affected by the positive abnormal height field at 500 hPa in Baikal Lake area to East Asia, and the abnormal wind field in the low level of 850 hPa divergence, with less precipitation. In June, the positive height anomaly center at 500 hPa in East Asia continues to develop northward from south to north to Baikal Lake area, and splits from the positive anomaly height in the east of China into two anomaly centers. At 500 hPa, Ningxia north and south areas are affected by the atmospheric circulation pattern of geopotential height anomaly being “north higher and south lower” and “west lower and east higher”, respectively. Meanwhile, at low level 850 hPa weak northerly and southerly anomaly wind prevails in the north and south area of Ningxia respectively, being with divergence and convergence. All of these atmosphere anomalies are conducive to less precipitation in the north and more in the south of Ningxia. For negative NAT phase, all the atmospheric circulation and precipipation anomalies are vice versa.

Key words: the North Atlantic, Triple type SST anomaly, precipitation, impact and mechanism, Ningxia