Abstract:

Based on the ground temperature from 20 meteorological stations in Ningxia Province, China since 1961 and the monthly geopotential height field data of NCEP/NCAR, the latest climatic evolution characteristics of the first frost date in Ningxia and the influence of circulation anomalies have been studied. The results are as follows. (1) The first frost date in Ningxia present the spatial distribution characteristics of “southern early and north late”. The loess hilly area is the earliest, followed by middle arid region, and the latest occurrence in irrigation region. This is consistent with the “low south and high north” distribution pattern in the daily average minimum temperature. Tongxin in the middle arid region and Shizuishan, Helan, and Wuzhong in the irrigation region are the latest in the entire region, and Longde in loess hilly area is the earliest. (2) The date of the first frost in Ningxia is significantly different before and after global warming. Compared with the climatic average (1981—2010), the first frost date before warming (1961—1980) is earlier, appearing on average in late September and seven days earlier on average everywhere. After warming (1981—2019) is late, on average in early October, on average two days later, and five days later, on average after 2000. (3) Since 1961, the first frost in Ningxia first occurred in early and mid-September in the 1960s and 1970s. The latest occurred in early November and late October after 2000. The linear trend of the first frost date is 3.0 d·(10a)^-1, of which irrigation area with 3.2 d·(10a)^-1 is the most prominent, and middle arid region; the southern mountain area are the second place, with 2.6 d·(10a)^-1 and 2.7 d·(10a)^-1. However, under the background of climatic warming, the first frost has been abnormally early in recent years. The early probability of three partitions since 2000 is 15%, 25%, and 30%. (4) There are significant interdecadal and inter-annual differences in the high, middle, and low atmospheric circulations between the early and late years of the first frost in Ningxia, and spatial distribution of the early years is opposite to that in the late years. When the first frost date was earlier (late), the East Asian trough was stronger (weaker) than usual; the Siberian high was stronger (weaker); the western Pacific subtropical high was weaker (stronger), and cold air was active (inactive).

Key words: data of first frost, climate change, linear trend, atmospheric circulation anomaly