High temperature weather occurs frequently in Shandong Province. Studying the variation law of different high temperature indexes and their circulation background is conducive to better defense against the adverse effects of high temperature weather. Based on the daily meteorological observation data of daily maximum temperature, daily minimum temperature and relative humidity of 122 national meteorological stations in Shandong Province from 1981 to 2022, the variation characteristics of high temperature weather in Shandong Province were studied by analyzing the annual maximum temperature, high temperature days, warm night days, and high temperature heat wave days, and the circulation situations of typical high temperature heat wave processes were analyzed. The results show that high temperature weather mainly occurs in the central and western regions of Shandong, and less in the peninsula area. The annual maximum temperature is higher in the west and lower in the east, and high temperature days, warm night days and high temperature heat wave days are characterize by the distribution of more in the west and less in the east. The annual maximum temperature, high temperature days, warm night days and high temperature heat wave days with different grades in Shandong Province show an increasing trend, and the increase range is larger in the west and smaller in the east. The increase range of annual high temperature heat wave days with different grades is mild, moderate and severe in descending order. The wet type high temperature heat wave weather is dominant and shows a significant increasing trend. When there is an obvious circulation situation of “two ridges and two troughs” or “two ridges and one trough” in the middle and high latitudes, it is prone to high temperature and heat wave weathers in Shandong Province, and the subtropical high pressure over the northwest Pacific Ocean is abnormally strong and northerly, and the downdraft under continuous fine weathers causes the temperature to rise and high temperature persist.

Based on daily temperature data from 122 national meteorological stations in Shandong Province from 1961 to 2018, three extreme low temperature indices were calculated, and it was found that the occurrence frequency of extremely low temperature events defined by the scale of drop in daily minimum temperature in 24 hours could better reflect the characteristics of extremely low temperature in spring in Shandong. And on this basis, ERA-Interim monthly reanalysis data and Hadley sea surface temperature data were used to analyze the spatial and temporal distribution characteristics of occurrence frequency of extremely low temperature events in spring in Shandong and the anomalous characteristics of atmospheric circulation. The results are as follows: (1) The occurrence frequency of extremely low temperature events had multi-time scale variation characteristics in spring in Shandong. (2) The obvious wave train structure on 500 hPa geopotential height field was existed in mid-high latitudes in the typical extreme low temperature years in spring in Shandong. (3) The North Atlantic Ocean to the south of Greenland was a key area for vertical wave flux transmission. In this key area, the energy in the lower layer transmitted upward, and dispersed outward in the upper layer, which was beneficial to the maintenance and enhancement of the extremely low temperature in spring in Shandong. (4) The triple pole mode of sea surface temperature in the North Atlantic in the preceding winter had a significant positive correlation with the occurrence frequency of extremely low temperature events in spring in Shandong. The triple pole mode of sea surface temperature excited the Eurasian wave, which led to the deepening and strengthening of 500 hPa trough over the Lake Baikal area. Due to the influence of cold air behind the trough, the extremely low temperature events occurred frequently in spring in Shandong.