It is of great significance to investigate the characteristics and underlying mechanisms of regional persistent high-temperature processes, as this can help to extract predictive indicators and provide theoretical references for short-term climate forecasting. Based on daily maximum temperature data from 122 national meteorological stations in Shandong Province in June from 1979 to 2023, a regional persistent high-temperature index (RPH) is constructed to reflect the changing characteristics of persistent high-temperature processes in June. Furthermore, ERA5 reanalysis data for June over the same period are used to analyze the relationship between RPH and large-scale background fields, including atmospheric circulation and sea surface temperature (SST), with a particular focus on North Atlantic SST anomalies. The main results are as follows: The regional persistent high-temperature processes in Shandong in June exhibit significant interannual variability and a linear upward trend, with both frequency and intensity increasing notably after 2000. In typical strong RPH years, a pronounced “+-+-” wave train pattern appears at the 500 hPa geopotential height anomaly field over the mid-high latitudes, accompanied by a corresponding “+-+-” pattern at the 850 hPa temperature anomaly field. There is a significant positive correlation between the North Atlantic Tripole (NAT) SST anomaly pattern and the June RPH. The Eurasian wave train excited by the negative phase of NAT closely resembles the pattern observed during typical strong high-temperature years. During NAT negative-phase years, upward energy propagation from the lower to upper troposphere and eastward wave activity fluxes result in significant energy convergence over Shandong. This supports the maintenance of a positive geopotential height anomaly. Under such conditions, enhanced subsidence and adiabatic warming, along with increased solar radiation due to reduced cloud cover, facilitate the development of persistent high-temperature processes.

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.