Under the background of global warming, the extreme high-temperature events become more frequent in recent years. During July-September in 2024, Zhejiang Province experienced a record-breaking high temperature event. The average high-temperature days there were 46 days, and the return period of this extreme high temperature event reached 82 years. Based on the observation data from the national meteorological stations in Zhejiang Province, High Resolution China Meteorological Administration Land Data Assimilation System (HRCLDAS), sea surface temperature from National Oceanic and Atmospheric Administration (NOAA), and reanalysis data from European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5), this study explored the atmospheric circulation background and the role of sea surface temperature over the North Atlantic by using the statistical analysis and dynamic diagnosis. The results are listed as below: (1) The enhancement and westward displacement of the western Pacific subtropical high, together with the strengthening and eastward movement of the South Asian high, lead to the persistent descending over Zhejiang Province, resulting in the decrease of in-situ cloud cover. The associated adiabatic warming and radiation warming contribute to the high temperature. (2) The tropical North Atlantic plays a key role. The anomalous warming of sea surface temperature over the tropical North Atlantic during the preceding April-June influences the atmospheric circulation over the region from East Asia to the western Pacific through the atmospheric teleconnection, inducing the enhancements of western Pacific subtropical high and South Asian high, thus the extreme high temperature in Zhejiang Province. (3) Decreased meridional circulation inhibit the southward movement of cold air. Meanwhile, the typhoons affecting Zhejiang Province were fewer than the climatology, and the associated precipitation anomalies couldn’t relief high temperature.
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.
Under the background of global change, extreme high-temperature events have occurred frequently, and their frequency has increased significantly since the 21st century, which has a profound impact on agricultural production and human health. To explore the spatiotemporal evolution patterns of extreme high temperatures in the Yili River Basin with complex terrain, this study calculated six extreme high-temperature indices, namely summer days (SU25), hot night days (TR20), warm days (TX90p), warm nights (TN90p), extreme maximum value of daily maximum temperature (TXx), and extreme maximum value of daily minimum temperature (TNx), based on daily temperature data from 11 meteorological stations in the basin during 1991-2020. Through linear trend analysis, Mann-Kendall abrupt change test, Empirical Orthogonal Function (EOF) decomposition, and Kriging interpolation method, the spatiotemporal variation characteristics of these six extreme high-temperature indices in the Yili River Basin were systematically analyzed. The results show that most extreme high-temperature indices in the Yili River Basin have exhibited an overall rapid growth trend and underwent significant abrupt changes from the 1990s to the early 21st century. Among them, the growth rates of SU25, TX90p, TXx, and TNx are particularly prominent, and all indices entered an accelerated growth stage after 2015. In terms of spatial distribution, most extreme high-temperature indices in the basin present an obvious pattern of “high in the northwest and low in the southeast”: the northwest region is a high-value area for high-temperature indices, while stable low-value centers are formed in the northeast of Zhaosu, Tekes, Gongliu, and the southwest of Nileke. Through EOF decomposition, the spatial distributions of TXx and TNx exhibit two typical modes, and their evolution characteristics are highly consistent with the overall variation trend of extreme high temperatures in the basin.
Based on daily maximum temperature observations from 54 national meteorological stations in Liaoning during 1961-2023 and reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), this study objectively identifies regional high temperature processes using established criteria, analyzes their spatiotemporal characteristics, and classifies the associated large-scale circulation patterns. A total of 24 regional high temperature events were identified during the study period, primarily affecting western Liaoning. The largest event impacted up to 55.56% of all stations. These events occurred between late May and mid-August, with mid-June showing the highest frequency. Most events lasted 3-4 days, accounting for 75% of the total. The frequency and spatial extent of regional high temperature events varied across decades, with fewer and less extensive events from the 1960s to the 1980s, and a notable increase in both frequency and coverage since the 1990s. Two primary circulation patterns were identified: warm high pressure ridge pattern (21 events) and zonal circulation pattern (3 events). In early and mid-summer, the warm high pressure ridge pattern dominated. In mid-summer, the frequency of the zonal circulation pattern increased with the northward shift of the Western Pacific subtropical high.