Search

Persistent extreme heat events (PEHEs) exert a more negative impact on society, including agriculture, plant phenology, power production and human health, compared to general EHEs. The temporal and spatial characteristics of summer PEHEs in eastern China were analysed based on a daily maximum temperature dataset from 759 stations over the period of 1961–2018. The results show the following: Persistent distributions of PEHEs show that they are characterized by an exponential decay with a drop in the decay rate. In terms of spatial distribution, there is an apparent regional difference in the duration of PEHEs. North China is dominated by multi-frequency and short-duration EHEs, while South China is the opposite. PEHEs in North China and the Huanghuai region mainly occur in June-July but mostly in July and August in South China. Strongly responding to global warming, the frequency and duration of PEHEs in North China have increased since the 1990s. However, the frequency of PEHEs in North China and the Huanghuai region has shown opposite trends in June-July since the beginning of the twenty-first century. Affected by the atmospheric circulations, the regional differences in PEHE frequency are also apparent. Since the beginning of the twenty-first century, the PEHEs in North China and the Huanghuai area have shown an increasing trend in August. The short-term PEHEs in the middle and lower reaches of the Yangtze River and South China increased rapidly in the 2000s, while long-term PEHEs increased in the 2010s. This study implies that attention should be paid to not only the frequency of EH days but also to the persistence of EHE which is a key characteristic of damaging EH. [ABSTRACT FROM AUTHOR]

We analyzed the anomalous characteristics of autumn rain in western China (ARWC) (26.2–36° N, 101.9–111.8° E) in 2017 and the related large-scale atmospheric circulations based on new monitoring indicators published by the China Meteorological Administration in 2015 and the National Center for Environmental Prediction reanalysis data. We found that the characteristics of autumn rain in the southern (33–36° N, 101.9–111.8° E) and northern (26.2–33° N, 101.9–111.8° E) regions of the monitoring area were different. The onset date of autumn rain in the north (south) of the monitoring area in 2017 was 14 (16) days earlier than in normal years, which is in the 4th (4th) place since 1961. The end of the autumn rain was 5 days later (earlier) than in normal years. The autumn rain period was 54 (63) days long, 19 (11) days longer than in normal years. The autumn rainfall in the north (south) of the monitoring area was 234.1 (322.2) mm, 72.6% (74.4%) higher than that in normal years. The amount of autumn rain in the southern region is in the second place since 1965. The cause of this significantly early onset of the ARWC in 2017 was the advanced transition of the East Asian atmospheric circulation system from a summer pattern to a winter pattern. The westerly jet in the upper troposphere appeared about 10 days earlier than in normal years. The meridional circulation of a west-high and east-low pattern was observed in the mid- and lower troposphere in the mid- and high latitudes of Eurasia. This circulation configuration resulted in an early onset of the ARWC. As a result of the influence of the persistent warming of the Indian Ocean basin-wide mode from spring to summer, the west Pacific subtropical high was extremely strong (the second strongest since 1981) and its westernmost point was greatly extended to the west (the second greatest extension since 1981) during the autumn rain period. The intensity of the moisture flux from the southwest of the western Pacific subtropical high was stronger than usual and the low trough of Lake Baikal was also strong. Cold air from the north and the abundant warm, humid water vapor from the south converged in western China, resulting in more precipitation during the autumn rain period. [ABSTRACT FROM AUTHOR]

In this study, the simultaneous atmospheric circulation system configuration characteristics of the four rainfall patterns (FRP) over the East China during the period 1951–2015 are analyzed in order to investigate their formation mechanisms. The results confirm that the FRP possess obvious differences in the upper-level, middle-level, and lower-level troposphere. In northern China rainfall pattern (NCP) years, the East Asian subtropical westerly jet stream (EAJS) shows a northward trend, with a higher intensity than normal; the blocking high (BH) in the mid-high latitudes is inactive; and the western Pacific subtropical high (WPSH) tends to be stronger, with a location to the north of its normal position. The East Asian summer monsoon (EASM) is stronger, which promotes vapor transport to northern China, and this leads to increased rainfall. In intermediate rainfall pattern (IRP) years, the EAJS position is close to that in normal years; the BH is inactive; the WPSH tends to be weaker, with a location to the east of its normal position; and the EASM is stronger, which is conducive to increased rainfall over the Huaihe River Basin. In Yangtze River rainfall pattern (YRP) years, the circulations are found to be almost opposite in their features to those in NCP years. In South China rainfall pattern (SCP) years, the circulations are found to be almost opposite in their features to those in IRP years. This leads to increased rainfall over South China. Therefore, the different circulation system configuration characteristics lead to the different rainfall patterns. [ABSTRACT FROM AUTHOR]