Search

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]

In this study, the summer rainfall patterns in the East China monsoon region during 1951-2015 were objectively classified into four typical categories: the northern China rainfall pattern (NCP), the intermediate rainfall pattern (IRP), the Yangtze River rainfall pattern (YRP), and the South China rainfall pattern (SCP). The periods of the four patterns show significant decadal characteristics. The NCP occurred mainly between the late 1950s and the early 1980s, and the IRP in the late 1950s to the early 1970s and the 2000s. The YRP occurred mainly between the 1980s and the 1990s, and the SCP between the mid-1990s and the early 21st century. The relationship between the East Asian summer monsoon index (EASM I ) and the four rainfall patterns was comparatively analyzed. The results confirmed that the four rainfall patterns have obvious differences in the EASM. In the NCP, IRP, or SCP years, the EASM I primarily showed a positive phase and a strong summer monsoon; in the YRP years, the EASM I primarily showed a negative phase and a weak summer monsoon. [ABSTRACT FROM AUTHOR]