Abstract
In this study, the large-scale circulation patterns (a blocking high, wave trains and the western Pacific subtropical high (WPSH)) associated with a wide ranging and highly intense long-lived heatwave in China during the summer of 2018 are examined using both observational data and reanalysis data. Four hot periods are extracted from the heatwave and these are related to anticyclones (hereafter referred to as heatwave anticyclone) over the hot region. Further analysis shows a relationship between the heatwave anticyclone and a synthesis of low, mid- and high latitude circulation systems. In the mid-high latitudes, a midlatitude wave train and a high latitude wave train are associated with a relay process which maintains the heatwave anticyclone. The midlatitude wave train acts during 16–21 July, whereas the high latitude wave train takes affect during 22–28 July. The transition between the two wave trains leads to the northward movement of the hot region. With the help of a wave flux analysis, it was found that both wave trains originate from the positive North Atlantic Oscillation (NAO+) which acts as an Atlantic wave source. Serving as a circulation background, the blocking situated over the Scandinavia-Ural sector is maintained for 18 days from 14 to 15 August, which is accompanied by the persistent wave trains and the heatwave anticyclone. Additionally, the abnormal northward movement of the WPSH and its combination with the high latitude wave train lead to the occurrence of extreme hot weather in north-eastern China occurring during the summer of 2018.
Highlights
Under a global warming background, more heatwaves with stronger intensities and longer durations are being observed around the world [1,2], including across China [3,4,5,6,7,8]
Because weather conditions are closely related to large-scale circulation [49], we mainly studied the contributions of different circulation patterns to the heatwave in this study
The high latitude wave train originating from the NAO+ over the North Atlantic contains a blocking high over the Scandinavia-Ural region with a duration of 18 days, which can be seen as a long-lived blocking event according to Luo et al [51]
Summary
Under a global warming background, more heatwaves with stronger intensities and longer durations are being observed around the world [1,2], including across China [3,4,5,6,7,8]. 41.1 ◦ C on 23 July in Kumagaya, Saitama (Japan Meteorological Agency, 2018) and South Korea had an all-time high temperature record of 40.7 ◦ C on 1 August in Hongcheon, Gangwon Province A blocking anticyclone was the most important circulation system for the Russian heatwave in the summer of 2010 [16] and the 2003 European heatwave was dominated by a persistent blocking high [29]. The mega-heatwave that occurred in Europe in July 2017 is characterized by a long-lasting subtropical high that favours the transport of warm air masses from the south [34]. Through composite analyses of four periods during the heatwave, we will see that a midlatitude wave train, a high latitude wave train and the northward movement of the WPSH are the three dominant circulation patterns.
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