Extreme high‐temperature event in southern China in 2016 and the possible role of cross‐equatorial flows

• Published in: International journal of climatology 2018-07, Vol.38 (9), p.3579-3594
• Main Authors: Ding, Ting, Gao, Hui, Li, Weijing
• Format: Article
• Language: English
• Subjects: Climatology; Correlation analysis; cross‐equatorial flow; El Nino; El Nino events; El Nino phenomena; extreme high‐temperature event; Flow; Madden-Julian oscillation; Maximum temperatures; Oceans; River valleys; Rivers; South Asian High; southern China; Summer; Temperature; Temperature effects; Tropical climate; Westerly flow; westerly flow over the tropical Indian Ocean; western Pacific subtropical high; Zonal winds
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.5518

An extreme high‐temperature (HT) event occurred in China in the summer of 2016. Northwestern and southern China experienced more than 20 HT days with a daily maximum temperature (DMT) greater than 35 °C. Compared with the average local climatology, southern China experienced 10–15 more HT days with temperatures greater than 35 °C and 5–10 more HT days with temperatures greater than 38 °C. The extreme HT event in 2016 in southern China began on July 20, responding to the end of the Chinese Mei‐yu in the region. The HT event lasted for approximately 2 weeks until August 2. The western Pacific subtropical high (WPSH) in the summer of 2016 was much stronger and more westwards than normal owing to a strong El Niño event. During the HT period, the WPSH shifted further westwards. Its western boundary reached 106°E, and it covered most parts of southern China. It was more westwards than its average position during the 1981–2010 reference period and the previous Mei‐yu period. The high experienced a notable shift northwards covering all regions south of the Yangtze River valley. The South Asian high moved eastwards covering the East Asian continent. Thus, the upwards flow at the lower tropospheric levels over southern China in the previous period was replaced by a much stronger downwards flow. The Chinese Mei‐yu ended and southern China therefore entered a dry and hot period. During the HT period, the Somalia cross‐equatorial flow (CEF), the Bay of Bengal (BOB) CEF, and the westerly flow over the tropical Indian Ocean weakened clearly. Lag correlation analyses indicate that the WPSH had a close relationship with zonal wind over the ocean. This suggests that the westwards extension of the subtropical high corresponding to the HT event was caused mainly by the weakening of the CEFs and the westerly flow over the tropical Indian Ocean. Case of 2017 HT event and composed circulations of 28 HT cases since 1981 also supported this result. In August 2016, the MJO was much active over the western Pacific, which weakened the WPSH and finally ended the extreme HT event. An extreme high‐temperature (HT) event occurred in China in the summer of 2016. The westwards extension of the subtropical high corresponding to the HT event was caused mainly by the weakening of the CEFs and the westerly flow over the tropical Indian Ocean. Sketch maps of circulation changes before (a) and during (b) the extreme HT period.