[A-AS03] Extreme Events and Mesoscale Weather: Observations and Modeling

[AAS03-P08] Frequency variation of winter low-temperature events in Guangxi, China and its response to Atlantic sea surface temperature from 1951 to 2020

*Xiuhua ZHOU¹, Yi TANG², Hong LU¹ (1.Guangxi Meteorological Bureau, China, 2.Guilin Meteorological Bureau, China)

Keywords:low temperature Frequency, interannual and interdecadal variation, East Asian winter monsoon, Atlantic sea surface temperature anomaly

Using the daily average temperature data of 92 national surface meteorological stations in Guangxi, China, and continuing the previous work, the frequency of low temperature at a single station is counted with 4 ℃ as the low temperature threshold. The results show that the interannual and interdecadal variation characteristics of the frequency of winter low temperature events in Guangxi, China, from 1951 to 2020 are clear. In the early 1960s, it experienced a significant shift from less to more, while in the mid-1980s, it experienced a change from less to less. The period with more frequency appeared from the mid-1960s to the late 1980s, and turned to less from the 1990s to the early 21st century. However, after the 2000s, there were extreme years with abnormally high frequency, such as 2008 and 2011, which made the overall frequency of low-temperature events contributed a weakly increasing trend. The frequency of low temperature in Guangxi, China, has an interannual cycle of 2-5-year and an interdecadal cycle of about 10-year. Before 1990, the frequency change was generated by the superposition of these two main cycles, and then exhibited decaying periodic signals until the re-emergence of 2-5-year cycles post-2005.
It is found that during years with more frequent low-temperature events, significant anomalies in monsoon circulation occur, including an intensified East Asian Trough, a strengthened Siberian High, and anomalous low-level northerly winds over northern China. These factors are closely associated with the strength of the East Asian winter monsoon, which reveals that the stronger East Asian winter monsoon is conducive to the increase of the frequency of low temperatures in Guangxi, China. Previous studies also show that the East Asian winter monsoon is closely related to the interannual and interdecadal changes of extreme low temperature events in China. Furthermore, abnormally low sea surface temperatures in the Atlantic Ocean, west of Europe, have triggered Eurasian (EU) pattern circulation anomalies in the mid-to-high latitudes of Europe and Asia, resulting in a negative height anomaly over China. Sea surface temperature anomalies in the North Atlantic region may influence high-frequency transient vortices in the area, subsequently affecting downstream Eurasian circulation anomalies through the dispersion of wave energy from upstream to downstream. These abnormally low sea surface temperatures in the Atlantic, combined with circulation anomalies caused by air-sea interactions, are possible drivers of significantly low temperatures and the abnormal increase in the frequency of low-temperature events in Guangxi, China.