University of Tehran Press Journal of the Earth and Space Physics 2538-371X 46 4 2021 01 20 Multiple-Scale Interactions during an Extreme Rainfall Event over Southern Vietnam Multiple-Scale Interactions during an Extreme Rainfall Event over Southern Vietnam 259 271 79565 10.22059/jesphys.2021.303443.1007215 FA Vu Van Thang Ph.D., Vietnam Institute of Meteorology, Hydrology and Climate Change, Hanoi, Vietnam Cong Thanh Instructor, Department of Meteorology and Climate change, Faculty of Meteorology, Hydrology and Oceanography, Hanoi University of Science, Vietnam National University, Hanoi, Vietnam Bui Minh Tuan Instructor, Department of Meteorology and Climate change, Faculty of Meteorology, Hydrology and Oceanography, Hanoi University of Science, Vietnam National University, Hanoi, Vietnam Journal Article 2020 05 27 In August 2019, southern Vietnam suffered its worst flooding to date, which was also associated with record-breaking extreme rainfall. This study seeks to explain how this extreme rainfall event can be distinguished from normal rainfall events. The bandpass filter applied to the observed rainfall shows that there were significant intensifications of 3–10-day variation and 11–60-day oscillations during the event. While the latter is characterized by the intensification of westerly flows from the Bay of Bengal to southern Vietnam, the former is related to more complex movements of a series of synoptic-scale disturbances over the western North Pacific. The notion of multiple-scale interactions, inducing the extreme rainfall event is supported by diagnosing the anomalous columnwise moisture divergence over the southern plain region of Vietnam. It is demonstrated that the anomalous convergences associated with the long-term mean moisture and the synoptic-scale moisture transported by the long-term mean flow are the most important factors for formation of the extreme rainfall event. In August 2019, southern Vietnam suffered its worst flooding to date, which was also associated with record-breaking extreme rainfall. This study seeks to explain how this extreme rainfall event can be distinguished from normal rainfall events. The bandpass filter applied to the observed rainfall shows that there were significant intensifications of 3–10-day variation and 11–60-day oscillations during the event. While the latter is characterized by the intensification of westerly flows from the Bay of Bengal to southern Vietnam, the former is related to more complex movements of a series of synoptic-scale disturbances over the western North Pacific. The notion of multiple-scale interactions, inducing the extreme rainfall event is supported by diagnosing the anomalous columnwise moisture divergence over the southern plain region of Vietnam. It is demonstrated that the anomalous convergences associated with the long-term mean moisture and the synoptic-scale moisture transported by the long-term mean flow are the most important factors for formation of the extreme rainfall event. https://jesphys.ut.ac.ir/article_79565_3630bdb83f02ab643c001f08c9e9c1df.pdf