9. The influence of easterly waves on rainfall in Central Vietnam

Minh Thái Thị Thanh, Tâm Lê Thị Thanh, Liên Thái Thị Mai

Abstract

Easterly waves are wavelike disturbances in tropical easterly winds, related to the northward movement of western Pacific subtropical high pressure. Rainfall of the central Viet Nam is affected by easterly waves. The data used for this study are the NCEP/NCAR reanalysis for 2006-2014 and the rainfall data of 13 meteorological stations. We consider only the April-November period. Most easterly waves often form between 500 mb and 200 mb, the waves tend to be strongest at 300 mb and 200 mb. Sometimes, the waves of the strong intensity can extend down to 700 mb. Easterly waves tend to form between 10°N and 20°N. Waves generally tilt eastwardly. The orientation of composite wave's axis can shift to northeast - southwest. Winds are generally from the NE ahead of axis and SE behind the axis. Easterly waves havethe inverted V shape.  When the inverted "V" shape occurs clearly in the low-level, it will rain more heavily than the upper level. Convergence occurs ahead of the wave axis with the value from 0 to 2 (s-1), while behind the wave axis we see divergence with the value from 0 to -1(s-1). The waves have a duration of 2-4 days or 4-6 days when combined with cold air in the low-level. Rainfall affected by easterly waves are varied in different regions of the central Viet Nam; in July and August, it rains in the north and middle of Central Vietnam, from September to November, rainfall occurs in the middle and south of central Viet Nam. In particular, it rains the most in the middle of central Viet Nam. The average rainfall affected by independent waves is about 20 mm and reaches 60mm with the highest wave's intensity. When combined with cold air in the low-level, easterly wave can cause heavy rain in the middle and south of central Viet Nam with average rainfall from 100 to 250 mm.

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Authors

Minh Thái Thị Thanh
tttminh@hunre.edu.vn (Primary Contact)
Tâm Lê Thị Thanh
Liên Thái Thị Mai
Thái Thị Thanh, M., Lê Thị Thanh, T., & Thái Thị Mai, L. (2017). 9. The influence of easterly waves on rainfall in Central Vietnam. Science Journal of Natural Resources and Environment, (18), 74–84. Retrieved from https://tapchikhtnmt.hunre.edu.vn/index.php/tapchikhtnmt/article/view/62
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