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.
Full text article
2. Carlson T.N (1969a), Synoptic histories of three African disturbances that developed into Atlantic hurricane, Mon. Wea. Rev, Vol 97, pp.256-276.
3. Carlson T.N (1969b). Some remarks on African disturbances and their progress over the tropical Atlantic, Mon. Wea. Rev, Vol 97, pp. 716-726.
4. TC Chen, Shin-Yu Wang, A. J Clark (2008), North Atlantic Hurricanes Contributed by African Easterly Waves North and South of the African Easterly Jet, Journal of Climate.
5. Dunn G. E (1940), Cyclogenesis in the Tropical Atlantic, Bulletin of the American Meteorological Society, No. 6, Vol. 21, June 1940, pp. 215-229.
6. Diedhiou A., S. Janicot, A. Viltard, P. de Felice, and H. Laurent (1999), Easterly wave regimes and associated convection over West Africa and the tropical Atlantic: Results from NCEP/NCAR and ECMWF reanalyses. Climate Dyn, Vol 15, pp.795-822.
7. Đặc điểm khí tượng thủy văn các năm 2006, 2007, 2008, 2009, 2010,2011, 2012, 2013, 2014, 2015, Trung tâm Khí tượng Thủy văn Quốc gia, Trung tâm Dự báo Khí tượng Thủy văn Trung ương.
8. Frank N. L (1969), The "Inverted V" cloud pattern - an easterly wave, Mon. Wea. Rev, Vol 97, pp. 130-140.
9. Grist J. (2002), Easterly waves over Africa. Part I: The seasonal cycle and contrasts between wet and dry years, Mon. Wea. Rev, Vol 130, pp. 197-211.
10. Nguyễn Văn Hưởng (2012), Xác định khách quan thời tiết trong các đợt mưa lớn trên khu vực miền Trung từ số liệu tái phân tích JRA25, Luận văn thạc sỹ.
11. Kiladis, G. N., C. D. Thorncroft, and N. G. Hall (2006), Three dimensional structure and dynamics of the African easterly waves, Part II: Observations, J. Atmos. Sci, Vol 63, pp. 2212-2230.
12. Reed, R. J., and E. E. Recker (1971), Structure and properties of synoptic-scale wave disturbances in the equatorial western Pacific. J. Atmos. Sci., Vol 28, pp.1117-1133.
13. Reed, R., D. Norquist, and E. Recker (1977), The structure and properties of African wave disturbances as observed during phase III of GATE, Mon. Wea. Rev, Vol 105, pp. 413-420.
14. Riehl H. (1945), Waves in the easterlies, Univ. of Chicago Misc. Report No. 17, Vol 79.
15. Riehl H. (1965), Varying structure of waves in the easterlies. Proc. Intern. Symp. on Dynamics of Large-Scale Processes. Moscow, pp. 411-416.
16. Thorncroft, C. D. and K. Hodges (2001), African easterly wave variability and its relationship to Atlantic tropical cyclone activity, J. Climate, Vol 14, pp.1166–1179.
17. Nguyễn Khanh Vân, Bùi Minh Tăng (2004), Đặc điểm hình thế thời tiết gây mưa, lũ, lụt lớn ở các tỉnh Thanh Hóa, Nghệ An, Hà Tĩnh thời kỳ 1997-2001, Tạp chí Khoa học Trái đất, 26(1), Trang 50-59.
18. Zawislak, J. and E. J. Zipser (2010), Observations of seven African easterly waves in the East Atlantic during 2006, J. Atmos. Sci, Vol 67, pp. 26-43.