ÑAËC ÑIEÅm muøa möA ÔÛ khu vöÏc nam boä
tải về 1.08 Mb.
|
- Điều hướng trang này:
- Heavy rain in South Vietnam by
- 1/ Introduction
I. INTRODUCTIONVietnam is narrow in width and stretches more than 1600km from north to south. All of Vietnam is impacted of monsoon, the northeast monsoon during the winter and the southwest monsoon during the summer. South Vietnam is one of main plain of this country, it is largest and strengthen from 8 to 12 north latitude with the wide Mekong River Delta, and also is the largest rice-producing area in Vietnam. In general, the climate of South Vietnam there is dry and wet seasons deeply conflict, correspond to two monsoons prevailing over the region. The studying show that the onset and withdraw of the rainy season and the progress of weather during the rainy season, the rainfall of the summer depend on the onset and withdraw of summer monsoon and its intensity. The information about the arrival date of monsoon will be helpful to the public. However, the problem of forecasting the march of foreward edge of the southwest monsoon is difficult because the starting mechanism has not been completely understood so far. In 1999, the weather of South Vietnam was changeable. The onset of wet season was early, monthly rainfalls were over normal, heavy rain and drought were alternate to each other, contracted the humid and wet regime in the large area clearly. Especially, three were the raingust during about 3-4 days caused the serious flast flood in the records in some river system of region. On the other hand, the activity of southwest monsoon was also very special, strong winds prevailing over the region in the long time, and two breaks of monsoon caused drought almost the region. For that reason, from the fact that in the practice of weather forecasting in the South Vietnam, there are the requirement we must be studying and analyse the mechanism of influence and to define the onset of the rainy season which generally coincides with the southwest monsoon. That is very useful and necessary to forecast for the major portion of agriculture operation for the main crop of the year in the Mekong Delta. II. THE METHOD TO STUDY II.1 The criterion of the onset of wet season and summer monsoon: Following some meteorologist, the onset of summer rainy monsoon of South Vietnam defined base on rainfall data, as the date of 5mm or more than 50mm per 2 pentads; the meaning is over the loss by evaporation. Southwest monsoon over South Vietnam usually onset later than the onset of rainy season about one month. The mean date for onset of the southwest monsoon over Southeast Asia is 17 May, earliest is 1 May and latest is 3 June as shown by Orig. The studying shows that the onset of the southwest monsoon over South Vietnam is considered as the sub-tropical ridge retreat to eastward and over north of 16 o N. There is a replacement of the lower-troposphere trade wind by the equatorial westerlies originating in the Indian Ocean Base on the criterion for the onset day of wet season, southwest monsoon, raingust, strong monsoon, by synoptic analyze and statistics, we points out that the monsoon in the Southern of Vietnam has closely feature to that of the Southeast Asian monsoon. We compared that criterion with the data of the season of this year, and analyzed the wind fields, synoptic situation to make clear the correlation and mechanism how the southwest monsoon impacts to the weather of South Vietnam in 1999. As mentioned by Riehl, the change from easterlies trade to equatorial westerlies is not always clear, and the rainfall can not be used to define the monsoon because the amount of rainfall in the pre-monsoon is similar with the monsoon rainfall. 2.2 The activity of summer monsoon and weather processes over South VN in 1999 2.2.1 The onset of rainy season and southwest monsoon: The synoptic conditions associated with monsoon onset were analyzed including surface pressure, wind fields and geopotiential heights at 850, 700, 500-hPa level Because of the effect by La-Nina, the dry seasons from middle of December to March, the rainfall always over normal. From 20-25 March, easterlies on the upper troposphere l was decreased, equatorial trough moves to the north hemisphere and overlies on 3-4 N latitude. There was a transition period from dry to wet season with more than a haft station had rainfall about 20 -30mm per 5 days. After only some days, the rainy season begins in the coast and islands first (27 March), and almost region from 29 March. The weather changed to wet season from late March. , And rainy onset in all of region was earlier than mean onset date of wet season about one and a haft month, earlier than 1998 more than two months. (1998 was affected by strong El-Nino phenomenon)
On 21 April, there is an anticyclone on 500hPa level with two closed iso geopotential heights (592 and 596 hPa) located over India – Myanma region, ITCZ moves northward rapidly and stays over 8 - 10 oN. The next day the Southwest winds prevailing over South Vietnam from surface up to 500-hPa level. We can see the strong SW wind speeds on 1500m about 5 –10m/s, some areas 15m/s. the weather changes to severe rain, thunderstorm and gust winds continuously. The onset of monsoon is 21 April, earlier than mean onset date about one month, and later than the onset of rainy season one month. The weather of South Vietnam is severe rain, thunderstorm and strong winds, special along the western coast and north provinces. Late April, Southwest monsoon decrease, there are an air mass from China moves southward to North Vietnam and extends over BienDoâng Sea, and ITCZ weak and moves southward. 2.2.2 Strong Southwest monsoon stages: To compare with some recent years, in 1999 the summer monsoon actives very strong during the period May to September, its is unusually. South Vietnam receives about 900 –95% precipitation from the moist SW winds, monthly rainfalls are always over normal. After the onset, SW wind is weak up to 15 May; the wind directions change to Southeast. On 18 May, the ITCZ moves north and jumps to 10 oN, Pacific subtropical ridge retreat to east and thus the Southwest monsoon is established over South Vietnam. It prevails from surface up to 3000m. The weather changes suddenly to heavy rain whole region one day after. During the period May to September, we can define five main strong Southwest monsoon stages, special from late July to early August because of strong monsoon accompanied by tropical depression is located over south BienDong sea, there is a heavy rain of records, which causes a serious flash flood over BinhThuan, DongNai provinces With surface - wind speeds from 15 to 20 m/s, special 20 -30 m/s and very strong at the upper levels.
First June, at 850 to 700 hPa levels, there are strong Southwest winds, the speed is 15 –22m/s and persist one week after. At 500 hPa level wind speed is 5-10m/s. At surface, strong winds flow over whole region during 5-7 days with max winds are 27m/s at Camau, 25m/s at Condao, 20m/s at Soctrang… The weather rains continuously, some places receive big rainfall. After that, the SW winds weak and the rainfall also decrease.
On 13 June, the ITCZ stays over South Vietnam; SW winds are strong again. But it only develops up to 850 and 700 hPa levels, at 500 hPa is easterlies. At surface, strong winds with max winds are 17m/s at Camau, 20m/s at Condao and Phuquoc, 17m/s at TSN… The rainfall increases. After that, the SW winds weak and the rainfall also decrease.
During 10 early days, SW winds is weak on the surface, On 11 July, from 850 to 700 hPa levels the Southwest winds increase 15 – 20m/s. At surface, strong winds flow over whole region during 5-7 days with max winds are 22m/s at Condao, 20m/s at Phuùquoác, 17 m/s at TSN… The weather heavy rains.
On 20 July, at 850 hPa level SW wind increase 12m/s, and from 22 July to 6 August strong SW winds prevailing over region from surface up to 500 hPa level, 15-22m/s at 3000m and 10 – 15 m/s at 6000m. At surface Condao 20m/s, Phuquoc 25m/s, TSN 17m/s, Rachgia 22m/s, Bachho 15-22m/s, some times 29m/s. During this period, ITCZ overlies central Vietnam. From 21 to 31 July severe weather over South Vietnam is severe with a big rainfall, causes flash flood suddenly. This is a symbolised strong Southwest monsoon of this year over South Vietnam.
After break, July, monsoon actives again, but not whole of region, it presents from surface up to3000m, Max wind on surface is 8 -10m/s , weather is rainy, mainly along the western coast. 2.2.3 Breaks of southwest monsoon: There are 2 breaks of monsoon on June and August when the Pacific subtropical ridge extends to westward, it make the ITCZ moved to the equator and dissapear. Almost South Vietnam is fair, no rain or very little rain during 8 – 10 days, from 20 to 27 June and from 7 to 15 August 3. APPLICATION TO FORECASTING AND SERVIVES 3.1 Methods for predicting The forecasting the onset of rainy season and the activity of monsoon is always the main subject for us. Statistical analysis of rainfall, wind speeds combines with synoptic situation is main method. We analysis on the surface and mainly on 500hPa and 700 hPa level, we try to find out the similar years to compare. Recent years we study the relation between El-Nino and La-Nina phenomenon with the activity of monsoon, ITCZ, subtropical ridge, tropical cyclones. In fact, we show that 1968 and 1989 have the best correlation with 1999.The relation between SOI Index with the activity of summer monsoon is clearly. Especially, 1998 and 1999 are the opposite of climate change because of effect by El Nino and La-Nina phenomena. We also consult the RAINMAN program of Australia to calculate the ability of outlook 3-month rainfall. 4. CONCLUSION The relation between Southern Oscillation Index with the activity of summuer monsoon and ITCZ, tropical cyclones and so on is clearly. Especially, 1998 and 1999 are the opposite of climate change because of effect by El Nino and La-Nina phenomena. In! 999 the weather is unnormal, the wet season begins so early lead the precipitation during the wet season is always over mean value. The conditions for onset of Southwest monsoon on South Vietnam are:
The onset of Southwest monsoon is critical for the start of agricultural operations for the main crop season of Mekong Delta. However, strong monsoon also causes severe weather as flash flood, thunderstorm, tornadoes and crumbling the coast of western (Camau, Kiengiang, and Cangio…) In 1999, the onset of rainy season is earlier than mean date one and a haft month, and onset of monsoon is also earlier than mean date about one month By mid June to August there are five strong monsoon periods, it causes severe flash flood, and there are two breaks of monsoon when subtropical ridge expands to westward and prevailing over BienDoâng sea and South Vietnam. The studying for the activity of Southwest monsoon is helpful and necessary for predicting, but it is difficult. HCM city, 1st November, 2004 Heavy rain in South Vietnam bySW monsoon and Tropical depressionLe Thi Xuan LanSouthern Regional Hydrometeorolorical Center ABSTRACT From 7-9 September, 2003 there was a tropical depression formed over central of BienDong Sea, moved westward and landed to NgheAn province in 9 September, 2003. After that the typhoon MAEMI (0314) over east Philippines moved to East Chine Sea. SW monsoon very strong prevailing over south BienDong Sea and South Vietnam during 7 -13 September. The weather of South Vietnam is heavy rain during a week from 8 to 13 September of convective rainstorms, but the heavy rain areas moved from south to north following the moving of typhoon. By synoptic analyzes and numerical models, we predicted the heavy rain areas almost exactly 1/ Introduction:South Vietnam is located in the equatorial tropical monsoon climatic zone with the two contrast seasons: dry season and rainy season affected by winter monsoon (NE) and summer monsoon (SW) respectively. In rainy season, the major circulations cause heavy rain over the large region in South Vietnam is SW monsoon combines with tropical cyclone activities over BienDong Sea. Statistically, the heavy precipitation produced by SW monsoon is closely related to the existence of a low pressure in the low level and a southwesterly flow located between 700 - 500 hPa. The tropical cyclone (Tc) activity over Bien Dong Sea that it plays a center to attract of the wind convection causes SW winds become stronger. Thus, SW monsoon with tropical cyclone has been an interesting and important topic because of its relationship with heavy rainfall. The intensity of rain gust depended on the position, intensity and that track of cyclone and southwesterly wind velocity. The objective of this paper is to examine the mechanisms responsible for the development of SW monsoon with the activity of cyclone over Bien Dong Sea in the lower troposphere. We have chosen to examine the actual event of 8-13 September. In section 2, a brief overview of weather during this period is given. In section 3, the results from synoptic analysis associated with numerical modeling with satellite images analyzing, show that the forecasting is acceptable. 2/ Overview of synoptic situation: 8 -13 September During 8-13 September 2003, heavy rainfall with rate of 60-130mm/day, especially 250-280mm/day occurred over the eastern plain (nearby the mountains) and 40-80mm/day over western of Mekong Delta (nearby the west- coastal) of South Vietnam... This weather system was characterized by the SW monsoon with a tropical depression over north Biendong Sea moving westward; it landed to Nghe Tinh province (17-18oN) in 9 September. Meanwhile, a typhoon over West Pacific ocean named MAEMI (0314) moved westnorthwest from 7 to 12 September, both of them lay on ITCZ. That is the reason why SW monsoon very strong prevailing over south BienDong sea and South Vietnam during 7 -13 September. When the ITCZ followed the position of typhoon MAEMI moved to northward. The weather of South Vietnam is heavy rain during a week from 8 to 13 September of convective rainstorms, but the heavy rain areas also moved from south to north part of South Vietnam. During this period, a deep west – east – southeast Intertropical Convergence Zone developed at upper level over central BienDong sea, beyond it is the sub-tropical high (west Pacific high) ridge lies along 27oN, extended from south Japan to central of China . Although the weather event lasted from 7 to 14 September, but this paper concentrates on the most intense mesoscale convection that occurred during the period of 12-13 September, 2003. Figures showing the 500 hPa and 850-hPa analyses from 0000 UTC 12 September through 0000 UTC 13 September, reveals a ITCZ extending from central BienDong sea and SW winds convergence in the upper level. On the surface, a ridge of high pressure from equator moved to the north hemisphere. The development of SW winds was closely related to the activity of ITCZ in the north and ridge of high pressure in the south. Table 1 showed that SW winds became stronger right after Td forming over BienDong Sea. Table 1: Maximum wind velocity (m/s) at some stations
Rainstorm over Dong Nai from 12 to 13 September as: LongKhanh 284mm, XuanLoc: 243m5m, Ta Lai: 108mm, Tuc Trung –Tam Bung: 70-90mm caused flash flooding in Long Khanh, ThongNhat, and XuanLoc. SW winds was very strong, destroy a lot of houses. 3/ Forecast procedures:
1/ SW monsoon only a. Sea surface isobar at 13 LT- 06 July, 2002 b. Rainfall distribution over south Vietnam 2/ Onset of rainy season a. Sea surface isobar at 13 LT- 21 May, 1998 b. Streamlines at 500 hPa level 3/ Onset of SW monsoon a. Sea surface isobar at 07 LT- 12 May, 2002
4/ Typhoon Kammuri over centre South China sea and SW monsoon a. Sea surface isobar at 13 LT- 18 August, 2002
5/ SW monsoon and trough of low pressure a. Sea surface isobar at 13 LT- 28 July, 1999 b. Rainfall distribution over south Vietnam, flash flood in Binhphuoc and Dongnai provinces 6/ SW monsoon and ITCZ a. Sea surface isobar at 19 LT- 22 June, 2001
6/ SW monsoon, typhoon Kaemi landing to central Vietnamand and ITCZ a. Sea surface isobar at 13 LT- 22 August, 2000
Каталог: haiphong haiphong -> Xác định đóng góp của khoa học và công nghệ vào Năng suất yếu tố tổng hợp (tfp) haiphong -> CỘng hòa xã HỘi chủ nghĩa việt nam độc lập – Tự do – Hạnh phúc haiphong -> CỘng hòa xã HỘi chủ nghĩa việt nam độc lập – Tự do – Hạnh phúc haiphong -> Mẫu số 10 Ban hành kèm theo Thông tư số 38/2010/tt-blđtbxh ngày 24 tháng 12 năm 2010 của Bộ Lao động-Thương binh và Xã hội CƠ quan có thẩm quyền công ty haiphong -> CỤc thống kê tp hải phòng cộng hoà XÃ HỘi chủ nghĩa việt nam haiphong -> CỤc thống kê tp hải phòng cộng hoà XÃ HỘi chủ nghĩa việt nam haiphong -> Nghị định của Chính phủ số 107/2004/NĐ-cp ngày 01 tháng 4 năm 2004 quy định số lượng Phó Chủ tịch và cơ cấu thành viên Uỷ ban nhân dân các cấp haiphong -> BỘ XÂy dựng haiphong -> Nghị ĐỊnh của chính phủ SỐ 75/2006/NĐ-cp ngàY 02 tháng 8 NĂM 2006 quy đỊnh chi tiết và HƯỚng dẫn thi hành một số ĐIỀu của luật giáo dụC haiphong -> BỘ TÀi chính tải về 1.08 Mb. Chia sẻ với bạn bè của bạn:
|