On the high resolution regional weather forecast model (hrm) and forecasting tropical cyclone motion over the south china sea

Vietnam Journal of Mechanics, VAST, Vol. 27, No. 4 (2005), pp. 193-203 ON THE HIGH RESOLUTION REGIONAL WEATHER FORECAST MODEL (HRM) AND FORECASTING TROPICAL CYCLONE MOTION OVER THE SOUTH CHINA SEA LE Duc1 ' LE CONG THANH2 ' KIEU THI XIN1 1 Hanoi National University 2 National Hydro-meteorological Service of Vietnam Abstract. Chan (1995) [2] has found that, only 70% in 60 cases of the tropical cyclone (TC) movement test (TMT-90) developed from steering flows. The 30% remain of cases have to be explained by nonbarotropic processes. Vie are of the opinion that all weak, slow-moving and unexpected changing TCs over the South China Sea are in this 30% set. The nonlinear interaction between barotropic and nonbarotropic processes has affected on motion and structure of such TCs. In this paper, we use the high resolution weather forecast model (HRM), which is able to simulate meso-scale phenomena in limited regions, to predict motion of TCs in the South China Sea in 2002-2004, including two typical weak, slow-moving and unexpected changing TCs Mekhala and Nepartc;tk. Vve have chosen two forecast domains with different areas and resolutions. The results show that with the smaller domain, appropriate buffer and higher resolution HRM can predict better motion of TCs operating in the South China Sea. 1. INTRODUCTION In recent years, the theory about tropical cyclone (TC) motion focus on the ideas which assume that TC-motion is caused by barotropic processes on the base of the conser- vation of t he absolute vorticity with two main mechanisms: the advective adjustment by environment flows of the relative vorticity related to TCs (steering flows) and the advective process including the nonlinear impact between steering flows and the gradient of planet vorticity and the circulations of vorticities. Chang (1995) [3] mentioned that those im- pacts are generated during the evolution of flows with different wave numbers . Advective process resulting from each wave number will generate distribution of vorticity tendency, combined later with the tendency developed from steering flows, which forms the direction of TC (the direction of steering flows) . Chan (1995) [2] has found this mechanism taking only 703 in 60 cases of the TC movement test (TMT-90). The 303 remain of cases have to be explained by nonbarotropic processes. Many current studies using numerical models indicated the role of nonbarotropic pro- cesses such as t he wind shear, the vertical structure of eddy and of the diabatic heating which are responsible for the motion of TCs. The aim of those kinds of studies is to build a theory of the impact of nonbarotropic processes on motions in the atmosphere including TCs motion beside steering flows. In t his paper we concentrate on improving the high resolution regional model (HRM) to predict the motion of the TCs coming into the South China sea with focusing on those which are weak, slow-moving and often change direction unexpectedly such as the two 1 9 4 L e D u e , L e C o n g T h a n h a n d K i e u T h i X i n t y p h o o n s M e k h a l a ( 0 2 2 0 ) o f 2 0 0 2 a n d N e p a r t a k ( 0 3 2 0 ) o f 2 0 0 3 . T h i s k i n d o f t y p h o o n s , a f t e r C h a n ( 1 9 9 5 ) [ 2 ] , i s o n l y i n 3 0 3 o f a l l T C s b u t t h e y o f t e n c a u s e h e a v y r a i n f a l l l e a d i n g t o f l o o d i n g , e c o n o m i c a n d s o c i a l l o s s e s . I n t h e n e x t p a r t w e p r e s e n t t h e v e r i f i c a t i o n r e s u l t s o f p r e d i c t i o n b y t h e i m p r o v e d v e r s i o n o f a h o r i z o n t a l r e s o l u t i o n o f 1 4 k m a n d 3 1 v e r t i c a l l e v e l s ( V N U H R M / V 1 4 - 3 1 ) i n c o m p a r i s o n w i t h t h e r e s u l t s o f t h e o r i g i n v e r s i o n ( H R M / V 2 8 - 2 0 ) a n d o f s o m e n u m e r i c a l o p e r a t i o n a l m o d e l s o f t h e o t h e r c o u n t r i e s . 2 . T H E H I G H R E S O L U T I O N R E G I O N A L M O D E L ( H R M ) H R M i s a n o p e r a t i o n a l n u m e r i c a l r e g i o n a l w e a t h e r p r e d i c t i o n m o d e l o f h i g h r e s o l u t i o n f r o m t h e G e r m a n W e a t h e r S e r v i c e a n d h a s b e e n p r o v i d e d t o t h e N a t i o n a l I n d e p e n d e n t R e s e a r c h P r o j e c t 2 0 0 0 - 2 0 0 1 f u n d e d b y M i n i s t r y o f S c i e n c e a n d T e c h n o l o g y o f V i e t N a m . S i n c e O c t o b e r 2 0 0 2 t h e H R M i s u s e d a s t h e f i r s t o p e r a t i o n a l m o d e l a t t h e V i e t n a m e s e N a t i o n a l H y d r o - M e t e o r o l o g i c a l Serv~ce . T h e d e t a i l s o f t h i s m o d e l c a n b e s e e n i n K i e u ( 2 0 0 2 ) [ 1 0 ] . 2 . 1 O n t h e H R M H R M i s a h y d r o s t a t i c a l n u m e r i c a l m o d e l f o r a - a n d ( 3 - s c a l e p h e n o m e n a o n l i m i t e d r e g i o n s , p r o d u c i n g t h e d e t a i l e d p r e d i c t i o n o f n e a r - s u r f a c e w e a t h e r p a r a m e t e r s a n d w e l l s i m u l a t i n g c l o u d s a n d r a i n f a l l . H e n c e , m e t e o r o l o g i c a l f i e l d s o f H R M c a n b e u s e d f o r e n v i r o n m e n t a l p r o b l e m s s u c h a s p o l l u t e d a i r m o d e l i n g o r s e a s t a t e s i m u l a t i o n . T h i s m o d e l i s a l s o a s e n s i t i v e r e s e a r c h t o o l . T h e H R M i s b u i l t o n a r o t a t e d l a t i t u d e - l o n g i t u d e g r i d o r a r e g u l a r g r i d w i t h t h e r e s o l u t i o n f r o m 0 . 2 5 ° t o 0 . 0 5 ° ( 2 8 k m t o 6 k m , r e s p e c t i v e l y ) , u s i n g a h y b r i d v e r t i c a l c o o r d i n a t e . T h e v e r t i c a l at~osphere o f H R M i s f r o m t h e s u r f a c e c h a r a c t e r i z e d b y P s ( x , y , t ) t o t h e u p p e r b o u n d a t 2 5 m b a n d c a n b e d i v i d e d f r o m 2 0 t o 3 5 l e v e l s . T h e p r o g n o s t i c v a r i a b l e s u , v , T , q v , q c , q i a n d t h e d i a g n o s t i c v a r i a b l e s s u c h a s t h e v e r t i c a l v e l o c i t y i n t h e p r e s s u r e c o o r d i n a t e w a r e d e f i n e d i n f u l l l e v e l s , w h i l e t h e g e o p o t e n t i a l h e i g h t ¢ , t h e v e r t i c a l v e l o c i t y i n t h e h y b r i d c o o r d i n a t e a n d t h e d i f f u s i o n f l u x e s a r e d e f i n e d i n h a l f l e v e l s . 2 . 2 F u n d a m e n t a l e q u a t i o n s o f H R M T h e p r o g n o s t i c e q u a t i o n s o f H R M a r e d e r i v e d f r o m t h e p r i m i t i v e e q u a t i o n s i n t h e h y b r i d c o o r d i n a t e . T h e r e a r e 7 e q u a t i o n s f o r 7 p r o g n o s t i c v a r i a b l e s u c h a s [ 1 0 ] : T h e s u r f a c e p r e s s u r e p 8 : B p s = _ 1 / 1 { ~ ( 8 p ) 8 ( 8 p ) } 8 t a c o s c p 8 > . . u O T J + 8 c p v c o s < f J O T J d T J - µ 1 & ( P s - P s l b ) . ( 2 . 1 ) 0 T h e h o r i z o n t a l w i n d s u , v : O U 1 o p 1 0 R T v 0 * O U - - - - Q - v c o s + K ) + - [ l n ( p ) ] + T J - = o t c o s . . a c o s . . O T J u ( o p ) - l O T > . ( o u ) = F H - g - - - + - - µ 1 & ( u - U l b ) ) 8 T J 8 T J 8 t s ( 2 . 2 ) On the High Resolution Regional Weather Forecast Model (HRM) .. . 195 av ap 1 a RTv a * 8v - + Q-u + --(1l + K) + --[ln(p)] + 77 - = Bt arJ a Brp a Brp a77 v ( op ) - 1 aT 'P (av ) FH - g - --+ - · -~llb(v-v1b) · ary ary at s (2.3) The temperature T: aT 1 [ aT aT] * aT ~ + u >:I \ + v cos cp~ + TJ ~ = ut a cos cp UA ucp T UT} R (w) T (f)p)-l DTJT (8T) Le = -Tv - + FH - g - -- + - + - Cvc - µlb (T-T1b) · cp P ary orJ at s cp (2.4) The specific humidity qv : oqv 1 [ oqi. aqv] * oqv - >:I + u >:I \ + v cos cp >:I + TJ a - ut a cos cp uA ucp TJ qv ( op )-1 DTJqv ( oqv ) ( ) F H - g aTJ aTJ + at s - Cvc - µ1b qv - qvlb . (2 .5) The cloud humidity qc: oqc 1 [ oqcv oqc] * 8qc - a + u >:I \ + v cos cp a + rJ 8 -t a COS '{J U A '{J TJ qc (8p) -l OTJqc (aqc) ( ) F H - g aTJ OrJ + at s - Cvc - µlb qc - qc1b . (2.6) The cloud ice content qi: aqi 1 [ aqi aqi ] * f)qi -0 + u >:i\ + vcoscp-;:;- + rJ ~ = t a cos cp UA ucp UTJ qi (ap) -l a'r/qi (8qi) ( ) av! pgqi F H - g OrJ OrJ + 8t 8 - Cvc - µlb qi - qilb - OrJ , (2.7) where Vi -is the falling velocity of water rain and ice rain. The last equation (2. 7) was added since the global model (GME) produces the qi variable (9/2003) to use as one more initial field for HRM. The HRM also computes 9 diagnostic variables with 9 equations. In the prediction products, there are also 4 indirect prognostic variables: the vertical velocity in t he pressure coordinate, t he geopotential height, the cloud cover factor and the diffusion parameter. 2.3 Boundary conditions and initialization To filter the internal gravity wave developed in high resolution models, the HRM uses the radiation upper boundary condition (RUBC) after Klemp, Durran and Bougeaul (1983) [7]. The lateral boundary conditions are taken from the global model GME, so called derived model, with a smooth algorithm after Davies· and Kalberg in order to enable gravity waves leaving the domain without a lot of reflections on the lateral boundaries. 1 9 6 L e D u e , L e C o n g T h a n h a n d K i e u T h i X i n I t i s w e l l k n o w n t h a t w e c a n ' t u s e d i r e c t l y o b s e r v a t i o n s a s t h e i n i t i a l c o n d i t i o n . O b - s e r v a t i o n s h a v e t o b e a d j u s t e d d y n a m i c a l l y t o f o r m a s e t o f a p p r o p r i a t e a n a l y s i s d a t a f o r m o d e l i n i t i a l i z a t i o n . T h e i n i t i a l i z a t i o n p r o c e d u r e m i n i m i z e s t h e g r o w i n g o f p o t e n t i a l g r a v i t y w a v e s a s t h e m o d e l r e s o l u t i o n b e c o m e s h i g h e r . I n t h e H R M t h e i m p l i c i t n o r m a l m o d e i n i t i a l i z a t i o n m e t h o d ( I N M I ) i s u s e d , t h e r e s u l t s o f w h i c h a r e t h e i n i t i a l i z e d f i e l d s u , v , T a n d P s · S i n c e M a r c h 2 0 0 5 i n s t e a d o f I N M I w e u s e t h e D i g i t a l F i l t e r I n i t i a l i z a t i o n ( D F I ) d e v e l o p e d b y D . M a j e w s k i . M o d e l o r o g r a p h y : F o r e a c h o f g r i d b o x , t h e a v e r a g e h e i g h t a b o v e t h e s e a l e v e l i s u p d a t e d f r o m t h e A m e r i c a n d a t a s e t , d e p e n d e d o n m o d e l r e s o l u t i o n . T h e s o i l t y p e i n e a c h b o x i s t a k e n f r o m t h e F A Q / U N E S C O m a p . 2 . 4 P h y s i c a l p r o c e s s i n H R M · w i t h t h e h o r i z o n t a l r e s o l u t i o n f r o m 2 8 k m t o 7 k m , m o d e l s c a n ' t a d e q u a t e l y r e p r e - s e n t t h e s u b g r i d - s c a l e p r o c e s s e s s u c h a s r a d i a t i o n , c o n v e c t i o n , h o r i z o n t a l a n d v e r t i c a l t u r b u l e n c e d i f f u s i o n a n d t h e s o i l p h y s i c a l p r o c e s s d i r e c t l y a n d t h e r e f o r e m u s t r e s o r t t o p a r a m e t e r i z a t i o n i n t h e H R M . R a d i a t i o n - t h e m o s t i m p o r t a n t f a c t o r f o r t h e w e a t h e r d e v e l o p m e n t i s p a r a m e t e r i z e d b y t w o s c h e m e s s e p a r a t e l y f o r l o n g w a v e a n d s h o r t w a v e r e s p e c t i v e l y i n t h e a t m o s p h e r e a n d a t t h e s u r f a c e ( D o m s a n d S c h a e t t l e r 1 9 7 7 ) [ 5 ] . H R M u s e s a p r o g n o s t i c s c h e m e f o r p a r a m e - t e r i z a t i o n m i c r o p h y s i c a l p r o c e s s e s o f g r i d - s c a l e c l o u d s i n v o l v e d i n r a i n f a l l g e n e r a t i o n . T h e s c h e m e o f T i e d t k e ( 1 9 8 9 ) [ 8 ] c a r r i e d o u t f o r p a r a m e t e r i z a t i o n o f d e e p c o n v e c t i o n , s h a l l o w c o n v e c t i o n a n d m e d i u m c o n v e c t i o n , w h i l e t h e h o r i z o n t a l t u r b u l e n c e d i f f u s i o n i s a s s u m e d a s a n u n i m p o r t a n t p h y s i c a l p r o c e s s a n d i s u s e d l i k e a f i l t e r t o r e m o v e s m a l l s c a l e n o i s e s . V e r t i c a l t u r b u l e n c e d i f f u s i o n p a r a m e t e r i z a t i o n i s b a s e d o n t h e g r a d i e n t f l u x a p p r o x i m a t i o n . V e r t i c a l d i f f u s i o n p a r a m e t e r s c a n b e i n f e r r e d f r o m t h e d i a g n o s t i c e q u a t i o n o f t u r b u l e n c e k i n e m a t i c s e r . S o i l m o d e l : T h e s u r f a c e t e m p e r a t u r e a n d t h e s u r f a c e e v a p o r a t i o n r a t e a r e n ' t t h e H R M v a r i a b l e s b u t t h e y a r e n e c e s s a r y i n t h e b o u n d a r y c o n d i t i o n f o r c o m p u t i n g t h e r a d i a t i o n a n d h e a t f l u x . T h e s o i l h u m i d i t y i n f l u e n c e s t h e w a t e r c o n t e n t i n t h e p l a n e t b o u n d a r y l a y e r t h r o u g h i t s p o s s i b l e e v a p o r a t i o n w h i c h a f f e c t s r a i n f a l l o r d r o u g h t . T h e H R M u s e s t h e t w o - l a y e r s o i l m o d e l o f J a c o b s e n a n d H e s s e ( 1 9 8 2 ) [ 6 ] , w h i c h e s t i m a t e s e v a p o r a t i o n f r o m o a r e s o i l s a n d t r a n s p i r a t i o n f r o m v e g e t a b l e s u s i n g b a s i c f u n c t i o n s o f w a t e r c o n t e n t f o l l o w e d a s i m p l i f i e d v e r s i o n o f D a v i s ' p a r a m e t e r i z a t i o n s c h e m e 1 9 8 4 . 3 . I M P R O V E D H R M A N D I T S I M P L E M E N T A T I O N T O P R E D I C T T C S M O T I O N O V E R T H E S O U T H C H I N A S E A 3 . 1 I m p r o v e d H R M A s w e m e n t i o n e d a b o v e , w i t h t h e t r a d i t i o n a l f o r e c a s t i n g m e t h o d s u s i n g i n V i e t n a m , w e r a r e l y p r e d i c t t h e m o t i o n o f s l o w - m o v i n g w e a k T C s u n e x p e c t e d l y c h a n g i n g t h e d i r e c t i o n o n c o m i n g i n t o t h e S o u t h C h i n a S e a a n d h e n c e p r e d i c t e r r o n e o u s l y t h e i r s l a n d f a l l . T h i s i s a s e r i o u s p r o b l e m i n t h e o p e r a t i o n a l f o r e c a s t i n g i n V i e t n a m . N u m e r i c a l m o d e l s o f n e i g h b o r c o u n t r i e s a r e u n a b l e t o g i v e a n y t h i n g b e t t e r t o o . T h e t y p h o o n N e p a r t a k ( 0 3 2 0 ) ( 2 0 0 3 ) i s a t y p i c a l e x a m p l e . A l l o f t h e c e n t e r s p r e d i c t e d i t s l a n d f a l l i n t o t h e m i d d l e o f V i e t n a m ( a b o u t 1 8 ° N ) o n 1 7 / 1 1 / 2 0 0 3 . I n f a c t , c o m i n g n e a r t h e s h o r e t y p h o o n N e p a r t a k c h a n g e d i t s d i r e c t i o n d r a s t i c a l l y , w e n t a h e a d t o t h e N o r t h a n d f e l l i n t o C h i n a . On the High Resolution Regional Weather Forecast Model (HRM) .. . 197 The operational implementing HRM with a horizontal resolution of 28 km, 20 vertical levels for the large domain of 5° S -35° N, 80° E -130° E (V28-20/L) proves that V28-20/L well predicts winter weather systems such as entries of cold air masses or t he winter monsoon. Its forecast in summer is of a little lower quality but considerably useful for forecasters to improve their forecast reports. The advantage of V28-20/L with the large domain using time variable lateral boundary conditions provided by a global model is the ability capturing the impact ing between large weather systems in the evolution of regional weather processes . Its main disadvantage is that the northwest boundary with the high mountains impacts on forecast qualities of the inside domain. Besides, TCs evolving over the model domain normally are weak and operating in a more limited region of the southwest Pacific . To understand t he impact of boundary conditions on model results and to find out the appropriate domain for prediction of weak-storm motion over the South China Sea, we have chose a small domain of 7° N-27° N and 97° E-117° E with the same resolution as the V28-20/ L which is called V28-20/ S. Disastrous weather phenomena in the tropical regions including TCs are mainly forced by tropical processes . The analysis of Carr and Elsberry (2000) [1] shows t hat as the TCs operates in inner tropical regions the errors in simulated positions are caused mainly by false simulation of mesa-scale physical processes. Thus, to simulate tropical physical processes, we need to increase the resolution higher than that in the extra-tropical region. Besides, to simulate the motion of weak TCs over the South China Sea, it 's necessary to detail the orography, which means a higher resolution. We have increased the horizontal resolution from 28 km to 14 km and with 31 vertical levels instead of 20 levels of the old version for the same domain as the V28-20/S . This new version we call V14-31/S. 3.2 Implementation of three versions to predict TCs motion over the South China Sea and results Three versions V28-20/ L, V28-20/S and V14-31/S have been applied to predict mo- tions of two typhoons Mekhala and Nepartak. The 2 days predicted errors of center position of typhoon Mekhala, started at OOZ of 24 , 25 , 26/ 09/2002 , and of typhoon Nepar- tak, started at OOZ on 16, 17, 18/ 11 /2003, by V28-20/L, V28-20/S and V14-31/ S are given in t he Table 1. Our results (not represented here) show that analysis errors of TCs center (in column 2-distance between best track and analysis track of GME) are greater than that of 6 hours forecast . This means that the GME analysis fields are not good enough while the GME- HRM system shows a good appropriateness. The decrease of errors from analysis value (in column 2) to 6 hours predicted value (in column 3) implies that HRM is able to simulate well the evolution of typhoons operating over the South China Sea region. The average errors (AE) of V14-31 / S in Table 1 increase slowly and systematically . with the forecast time (its AE are 69 km of one day forecast and 120 km of two days forecast) and in general considerable lower than errors of many other models. Taking t he Australian TCLAPS model as an example for comparison, we see that t he AE of TCLAPS are 143 km and 236 km respectively for 2001 year. In the Figs. 1 and 2 we plotted tracks of above-cited typhoons, which is a line linked every 6 hours minimum surface pressure points estimated from forecast surface pressure field by the Downhill method. 1 9 8 L e D u e , L e C o n g T h a n h a n d K i e u T h i X i n T a b l e 1 . P r e d i c t e d c e n t e r p o s i t i o n e r r o r s ( k m ) o f t y p h o o n s M e k h a l a a n d N e p a r t a k b y t h r e e v e r s i o n s : V 2 8 - 2 0 / L , V 2 8 - 2 0 / S & V 1 4 - 3 1 / S V e r s i o n s O O h M e k h a l a V 2 8 - 2 0 / L 6 1 V 2 8 - 2 0 / S 5 5 V 1 4 - 3 1 / S 8 5 N e p a r t a k V 2 8 - 2 0 / L 1 1 6 V 2 8 - 2 0 / S 1 0 4 V 1 4 - 3 1 / S 1 1 6 M e a n e r r o r V 2 8 - 2 0 / L 8 8 V 2 8 - 2 0 / S 7 9 V 1 4 - 3 1 / S 1 0 0 P R E D I C T E D T R A C K O F U E K K f W . A S T A R T E D O O Z - Z f / 0 9 / 2 0 0 2 8 Y H R U , 24N,-~~~~~~~~~~~~~~~~~~~~~ , . , , _ ; - - - ; . : ; : \ ' : , , . ) ' i v ' " ' / I r · · 2 ° " 1 ~ . . . > , ' / . j . ~j 1 9 N . . . . , : : · · ( · . . . . , \ 1 B N " " ' _ . \ !\ · : 1 7 " . . · ! · . . ,~':';~ , :;) -,~ j j , : : r y 2 2 N 2 1 N L , : / ' : C · . 1 5 N 1 2 N • · . . / . . T, . ~·' . / ~ ; ; - - ( " ; , . 1 0 " " ' > " " . . . . . . . . . . . . . / \ , ~~OJE 1 ; 4 E 1~( ;~~ 1 0 7 E 1 d a E 1 0 9 E I 1 0 E 1 1 I E 1 1 2 ( 1 f 3 E 1 H E 1 1 5 E 1 1 6 £ 1 1 7 E I f l l E 1 2 h 6 9 3 9 5 4 2 4 h 3 6 h 4 8 h 1 0 0 1 8 1 9 8 1 4 0 8 7 1 3 5 1 2 7 1 6 3 2 8 5 1 1 4 9 0 5 1 6 5 1 1 2 1 3 2 2 3 3 1 0 6 1 1 5 6 9 1 0 0 1 2 0 P R E D I C T E D T R A C K OF M EK K H . A L A S T A R T E D O O Z - 2 6 / 0 9 / 2 0 0 2 B Y H R U 2~..-~~~~~~~~~~~~~~~~~~~~,,., ::f~;r.)" -- ~"i. : \~ .)\~/"';,j .• . 2 1 N { - : . . · . . / : . . : . .• . . ! .. ' . . . 2 ( ) J ·~; . . . ; / :~ _;(;j,\~\\ · r : : ' " ' . " . } ,( · : - : ( •. \ 1 J N "<:~ : . . : . . : J '/ : : \ - ; : : : ; . . . ; • . . . ) P t f o 3 E 1 0 f E 1 0 5 E 1 0 6 £ 1 0 7 E 1 C i 8 E 1 0 9 E 1 f O E h l E 1 f 2 E 1 1 J E I H E 1 f 5 E 1 1 6 £ 1 f 7 E 1 1 8 E F i g . 1 . M e k h a l a ' s p r e d i c t e d t r a c k , s t a r t e d a t O O Z , 2 4 0 9 2 0 0 2 ( t o p ) , a t O O Z , 2 6 0 9 2 0 0 2 ( b o t t o m ) . 0 0 0 : V 2 8 - 2 0 / L , £ : V 2 8 - 2 0 / S , ' : V 1 4 - 3 1 / S , g : B e s t t r a c k C o m p a r i n g p r e d i c t e d e r r o r s o f V 2 8 - 2 0 / L w i t h o n e s o f V 2 8 - 2 0 / S w e c a n d e d u c e t h a t r e d u c - i n g t h e f o r e c a s t d o m a i n i s a n a p p r o p r i a t e s t e p t h a t d e c r e a s e s p r e d i c t e d e r r o r s d r a s t i c a l l y a n d s y s t e m a t i c a l l y , f r o m 1 3 2 k m t o 1 0 6 k m f o r f i r s t d a y f o r e c a s t a n d f r o m 2 3 3 k m t o 1 1 5 k m f o r 2 n d d a y s f o r e c a s t . T h e 6 t i m e s r e d u c e o f i n t e g r a t i o n t i m e i s a m o r e i m p o r t a n t i m p r o v e - m e n t b e c a u s e o f e c o n o m y o n c o m p u t e r t i m e . P r e d i c t e d e r r o r s o f V 1 4 - 3 1 / S s h o w t h a t On the High Resolution Regional Weather Forecast Model (HRM) ... 199 with a higher resolution and an appropriate smaller domain , t he forecast quality has been improved remarkably. The posit ion errors are 69 km and 120 km for one day and two days forecast respectively. But the most significant improvement we can notice here is t hat V14-31 / S shows a good capture of Nepartak's deflection started at OOZ-17 / 11 / 2003, its predicted track is the third line from the left- the most closed to t he best track (F ig. 2), while the V28-20/ L predicted the landfall of Nepartak into the Middle of Vietnam (about 18° N) shortly before OOZ-19/ 11 /2003 (the end of first line on t he left in Fig. 2) , and all forecast centers of neighbor countries gave nearly the same results. The version V28-20 / S has captured t his deflection in t he first day of forecast but took a turn to the north-west again in t he second clay of forecast (the second line from t he left in Fig. 2) and hence its predicted errors are larger than those of V14-31 / S respectively. So we can say t hat t hese results ensure the skill of improved version V14-31/S . Figs . 3 t o 12 depict 2 days forecastecl tracks by V14-31/ S of 10 storms (of 2002-2004) coming into the South China Sea and their corresponding best tracks. The results enable forecasters to increase systematically its forecast skill for TCs motion. From all forecasted tracks represented in Figs. 3 - 12 we can see t hat t he TCs occurring in t he first half of storm season in which t he summer monsoon governs (such as Krovanh and Chant hu in June, Koni and Imbudo in July, Kammuri and Vongfong in August , Hagupi t and Mekhala in September) normally deflect to the northeast of the analysis. On the contrary, t he TCs occurring in the second half of storm season in which the winter monsoon governs (such as Nepartak and Muifa in November ); deflect to t he southwest of t he analysis. Those results say t hat monsoon circulations affect strongly the velocity and direction of T Cs motion over t he South China Sea, and hence theirs landfall. PREDICTED TRACK Of" NEPARTAK STARTED OOZ-17 /1 1 /2003 BY HR~ 2JN . . · . r · ..... ........ .. :·· ···· ··r~: : <: . : . :: ' . .. ·. ~i<+-i,.',•. -.'.·,·· · : "::=-:::. -2~ .. . ) . . /~ . . ·; · 19N . ~:~··_ · · · .. "" J.s':) HN · ,,. --~· ·· ... H 12N . . . . "/,:1 .. ··: ·· 11ti.I ~ --) :. _.---·.:.:_ ~·-. , ·', ....... . "'' { '. l')f' 91j10 3E 104£ 105[ 106( 107E 108[ 10i:IE I 10E 111E 112E 11JE I HE 115£ 11 &C I 17E IUE 1JN PREDICTED TR.~CK OF NEPARTAK STARTED OOZ - 18/1 1 /2003 BY HRU . . ( ": '' j ":' " './ :· 12N ..1~:· . · I,. ., \· :l 11N :, } . . ~ j ":""° ; ; . ·: ·j··f 'j/> . . . . . . IOJE 104E 105E 106£ 107E 108E 10\'IE 110E: 11IE112[ 1lJE1HE 115E 1\6E 117£ 118£ Fig . 2. Nepartak's predicted track, started at OOZ, 17112003 (left), at OOZ, 18112003 (right). 000 : V28-20/ L, £: V28-20/ S, ~: V14-31 / S, g: Best track. We have performed some verificat ion of predicted motions using the V14-31/ S by comparison with operational models from two countries. The results are given in the 2 0 0 L e D u e , L e C o n g T h a n h a n d K i e u T h i X i n T a b l e 2 , w h e r e t h e e r r o r s o f V 1 4 - 3 1 / S a r e a v e r a g e d o v e r 1 0 a b o v e - c i t e d T C s . T C L A P S i s a n A u s t r a l i a n c o u p l e d s y s t e m b e t w e e n a g l o b a l · m o d e l a n d a l i m i t e d r e g i o n a l m o d e l w i t h a b o g u s a r t i f i c i a l c y c l o n e . K E R i s a m o v i n g n e s t e d m o d e l e m b e d d e d i n t h e g l o b a l m o d e l T 1 2 6 w i t h a n i m p r o v i n g c y c l o n e - s e t s c h e m e u s i n g t h e o p t i m a l i n t e r p o l a t i o n t e c h n i q u e t o d e f i n e e n v i r o n m e n t a l f i e l d s i n s t o r m r e g i o n s . P R E D I C T E D T R A C K O f K A U I J U R I S T A R l E D O O Z - O J / O B / 2 0 0 2 B Y H R U . 1 2 C N - f - : ( 2 ' 4 1 - 1 4 / . . ' . . . - - . . : \ : . E 1 C i o E 1 0 2 E 1 0 ·' 4 £ 1 0 6 E l < f i ! ! I E 1 1 0 E 1 f 2 E 11 ° ' 4 E 1 ( & : F i g . 3 . K a m u r i ' s p r e d i c t e d t r a c k s , s t a r t e d a t O O Z o f 0 3 , 0 4 & 0 5 / 0 8 / 2 0 0 2 . " : V 1 4 - 3 1 / S , g : B e s t t r a c k . P R E D I C T E D T R A Q < O f H A G U P I T S T A R T E D 1 2 2 - 1 O / o 9 / 2 0 0 2 B Y H R I J 2 0 N I · . J : , . . · · , r : , . . , ) , _ , ~ ' . . " " ' . · ; _ _ [ : " . . . . ,. J-.·~·i_,~· . , : ' · < ( ' ' . , / . . . , , , , . , . ~ - . , . \ 2 t • d . . r,..~ . . , , . . . ~ / r · , : · ' , ~ - - I * 1~ I~ 1~ l f i l 1~ 1~ F i g . 5 . H a g u p i t ' s p r e d i c t e d t r a c k s , s t a r t e d a t O O Z o f 1 0 , 1 1 , 1 2 , 1 3 & 1 4 / 0 9 / 2 0 0 2 . ' = V 1 4 - 3 1 / S , 9 : B e s t t r a c k . P R E D I C T E D T R A C K O F V O N G F O N G S T A R T E D O O Z - 1 6 / C H ! / 2 0 0 2 B ' r ' HR~ " ' " ' ~4N· ~ ·-•)" . . \ .l · r·-:'··· ·-·~-/ "'"~1 " " . ,.,.~ . : . • , . :i .~J...J l : •' _ ; . . \ .. . . : . -....:~-= . . . . //~·- 2 C N 1 · · · • - . . . 8N-f · · : :~ . . ,~~ -- ·\. ~j . . . . . ·. ; g 6 ( 1 0 o E 1 C i 2 E 1 0 .' 4 E 1 C i 6 E 1 0 B E 1 f O E 1 1 " 2 . £ 1 1 ·' 4 E 1 1 ° & £ F i g . 4 . V o n g f o n g ' s p r e d i c t e d t r a c k s , s t a r t e d a t O O Z o f 1 6 , 1 7 , 1 8 & 1 9 / 0 8 / 2 0 0 2 . 1 ' : V 1 4 - 3 1 / S , 9 : B e s t t r a c k . P R E D I C T E D T R A C K O f U E K K H A L A S T A R T E D O O Z - 2 J / 0 9 / 2 0 0 2 B Y H R I J ' " " ' · · . . 1 ( ( 2 4 N - f ; , , , _ . . . . ~ . 8N~ . ' . 1 " " · · \ -~ ~ · - - 1~ ~ 1~ 1~ 1 i l i 1~ 1~ F i g . 6 . M e k h a l a ' s p r e d i c t e d t r a c k s , s t a r t e d a t O O Z o f 2 3 , 2 4 , 2 5 , 2 6 & 2 7 / 0 9 / 2 0 0 2 . 1 ' : V 1 4 - 3 1 / S , 9 : B e s t t r a c k . . On the High Resolution Regional Weather Forecast Model {HRM) .. . 201 PREDICTED lRA.CK OF KONI SH.RTED 12z-1g/07/2DOJ BY HRl.l SI& 1~ 102£ 104£ 106( 108E 110[ 112[ 1HE 116£ Fig. 7. Koni's predicted tracks, started at OOZ of 19, 20 &21/07 /2003. " : V14-31/S, 9: Best track. PREDICTED TRACK Of KROYANH STARTED OOZ-2+/08/200J BY HRIJ Fig. 9. Krovanh's predicted tracks, started at OOZ, 11-12/ 06/2003. 1': V14-31/S, 9: Best track, PREDICTED lRA.CK Of llJBUOO STARTED 12Z- 2J/07/200J '"'. i :/ BV HRIJ 9&: 100E 102.E 10'4£ 1Cla( JOBE 110[ 112( 1HE 11&£ Fig. 8. Imbudo 's predicted tracks, started at OOZ, 23-24/ 07 /2003. Best track. 1': V14-31/S , 9: PREDICTED TRACK Of NEPARTAK STARITO 002-1 6/11/2003 BY HRIJ Fig. 10. Nepartak's predicted tracks, started at OOZ, 16, 17 &18/11/2003. ": V14-31/S, 9 : Best track. The results in Table 2 shows that predicted errors of V14-31 / S in term 12 hours t o 48 hours increase more slowly and are, systematically, lower than those one of TCLAPS and of KER. The remarkable thing is a too large analysis error for V14-31 /S, which we can attribute for the quality of GME initial fields . However, after 12 hours integration, the 12- hours error is less than the analysis error ( 103 km in comparison t o 119 km). This means that V14-31/S simulated meso-scale and micro-physical processes in this tropical domain 2 0 2 L e D u e , L e C o n g T h a n h a n d K i e u T h i X i n r e l a t i v e a c c u r a t e l y , l e a d i n g p r e d i c t e d f i e l d s m o r e a n d m o r e c l o s e l y t o t h e t r u e f i e l d s d u r i n g t h e f i r s t 1 2 - h o u r s i n t e g r a t i o n . S o i f w e c a n d e c r e a s e a n a l y s i s e r r o r s , t h e s k i l l o f V 1 4 - 3 1 / S w o u l d b e b e t t e r , w h i c h i s o n e o f t h e m o s t i m p o r t a n t m e t h o d s t o i n c r e a s e t h e m o d e l s k i l l . P R E D I C T E D T R A C K O F C H A H T H U S l A R l E D 1 2 2 - 1 1 / 0 6 / 2 0 0 + B Y HR~ 2 ! > 1 l ' / , . i " " ' l ' < " \ . :~:\ >)"~;j~(- ~ ~' .N' '.~ : : ' . \ / · . • . C~ ' " " : : t f rL~~i;l}' 1 : _ . . . . . BN~ :~('\ : \ . . \ I I & 1 0 0 E 1 0 2 [ 10~E 1 0 6 E \ 0 8 E 1 1 0 [ 1 1 2 E 1 f ' 4 E 1 1 " 6 £ F i g . 1 1 . C h a n t h u ' s p r e d i c t e d t r a c k s , s t a r t e d a t O O Z o f 1 1 & 1 2 / 0 6 / 2 0 0 4 . 1 ' : V 1 4 - 3 1 / S , g : B e s t t r a c k . P R E D I C T E D l R . A . C K O f l . I U I F A S T A R T E O o o z - 2 1 / 1 1 / 1 0 0 + B Y H R U ~ - - I N - - 1~1fil 1~ 1~ F i g . 1 2 . M u i f a ' s p r e d i c t e d t r a c k s , s t a r t e d a t O O Z o f 2 1 , 2 2 , 2 3 & 2 4 / 1 1 / 2 0 0 4 . 1 ' : V 1 4 - 3 1 / S , g : B e s t t r a c k . T a b l e 2 . T C s c e n t e r p o s i t i o n e r r o r s ( k m ) , p r e d i c t e d b y V 1 4 - 3 1 / S ( 2 0 0 3 - 2 0 0 4 ) , T C L A P S ( 2 0 0 1 ) a n d K E R ( 1 9 9 5 ) . M o d e l O O h 1 2 h 2 4 h 3 6 h 4 8 h T C L A P S 8 5 1 5 8 2 4 4 3 1 1 K E R 1 4 3 2 3 6 V 1 4 - 3 1 / S 1 1 9 1 0 3 1 3 2 1 4 8 2 1 8 4 . C O N C L U S I O N F r o m t h e r e s u l t s w e c a n d e d u c e t h a t t h e i m p r o v e d v e r s i o n b y h i g h e r r e s o l u t i o n c o m - b i n e d w i t h a n a p p r o p r i a t e d o m a i n V 1 4 - 3 1 / S i s a b l e t o s i m u l a t e r e l a t i v e l y w e l l t r o p i c a l m e s o - s c a l e a n d m i c r o - p h y s i c a l p r o c e s s e s s o a s w i t h o u t b o g u s c y c l o n e s e t t i n g V 1 4 - 3 1 / S c a n p r e d i c t T C s m o t i o n a n d i t s l a n d f a l l m u c h b e t t e r t h a n o t h e r o p e r a t i o n a l m o d e l s o f A u s t r a l i a a n d o f U S A . I t ' s e v i d e n t t h a t t h e p r e d i c t e d s k i l l o f H R M w i l l b e i m p r o v e d w h e n i t i s s e t b o g u s c y c l o n e s . W e h a v e a l s o p r e d i c t e d m o t i o n s o f t y p h o o n s M e k h a l a a n d N e p a r t a k w i t h t h e " W B A R m o d e l a n d a 3 - l a y e r s s h a l l o w w a t e r m o d e l ( K i e u e t a l l , 2 0 0 2 ) [ 1 0 ] . T w o t h o s e m o d e l s h a v e p r e d i c t e d M e k h a l a r e l a t i v e a c c u r a t e l y b u t t h e y d i d n o t c a p t u r e t h e d e f l e c t i o n o f N e p a r t a k . T h i s d e m o n s t r a t e t h e a d v a n t a g e o f h y d r o - d y n a m i c a l m o d e l s o f h i g h r e s o l u t i o n i n c o m p a r i s o n w i t h b a r o t r o p i c m o d e l s b e c a u s e h y d r o - d y n a m i c a l m o d e l s o f h i g h r e s o l u t i o n c a n d e s c r i b e t r o p i c a l n o n b a r o t r o p i c p r o c e s s e s a s w e l l a s o r o g r a p h i c c h a n g e s i n s h o r e , w h i c h i m p a c t o n t h e e v o l u t i o n a n d d e f l e c t i o n o f T C s . On the High Resolution Regional Weather Forecast Model (HRM) ... 203 And we can assert the predicted skill of HRM for Vietnam and the South China Sea region. V14-31/S is running operationally at the Viet Nam National Hydro-Meteorological Service since 2002 October. Since then its results contribute considerably to t he improve- ment of weather forecast quality in Viet Nam. REFERENCES 1. L. E. Carr, R. L. Elsberry, Dynamical tropical cyclone track forecasting errors, Part I: Tropical region error sources, Wea. Forecasting 15 (2000) 641-661. 2. J . C. L. Chan, Prediction of annual tropical cyclone activity over the ·western North Pacific and the Sout h China Sea, International Journal of Climatology 15 (1995) 1011-1019. 3. C. P. Chang and T. C. George, Tropical circulations associated with southwest monsoon onset and westerly surges over the South China Sea, Mon. Wea. Rev. 123 (1995) 3254-3267. 4. R. E. Dickinson, Modeling evapo-transpiration for the three-dimensional global climate mod- els , Climate processes and climate sensitivity 29 (1984) 58-72. 5. G. Doms, U. Schaettler, Eds, The nonhydrostatic limited area model Ll\IL Part I: Scientific documentation, Deutscher Wetterdienst Rep. LM F90 ,1999. 6. I. Jacobsen and E. Heisse, A new economic method for the computation of the surface tem- perature in numerical models, Beitr.Phys. Atm. 55 (1982) 128-141. 7. J. B. Klemp and D . R. Durran, An upper boundary condition permitting internal gravity way radiation in numerical weather scale models , Month. Wea. Rev. 111 (1983) 430-444. 8. M. Tiedtke, A Comprehensive Mass flux scheme for cumulus parameterization in large scale models , Month. Wea. Rev. 117 (1989) 1799-1801. 9. C. T . Le and T. X. Kieu , A 3-layers shallow water model testing for prediction of storm traj ectories over the South China Sea, Vie. Hyd. Met . Rev. 12 (5 16) (2003) 1-7. 10. T . X. Kieu et all, Research on application of high technological numerical models for prediction of storm movements over the South China Sea. Result Report of the 2000-2001 National Separate Scientific Technological Theme, 2002 . Received April 29, 2005 MO HINH DU BAO THCJI TIET KHU vuc PHAN GIAI CAO HRM VOi DU nAo cHuYE°N DQNG c-OA xoAY THU~N NHI$T DOI TREN BIEN DONG Nghien ClrU cua Chan (1995) da chi ra rang 70% trong 60 xoay thu~n nhi~t c1&i dU'<(C nghien ClrU c6 chuyen d<~'mg xac djnh b&i dong clan. 30% tnrang hqp con l<,'i can dm;rc giai thich bang cac qua trlnh phi chinh ap. Chung toi cho rang cac xoay thu~n nhi~t d&i yeu, chuyen d~mg ch~m va doi lm&ng d9t ng9t ho<,'t d9ng tren bien Dong nam trong 30% t nrang hqp nay. Tuang tac phi tuyen giiia cac qua trlnh chinh ap va phi chinh ap tac d9ng den chuyen d9ng va cau true cua nhiing xoay thu~n nhi~t d&i lo~i nay. Trang bai bao nay chung toi st'r di,mg mo hlnh dv bao thai tiet pha.n giai cao (HRM) c6 the mo phOng cac hi~n tuqng thai tiet quy mo trung blnh a m<rc c19 khu vvc de dv bao chuyen d9ng cua xoay thu~n 11hi~t d&i tren bien Dong trong cac nam 2002-2004, trong so d6 c6 hai can bao yeu chuyen d9ng ch~m va thay doi hu&ng d9t ngi?t dien hlnh Ia Mekhala va Nepartak. Chung toi da Iva chc;m hai mien dv bao khac nhau ve vj tri, di~n va di? phan giai. Ket qua cho thay v&i mien nho c6 vung d~m thich hqp va di;> phan giai cao HRM c6 the dv bao tot han ro r~t chuyen d~mg cua cac xoay thu~n nhi~t d&i nay tren bien Dong.