TYPHOON PROCESS AND ITS IMPACT ON THE SURFACE CIRCULATION IN THE NORTHERN SOUTH CHINA SEA

95Available online at www.sciencedirect.comScienceDirectHHDJoumal of HydrodynamicsELSEVIER201 1,23(1):95-104www. sciencedirect com/DOI: 10.1016/S1001-6058(10)60093-5science/jounal/10016058TYPHOON PROCESSAND ITS IMPACT ON THE SURFACECIRCULATION IN THE NORTHERN SOUTH CHINA SEATANG Ling, ZHAN Jie-min, CHEN Yi-zhanDepartment of Applied Mechanics and Engineering, Sun Yat-sen University, Guangzhou 510275, China,E-mail: sunnytl969@163.comLI Yok-sheungDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, ChinaNIE Yu-huaSouth China Sea Branch, State Oceanic Administration, Guangzhou 510300, China(Received November 4, 2010, Revised December 28, 2010)Abstract: A severe typhoon Utor, ocurring between July 3 and 8, 2001, brought heavy rinfall, strong wind and storm surge. Utorwas responsible for tremendous destruction and economic losses in Philippines, Taiwan and Guangdong. An air-sea model system(MM5 and Princeton Ocean Model (POM)) was built to simulale meteorological dynamics and ocean circulation in the South ChinaSea (SCS). In the POM the output of MM5 was used as the input data. With an increased number of vertical levels, a high-resolutionplanetary boundary layer scheme and updated landuse/vegetation data, the accuracy of computing wind, temperature and othermetcorological fields are improved in near surface and upper levels in MM5 simulations. The simulated trajectory and wind speed ofUtor are close to the observed resuls. The simulated distribution of rainfall is accorded well with measured data in the Pearl RiverDelta (PRD) area. At different meteorological stations in Hong Kong, the wind, temperature and sea surface pressure are wellsimulated. The simulated ocean surface current and surface temperature fields have an obvious rightward-biased response to thetyphoon Utor, and the maximum velocity and the lowest temperature region appear in the 30 km of the right side of the typhoon track.The typhoon Utor could make the water 50m under the surface ocean unwell to surface and the ocean surface temperature decreaseby about 2°C.Key words: mesoscale model MMS, Princeton Ocean Model (POM), air-sea coupling, occan surface circulationIntroductionChina in spring and autumn, sometimes in summer.A storm surge is a rise of sea level generated by aAccording to the statistics of the National Maritimelow pressure weather system. Storm surges are causedBureau, China, during the 50 years between 1949 andprimarily by a drop of the atmospheric pressure and1998, storm surges with higher than I m sea level risethe associated strong winds dragging the sea surface.occurred 270 times, more than five times a year onIt belongs to the class of long gravitational wave, withaverage. Storm surges with higher than 2 m sea levela period ranging from a few hours to several days.rise occurred 48 times and those with higher than 3 mStorm surges usually occur in the coastal areas ofsea level rise occurred 15 times. Among those stormthose countries frequently hit by typhoons in summersurge events, great damage and losses were recordedand autumn. Less severe storm surges generated byfor 112 times. Severe storm surges bring disasters tocyclones usually occur in the north coast of Europe,coastal areas in China, especially in the river estuaries,the east coast of the United States and Bohai Bay ofgulf coast and coastal low lands. The Guangdongcoastal area and Pearl River Delta (PRD) region havebeen中国煤化工y in summer and* Biography: TANG Ling (1979-), Male, Ph. D.autun; dense populationCorresponding author: ZHAN Jie-min,andYHCNMH(aking correct andE-mail: cejmzhan@gmail.comeffective defense measures to minimize the96destruction and losses caused by storm surges isof frontal passage through the Lake Erie region. Theimportant for the sustainable development of economyMM5 provided surface heat and momentum fluxes toin these regions'".the POM, which returmed lake surface temperatures toNumerical simulation of storm surges consists ofhe MM5. The MM5 provided 10 m winds to thethree aspects: the simulation of pressure and windGDM, which returned sea state information to thefields, the simulation of sea level rise caused by stormMM5. To study the ocean circulation along theand the coupling with astronomical tide. TheCaliformnia Coast in June. 1999 and upwellingcommonly used mesoscale atmosphere models arevariability, Gordana et alused the POM toMMSI2l and WRFI) developed in the US, highcompute interactively wind stress and surface heatresolution MESO-NH from France for simulation offluxes and the MMS provided atmospheric fields usedurban heat island effect, Regional Spectrum Modelin the surface flux estimates during the POM runs. Qi(Ncep/RSM) from Japan, HLAFS and the newet al.l2l used the MM5 and Ecom-si to complete ageneration mesoscale model GRAPES-MESO used bysynchronous coupled air-sea numerical model. Thethe National Meteorology Centre， China. In thelower layer boundary of MM5 was obtained from thenumerical simulation of storm surge, the, widelySea Surface Temperature (SST) predicted by the seaapplied models are the new generation SLOSH4 (Sea,model and the upper layer boundary of Ecom-si wasLake and Overland Surges from Hurricanes)obtained from the MM5 output. A passing cyclonedeveloped by the National Oceanic and Atmosphericevolving over the Yellow and East China Seas in 1995Administration (NOAA) and National Weatherwas simulated by this coupled system.Service (NWS) of the US， DELFT3D fromThe mesoscale atmosphere model MM5 can beNetherlands which can reproduce the extent of theused to simulate accurately the typhoon trajectory,inundated and destroyed area. Zhou et al."5l used thesurface wind speed, sea level pressure, eyewall, spiralwave model WAVEWATCH-1II to simulate seacloud band and corresponding precipitation!'. In thissurface directional wave spectra under typhoon windarticle, the MM5 and POM were coupled to simulateforcing in the South China Sea (SCS) and thethe typhoon Utor occuring in the scs and PRD insimulation results agreed well with the buoy2001. The input data of POM model were obtainedobservations. Liu et al.o analyzed the mixing in everyfrom MM5 output. The coupled air-sea model waswater layer before and after the passage of Typhoonused to simulate and analyze the storm surge and thePabuk in the northerm SCS from August 4 tovariation of surface circulation in the SCS region".September 6, 2007. The results showed that theinternal-wave-scale dissipation rate and the mixingrate in every water layer increased by about two1. Models descriptionorders of magnitude, while the turbulent dissipation1.1 MM5rate increased by about an order of magnitude. A caseMM5 (the Fifth- Generation NCAR/Penn Stateof abrupt strong current was also analyzed and theMesoscale Model) is the latest in a series developedmixing rate was calculated. However, there was anfrom a mesoscale model used by Anthes at Penn Stateincrease in mixing only in the lower layer where thein the early 1970s. After many years of development,abrupt strong current was particularly strong. Xu ethe broadened capabilities include multiple-nest,al!"T examined and analyzed the annual mean andnonhydrostatic dynamics， 4-D data assimilation,seasonal variability of the Yellow Sea Warm Currentincreased number of physics options and portability to(YSWC) by using a 3-D ocean model together witha wider range of computer platforms, includingseveral experiments. The results showed that the localOpenMP and MPI systems.monsoonal forcing and local wind-stress forcingA variety of Planetary Boundary Layer (PBL)played important roles in modulating the seasonalschemes and explicit and implicit microphysicalvariability. Xia et al.' adopted the Princeton Oceanprecipitation processes have been developed in theModel (POM) to simulate the climatologicalMM5. There are also a variety of explicit moisturecirculation and the results showed that the POM hasschemes, from simple warm rain and simple icesound ability to simulate the coastal circulation asschemes to the Goddard and Reisner schemes whichwell as the general ocean circulation.involve detailed and complicated physical processes.For coupled air-sea models, in order to reproduceThe interaction of cumulus clouds with thethe extreme storm surge height, Kim and Y amashital9atmosphere is very important for the numericalused the synchronous coupled wind-wave-surgesimulation of meteorological fields. The commonmodel composed of MM5 for the wind and sea surfacer are Anthes-Kus,pressure, Wavewatch III for waves and the PrincetonGrell中国煤化IihchapepOcean Model (POM). Jordan and Mark 0 combinedand I1HCNMHGthe MM5， POM and the surface wave model1.1.1butulllig CyuallUis UI IIVIJ(GLERL-Donelan Wave Model) to simulate an eventIn terms of terrain following coordinates97( x,y,σ ), the goveming equations for the basic2+Ip(5)variables of the nonhydrostatic model are givenc。6below.(1) PressureThe advection terms can be expanded asp'_,- Pogw+ ypV.V =-V.Vp'+'rp(2. + I工,V.VA=mu+mvAA。。AA(6)2tT(cp日° )axdy dσ(1wherewhere p' is perturbation pressure, p is pressure,V is velocity vector, w is vertical component ofmσ ap(7)velocity，c。is specific heat capacity， T is airp°p° dxp° dytemperature, T and P。 are respectively referenceThe divergence term can be expanded asair temperature and density， Q is nonadiabaticheating term.V.V=m2 dmσdp"du+m2(2) Momentumx(m)p xo+" m)Momentum in the x-directionmσap' 2v_ Po8 2wdu. + m(ap'_ σ ap ap'(8)= -V.Vu+p'dydσp'dσp(dxp'dx8σ)In the model, Eq.(1) does not include the lastam_., am- ewcosa -uW-+D。 (2)term with parentheses on its right side. This isvf+u-vxearhneglected and it represents a pressure increase due toheating which forces the air to expand. EquationsMomentum in the y-direction(2)-(8) include terms (eu and ew) representing theusually neglected component of the Coriolis force,v+m(ap’_σap'ap')_V.Vv-where e= 25cosh, a=φ-p，n is the latitude,dt° ρdy p° dydσφ is the longitude, and P。is the central longitude.u0m/dy，vam/dx and r。 h terms representuf+u)m__ 2m+ ewsina--+D. (3)vwcurvature effects. Equations (2), (3) and (8) includethe terms to account for the sloped sigma surfaces indyCerthcalculating horizontal gradients.In addition, the equations for moistureMomentum in the z-directionconservation and other microphysical variables (suchas cloud and precipitation) also include advection anddw_ P。 g ep'+gp'PoT'_different source/sink terms. In spatial finiteat ρ p°0σ γpp T。differencing, a staggered scheme of Arakawa B-gridwas used. In temporal finite differencing, asecond-order leapfrog time-stepping scheme was used,+D。 (4)but some terms were handled using a time-splittingC, Pscheme to increase calculation efficiency.There are different lateral boundary conditionwhere u and v are horizontal components of velocity,schemes in the MM5 system, including the fixedm is map-scale factor, ρ is air density， p' islateral boundary condition, time-dependent/nest lateralreference pressure difference between the top andboundary conditions and relaxation/inflow-outflowlateral boundary conditions. In the nonhydrostaticbottom pressure of the model, D is divergence term.dynamics system, choosing the relaxation/inflow-(3) Temperatureoutt中国煤化工-)ns can improve-V.VT +.1+V.Vp'- Pogw +simulC N M H Ghich could reduce: scheme designedPC, ((子he reriectlon oI energy Irom Ine model top, thuspreventing some spurious noises'. The expression is98as followsareas and estuaries. After continuous improvementand updating, it has been successfully used in manyp= PNw(9)fields of marine science, and widely accepted byKphysical oceanographic researchers.1.2.1 Computational grid and boundary conditionsThe POM model computational domain,whereP and W are the horizontal Fourier98"E-126°E and 39S-26'N, covers the SCS as showncomponents of pressure and vertical velocityin Fig.2. The horizontal resolution of the grid wasrespectively，p is the density of air, N is0.250 x 0.25° and 15 vertical sigma levels were used.buoyancy frequency and K is the total horizontalThe topography was interpolated from the global 5' xwave number.5' ETOPO5 and the maximum calculated depth was1.1.2 Model setup of MM55 500 m. All computational boundaries were fullyIn the simulation MM5 v3.6 with theclosed. The extermal and intermal time steps were setnonhydrostatic dynamics capacity was used. Theto 12 s and180 s, respectively. .model employed two nested domains for two-wayinteraction. The horizontal resolutions of the twodomains were 40.5 km and 13.5 km. The grids wererespectively 105 X 147 and 121 x 148 (Fig.1). Thelarger domain covered almost the whole SCS. Theterrain following σ coordinate was used in thevertical direction. There were 35σ levels from thesurface to the upper atmosphere. The 30 global terraindata and 25-category (USGS) vegetation data(updated to new landuse data of PRD in 2001) wereused in this model. The NCEP I x 1 resolutionmeteorological reanalysis data were input as the initialguessed fields. Mixed-phase, which adds supercooledwater to the above and allows for slow melting ofsnow, was chosen as the explicit moisture scheme.The planetary boundary layer was set to theFig.2 Regional grid and topography of POM22high-resolution MRFII scheme and Blackadarscheme which included the free convective mixed2. Coupling of MM5 with POMlayer. The 4-D grid data assimilation methodIn this article, MM5 was coupled with the POM(Newtonian nudging) was used on the surface and 3-Dto construct an air-sea coupling system. The steps ofatmosphere during the model integration.model coupling were as follows:(1) Taking 360 d in a year, POM was warmned up0012from a motionless state in June. After 50 d calculation,POM had achieved stability and could simulate thesea condition from mid-July onwards. Afterinitialization of POM, SST was output.Dom0220t 2250Fig.1 Two nested domains in MMS modeling system上22251.2 POM? PantRineDelaThe POM was adopted to simulate the response14001425'Eof the ScS to the typhoon Utor and quantitativelyanalyze the calculated results. The POM is a 3-Datations in Hong Kongprimitive equation model established by Blumberg中国煤化工and Mellor at the Atmospheric and Oceanic SciencesLaboratory of Princeton University in 1977. It wasMHCNMHGputtoMMSastheinitially used in the circulation simulation of coastalsurface temperature. Since the grids of MM5 and3.6厂32厂2r8F2828上4F24上2420 r0F20 t1.612 t量08-)8 F04)4 F0.40s1015Wind spedhmsWindspedm:s'Wind: seedms'Windspeedhm.s"间) 25 bovete向) 35 leveds(G) 40 beveds(曲s0 lovelsFig.4 Simulated vertical wind profilesPOM were different, MM5 attained temperature byare simulated in the MM5 and thus meteorologicaldistance weighted interpolation of the nearest fourfields in different vertical levels are interactive. Hencepoints at each gridpoint. After integration, MM5improving the accuracy of meteorological fields inoutput wind field and heat flux needed by POM.upper levels would lead to better simulation results in(3) POM used the output of MM5 as input data tolower levels. Through the sensitivity tests, it wasintegrate and output new SST data.found that if there were too many vertical levels under(4) MM5 used the new SST as input to run for2 000 m, the wind profile would be distorted. Innext time step (using the restart mode).addition, more vertical levels and grid cells would(5) Repeating Step (3)-(4) until calculation wasrequire greater amount of computer time and mightcompleted.even induce instability. The optimum number ofvertical levels was 35.3. Sensitivity tests for vertical σ levels in MM5We studies four cases using the same model4. Typhoon Utorparameters and meteorological conditions besidesUtor was a severe typhoon which brought greatdifferent number of vertical σ levels: 25, 35, 40 anddestruction to many places. Utor was unusual in that it50 levels. The simulated vertical wind profiles at GZlpersisted for more than 40 h, a very rare event in the(location of GZI is shown in Fig.3) are shown in Fig.4.last 30 years. Utor attained typhoon strength in theCompared with that of the 25 vertical levels inafernoon of July 3, 2001 and attained its peakFig.4(a), the simulated wind speed under 20 000 mintensity that night with the maximum sustained windsbecame roughly uniform and stable in Figs.4(b), 4(c)and minimum sea-level pressure near its centerand 4(d). Using more vertical levels in both the lowerestimated at 130 km/h and 965 hPa, respectively. Aand upper atmosphere, we could obtain more detailedlarge and irregular eye was discemible in satelliteand accurate vertical wind profile and otherimagery. Utor's circulation was extensive, its radiusmeteorological fields. In particular, the density 0reaching some I 000 km. Crossing the Luzon Strait onvertical levels above 2 000 m is usually sparseJuly 4, Utor's outer rainbands inflicted severe damagecompared with that near surface levels. Increasing thein Philippines and Taiwan. After entering the SCS innumber of vertical levels above 2000 m can improvethe early morming of July 5, Utor slowed down togreatly the accuracy of simulation in upper levels,20 km/h as it approached the coast of Guangdong. Itresulting in better analysis of weather phenomena,made中国煤化工-8 a.m. on July 6such as the southwest low-level and high-level jetsaical storm. Utorwhich have significant influence in the South China inweakefYHC N M H Gepression on Julysummer. To take into account the vertical convection7 and dissipated the following morming while enteringbetween different vertical levels, the buoyancy effectsGuangxi.100Utor caused 23 deaths in Guangdong whereUtor, another typhoon, Durian, which had weakenedover 4 000 houses were destroyed, 758 hectares ofgrcatly and was dissipating can also be seen.farmland inundated and 500 hectares of fishponds lost.In neighboring Guangxi, because of torrential rain, thewater level of the Yongjiang River rose to 5.4 mabove the danger level, the highest in 50 years. Duringthe passage of Utor, about 0.15 m of rainfall wasbrought to most parts of Hong Kong. The heaviestrain fell on the Lantau Island, where more than 0.3 mof rain were recorded. The strong winds and lowpressure of Utor also brought storm surge to HongKong on July 6. Coupled with the astronomical highi5I25'Etide, sea levels reached 3.6 m in Tsim Bei Tsui and3.4 m in the Quarry Bay around 9 a.m to 10 a.m. TheFig.7 Sacllie image at 20:00 on July3reading in the Quarry Bay was the highest recorded inthe Victoria Harbour since the typhoon Wanda in^Np1962.25七5. Analysis of MM5 simulation results5.1 Typhoon irajectory and highest wind speedIt can be seen from Fig.5 that the simulatedtyphoon trajectory is very close to the observed one.51The simulated maximum wind speed is about 26 m/sin the simulation region (showen in Fig.6), while the05lis125°Ehighest recorded wind speed is approximately 30 m/s.After entering the SCs, the simulated results are aFig.8 Simulated wind vectors at 20:00 on July 3little smaller than the observed values.001012130°下-3988Sim __5r 20」109010012030140 °EFig.9 Observed sea level pressure at 8:00 on July 5Fig.S Simulated and observed tajcctorics of Utor. 100__ 129，130°E-Ng1020601/Fig.6 Simulated highest surface wind speed in the simulationFig. 10 Simulated sea level pressure at 8:00 on July 5region5.2 Satellite image and simulated wind vectors5.3.中国煤化工=ely the contours ofIt can be seen from Figs.7 and 8 that thesimulated typhoon center position and impact radiusobserMYHCN M H Gressure at 8:00 onfit well the satellite observation results. To the left ofJuly 5. The simulated typhoon center location accordsU1well with the observed data. The gradient andon July 6. It shows the rainfall distribution in the PRD,distribution of sea level pressure in the two figures areespecially in Hong Kong. The echoes coded in yellowvery similar. This shows that the simulation results arerepresent rainfall concentration areas (greater thancredible and accurate.30 mm/h). Figures 14(a) and 14(b) are respectively the5.4 Simulated temperaturecomputed total precipitable water and precipiationThe location of the typhoon center and thethree hours later. It can be seen from the two figuresdistribution of sca level pressure at 00:00 on July 6 arethat the simulated rainfall and rain belt accord with theshown in Fig.11. The distibution of simulatedradar echoes, but the simulated results have a time lagtempetature at 00:00 on July 6 is shown in Fig.12. Itof about 3 h.can be seen from Fig.12 that the temperature of landsurface is 3° to 5° lower than that of the sea surface.11。120°EThe temperature near the typhoon center is about 2°"Nlower than that in the surrounding arca because ofheavy rainfall and upwelling of sea water of lowertemperature to the surface near the typhoon center.010011020_ 130°E'N110 mmFig.14(a) Contours of total precipiable water at 22:00 on July 6A1.1Fig.11 Simulated sca level pressure at 00:00 on July 62226 mm-2Fig. 14(b) Contours of total precipitation at the same instant5.6 Simulation results of meteorological fields atobservation stations5.6.1 Wind vector time seriesThree observation stations, CCH, KPS and LFSFig.12 Simulated temperature at 00:00 on July 6(shown in Fig.3)， were chosen to compare theobserved and simulated wind vector time series inHong Kong. In Figs.15(a)， 15(b) and 15(c)， the“Observation”and “Simulation." respectivelyrepresent observation and simulation results. The twosets of results for wind direction at the three stationsare basically coincident every hour, but the simulatedwind speeds are lower at WGL (an outlying islandstation), higher at KPS (an urban station) and roughlyequal at LFS (a suburban station).5.6.2 TemperatureThe simulated and observed time variations otemperature at KPS in Hong Kong are shown inFig.13 Radar echoes captured at 19:00 on July 6Fig.1obsen中国煤化工”we wu thecatches well the5.5 Total precipitable water and precipitation0HCNMH Gthat relected thesimulatedFigure 13 is the radar echoes captured at 19:00highest and lowest temperatures were also very close102to the observed ones.during the episode was respectively 982.3 hPa atWGL occurring at 17:00 on July 6, 981.7 hPa at TKLat 16:00 and 982.0 hPa at 17:00 at LFS. Compared20; 10with the observation data from the Hong KongObservatory in Table 2, the simulated lowest sIp was-103.7 hPa higher at WGL and 1.7 hPa higher at both20 406080100 121MTKL and LFS. The simulated lowest SLP are veryclose to the observation data. The time that the lowestsIp occurred lagged behind by about 10 h at the threestations.02040608010012Table I Simulation results of the lowest sea level pressures(a) CCH StationStationLowest SLPTimeDay!_(hPa)MonthWGL982.317:00/7善σTKL981.716:006/7如80 100 12LFS982.05/710台。Table 2 Observation results of the lowest sea level pressuresLowestDay/SLP0 2040980100120.(b) KPSStation978.65:16980.06:396/g 0f980.38:14080 100 120。10苦004 (1000二aL020406096FS(C) LFS Sution992Fig.15 Time series of wind vector984207-442001-7-50:000.00二So36 FFig.17 Simulated lowest sea level pressure at WGL, TKL andLFS Stationssor24-6. Analysis of POM resultsThe simulation results indicate that the response408000 120of the SCS to the typhoon is rightward-biased becauseof the following reasons. Firstly, the typhoon windFig.16 Comparison betweensimulated and observedfield is rightward-biased as the right-hand side windtemperaturespeed is much higher than that of the left-hand side.Secondly, the right-hand side of the ocean flow moves5.6.3 Sea level pressureFigure 17 shows the simulated Sea Levelin the same direction as the typhoon trajectory. WhatPressure (SLP) variations with time by hours at WGL,is m中国煤化工side of the oceanTKL and LFS stations (shown in Fig.3). The lowestflow; Coriolis force.TheseHCNMHGt with those ofslp occurred around 16:00 on July 6. In particular, itPricelE1 and Walker et al.!41can be seen in Table 1 that the simulated lowest SLP03high velocity region in the right-hand side of thetyphoon trajectory and the maximum velocity was1.26 m/s. In the second stage, there was anKGicTance vccosapproximately oval cyclonic eddy in the sea surfacecurrent field. After landfall of the typhoon, the extentof the flow loop rapidly decreased and disappearedwithin 50 h. The maximum velocity on the right-handside of the typhoon decreased to 0.4 m/s and theinertial flow continued for about 4 d.6.2 Response of ocean surface temperature110lis120"EThe ocean surface temperature decreased b(a) Ocansurface avrngecuront in Julyabout 2°C with a rightward-biased response to thetyphoon (Fig.19) and the location of the lowestIerlcrance vetorstemperature region was about 30 km to the right of thetyphoon trajectory. Due to the strong mixing process,here was a large low temperature area near thetyphoon center, which was linked to the typhoonintensity. After the typhoon landing, the temperaturebegan to increase and returmed to the initial state in30 h.16+115l20"E(6) Reponseof sufice caument at 1200m lulys7. ConclusionsThe typhoon Utor occurred between July 3 andFig. 18 Comparison of simulated ocean surface current fields8，2001. A coupled air-sea mesocsale numericalsimulation system (MM5 and POM) has beenconstructed to simulate the meteorological dynamicsand ocean circulation in the SCS area. Thconclusions are:(1) With two-way interaction between nested日26domains, 4-D data assimilation, high resolution20planetary boundary layer schemes and new vegetationdata, the MM5 can simulate accurately wind vector,temperature, typhoon trajectory, pressure near thetyphoon center and rain belt of typhoon Utor.115120°E22 .(2) Higher horizontal and vertical resolutions can间) Ocansrface avongcunat inulyimprove the accuracy of computed wind, temperatureand other meteorological fields in near surface and。Nupper levels in MM5 simulations. In the studied case,24the horizontal resolution of the sub-domain is 13.5 kmand the number of vertical levels is increased to 35.These have improved the stability and accuracy of the20-simulation.(3) The MM5 has been coupled sccessfully withthe POM for studying and analyzing the ocean16circulation in the SCS. Using the improved output of11120"E 22MM5 as input, the POM has simulated well the oceanb) Responseof surface ounem a0:00oJuly6response to typhoon Utor.(4) The ocean response to the typhoon isFig. 19 Comparison of simulated ocean surface tenperaturesrightward-biased. The extent and strength of the windfield on the right-hand side of the typhoon are much6.1 Response of ocean surface current fieldThe ocean surface current field has a stronglarger and stronger than those on the left-hand side.response to typhoon. in the simulation as shown inThe中国煤化工west temperatureFig.18. Price et al.251 divided the response processregior; right side of theinto the force phase and recovery phase based ontyphoHCNMHG(5) Because' ot ine typnoon entrainment effect,measured data. In the simulation, the frst stage of thethe cold water of the bottom ocean was pumped to theforce phase was around 20 h. In this stage, there was aocean surface, resulting in a decrease of the ocean[12] Qi Chun-xia, HUANG Li-wen and WU Guo-xiong et al.surface temperature. In this simulation, the typhoonNumerical experiment of a coupled air-sca mesoscalemodel mm5 v3/ecom-si[J]. Journal of WuhanUtor could make the water 50 m under the surfaceUniversity of Technology (Transportation Scienceocean unwell to surface， and the ocean surfaceand Engineering)2003, 27(4): 445-448(in Chinese).temperature decreased by about 2°C.[13] . ZHONG Zhong, ZHANG Jin-shan. Explicit simulationon the track and intensity of tropical cyclone winnie(1997)[]. Journal of Hydrodynamics, Ser. 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