利用POM模拟海州湾温带风暴潮

Numeric simulation of extratropical storm surge in Haizhouwan Bay by POM

利用POM模式模拟了2007年0303号温带风暴潮在海州湾的增减水过程,以期为风暴潮预报提供参考。模式计算时采用2重嵌套网格,大网格为小网格提供边界水位和边界流速。风场、气压场由连云港观测站实测资料逐步订正后得到。水位计算值与实测结果基本吻合,很好地再现了风暴潮增减水过程。

Extratropical storm surge happens frequently in Haizhouwan Bay.At present,statistical method is still used at the operational forecast center for positive and negative setup of the storm surge,and the result is not satisfactory.In this study 0303 extratropical storm surge of 2007 in Haizhouwan Bay is numerically simulated using POM model with an aim of improving operational forecast result.The model was run on two fold embedded grids,in which the boundary water level and current velocity of the internal grid were provided by the calculated results of the external grid.The calculation area of the external grid is 117°～128°E and 25°～41°N,which covers the Bohai Sea,the Yellow Sea and part of the East China Sea,with a spatial resolution of 20′×20′.The time steps of external and internal model are 1 s and 30 s respectively.Sea surface atmosphere pressure was obtained from numeralization of the surface weather map,and the sea surface wind stress from CCMP（Cross-Calibrated,Multi-Platform ocean surface wind velocity product） of NASA.The normal velocity on the solid boundary was set to zero,and the water level on the open boundary was calculated with the harmonic consistent of 8 partial tides of M2,S2,N2,K2,K1,O1,P1 and Q1.The calculation area of the internal grid is 119.1°～119.9°E and 34.5°～35.5°E,which covers the Haizhou Bay.An orthogonal grid was used to adapt to the coastline.There are 50 grids along meridional direction and 60 along transmeridional direction,and the side lengths of the grids are about 1 km.The water level and current velocity on the open boundary were set according to the calculated results of the external grid.The water depths were obtained by bi-linear interpolation of the digitalized 1∶120 000 chart from Rizhao Port to Guanhe River mouth,which is surveyed and mapped by the Navigation Guarantee Department of the Navy Headquarter,the People＇s Liberation Army of China.As the model was set up,a case of 0303 extratropical storm surge of 2007 was studied.From March 3,2007 to early March 5,a strong extratropical storm surge occurred in the area from Bohai Sea to Haizhou Bay resulted from the combined action of the Huanghai Sea cyclone and intense cold air from northern China.On March 3,a surface inverted trough came into being in Jianghuai area,and moved northeastward.Up to 8：00 a.m.on March 4,a cyclone formed in northern Huanghai Sea.From March 4 a strong northerly gale occurred in Haizhou Bay with a mean force of 6~7.At 3：00 a.m.the storm surge setup reached 73 cm.At 8：00 p.m.on the day,the low pressure center moved to Korea Peninsula,and the wind direction at Haizhou Bay turned from northward to eastward as before the storm surge.The model was run from Feb.24,2007,ten days ahead of the beginning of the storm surge,in order to eliminate the influence of initial conditions.Firstly,the tide harmonic constant and then the astronomical tide was calculated with one year observed data from a long-established tidal station at 34°47′N,119°26′E.Secondly,simulated storm surge sea level was obtained by simulated sea level minus the astronomical tide.And the observed storm surge sea level was obtained likewise.Finally,the simulated results from March 2 to 4 were compared with the observed storm surge,which shows that the highest sea level is only 2 cm greater,but 12 h ahead of actual setup,and the lowest is 22 cm smaller,but very close to the negative setup（2 h ahead）.The simulated trend of sea level agrees with the observation.The numerical simulation shows that it is effective to use POM to simulate the extratropical storm surge in Haizhou Bay.The simulation error is mainly due to the low spatial resolutions of water depth,wind and atmosphere pressure,and also the error of boundary conditions.