基于Nudging方法对全球海洋M_(2)和m_(1)分潮的同化研究

Assimilation of Global Ocean M_(2) and m_(1) Tides Based on Nudging Method

基于全球海洋模式OGCTM(Ocean General Circulation and Tide Model),利用19年(1992—2011年)的卫星高度计资料调和分析得到全球分潮调和常数回报逐时正压潮水位;采用Nudging(牛顿松弛逼近)方法进行潮汐同化,针对Nudging松弛项的差分方案以及松弛系数进行了数值试验研究。一系列试验结果表明,不论采用显式还是隐式Nudging松弛方案,模式结果的偏差会随着松弛系数的增加先减小后增大,松弛系数最优值为1×10^(-5);当松弛系数太大时,会造成模式的溢出。Nudging松弛项采用隐式差分方案可以显著提高松弛系数的阈值;松弛系数在适当的取值范围内时,加入Nudging松弛项的数值试验描述的潮汐特征要明显优于未加Nudging松弛项的数值试验描述的潮汐特征;在最优Nudging松弛方案下,Nudging松弛方法对全日分潮的振幅模拟准确度可提高50%,对半日分潮的振幅模拟准确度可提高56%。试验结果也表明了Nudging方法作为一种简单的同化方法的可行性和有效性。

Based on a global Ocean Model OGCTM(Ocean General Circulation and Tide Model),19 years of satellite altimeter data harmonic analysis are used to get the global tidal harmonic constant.Return hourly barotropic tide.By Nudging(Newtonian relaxation approximation)method for tidal assimilation,design numerical experiments about different Nudging relaxation scheme and Nudging relaxation coefficient.Analysis the output sea level by a series of experiments using T-TIDE,obtaining the harmonic constants of M2 and m1((K1+O1)/2).A series of experiments show that the tidal features of the numerical experiment with Nudging relaxation term are significantly better than those without Nudging relaxation term.Regardless of explicit or implicit Nudging relaxation scheme,the deviation of mode result decreases first and then increases with increasing relaxation coefficient,with optimal value of 1×10^(-5).When the relaxation coefficient is too large,the mode will overflow.When the relaxation coefficient is within the appropriate range,the tidal characteristics described by numerical experiments with Nudging relaxation term are significantly better than those described by numerical experiments without Nudging relaxation term.Under the optimal Nudging relaxation scheme,the amplitude of the full-day tide can be improved by 50%,and the amplitude of the half-day tide can be improved by 56%.The experimental results also show that the Nudging method is effective as a simple assimilation method.