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HAN Lei. 2014. An error evaluation on the vertical velocity algorithm in POM. Acta Oceanologica Sinica, 33(7):12-20
An error evaluation on the vertical velocity algorithm in POM
模态分离的环流模式POM的垂向速度算法的误差估计
Received:January 14, 2013  Revised:November 26, 2013
DOI:10.1007/s13131-014-0505-7
Key words:mode splitting  asselin filter  velocity adjustment method  POM
中文关键词:  模态分离,计算误差,POM模式
基金项目:The National Science Foundation of China under contract Nos 40906017 and 41376038;the National “863” Project of China under contract No. 2013AA09A506;the National Key Scientific Research Projects of China under contract No. 2012CB955601;the Special Projects on Public Sector under contract Nos 200905024 and 201409089.
Author NameAffiliationE-mail
HAN Lei First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China
Institute of Oceanography, Chinese Academy of Sciences, Qingdao 266071, China 
hanlei@fio.org.cn 
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Abstract:
      A time splitting technique is common to many free surface ocean models. The different truncation errors in the equations of the internal and external modes require a numerical adjustment to make sure that algorithms correctly satisfy continuity equations and conserve tracers quantities. The princeton ocean model (POM) has applied a simple method of adjusting the vertical mean of internal velocities to external velocities at each internal time step. However, due to the Asselin time filter method adopted to prevent the numerical instability, the method of velocity adjustment used in POM can no longer guarantee the satisfaction of the continuity equation in the internal mode, though a special treatment is used to relate the surface elevation of the internal mode with that of the external mode. The error is proved to be a second-order term of the coefficient in the Asselin filter. One influence of this error in the numerical model is the failure of the kinetic boundary condition at the sea floor. By a regional experiment and a quasi-global experiment, the magnitudes of this error are evaluated, and several sensitivity tests of this error are performed. The characteristic of this error is analyzed and two alternative algorithms are suggested to reduce the error.
中文摘要:
      时间分裂技术是若干自由面海洋模式的常用技术。内外模态方程的不同的截断误差要求进行必要的数值调整,以保证算法能够正确地满足连续性方程,且使得示踪量守恒。POM模式应用了一种简单的将内模态流速的垂向平均调整为与垂向积分的外模态流速一致。但是,由于控制数值不稳定的Asselin时间平滑算法的引入,POM的速度调整方法不再能保证连续性方程严格成立,即使它采用了特殊的处理根据外模态水位来定义内模态的水位。误差被证明是Asselin平滑算子的二阶项。该误差的在数值模式中的一个影响为海底的运动学边界条件不再满足。通过一个区域模拟和一个准全球模拟实验,对该误差的量级进行了估计,并进行了若干敏感性实验。文章分析了该误差的特征,并提出了两个减少误差的算法。
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