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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
Received:January 14, 2013  Revised:November 26, 2013
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 
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      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.
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