The Influence of Round-off Error on the Atmospheric General Circulation Model
舍入误差对大气环流模式模拟结果的影响

Round-off error has an influence on the numerical model computations.It is easy to determine the differences between the results of the model SAMIL with different CPUs.After the analysis of the ten-year integration of SAMIL,the error range of global mean height at 500 hPa is determined;it is also found that the global mean height error is decreased at the same level using double precision.The experiment described in the paper proves that the error that arises out of the change in computation sequence is acceptable and that the double-precision computation can help reduce the computing error.Though the global mean error is not very large,the standard error of the difference is not small,and it can be estimated by the experiments in the paper.The estimation shows that it has the same magnitude as the annual change of the simulation results.Therefore,the distribution of mean error cannot be ignored when the model is used to study such cases as annual climate change.In this paper,three different methods adopted to analyze the round-off errors of a complicated numerical model are listed.The equivalence of the three under some conditions is discussed in the paper,as well as their particular applicability conditions.Moreover,the authors introduce a new type of ensemble forecast(RME,Round-off error Mean Ensemble) method to decrease round-off error in climatic study.These methods may be helpful to users who want to analyze the influence of round-off errors of other numerical models.