IAP AGCM-4动力框架的积分方案及模式检验

The Computational Scheme and the Test for Dynamical Framework of IAP AGCM-4

以灵活性跳点格式和时间分解算法为重点,介绍了IAP(中国科学院大气物理研究所)AGCM-4的动力框架,并用R-H(Rossby-Haurwitz)波和Held-Suarez方案对框架进行了检验。结果表明:高纬灵活性跳点格式很好地保持了普通跳点格式的各种性质,未产生计算紊乱现象,可在一定程度上增大时间步长,在未采用滤波处理时增大时间步长的效果更为显著;时间分解算法,即将平流过程与适应过程分开计算,二者都采用3次非线性迭代积分方案,在N=5和N=10(N为平流过程时间步长与适应过程时间步长的比值)的情况下,可分别节省CPU时间10.7%和19.9%;R-H波检验表明,在积分的前80天,框架较好地保持了R-H4波的波形,总有效能量仅衰减0.1%,从第80天开始,风场波形开始变形和破碎,对应的动能和总能量也开始急剧衰减,至第365天,总有效能量衰减约8%,此时,风场和高度场亦变得较平直。经分析,第80天R-H波破碎的主要原因是平流项的计算误差使R-H波失稳,而其后的高度场和风场的变平直是典型的旋转适应机制;Held-Suarez方案检验也证明该框架是可靠的。

A flexible leaping-point scheme and a time-splitting method are introduced to the new generation of IAP （Institute of Atmospheric Physics, Chinese Academy of Sciences） atmospheric general circulation model （IAP AGCM-4）, and the model＇s dynamical framework is tested by Rossby-Haurwitz （R-H） wave and by Held-Suarez proposal. The results show that the flexible leaping-point scheme can also conserve the available energy without computational chaos, and it can enlarge the time step especially in the model without filter. A time-splitting method is adopted to compute adjustment process and advection process respectively, and a nonlinear iterative time integration scheme with 3 times iteration is applied to both the processes. The time-splitting method can economize CPU time by 10.7% （N=5） and 19.9% （N=10）, respectively. As R-H-type pattern of wave number 4 is taken as the initial condition, in the first 80 days of integration, the dynamical framework can preserve the wave pattern well, and the total available energy only reduce 0.1%. From the 80th day, the wave pattern of zonal wind becomes deformed and then breaks, while the corresponding kinetic energy and total available energy begin to decrease sharply. By the 365th day, the fields of zonal wind and geopotential height become parallel to the longitudinal direction, and the total available energy has decreased 8%. The analysis shows that it is due to the rotational adaption and the dissipation of advection term. The test by Held-Suarez proposal also shows the reliability of the dynamical framework of IAP AGCM-4.