flexpart-wrf模式COMMAND设置

myhx

请教flexpart-wrf模式，COMMAND设置里面：
CTL    (real)     factor by which time step must be smaller than tl
IFINE  (int)      decrease of time step for vertical motion by factor ifine
请问这两项参数  是怎么理解的？一般设置多少呢？
试了一下，CTL设大于0和小于0，模拟结果完全不一致

linhongxiao

FLEXPART can be used in two different modes. The computationally faster one (ctl<0) does not adapt the computation time step to the Lagrangian time scales  and FLEXPART uses constant time steps of one synchronisation time interval (lsynctime, typically 900 seconds)。在这种模式下，自相关性很低，同时湍流描述不够好。
如果想更好地描述湍流过程，必须采用拉格朗日时间尺度（通过一些边界层参数可以算出）来限制郎之万方程的时间步长（水平：&#8710;t_i，垂直：&#8710;t_w）。ctl(在拉格朗日时间尺度上进行控制)是一个比例系数，用来控制&#8710;t_i的大小（最小1s）。Since the vertical wind is most important, For solving the Langevin equation for the vertical wind component, a shorter time step&#8710;t_w=&#8710;t_i/ifine is used。
This strategy (given suf&#64257;ciently large values for ctl and ifine) ensures that the particles stay vertically well-mixed also in very inhomogeneous turbulence, while keeping the computational cost at a minimum.
采用这两个因子来使郎之万方程的时间步长远小于拉格朗日时间尺度，来保证在非均相湍流中粒子在垂直层混合均匀。