求助大侠：wrfout小时数据，如何做日均图？

ellen

小白求助。
wrfout文件，有如下小时的数据。剔除上一日18-22时数据，计算2015-05-02_00:00:00至2015-05-02_22:00:00平均值。
(0)        Working on time: 2015-05-01_18:00:00
(0)        Working on time: 2015-05-01_20:00:00
(0)        Working on time: 2015-05-01_22:00:00
(0)        Working on time: 2015-05-02_00:00:00
(0)        Working on time: 2015-05-02_02:00:00
(0)        Working on time: 2015-05-02_04:00:00
(0)        Working on time: 2015-05-02_06:00:00
(0)        Working on time: 2015-05-02_08:00:00
(0)        Working on time: 2015-05-02_10:00:00
(0)        Working on time: 2015-05-02_12:00:00
(0)        Working on time: 2015-05-02_14:00:00
(0)        Working on time: 2015-05-02_16:00:00
(0)        Working on time: 2015-05-02_18:00:00
(0)        Working on time: 2015-05-02_20:00:00
(0)        Working on time: 2015-05-02_22:00:00
(0)        Working on time: 2015-05-03_00:00:00

截取官网的ncl脚本，Basic Surface Plots   wrf_Surface1.ncl
请问怎么做，才能做日均值图呢？
What times and how many time steps are in the data set?
  times = wrf_user_getvar(a,"times",-1)  ; get all times in the file
  ntimes = dimsizes(times)         ; number of times in the file

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

  do it = 0,ntimes-1,2             ; TIME LOOP

    print("Working on time: " + times(it) )
    res@TimeLabel = times(it)   ; Set Valid time to use on plots

dunbating

同问，并不懂