calculating monthly mean and ensemble mean

Question

I have GLB_JJA_PRECT.nc contains JJA season climatological mean 1981-2010 for 205 members looks like:- me@mali:/mnt/hgfs/t/data+plots/k$ cdo info GLB_JJA_PRECT.nc -1 : Date Time Level Gridsize Miss : Minimum Mean Maximum : Parameter ID 1 : 1981-07-09 22:41:52 0 3600 0 : 4.5667e-11 2.7681e-08 4.0864e-07 : -1
2 : 1981-07-09 22:41:52 0 3600 0 : 3.5674e-11 2.7657e-08 3.9481e-07 : -1
3 : 1981-07-09 22:41:52 0 3600 0 : 6.0882e-12 2.6316e-08 2.6459e-07 : -1
4 : 1981-07-09 22:41:52 0 3600 0 : 1.3473e-11 2.6756e-08 3.0247e-07 : -1
5 : 1981-07-09 22:41:52 0 3600 0 : 1.4372e-11 2.7102e-08 2.8263e-07 : -1
6 : 1981-07-09 22:41:52 0 3600 0 : 2.2106e-11 2.6214e-08 3.2279e-07 : -1
7 : 1981-07-09 22:41:52 0 3600 0 : 3.5954e-11 2.6145e-08 2.9494e-07 : -1
8 : 1981-07-09 22:41:52 0 3600 0 : 4.8026e-11 2.6042e-08 3.2751e-07 : -1
9 : 1981-07-09 22:41:52 0 3600 0 : 3.7863e-11 2.5948e-08 3.6591e-07 : -1
10 : 1981-07-09 22:41:52 0 3600 0 : 2.4222e-11 2.5728e-08 4.2891e-07 : -1 . . .
to 205

when i did splitstep,1 i got all 205 files, each file has same attr information and different var values me@mali:/mnt/hgfs/t/data+plots/k$ cdo sinfo GLB_JJA_M_000001.nc File format : NetCDF -1 : Institut Source T Steptype Levels Num Points Num Dtype : Parameter ID 1 : unknown GAMIL v instant 1 1 3600 1 F32 : -1
Grid coordinates : 1 : lonlat : points=3600 (90x40) lon : 0 to 356 by 4 degrees_east circular lat : -87.75 to 87.75 by 4.5 degrees_north Vertical coordinates : 1 : surface : levels=1 Time coordinate : time : 1 step RefTime = 1975-01-01 00:00:00 Units = days Calendar = 365_day Bounds = true YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm:ss YYYY-MM-DD hh:mm:ss 1981-07-09 22:41:52

cdo sinfo: Processed 1 variable over 1 timestep [0.02s 45MB]. me@mali:/mnt/hgfs/t/data+plots/k$ cdo info GLB_JJA_M_000001.nc -1 : Date Time Level Gridsize Miss : Minimum Mean Maximum : Parameter ID 1 : 1981-07-09 22:41:52 0 3600 0 : 4.5667e-11 2.7681e-08 4.0864e-07 : -1

i would like to calculating back the june, july and august monthly mean values 1981 - 2010 for each member, and also the monthly enseble of each month using NCO ??