Technique to delete spin-up frames from WRF

Question

I'm a user of WRF V3.5 aiming at meteorological simulation.
Sometimes, I'll run the model for a long period.

My attempt

I split the long period(e.g 1 year) into serval short ones.

For example:

 ## WPS namelist.wps      
 start_date = '2014-01-01_06:00:00'
 end_date   = '2014-01-31_23:00:00'  

 ## WRF run period setting in .csh file.    
 set year = "2014"
 foreach strtime (010106010512 010500011012 011000011512 011500012012 012000012512 012500013012 013000020100)

 set smon = `echo ${strtime}|cut -c1-2`
 set sday = `echo ${strtime}|cut -c3-4`
 set shr  = `echo ${strtime}|cut -c5-6`
 set emon = `echo ${strtime}|cut -c7-8`
 set eday = `echo ${strtime}|cut -c9-10`
 set ehr  = `echo ${strtime}|cut -c11-12`  

 &time_control
 run_days                            = 0,
 run_hours                           = 132,
 run_minutes                         = 0,
 run_seconds                         = 0,
 start_year                          = ${year},${year},
 start_month                         = ${smon},${smon},
 start_day                           = ${sday},${sday},
 start_hour                          = ${shr},${shr},
 start_minute                        = 00,00,
 start_second                        = 00,00,
 end_year                            = ${year},${year},
 end_month                           = ${emon},${emon},
 end_day                             = ${eday},${eday},
 end_hour                            = ${ehr},${ehr},
 end_minute                          = 00,00,
 end_second                          = 00,00,
 interval_seconds                    = 21600

In these short period, I set the first 12-h as the spinning period(except the start one.)

This is the schematics of the temporal modeling setup which I clipped from the Internet.

http://i12.tietuku.cn/afd906ddd823ddd6.png

Result

It generate 8 .nc file which each contain 132 frames of data.
For now, I use the The netCDF Operators(NCO) to deal with the output files.

1. Using ncks to delete the first 12-h frames for each file separately.

2. Using ncrcatto concat all 8 .nc files together to get one file represent the whole simulation period.

Problem

I was using this method for a while. But when the amount of files are huge, it really a dump approach.

Are there someone offering your approaches to dealing with spin-up data deletion?

My target

• The model can generate only one file which contain all the simulation period.
• The spin-up time can be covered by last file's frames automatically.

Update: Wish you share your approaches!

Answer 1

Here is my present approach.

1. All wrfout-files are located in the same path.

2. Using pynco in python loop to split the spin-up dataframe

   import glob
   nco = Nco()
   for fn in glob.iglob('*.nc'):
       filename, extname = os.path.splitext(fn)
       output_fn = filename[11:22] + str(int(filename[22:24]) + 12) + extname
       nco.ncks(input=fn, output=output_fn, dimension='Time,13,')  
   

The input shows like: 2014-04-04_12.nc(120 frame inside)
The output shows like:wrfout_2014-04-04_00:00:00.nc(133 frame inside)

Answer 2

There is an feature of the -d option that makes the call of ncks redundant. However, it is available since NCO version 4.2.1 (Aug. 2012).

ncrcat -d Time,13,,132,120 wrfout* summary.nc
# -d dim,[min][,[max][,[stride][,[subcycle]]]]

This feature is deeply hidden in the online manual. You find it here: nco.sourceforge.net/nco.html#Subcycle .

Explanation:

• 13: first time step we consider
• [empty]: till the end
• 132: we have a cycle length of 132 steps
• 120: we take the first 120 values (starting from the 13th) of each cycle

If we write -d Time,13,0,132, which equals -d Time,13,0,132,1, we would only get each 132nd value starting with the 13th.

I do not process WRF output but we work with the Chemistry Transport Model CMAQ. We get hourly resolved concentration output files for each day. These files have 25 time steps (0 o'clock of the current and the next day) and we need to remove one of the ) o'clock time steps and append the files. For this purpose, I use ncrcat -d TSTEP,0,,25,24 [infiles] [outfile].

The straight forward approach would be to write a Fortran program for this purpose. But, I also prefer the NCO's. Maybe you could try the cdo's (code.zmaw.de/projects/cdo) as an alternative. However, my solution with cdo's for this task was more bulky than the NCO solution.