Changes between Version 4 and Version 5 of Documentation/UserGuide/Perturb

Timestamp:

2017-01-19T10:30:22+01:00 (7 years ago)

Author:

luyssaert

Comment:

--

Documentation/UserGuide/Perturb

@@ -20 +20 @@
 The folder /ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/ELI-128x118x39-2010-R2 should now look as an independent folder. The initial atmospheric conditions are given in /ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/ELI-128x118x39-2010-R2/ATM/Output/Restart/ in the file JOBNAME_YEAR_start.nc as the variable called TETA. Subsequently we will open this file, perturb TETA by a random field of small perturbations and then save the file with a perturbed value for TETA. Several libraries with ncdf4 functionality (confirmed for nco, R and python) contain commands that enable you to manipulate a variable in a netcdf file. In this example a python script was used to perform these tasks.
 
+{{{
+#!/usr/bin/env python
+#-------------------------------------------------------------------
+# Objectives
+#-------------------------------------------------------------------
+# The script opens the limit file from LMDZOR and perturbs the 
+# initial temperature (TETA) as described by Fisher et al.
+ 
+#-------------------------------------------------------------------
+# Load modules and functions Definitions
+#-------------------------------------------------------------------
+import netCDF4
+from netCDF4 import Dataset
+import numpy as np
 
+#----------------------------------------------------------------
+# Simulation settings
+#----------------------------------------------------------------
+year = 2101
+mu = 0.0
+sigma = 0.00001
+jobname = 'ELI-128x118x39-2100-RCP85-P2'
+path = '/ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/'+ jobname+'/ATM/Output/Restart/'
+file_name = jobname +'_'+str(year)+'_start.nc'
 
+#----------------------------------------------------------------
+# Open file and extract some dimensions 
+#----------------------------------------------------------------
+fullfile_name = path+file_name
+ncfile = Dataset(fullfile_name, mode='r+')
+lon = ncfile.variables['rlonu']
+lat = ncfile.variables['rlatu']
+lev = ncfile.variables['nivsigs']
+teta = ncfile.variables['teta']
+n_lon = len(lon)
+n_lat = len(lat)
+n_lev = len(lev)
+print teta[:,:,:,:]
+perturbation = np.random.normal(mu, sigma,[1,n_lev,n_lat,n_lon])
+ncfile.variables['teta'][:,:,:,:] = teta[:,:,:,:] + perturbation[:,:,:,:]
+ncfile.close()
+}}}
+
+Before running the script, copy the initial start file because the script will overwrite it. If something goes wrong you will loose the initial values of the ELI simulation. Remember to change the permissions so that python can write the changes into the netcdf file.
+{{{
+cd /ccc/store/cont003/dsm/p529luy/IGCM_OUT/LMDZ/ELI-128x118x39-2010-R2/ATM/Output/Restart/
+cp JOBNAME_FIRESTYEAR_start.nc JOBNAME_FIRSTYEAR_start_original.nc
+chmod 744 JOBNAME_FIRESTYEAR_start.nc
+}}}
+
+If all went well JOBNAME_FIRESTYEAR_start.nc should have been changed. This can be easily checked by comparing TETA in JOBNAME_FIRESTYEAR_start.nc against JOBNAME_FIRESTYEAR_start_original.nc. A map with the random perturbations should appear. For example,
+{{{
+ferret
+use JOBNAME_FIRESTYEAR_start.nc; use JOBNAME_FIRESTYEAR_start_original.nc; shade TETA[k=1,d=1]-TETA[k=1,d=2]; go land
+}}}