WRF demo/tutorial

12-13-2004Robert Fovell

rfovell@ucla.edu

Background on WRF model

• “Weather Research and Forecasting”

• Co-developed by research and operational communities

• Replaces MM5 and Eta models

• Current version 2.0.3.1

• Platforms (for model): Linux, IBM/AIX, SGI, Cray, Darwin… and Sun (hideous)

WRF advantages

• Better numerics than MM5– Arakawa C grid, R-K scheme, odd order advection

w/ implicit diffusion– Much less diffusive, larger effective resolution,

permits longer time steps

• Better topography than Eta• GUI-driven domain configuration, initialization• Fortran 95 (MM5 was F77)• NetCDF output

Further advantages

• Allows real data and idealized simulations in same framework

• Plug-in architecture (different groups will supply WRF “cores”)

• What I’m calling WRF is really the “Advanced Research WRF” (ARW) core

WRF disadvantages

• Bleeding edge• Smaller range of physics choices

overall• No radiation upper bdry condition [yet]• Software design cumbersome, obtuse

[opinion may change with experience]• Nesting is very serious pain [that will

change]

Overview

• WRF Standard Initialization (WRFSI)– Set up domain– Prepare data for model run– MM5 equiv: terrain, pregrid, regridder

• WRF model– Initialize model (MM5’s interpf)– Run model

• WRF post-processing• WRF 3DVAR (not covered today)

Web stuff…

• http://www.mmm.ucar.edu/wrf/users/user_main.html (WRF model users’ site)

• http://www.mmm.ucar.edu/wrf/users/wrfv2/wrf-namelist.html (WRF namelist.input page)

• http://www.mmm.ucar.edu/wrf/users/docs/user_guide/contents.html (WRF users guide)

• http://www.mmm.ucar.edu/wrf/users/tutorial/tutorial-2004.htm (Slides from 2004 WRF tutorial at NCAR)

• http://www.atmos.ucla.edu/~fovell/WRF/WRF_ports.html (Darwin/Mac OS X port)

• http://www.wrf-model.org/si/ (WRFSI home page)• http://www.mmm.ucar.edu/wrf/WG4/tutorial/wrf3dvar_download

_data.htm (WRF 3DVAR tutorial)

WRF for real data run

Example:

24-26 October 2003 (Simi fire)

Directory structure

• …/WRFV2/– Parent directory

• …/WRFV2/wrfsi– WRFSI location

• …/WRFV2/wrfsi/domains/SoCal– Domain setup “SoCal” location

• …/WRFV2/test/em_real– Where real data run will be made

WRFSI

…/WRFV2/wrfsi/wrf_tools

Domain 1terrain

Output from WRFSI

• …/WRFV2/wrfsi/domains/SoCal/siprd

• IC, BC files for D1, IC file for D2• Move or link into …/WRFV2/test/em_real

WRF model

…/WRFV2/

Directory structure

• In ../WRFV2– main/ is where executables live– arch/ default config stuff– frame/ model framework stuff– phys/, dyn_em/ model physics, solver– external/ mainly I/O, MPI stuff– test/ test cases live here– run/ can run model from here, too

Preparing to run

• Configure– ./configure– Select platform, compiler, & whether single

threaded, OpenMP or MPI

• Compile– ./compile em_real– Creates real.exe and wrf.exe in ../WRFV2/main– Creates links to real.exe, wrf.exe in

../WRFV2/test/em_real

Configuring

• ./configure presents option list

• Example: chose option 3, MPI

Compiling

• ./compile presents options

• Example: chose compile em_real– Eulerian mass-coordinate real-data model

Final initialization step

• Move to .../WRFV2/test/em_real

• Edit namelist.input– Lots to do here…

• Execute ./real.exe– Creates wrfinput_d01, wrfbdy_d01 files– Run for each nest separately [ouch]

• Model executable is wrf.exe

Editing namelist.input

• Web resource– http://www.mmm.ucar.edu/wrf/users/

wrfv2/wrf-namelist.html

• Namelist sections [partial list]– &time_control– &domains– &physics– &dynamics

Setup for single domain run

Columns provided for 3 domains (parent & 2 nests)but if max_dom =1 extra columns ignored

Setup for single domain run

time_step ~ 6*DX (3*DX for MM5)… unless convective;Change max_dom when ready to activate nest

Setup for single domain run

Here I have my MOAD dimensions (80x67) andnest dimensions (61x37) entered. Third column ignored since

I only created 2 domains

Setup for single domain run

s_we = start index for west-east direction, always 1.e_we = end index west-east, that’s your dimension

Setup for single domain run

Make sure dx, dy set correctly-- the model does NOT check GUI-created inputs!

Setup for single domain run

Columns provided for 3 domains (parent & 2 nests)but if max_dom =1 extra columns ignored

Setup for single domain run

Here, subgrid mixing and computational diffusion is deactivated;model’s odd order advection is diffusive

Run real.exe & wrf.exe

• ./real.exe– Look for real_em: SUCCESS COMPLETE

REAL_EM INIT message

• mpirun -np 2 wrf.exe &– MPI version creates rsl.out.000* and

rsl.error.000* files– tail -f rsl.out.0000– Look for wrf: SUCCESS COMPLETE WRF

Files created by WRF run

• Named like:

wrfout_d01_2003-10-24_12:00:00

[d01 = domain 1;

file started 12Z 24 October 2003]

• Files can be HUGE (NetCDF inefficient)

- to split output files, namelist entry

frames_per_outfile in &time_control

WRF postprocessing

• RIP (just like MM5)

• WRF2GrADS converter

• WRF2VIS5D converter

• Software that can handle NetCDF

RIP

• RIP version 4 required• Real data runs only• ripdp_wrf expname all wrfout*

– Will unpack every wrfout* files in local directory and all variables and call extracted files “expname”

– Replace “all” with “basic” for less output

• RIP4 unpacker for MM5 is now ripdp_mm5 expname MMOUT*

Animation using RIP

• Part of Domain 1 shown for 24Oct2003 case

QuickTime™ and aVideo decompressor

are needed to see this picture.

Color: 2 m temperature; topo contours; 10 m wind vectors

Nesting

• Created domains 1, 2 for SoCal in WRFSI• WRFSI created wrf_real_input_em* files for

both domains• Need to run real.exe once for each domain• namelist.input needs to be edited for each

real.exe run• Files have to be renamed to “fool” real.exe• Web page explanation:

http://www.mmm.ucar.edu/wrf/users/wrfv2/runwrf.html

MM5 v. WRF on nesting

• MM5:– Need only initialize parent (outer) grid– MM5 interpolates to nests, using nest terrain files

created using terrain

• WRF– If let model interpolate to nests, higher res topo

files are NOT used, unlike MM5– So, you need to init each domain separately with

real.exe, and that takes fooling real.exe…

Fooling real.exe - 2 domain example

• Start with domain 2 first• Edit namelist.input, putting nest information in

first column– Previously, that info was for parent grid

• Rename wrf_real_input_em.d02* IC file as wrf_real_input_d01* [after saving “real” d01 file!!!!]– Here, it’s wrf_real_input_em.d02.2003-10-24_12:00:00 being

renamed as wrf_real_input_em.d01.2003-10-24_12:00:00

• Then…

Fooling real.exe - 2 domain example (cont.)

• This creates a wrfinput_d01 file (since real.exe thinks it’s domain #1)

• Rename that file as wrfinput_d02 (since it’s really for domain #2)

• Restore original domain #1 IC file– Here, it’s wrf_real_input_em.d01.2003-10-24_12:00:00

• Re-edit namelist.input, making sure domain #1 info in 1st column, domain #2 in 2nd…

• Run real.exe again– Creates wrfbdy_d01, wrfinput_d01

Nesting initialization, step by step

• This should be scripted somehow, to avoid mistakes

• Create your namelist.input, with parent and nest domain info, start and stop times, etc…– Set max_dom = 2– Set input_from_file = .true., .true.

• ICs for both domains will be read in from files• Those filenames will be wrfinput_d01, wrfinput_d02

Nesting initialization, step by step (cont.)

• Rename original d01 IC file as

• Copy d02 IC file with d01 IC file original name

• Copy namelist.input as namelist.input.real• Edit namelist.input

– This is your temporary namelist.input file– Set stop time = start time [only want IC]– Replace parent domain info in column #1 with nest info from

column #2

Nesting initialization, step by step (cont.)

• Temporary namelist.input’s &time_control

Nesting initialization, step by step (cont.)

• Temporary namelist.input’s &domains

• Run real.exe• Rename wrfinput_d01 as wrfinput_d02

Nesting initialization, step by step (cont.)

• Clean up:– Move namelist.input.real to namelist.input– Move wrf_real_input_em.d01.2003-10-24_12:00:00.real back to

wrf_real_input_em.d01.2003-10-24_12:00:00

• Run real.exe again, this time creating wrfinput_d01 and wrfbdy_d01

• Now you have– wrfinput files for d01 and d02– wrfbdy file for d01– namelist.input file controlling both domains

• Run the model!

Animation of nest

• Domain 2 shown for 24Oct2003 case

Color: 2 m temperature; topo contours; 10 m wind vectors

QuickTime™ and aVideo decompressor

are needed to see this picture.

Restarting WRF

• In namelist.input, set restart_interval to desired restart output file interval (minutes)

• To restart a simulation– Set restart = .true.– Set start_* time to reflect restart time

WRF performance on my machines

Compile flag notes

• On PCs, Intel beats PGF handily– But use -mp flag for accuracy, consistency as

number of CPUs varied• This flag does NOT refer to multiprocessing w/ Intel

compiler

– Don’t use -xW [vectorization] flag w/o checking (my results so far always wrong)

• On Macs, IBM xlf is a great compiler– But use -qfloat=nomaf flag for accuracy– My tests: virtually identical results between

optimized and non-optimized when nomaf used

WRF for idealized cases

• Ready-made examples include 2D squall lines and 3D supercells

• compile em_squall2d_x for the 2D x-z plane squall line example

• In …/WRFV2/test/em_squall2d_x, run ideal.exe and then wrf.exe

• To change IC for this case, modify …/WRFV2/dyn_em/module_initialize_squall2d_x.F and recompile

Ideal run output using WRF2GrADS

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