WRF ARW User's Guide - MMM - UCAR

WRF-VAR
files. Please see http://www.mmm.ucar.edu/mm5/mm5v3/data/free_data.html for the
sources of some freely available observations and the program for converting the observations
to LITTLE_R format. Because the raw observation data files could be in any of
formats, such as ASCII, BUFR, PREPBUFR, MADIS, HDF, etc. Further more, for each
of formats, there may be the different versions. To make WRF-Var system as general as
possible, the LITTLE_R format ASCII file was adopted as an intermediate observation
data format for WRF-Var system. Some extensions were made in the LITTLE_R format
for WRF-Var applications. More complete description of LITTLE_R format and conventional
observation data sources for WRF-Var could be found from the web page:
http://www.mmm.ucar.edu/wrf/users/wrfda/Tutorials/2009_Jan/tutorial_presentation_win
ter_2009.html by clicking “Observation Pre-processing”. The conversion of the userspecific-source
data to the LITTLE_R format observation data file is a users’ task.
The purposes of OBSPROC are:
• Remove observations outside the time range and domain (horizontal and top).
• Re-order and merge duplicate (in time and location) data reports.
• Retrieve pressure or height based on observed information using the hydrostatic
assumption.
• Check vertical consistency and super adiabatic for multi-level observations.
• Assign observational errors based on a pre-specified error file.
• Write out the observation file to be used by WRF-Var in ASCII or BUFR format.
The OBSPROC program—obsproc.exe should be found under the directory
WRFDA/var/obsproc/src if “compile all_wrfvar” was completed successfully.
a. Prepare observational data for 3D-Var
To prepare the observation file, for example, at the analysis time 0h for 3D-Var, all the
observations between ±1h (or ±1.5h) will be processed, as illustrated in following figure,
which means that the observations between 23h and 1h are treated as the observations at
0h.
WRF-ARW V3: User’s Guide 6-8