3DVAR Tutorial
a. Downloading Test
Data
(06/09/2003)
In the 3DVAR tutorial,
you will be running the 3DVAR observation preprocessor (3DVAR_OBSPROC) as well
as 3DVAR itself. This page describes how to access test datasets to run both
3DVAR_OBSPROC and 3DVAR. If you don't know anything about 3DVAR, you should
first read the 3DVAR Overview.
1. Required
Data
The 3DVAR_OBSPROC
code currently inputs observations in “LITTLE_R” format (so-called because it
is the format of the previously used LITTLE_R
objective analysis package). In addition, 3DVAR_OBSPROC requires an MM5 format
file (the first-guess forecast) from which header information describing the
domain is retrieved in order to reject observations that are outside the area
of interest. The 3DVAR_OBSPROC algorithm performs gross quality control and
writes an observation file in “3DVAR” format ready for ingest into 3DVAR. The
3DVAR_OBSPROC system is described in further detail later in the tutorial.
The 3DVAR system
requires three input files to run. In addition to the first guess and
observation files used by 3DVAR_OBSPROC, a background error statistics file
(containing background error covariances currently calculated via the
“NMC-method). The use of these three data files in 3DVAR is described later in
the tutorial.
The following
table summarizes the above info:
|
Filename |
Created By |
Used In |
|
ob.little_r |
User’s
Decoder |
3DVAR_OBSPROC |
|
fg |
INTERPF
or MM5 |
3DVAR_OBSPROC,
3DVAR |
|
ob |
3DVAR_OBSPROC |
3DVAR |
|
be |
NMC_STATS |
3DVAR |
In this tutorial,
example ob.little_r, fg, and be files are given. In your
own work after the tutorial, you will need to create the input data sets
yourselves.
2. Downloading
Test Data
In this tutorial,
we will store data in a directory defined by the environment variable $DAT_DIR
and run 3DVAR in a directory defined by the environment variable $RUN_DIR.
It is OK to set them equal if you wish. These directories can be in any
location that can be read and written to from your current machine and which
have at least 200MB of memory available (for this test case, may be more for
other cases). To set these
variables, type
setenv DAT_DIR
dat_dir
setenv RUN_DIR
run_dir
where dat_dir and
run_dir are your chosen directories. Create these directories (if they don’t
already exist) and type
cd $DAT_DIR
Download the
tutorial test data for our standard case from the NCAR ftp
site. Once you have downloaded the 3dvar_test_data.tar.gz file to $DAT_DIR,
then extract it by typing
gunzip
3dvar_test_data.tar.gz
tar -xvf 3dvar_test_data.tar
You should then
see the be, fg, ob.little_r (and maybe a few other) data files in
directory $DAT_DIR. If so, then to save space type
rm 3dvar_test_data.tar
3. What
next?
OK, now you’ve
downloaded the necessary data, you’re ready to do some observation
preprocessing. Go to
Trouble Shooting:
1. Having trouble, ask mesouser.