3DVAR Tutorial
a.
Downloading Test
Data
(03/23/2004)
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. If users do not have a first-guess file ready to be
available, the
geographical and domain information could be provided through an
alternative
namelist file namelist.3dvar_obs
(See OBSPROC presentation),
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 3DVAR_code_data. 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 a subdirecotry Tutorial_data.
cd Tutorial_data You
will see the
be, be_global, fg, ob.little_r, obs_gts.3dvar data files, and a
README file in directory ${DAT_DIR}/Tutorial_data. To know what
these files
are, look at README file. To save space, cd ${DAT_DIR}, and 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.