[Wrf-users] OBS nudging

Fri Aug 26 12:38:07 MDT 2011

I'm replying to my own question here, so others can find the solution.
Solved.  Tags for searching: hourly OBS nudging, OBSGRID, WRF 3.3.
Solution first, statement of the problem below.

SOLUTION:

In namelist.wps, set (among other settings):

&share

interval_seconds = 21600  

to match your input GRIB data (every 6 hours for my data).

Make your obs_filename (OBS:*, little_r format) files each contain only
1 hour of data.  This conflicts somewhat with the statement in the WRF
v3.3 Users Guide
<http://www.mmm.ucar.edu/wrf/users/docs/user_guide_V3/users_guide_chap7.
htm#namelist> , Chapter 7, under OBSGRID Namelist: "Ideally there should
be an obs_filename for each time period for which an objective analysis
is desired."  I suppose I should interpret "objective analysis" as
either the 3D objective analysis or the 2D surface analysis.

I believe it should say that there should be an obs_filename for each
intf4d (surface analysis) period.  This is the key.  

In namelist.obsgrid, set (among other settings):

&record1

interval =  21600

&record2

obs_filename = path/to/OBS

&record7

f4d      = .TRUE.

intf4d   =  3600

This will produce OBS_DOMAIN101 with 1 hour of data (+/- 30 minutes from
the start time); OBS_DOMAIN102 with 5 hours of data; OBS_DOMAIN103 with
1 hour of data (+/- 30 minutes from start + interval [6 hours]); etc.

You must concatenate all the OBS_DOMAIN1?? files into a single
OBS_DOMAIN101 file in the WRF run directory.  The Users Guide does not
explicitly state this, though the latest tutorial does.

auxinput11_interval_m is the minimum time interval you would like to
check for new observations.  If you want to nudge every hour, set this
to 3600.   Note that this is listed in test/em_real/README.obs_fdda as
auxinput11_interval_s = 180, (180 seconds) which I believe is a typo.
They problem meant 180 minutes (3 hours).

auxinput11_end_h is the time at which you want to WRF stop reading
OBS_DOMAIN101.  

PROBLEM:

Following the WRF v3.3 Users Guide, Chapter 7, my obs_filename (OBS:*,
little_r format) files each contained 6 hours of data (to match interval
= 21600).  

At each intf4d time interval, OBSGRID opens an obs_filename file with
the current time-stamp.  It DOES NOT check for the existence of the file
before it opens the file.  

So if your obs_filename (little_r) files each contain 6 hours of data,
then at hour +1 it opens (and thus creates) a file with that time-stamp.
Of course it's empty (newly created) so no data are read, and no data
are output to the OBS_DOMAIN* file for that hour.  If you started with
obs_filename files like this:

-rw-rw-rw- 1 username 650M Aug 25 10:02 OBS:2008-01-29_12

-rw-rw-rw- 1 username 630M Aug 25 10:10 OBS:2008-01-29_18

-rw-rw-rw- 1 username 650M Aug 25 10:16 OBS:2008-01-30_00

Then after OBSGRID.EXE had run, you'll have files like this:

-rw-rw-rw- 1 username 650M Aug 25 10:02 OBS:2008-01-29_12

-rw-rw-rw- 1 username    0 Aug 25 10:03 OBS:2008-01-29_13

-rw-rw-rw- 1 username    0 Aug 25 10:05 OBS:2008-01-29_14

-rw-rw-rw- 1 username    0 Aug 25 10:06 OBS:2008-01-29_15

-rw-rw-rw- 1 username    0 Aug 25 10:07 OBS:2008-01-29_16

-rw-rw-rw- 1 username    0 Aug 25 10:08 OBS:2008-01-29_17

-rw-rw-rw- 1 username 630M Aug 25 10:10 OBS:2008-01-29_18

-rw-rw-rw- 1 username    0 Aug 25 10:10 OBS:2008-01-29_19

-rw-rw-rw- 1 username    0 Aug 25 10:12 OBS:2008-01-29_20

-rw-rw-rw- 1 username    0 Aug 25 10:13 OBS:2008-01-29_21

-rw-rw-rw- 1 username    0 Aug 25 10:14 OBS:2008-01-29_22

-rw-rw-rw- 1 username    0 Aug 25 10:15 OBS:2008-01-29_23

-rw-rw-rw- 1 username 650M Aug 25 10:16 OBS:2008-01-30_00

and your OBS_DOMAIN1?? files will contain only data +/- 30 minutes from
each interval (each 6 hours).  

Bart

From: wrf-users-bounces at ucar.edu [mailto:wrf-users-bounces at ucar.edu] On
Behalf Of Bart Brashers
Sent: Wednesday, August 24, 2011 5:09 PM
To: wrf-users at ucar.edu
Cc: wrfhelp at ucar.edu
Subject: [Wrf-users] OBS nudging

I have a few questions about using OBS nudging in WRF v3.3.  I'm using
the 12km NAM data, which comes in 6 hour intervals.  WPS ran fine, and I
have met_em files every 6 hours.

I have processed MADIS data to little_r format, and named the files
OBS:YYYY-MM-DD_HH.  Each file contains 6 hours of data, which I've
confirmed via grep (e.g. "grep 200801 OBS:2008-01-29_18 | cut -c 327-336
| sort | uniq" shows the right time-stamps).

1. OBSGRID.EXE creates OBS_DOMAIN101, OBSDOMAIN102, etc.  But each file
contains only ONE hour's data (the analysis hour +/- 30 minutes).  The
OBS data for the next 5 hours is not output.  How can I get OBSGRID.EXE
to create OBS_DOMAIN1* files that contain ALL the available data?  I
want to nudge every hour, not every 6 hours.

2. The most recent notes in the WRF User's Guide
<http://www.mmm.ucar.edu/wrf/users/wrfv3.1/How_to_run_obs_fdda.html>
make no mention having to concatenate the OBS_DOMAIN1* output from
OBSGRID.EXE to OBS_DOMAIN101, but the tutorial notes
<http://www.mmm.ucar.edu/wrf/OnLineTutorial/Class/cases/obs_nudging1.php
>  do say so.  Which is correct?  Will WRF not read OBS_DOMAIN102,
OBS_DOMAIN103, etc.?

3. If I want to nudge every hour, do I set auxinput11_interval_m = 60 in
WRF's namelist?  Or is that supposed to match OBSGRID's record1 interval
?

4. If I want to keep nudging till the very end of my simulation, can I
set auxinput11_end_h = 99999?  

The meaning of these two values is pretty unclear in the
README.namelist, README.obs_fdda, as well as the WRF User's Guide and
tutorial notes.  If anyone can shed some light, I'd be most
appreciative.

Thanks,

Bart

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