[Mitgcm-support] Note: January 11, 2001
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Wed Jul 9 15:56:41 EDT 2003
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NOTES FROM THE ASSIMILATION MEETING : 11 January 2001
1) K-filter
------------
- The assimilation code that was lost in December has been
reconstructed and deposited to CVS; see posting[1]. Furthermore,
the baroclinic and barotropic codes have been combined to perform
the assimilation simultaneously.
- Two baroclinic filter runs that were lost in December have been
recovered. Two more barotropic filter runs are being carried
out.
- In the process of recovering the code, we discovered that
previous calculations were using outdated topex data files (dated
5/11/00 instead of 7/20/00) that had a bug at some data
locations.
- It was also discovered that the previous K-filter runs were using
suboptimal fortran optimization. Optimization by
set FOPTIM = ( '-O3 -OPT:Olimit=0:roundoff=3:div_split=ON:alias=typed')
gives 40% speedup in code execution. Now the baroclinic K-filter
code runs take 4 hours/model-year instead of 8 hours. In
comparison, the forward model alone (control) takes 3
hours/model-year.
====> ACTION : Benny to post summary description of what the
optimization flags do.
- The recovered baroclinic results are comparable to what we had
before, even after the bug correction of T/P data. This figure[2]
compares the dynamic update skill (simulation residual minus
innovation) of the old result (top two) with recovered results
(lower two). kf023 assumes process noise Q to be NCEP wind
covariance. kf024 assumes a larger Q the scaling of which is
from covariance matching.
- The negative patch seen in the skill plot above east of the
Philippines indicates degradation by the filter. Sea level time
series are compared at this and other locations in 6-deg bins to
see what may be the cause of this degradation; 138E-27N[3],
183E-27N[4], 223E-0N[5]. In these figures, black is T/P, blue is
simulation, red is kf023 and green is kf024a. The major
difference between model and T/P east of the Philippines
(138E-27N) appears to be a trend in the model; Note black curve
being lower than the colored curves during 1993-1994 while it is
opposite during 1996-1997. Such trend may indicate
time-correlated process noise which the present K-filter does not
account for. Similar trends and degradation were corrected in
the MOM assimilation by removing trends in computing the
model-data difference.
====> ACTION: Assimilation to be repeated with trend removal.
Such trend is not obvious at other locations where the filter
does not degrade the model estimate. In particular, see how the
filter corrects the blue simulation at 223E-0N.
- More model-data comparisons will be done with the assimilated
results; e.g., XBTs.
====> ACTION: Comparison of K-filter results with XBT data [Dimitris].
Detlef shows an example of such comparison based on
upper ocean heat content.
2) Ames Origin 2000
-------------------
- Ames queue allows time-sharing; i.e., multiple jobs are allowed
to run simultaneously. Therefore, our present helper algorithm
will not work at Ames. There is also a possibility of
oversubscription.
====> ACTION: Zhangfan to see if some other helper algorithm
can be implemented.
- Ames computer is indeed faster than alhena. Last week's
assessment was in error. The summary[6] has been updated.
In particular,
* lomax is large and faster than alhena
* although the queue is crowded during non-prime-time[7],
prime-time usage is low and should be taken advantage of
if the application can be run within 2-hours wall clock.
3) Others
----------
- The Division requires us to heighten our awareness and compliance
of our working hours. A 45-min lunch time is excluded from the
8-hour work hours. Telecomuting (working from home over the
network instead of working on lab) is not approved.
====> ACTION: Notify Ichiro of your normal start and end times
(e.g., 9am-5:45pm).
- Communication needs to be improved within the team to eliminate
duplication and to achieve a higher level of productivity (e.g.,
some were not aware of the fortran optimization above that
speed-up code execution.)
====> ACTION
* Each member should summarize at the weekly meeting what he
has been doing the previous week and to describe what he will
be doing next. Each member should think of this before the
meeting and come prepared.
* More postings to the forum should be made.
* The forum should be upgraded to allow searching strings
within the text of the postings.
- A 50-year run (1950-2000) will be conducted to establish a
benchmark for a longer assimilation and as a headstart for the
50-year assimilation (one of the ECCO goals).
====> ACTION:
* Dimitris to look into obtaining the necessary 50-year
forcing.
* Zhangfan to put the forcing field on Ames. Assess whether
it would be better to archive the fields on the Ames mass
storage or to rsync the fields from alhena:/tmp whenever the
fields are necessary.
- The present control (c20000630) and K-filter need to be extended
further into the future.
=====> ACTION:
* Zhangfan/Benny to ask Akiko for the data and prepare them
for assimilation.
* Tony will retrieve the forcing field from Charmaine.
(up to Oct 2000)
* The T/P data and forcing preparation need to be done on a
routine basis.
- The operating system on three Linux boxes (nautilus, giant,
stormy) will be upgraded next week. [Zhangfan]
- The parallel version of the doubling program will be finished
this week. [Zhangfan]
- Nick is calibrating prior error for assimilation with a wind and
pressure driven global barotropic model. Errors are being
estimated so as to make the innovation sequence as small as
possible. The best results are obtained with NCEP pressure
covariance scaled by 0.1%, which seems too small (if P rms is
20mb, the error would be 0.6 mb). The error in pressure is
believed to be about 2 to 3 mbar.
- Escher disks are full. Tony needs ~20 GB.
=====> ACTION: Everyone to review what he has on guppy and delete what
is not needed.
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[1] http://escher.JPL.NASA.GOV:2000/HyperNews/get/forums/cvslog/10.html
[2] http://escher.JPL.NASA.GOV:2000/hosts/escher/escher2/medea/if/forum/t73f5c.ps
[3] http://escher.JPL.NASA.GOV:2000/hosts/escher/escher2/medea/if/forum/t73c6d_1.ps
[4] http://escher.JPL.NASA.GOV:2000/hosts/escher/escher2/medea/if/forum/t73c6d_2.ps
[5] http://escher.JPL.NASA.GOV:2000/hosts/escher/escher2/medea/if/forum/t73c6d_3.ps
[6] http://lochness.jpl.nasa.gov/naso2k.html
[7] http://escher.JPL.NASA.GOV:2000/HyperNews/get/forums/comp/21/3.html
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