[Mitgcm-support] Note: February 1, 2001

[mitgcm-support at dev.mitgcm.org]

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NOTES FROM THE ASSIMILATION MEETING : 1 February 2001    

1) Figure for Eric
-------------------
   - Eric Lindstrom has requested a plot highlighting our work to be
     included in a NASA Report (Earth Science Enterprise).  The plot
     is needed by Monday.  He rejected the following suggestions;
        * Trajectory plot
        * Assimilation's reduction of model-data residuals
        * Term balance
        * ssh Hovmoeller diagram
     He says these are "science journal stuff" and not for public
     consumption.  He wants "eye candy" and a "sense of usefulness."  

     The following were discussed as alternatives;
        * Change of Equatorial Currents.
           Undercurrent, Counter Current.
           Show change as a function of xy, xz, or yz.
        * Focus in the upper 150m where changes are largest. 
        * Plots should be of assimilation. 

   - This sort of request will recur and we need to be prepared.  We
     should collectively think of what to highlight and keep a copy of
     plots handy.  

2) K-filter 
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   - A summary of the effects of trend on the skill of assimilation
     was posted[1].  Removing the trend in sea level reduces model
     degradation by the assimilation.

   - Model process noise is being calibrated so that uncertainty
     estimates used in assimilation are consistent with actual
     model-data differences.  Run kf023a, in particular, described in
     the summary above is not consistent in this regard even though it
     results in little degradation.  When process noise is calibrated
     (matched) to be comparable to prior model error estimate
     (kf024f), the assimilation once again leads to degradation off
     Taiwan.  It is speculated that the degradation is due to
     unrealistic K-filter updates at the northwestern cell boundary;
     The cellular filter's error estimate should taper to zero at open
     boundaries due to representation error.  When corrections are
     forced to zero at the north-south boundary (20N, 20S) of the
     Pacific cellular filter (kf024i), the degradation indeed is
     diminished even when using the calibrated process noise.

  [Addendum] This figure[2] compares skill of dynup over 1993-97 for
     kf024f (top left; calibrated Q), kf024i (top right; calibrated Q,
     tapered P at NS boundary), and kf023b3 (bottom left; uncalibrated
     Q).  kf024i has nearly as small a degradation as kf023b3.  

     Summary of this error calibration will be posted shortly.

   - K-filter comparison with XBTs described last week have been
      posted[3].  The largest improvement is found in the eastern
     equatorial Pacific.  There is non-trivial change outside the
     tropics.  

   - T/P data for K-filtering has been extended to end of 1999.  The
     problem with the data reported last week was in Akiko's
     processing (some of her input files were incorrect?). Benny has
     posted a summary package of preparing the T/P data here[4]. 

3) Adjoint 
-----------
   - The one-year adjoint has completed 12 iterations.  This analysis[5]
     at the end of the 10th iteration shows improvement beyond the 5th
     iteration (i.e., 10th better than the 5th iteration).

   - Dimitris has implemented Moto's term-balance diagnostics to the
     forward code of ECCO (the adjoint assimilation code).  Benny is
     making the implementation compatible with TAMC.  The diagnostics
     will allow term-balance analysis of the adjoint assimilation.

4) Other
---------
   - Extension of control (c20000630) to end of 1999 is ongoing at
     Ames.  

   - Zhangfan has implemented the automatic e-mailing of disk backup
     information.  Each user should keep an eye on it.  If you don't
     receive any e-mail, that means nothing is done.  If you receive
     the message, check if the disk was backed up successfully or not.

===> Everyone to monitor the e-mail and be aware of when your disks
     were last backed up successfully and take corrective action if
     necessary .  

   - Nick found assimilation skill of his barotropic model (with
     respect to independent bottom pressure data) to be slightly
     better than the MITgcm K-filter run when he reduced the magnitude
     of his process noise.   
  
     However, this improvement is limited to periods longer than
     15-days, similar to what was found with the MITgcm.  This means
     that there is no gain in doing assimilation as far as T/P
     de-aliasing is concerned; simulation is good enough.  However,
     the assimilation was done with stationary model error P.  Taking
     into account the time variation in P (due to inhomogenous
     T/P sampling) may allow improvements at higher frequencies.  

   - The new forum is not up yet.  

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