May 25
------

VPR survey operations continued.

Forecasting Activities
----------------------

Much of the day was spent investigating the potential causes of the
decrease in forecast skill we have experienced in the last drifter
deployment.  A set of five sensitivity experiments were conducted 
around the May 24 central forecast EN324_FC.38.  The first (run 40)
represented an attempt to "restart" the forecast system based on 
the canonical forecast timing parameters used at the December meeting
at NCSC.  This differs from the timing scenario described in the
May 22 narrative in that ADCP data during the drifter deployment
is assimilated.  Thus, such a run test our ability to hindcast the
drifter trajectories rather than to forecast them.  The timing
diagram is as follows:

###########
EN323_FC.40
###########

                             ----------------------------------------   Q4.2,3
                           *
                        HS                       [Dye--->
              -------------------------------------------------------   Q4.1
            *                                    [Drifters
         CS                               [ADCP-----------]

Year Day 134  135  136  137  138  139  140  141  142  143  144  145  146
     May  15   16   17   18   19   20   21   22   23   24   25   26   27
                                                  [Wind]

Analysis of the results from EN323_FC.40 revealed some large spikes in
the ADCP data record.  The bad values were edited out, and simulation
EN323_FC.41 was run with the new data record.  Run EN323_FC.42 reverted
back to the mass fields created from the last broadscale survey
conducted on Oceanus; TDBCS were turned off in run EN323_FC.43, and
atmospheric forcing was turned off altogether in run EN323_FC.44.

The table below shows the mean forecast error for each run, in 
addition to the separations for each drifter.  As these runs were
being carried out, it appeared to us that there may be an error in
the launch point location of the 13m drifter provided in the .ind
file.  This was corrected in run EN324_FC.41cdr, and resulted in
significant improvement in the forecast skill.  Beyond that,
the results of the sensitivity experiments were qualitatively
consistent with our experience up to this point (i.e. runs 42-44).
Still, the forecast error remains higher than it was preceding
the series of wind events we have had recently.  The cause of
this is still under investigation.

                                  13m    8m   33m   Mean

EN324_FC.40     (38) new timing  (10.2) 2.9   8.2   (7.1)
EN324_FC.41     edited ADCP file (10.2) 5.7   5.5   (7.1)
EN324_FC.41cdr  edited ADCP file  5.4   5.5   2.1    4.4
EN324_FC.42     OC Mass fields    5.0   4.9   4.8    4.9
EN324_FC.43     TDBCS off         5.1   4.8   5.2    5.0
EN324_FC.44     Tau, Q off        5.0   6.2   4.3    5.1

** () indicates statistics which are affected by the suspected
      problem in the release location of the 13m drifter.

Operational Products
--------------------

No new operational products were issued on May 25.