May 24
------

Survey operations continued.  Once the large scale survey of
the dye distribution was completed, an extensive set of lines
were occupied to map the Calanus patches in the area.  At approximately
2000h, survey of the dye patch recommenced.  Throughout these survey
operations, periodic lines to the front were occupied to measure the
distance between the front and the dye/Calanus patches of interest.

Forecasting Operations
----------------------

The May 24 Central forecast EN324_FC.38 was computed with all the
latest forcing products and data records.  Once again a twin
experiment was conducted with a delayed starting time (EN324_FC.39).

The first set of drifter observations from the latest deployment
arrived (3 tracks from Manning), permitting some quantitative
evaluation of forecast skill.  Figure 0524.1 compares the observed
drifter trajectories with simulated tracks from the central forecast.
In general, forecast skill is not as good as we have become 
accustomed to in earlier deployments.  The 8m drifter released at 
the 65m isobath is the only case in which there is appreciable
skill; a 2.8km separation develops between the simulated and
observed trajectories as they move to the southwest during the
two tidal cycles of observations.  Comparisons with the 13m and 33m
drogues are poor, with separations in excess of 9km developing during
this relatively short data record.  The 33m simulated drifter moves
south-southeast in contrast with the observed movement to the
southwest.   The west-southwest direction of the simulated 13m
drogue is approximately correct, but the movement is far too slow.
Furthermore, there is a large error in the tidal phasing by the
end of the record.  We have not seen this type of error in any of
our forecast experiments thus far.  Perhaps a mistake may have been
made either in data processing or in incorporation of the simulated
drifter into the model solution.  We will look into this further.

Even if there is a problem with the 13m drogue, there is no denying
this forecast is of inferior skill.  In radio communications the 
morning of May 25, the modeling team on board the Edwin Link
reported similar results.  The discussion led to some speculation
that decrease in forecast skill may have something to do with the
lack of spatial overlap between the drifter data and the current 
ADCP velocity measurements which are being assimilated.  For reasons
described in earlier transmissions, Edwin Link and Endeavor have
separated by about 30km in terms of their operational area.  Given
the recent outage of the ADCP on the Edwin Link, it is primarily
Endeavor's ADCP data which are being assimilated.  Thus, in the
forecast evaluation described above, we are essentially trying to
predict the path of Edwin Link's drifters some 30 km east of the
area in which recent velocity measurements are available.  This
could explain the lack of forecast skill.  Shortly we will have the
opportunity to compare the model results with Endeavor's drifter 
tracks, which are closer to the area of velocity observations;
such a comparison should help shed light on these issues.


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

An updated forecast trajectory for the dye patch based on the May 24 
central run was provided to the chief scientist (Figure 0524.2)
The results suggest a brief period of eastward movement associated
with the southerly wind event, then motion back toward the west.
Given the issues brought to light by the most recent evaluation,
the operational products for this day were provided with the caveat 
that forecast skill was "uncertain relative to prior results obtained
thus far on the cruise."