Archive for June 24th, 2010

update 23 june 2010

Thursday, June 24th, 2010

Hola a todos ¡

Firstable, let me thanks you Scott, Josh, Oscar and all the Cook team for this great blog present.

I would like to introduce this post with an update for 24th june 2010, NCOM and Hycom current fields (blogged by you) show that the last current disagreement stint apparently has finished (58-55 W).

Fig 1.- Current fields. 23th June 2010 (Geostrophic field, up and Total field, down).

igure 1 show that surface Hycom and NCOM data show a new agreement segment with strong surface currents flowing west at > 0.7 knots (red colour) in some windows.
The Figure 2 (SSHa field) shows that Cook flies on the south border of a N warm eddy or, in other words, in the north border of a S cold eddy. This borderline with a strong SSHa front seems very active. That would mean ahead COOK and in the26.3 N line a similar landscape to these observed the last segments (strong currents flowing west).

Fig 2.- SSHa fields. 23th June 2010. Red colour represents currents >0.7 knots.
Finally an interesting remark observed in the thermocline depth field (Fig. 3). Cooks flied a very active area with strong thermocline depth variations with deep blues anticyclonic gyres and white shallow cyclonic ones. It could affect the disagreement observed behind COOK.
Now Cooks is flying (apparently) a “remanse of peace” reading the thermocline depth update (not strong differences around).

Fig 3.- Thermocline depth fields. 23th June 2010.

Thanks again for this great blog present.

Force wind, sea and honour to all of you
Antonio G. Ramos

Cook’s Flight Characteristics

Thursday, June 24th, 2010

While analyzing Cook's flight characteristics, we have noticed that the glider is experiencing a drastic heading error at the start of each dive and climb.  In the figures below, the blue lines represent downcasts, and the red lines represent upcasts.  At the start of each dive, Cook veers 100 degrees or more to the left, and at the start of each upcast veers about 50 to 60 degrees to the right.  The glider seems to experience a larger range of heading error on downcasts than on upcasts as well.  The first plot shows typical heading error, and the second plot shows a more drastic error in which the glider actually rotated a full 360 degrees.

Taking a closer look at the previous plot (shown below),   the yellow points show that Cook's heading error went from about -2 radians (-120 degrees) to +3 radians (+170 degrees) in less than 10 meters.  From this data, we conclude that the glider rotated a full 360 degrees before heading in the correct direction.  Typically, the fin should be able to steer the glider in the desired direction.

The fin responded to Cook's heading error, but was not able to correct the deviation.  Once the glider was facing more than 180 in the wrong direction, the fin quickly changed position so that Cook would continue spinning in the same direction back to its correct heading.  The figure below shows the position of the fin in radians.

The pitch and roll do not seem to be affected by Cook's heading error and fin position.  The roll, however, does see a slight difference during upcasts and downcasts.  The roll never reaches more than 5 degrees in either direction, but is always slightly to the right and larger during upcasts.