Hey guys..

This week and the previous one have been really busy for Silbo and his team. The aftermath of Katia has not been exactly a blue paradise, sunglasses, a fresh drink and tons of pop corns.

THE WEATHER
The weather has improved and the slight storms reported have been crossing North Silbo. Silbo can now enjoy the stars brightning in the sky at night surfacings before calling home. There are no spetial mentions for the meteo the last week. However, waiting for the calcules of the heat fluxes, it looks that silbo has well reported that tropical storms definitely affect the water column at great depth. Changes on salinity and temperature fields at depth are obvious on vertical profiles.

Figure 1.- Temperature and salinity fields reported by Silbo (23th jun – 23th september).

Another important remark related the meteo, is that last swells affect, but it do not seem to –inertially- oscillate the currents like in the previous week… On Monday, we will have another perturbation coming from the west and the swell would slightly increase the significant height (Hs) of the waves following the forecast of the Spain,s system of marine weather forecasting.

Figure 2.- Marine wearther forecast 25 and 26 september 11.

THE WALL
However, as we posted some days ago, the toast of the week goes to an old and well-known feature.  We have another WALL ahead. It has been the great headache of this week. Our little and brave droid becomes another brick in this liquid wall by moments. The first result of finding a wall is that the glider stops and drifts to any resultant random direction. We found two of these particular glider obstacles during the RU27 mission: The first, was a system of two warm eddies gyring in front and behind scarlet. Currents headed the glider when we move East, and pushed to South when we come back. The other wall found by RU27 was a great inertial oscillation changing the current direction 360 º around scarlet each 16 hours…during some weeks…http://www.i-cool.org/?p=6944

This particular liquid WALL found by silbo some days ago, is clearly associated to the western side of a warm (Sun) eddy that has stopped (literally) to our brave droid. We are crossing by the Western (bad) side with counter currents flowing at >0.3 m/s and strong SSHa gradients up to 3 cm/nm. He cannot fight with the strong currents flowing direct to his nose and his flying line. We have suffered some stints with Northern moderate drifting.

Figure 3.- Surfacings of 21th of September 2011.

OPTIONS
The question: How to cross it ?
We tried to convert our great Silbo in a 4*4 (strong), but fast (>0.3 m/s) glider to fight the current.

1.- The first option that we tried, changing our WP to 27 W (180 degrees with the current direction). Our aim was to head the wall and try to cross it increasing his speed and changing his navigation schedule. On 27 W we identified a jet stream flowing south. We want to get this good opportunity to get south currents for a while. But it didn’t work. Silbo can hardly advance only a few km/day…

Figure 4.- Current field (down) and N-S meridional component (up).

2.- We also changed to full buoyancy mode since we were drifting to back. During some stints with similar currents and diving periods, we got some interesting numbers. We increased our glide speed from 0.24 to 0.31. And we run a 5 % more of distance by stint: without (4.28km) and with (4,61km) full buoyancy.

Figure 5.- Surfacing reports at half and full buoyancy modes. 22th and 23th of September 2011.

3.- Other options discussed and finally do not executed by different reasons (energy consumption..). Increasing the pitch (better diving speed but shorter distance run) and switching on the Current Corrector.
However, sometimes during this meridional (N-S) mission, we have been forced by the circumstances to give and step back, and see the problem with a little bit more of perspective. We could hardly advanced only some more km/day with this new schedule. Thus, we decided to completely change our GLOBAL strategy. If you can cross the wall, surround it…

Figure 6.- SSHa field. 21th september 2011.

Thus, we changed the WP to the East (22 W), < 180 º related to current direction. As a result, since thursday, we have been drifting to SE-E for some stints. We are still suffering the effect of this great wall (strong NE current). Our target was/is to pass it flying to the centre of the eddy, and then, flowing to the SW again with the South oriented current of the other right side of this warm eddy. We would also avoid the seamounts located around the 44.5 N 25 W. Then, free riding to our little cowboy until the Azores. A visual inspection at sea is projected to be held there.

Figure 7.- Current field. 21th september 2011.

 

If you can cross the wall, you can surround it…But you can also pass UNDER THE WALL..That is another idea floating in the core group: Changing the flying depth range of silbo. This operation would be especially useful when silbo crosses bad strong upper currents. Diving and climbing at deeper waters like thermal gliders do (for ex Cook, 300-1000 m) would be an interesting option since current fields (soft some areas) would be of moderate currents when compare with these flowing in upper layers.

The core group is working right now on some simulations and technical issues and how we use the layered data of the ocean (NLOM, HYCOM, MyOcean) and how to take advantage for our purposes.  We would update it ….

Finally, just a little reference to the toast of the team this week:  Lauren COONEY from TWR. She has done an incredible great job the last days …

Force, wind, sea and honor all

Antonio RAMOS, Nilsen STRANDSKOV and Lauren COONEY