Archive for July 13th, 2008

Satellites tell all

Sunday, July 13th, 2008

Today's thanks go out to our friends keeping the satellites flying.  A weekends worth of work on the satellite Sea Surface Temperature (SST) and Sea Surface Height (SSH) has really paid off.  We still have some cleaning up of the details, but the path is clear, and we now know how close we came to breaking through this past week before we were turned around by the currents.

 First is the satellite Sea Surface Temperature image below.  It is gives us the general conditions between RU17's present location and the Azores, located about 1200 km to our east.  We are working this front we have enhanced in the SST imagery to show temperatures between 21C and 26 C.   The front is not clean like the mighty Gulf Stream.  But it is a front the large sea turtles seem to like on their trips to Spain.  John got these images working over the weekend.

The satellite altimter fills in the complex eddy field between RU17 and the Azores by mapping the Sea Surface Height.  The highs (red) and lows (blue) in the sea surface height are very similar to the high pressure and low pressure systems you see in your NOAA atmospheric weather maps.  The currents swirl around these highs and lows, and our job is to use this maps to find the best path east.  These are the interstate highways of the ocean. Sometimes to get east, the best way is to fly west for a bit to pick up the interstate.  Justin got these maps working over the weekend.

 Now we zoom in on the temperature map to see the features in the eddy field in the immediate vicinity of RU17. You can see near 47W our loop around the southern side of the cold eddy where we found what we think are remoras.  We exit the eddy on the eastern side, and suddenly were turned around to the southwest by strong currents.

 Zooming in on the Sea Surface height map, we see the local access to the highways.  The clockwise circulation around the cold eddy with the remoras is clearly seen near 47 W. We were flying in the green colors, trying to cross that high region in the sea surface height when the currents to the southwest got too strong for us.  The new feature in the field we did not see before is the small cold eddy we see as a low located near 39 N, 42W.  Where did that come from?  its a new feature for me.  But the southwest currents proved too much for us, and we where turned back.  At least we now know why.  We were so close to reaching those eastward currents along 39 N, but with a glider, you only have about 25 cm/sec of forward speed to work with.  Currents have been running near this speed or higher against us, so no matter what we do, that path is blocked.

So based on the above roadmap, which we also know is constantly changing, we can see that the best way east is to first travel west.  We moved the next waypoint for RU17 to 38 30'N, 45 45'W so we can fly perpendicular to the southwest currents, just like a swimmer in a rip current.  We will fly northwest till we get into the outer edges of that cold eddy and ride it north.  Hopefully the remoras leave us alone.