Figure 1: Here we take a look at the track of Cook on the basin scale.  At the end of last week we set the next waypoint for Cook as the top of the Mid-Atlantic Ridge.  This will be the section of the flight that the summer students concentrate on.  Lets see if we can make the European side of the Ridge before they leave.   Once on the European side of the Atlantic, we set our sights on the fall transit to the Canaries.   The present distance to the Canaries is about 3,500 km.  If we look at our progress along 26.5 N, we made the turn back on May 11.  Since making the turn, we have traveled 1,150 km.  In 6 days we’ll take another check to see how far we have made it in 2 months.  Still we know the approximate numbers.  We took about 2 months to go 1/4 of the distance to the Canaries.  Maintaining this average speed gets us to the Canaries in another 6 months – again – not a great time to be out on the North Atlantic in small boats.  We also have to worry about the thermal engine, and how much temperature change we need from top to bottom.  We like to have a 15 C temperature difference, but can we live with less?  A good question. That is about the time that the surface to 1200 m temperature difference reaches a minimum, giving us another envelope to push.  So there is a lot of talk right now between our students in the U.S. and our friends in the Canaries.  What temperature range do we expect this winter, and how will Cook handle it?  Should we give up trying to maintain the 26.5 N line, and instead use the currents to our advantage to speed across like we did with RU27?

Figure 2: Lets look at the HyCOM forecast, this time for sea surface height (color) and surface currents (black arrows).  The Cook currents have been switched to red so they show up.  We are presently going against the current that is circulating clockwise around that sea surface high to our north in red.  HyCOM says small currents are on the way as we cross into the blues.

Figure 3: Overlaying the HyCOM currents on the satellite sea surface temperature map gives us a lot of confidence in HyCOM.  We see lots of features in the forecast currents lining up with the fronts and features in these satellite observations.

Figure 4: But now we overlay the HyCOM currents on the satellite altimeter sea surface heights and geostrophic currents, and we loose a little confidence in the model in some regions.  Here we see that some features are lining up with HyCOM & the satellite SST, giving us strong confidence in these features.  But some are not lining up.  These we have less confidence.  if we had time, and our mission was data assimilation, we would head Cook straight into these regions of disagreement.  If we are racing against time, we do the opposite, and head Cook into regions with known favorable currents.  But in our case, we are still on a heat flux science mission, so we’ll maintain this line for as long as we can and still make the Canaries.