Archive for June 13th, 2010

Cook finds a different circulation pattern

Sunday, June 13th, 2010

Figure 1. Above is the HyCOM forecast for today showing sea surface height as color fill and surface currents as black arrows.  Cook is in the blue region with with low currents, confirmed by the glider.  The directions do not line up, but that can be expected.  Cooks currents are averaged over 1200 m, and the HyCOM currents we plot here are surface.  So variations can be expected.

Figure 2.  Here we zoom into Cook, and compare the glider currents to the surface geostrophic currents obtained from the altimeter.  While the same reasoning applies, that the map is surface currents and the glider reports depth average currents, the currents associated with the highs and lows in sea surface topography often extend to significant depths.  What is especially surprising is that there is not just a small offset in direction.  Cook is telling us that the entire sense of rotation of the counterclockwise green eddy in the altimetry is in the wrong direction.  it will be interesting to see what is on the other side of this green eddy as we continue across. This must be  a particularly challenging spot for the data assimilation in the models.  One dataset, the altimeter, seems to say the eddy is rotating counterclockwise, and the glider is starting to say it is rotating clockwise.  Both are reliable datasets.  It will be interesting to see how it sorts itself out over the next week.

Figure 3.  Some of it may be that the eddy we are looking at in the altimetry is shallow.  Above is the temperature section Cook is collecting.  We do see a shallow warm layer at the surface.  This will be a topic of study by year's summer students.