Sea Surface Height Data Viewers - Dick LaRosa

http://jeffreyearly.com/science/qg-eddies-paper/

http://eddy.colorado.edu/ccar/data_viewer/index

The first link above leads to Jeffrey Early's animated global display of westward propagating clockwise and counterclockwise eddies. One can clearly see both CW (red spots) and CCW (blue spots) eddies forming where the Amazon River discharge meets the North Brazil Current. These red and blue spots pass through the Caribbean Sea toward the Yucatan Channel, where the blue spots seem to pass smoothly into the Gulf of Mexico, while the red spots seem to hesitate, and then pop into the Gulf. But there appear to be fewer red spots entering the Gulf than are arriving at the Yucatan Channel. This leads me to think that the CW eddies are trapped in the Loop Current's loop, and lose their individual identity. Then new rings break off from the Loop Current and drift westward in the Gulf of Mexico.

The second link above leads to several data viewers of the Colorado Center for Astrodynamics Research (CCAR). One of them is a global display of sea surface height (SSH) anomalies - departures from the time average of SSH in a given map location. Red dots mark locations of SSH hills associated with CW rotating eddies, while blue dots mark locations of depressions associated with CCW eddies. I am looking at the Northern Hemisphere. Rotations would be opposite in the Southern Hemisphere. There are no spots where the Amazon River discharge meets the North Brazil Current. Why does Jeffrey Early's website show eddies at this location while the CCAR viewer does not? Early mentions that his data is filtered to isolate the westward propagating features. With my limited understanding, I can only infer that there are ways to process data to bring out important features, and unless you use them, you miss the show.

CCAR also has SSH data viewers for the Gulf of Mexico. The old viewer covered 1993 until just recently, and new viewers have replaced it. The second link above takes you to the new viewers. I don't know how to find the old viewer or whether it still exists. You can specify dates in the period covered by the old viewer and I have many old printouts to compare with the new viewers. The new and old resemble each other. The old printouts have lots of warts, while the new ones look like they came out of the beauty parlor nicely smoothed over. There are many periods during which the old plots showed SSH contours perpendicular to the northern coast of Cuba. I was interpreting these as pileups of water due to incoming eddies, resulting in gradient-driven flow parallel to the coast. The new plots have mostly SSH contours parallel to the coast, indicating geostrophic flow. So once again, it looks like it's all in the processing. Which one should I believe?

Comments

[Dick LaRosa]

I did not insert any links in the body of my text. A well-meaning Gremlin has created a link to the Brazil Current, which is not the same as the North Brazil Current. Other links created by the Gremlin lead nowhere, or are distracting when I click on them. A couple of my previous posts have been similarly sabotaged by the Gremlin. I try to write them simply and clearly. Even the good links on North American Monsoon and watercraft stability overloaded my poor little brain. I could just hear some Wikipedia showoff saying, "Have I lost you yet?"

[Jerry]

Sorry Dick,I'm the gremlin (with the help of TypePad). I won't activate any more of the links.