Archive for July 10th, 2010

Four Drifters reaching decision points

July 10th, 2010 No comments

Figure 1: Newspapers here say the Gulf weather has improved so there is lots of activity planed around the drill site.  Checking my favorite website for ocean related weather, , we see the above map of ship reports for the Gulf of Mexico.  Much lighter winds and more variable directions.  Most of the winds in the area around the spill are from the west.

Figure 2: The IOOS Overview. Today we’ll do our usual look more closely at the slick, and we’ll check in on the Navy drifters in the southern Gulf.

Figure 3: The zoom into the slick forecast shows the dramatic changes as a result of the new wind pattern.  The winds from the west are blowing the heaviest slick to the east, forming a new plume that heads east along the shelf break.  The inshore slicks pushed ashore by the strong winds from the southeast over the past week are now hitting the southern side of the birdsfoot.  The strong currents flowing to the south in the HF Radar line up with the slick that is just south of the Mississippi coast.

Figure 4: Here is the HyCOM forecast for today.  Color fill is the sea surface height (red is high. blue is low), and surface currents are the white arrows. If we look at the large Loop Current Eddy (red) in the center and the smaller  clockwise eddy (yellow) between it and the Florida shelf break, we see that the Horizon Marine drifter on the far south is doing a great job of defining the southern extent of the large Loop Current Eddy. The question for this buoy, will it go around for another loop, or will it follow that narrow band of HyCOM currents to the south into the Loop Current where it can exit the Gulf.  Also check the Navy drifters shown as the purple dots, specifically drifters 42575 and 42574.  These two drifters define a second path out of the Gulf. 42575 was in the big Loop Current Eddy, but looks like it was ejected and is about to be entrained by the smaller clockwise eddy.  42574 already followed this path out of the large Loop Current Eddy, has looped around the northern side of the small eddy, and is now approaching another decision point.  Will it circle around for another lap or will it be entrained by the Loop Current and exit the Gulf.

Figure 5: And now back to the Horizon Marine drifter way north in the Gulf Stream.  It is reaching the bottom of the Gulf Stream meander trough.  Will it continue to loop around and begin climbing up towards the next meander crest, or will it be ejected to the south in what appears to be a cold core ring just to the southeast interacting with the Gulf Stream?