attention loop current – here it comes

from Dr. Jeff Masters at Weather Underground

Satellite imagery today from NASA’s MODIS instrument confirms that a substantial tongue of oil has moved southeast from the Deepwater Horizon oil spill and entered the Gulf of Mexico’s Loop Current. The Loop Current is an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and then along the west side of the western Bahamas. Here, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. Once oil gets into the Loop Current, the 1 – 2 mph speed of the current should allow the oil to travel the 500 miles to the Florida Keys in 10 – 20 days. Portions of the Loop Current flow at speed up to 4 mph, so the transport could be just 4 – 5 days. It now appears likely that the first Florida beaches to see oil from the spill will be in the Lower Florida Keys, not in the Panhandle.

Figure 1. Satellite image of the oil spill taken at 12:40 EDT Monday May 17, 2010. The location of the Loop Current is superimposed. Image credit: University of Wisconsin and NASA.

Why is oil getting into the Loop Current?
The winds over the oil spill location are offshore out of the northwest today, and offshore winds will continue intermittently through Wednesday, which should allow a substantial amount of oil to enter the Loop Current. The major reason oil is moving southwards is because of the instability of the currents in the Gulf of Mexico. The Loop Current is not a stable feature, and tends to surge northwards and southwards in a chaotic fashion, and in response to changes in the prevailing winds. Over the past week, chaotic behavior of the Loop Current and a clockwise-rotating eddy just to its north, just south of the oil spill location, have combined to bring a current of southward-moving surface water to the oil spill location. As strong on-shore winds from the southeast slackened this past weekend, oil has been drawn southward into the Loop Current. The latest NOAA trajectory forecasts failed to anticipate the movement of the oil into the Loop Current. The latest surface current forecasts from NOAA’s HYCOM model show that oil could continue pouring into the Loop Current for most of the rest of the week. It is highly uncertain how diluted the oil might get on its voyage to northwestern Cuba and the Florida Keys this week, but the possibility for a major ecological disaster in the fragile Keys ecosystem cannot be ruled out. Southeast to east winds of 10 – 15 knots are expected to develop late this week and extend into early next week, which may be strong enough to impose a surface current that will shut off the flow of oil into the Loop Current by Friday or Saturday.

Figure 2. Forecast made at 8pm EDT Sunday May 16, 2010, of the Gulf of Mexico currents by NOAA’s HYCOM model. A persistent southward flowing surface current is predicted to occur this week between the oil spill location (red dot) and the Loop Current. Image credit: NOAA.

Likely areas of impact
Based on a study of 194 floating probes released into the Northeast Gulf of Mexico during a 1-year study in the 1990s (Figure 3), the west coast of Florida from Tampa Bay southwards to the Everglades is at minimal risk of receiving oil from surface currents. There is a “forbidden zone” off the southwest Florida coast where the shape of the coast, bottom configuration, and prevailing winds all act to create upwelling and surface currents that tend to take water away from the coast. This study implies that the greatest risk of land impacts by surface oil caught in the Loop Current is along the ocean side of the Florida Keys, and along the coast of Southeast Florida from Miami to West Palm Beach. Eddies breaking away from the Gulf Stream would also likely bring oil to northwest Cuba, the western Bahamas, and the U.S. East Coast as far north as Cape Hatteras, North Carolina, though at lesser concentrations. Southwest Florida cannot rest entirely, though–the “forbidden zone” is only true for surface waters, and there is onshore flow below the surface. Since recent ship measurements have detected substantial plumes of oil beneath the surface, southwest Florida might be at risk if one of these plumes gets entrained into the Loop Current. These subsurface plumes were also detected by current probes launched into the oil spill on May 8 by one of NOAA’s hurricane hunter aircraft, according to one scientist I spoke to at last week’s AMS hurricane conference. There are plans for the Hurricane Hunters to go out again tomorrow and drop more probes into the spill to attempt to get a better handle on where the oil is and where the currents are taking it.

Figure 3. Paths of 194 floating probes released into the yellow-outlined area in the northeast Gulf of Mexico between February 1996 and February 1997 as part of a study by the Mineral Management Service (MMS). The probes were all launched into waters with depth between 20 and 60 meters. Image credit: Yang, H., R.H. Weisberga, P.P. Niilerb, W. Sturgesc, and W. Johnson, 1999, Lagrangian circulation and forbidden zone on the West Florida Shelf, Continental Shelf Research Volume 19, Issue 9, July 1999, Pages 1221-1245 doi:10.1016/S0278-4343(99)00021-7

When will a Loop Current eddy break off?
Every 6 – 11 months, the looped portion of the Loop Current cuts off into a clockwise-rotating ring of water that then slowly drifts west-southwest towards Texas. When one of these rings breaks off at the peak of hurricane season, it provides a source of heat energy capable of providing fuel for rapid intensification of any hurricanes that might cross over. The Loop Current is not predicted to shed an ring over the next month, as predicted by the latest 1-month forecast from the U.S. Navy. However, the last eddy broke off in July of 2009, ten month ago, and it is unusual for the Loop Current to go more than eleven months without shedding an eddy. I expect we’ll see the Loop Current shed an eddy in July or August, just in time to pose the maximum threat for hurricane season. According to an interesting February 2004 article published by offshore-engineer.com, reliable forecasts of these currents and eddies are not available yet. Keep in mind that surface currents are largely driven by winds, and wind forecasts are not reliable out more than about 10 days.

References
Yang, H., R.H. Weisberga, P.P. Niilerb, W. Sturgesc, and W. Johnson, 1999, Lagrangian circulation and forbidden zone on the West Florida Shelf, Continental Shelf Research Volume 19, Issue 9, July 1999, Pages 1221-1245 doi:10.1016/S0278-4343(99)00021-7.

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~ by maringouin on Monday, May 17, 2010.

2 Responses to “attention loop current – here it comes”

  1. While watching the latest news about the BP Oil spill, a frightening thought came to mind: what if we can’t stop the oil? I mean, what happens if after all the measures to cap the pipe fail, (i.e., “Top Hat”, “Small Hat” and “Top Kill”). What then? An accident this problematic is new territory for BP. The oil pipeline is nearly a mile down on the ocean floor, accessible only by robots. Add on top of that the extreme pressure at which the oil is flowing out of the pipeline and there you have it: the perfect storm.

    Moreover, scientists also claim that they’ve found an enormous plume of oil floating just under the surface of the ocean measuring approximately 10 miles long, 3 miles wide and 300 feet thick. (I’m no math genius, but I bet one of you reading this could figure out just how many barrels of oil that is…)

    There are new estimates that the amount of oil spewing into the Gulf of Mexico is anywhere from 50,000 to 100,000 barrels of oil a day: that’s a far cry from BP’s estimated 5,000 barrels a day. If BP’s estimates are correct, the total amount of oil now in the Gulf would be approximately 150,000 barrels (or 6,300,000 gallons). That’s barely enough to fill 286 swimming pools: sixteen feet, by thirty-two feet, by eight and a half feet deep. That wouldn’t cover an area the size of New York City, let alone an area the size of Delaware. Obviously, the spill is much larger than we are being led to believe. If the leak can’t be stopped, in a year’s time, we’ll have roughly 18,250,000 barrels of oil (or 766,500,000 gallons) in our oceans, killing our marine and animal wildlife. Such a calamity would be environmentally and economically disastrous. I’m not a religious man, but I pray that BP and our government work fast to end this catastrophe.

    http://www.calculateme.com/Volume/Barrels(Petroleum)/ToGallons.htm

    http://blogs.howstuffworks.com/2010/05/17/latest-news-from-the-oil-spill-in-the-gulf-of-mexico-is-grim/

    http://blogs.creativeloafing.com/dailyloaf/2010/05/20/scientist-says-oil-spill-is-leaking-100000-barrels-of-oil-a-day-not-bps-estimate-of-5000/

  2. There is a grim outlook going around New Orleans, which hasn’t been picked up by the press, that if the top kill maneuver fails, this gusher will grow exponentially larger and it will be impossible to stop the flow. The possibility that this cannot be stopped is very real.

    And if this oil somehow gets up the Mississippi River to New Orleans, then the potable water supply for the entire region will be contaminated. Subsequently you just might see the abandonment of a major metropolitan city. BP might accomplish what Katrina failed to do.

    BP needs to be obliterated – they are the perpetrators of a heinous crime and they MUST BE STOPPED NOW!!!

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