Loop Current eddy merger exposed by satellites during Gulf of Mexico oil spill

Abstract

The clockwise flow of water that extends northward into the Gulf of Mexico known as the Loop Current, and its associated eddies, regularly produces strong currents of 2–4 knots in the northern Gulf. Cyclonic (i.e., counterclockwise rotating) eddies, migrating along its outer margin, are difficult to study due to their rapid and unpredictable growth and propagation, as well as persistent cloud cover. We have found that night-time midinfrared satellite images obtained every 30 minutes from geostationary satellites used to quantify sea surface temperature, superimposed with daily updated gridded sea surface height data based on several satellite altimeters, allows us to track the Loop Current and cyclonic eddiesmore effectively than previous methods.1, 2 During the Deepwater Horizon oil spill, we assessed daily changes in the motion of the Loop Current, its cyclonic eddies (called Loop Current frontal eddies), and detached anticyclonic eddies by analyzing daily-updatedmaps of sea surface temperatures and heights. We used ship-board acoustic Doppler current profiler current measurements and time-series positions from satellite-tracked Global Positioning System (GPS) buoys to validate our satellite data interpretations.3 Surface oil is often mapped using readily available passive radiometric optical imaging, such as ‘true-color’ images from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) sensors (see Figure 1). During the Deepwater Horizon oil spill these data were useful, but not totally reliable due to solar interference with the optical sensors. Synthetic aperture radar (SAR) sensors proved more valuable, as the backscatter signal is very sensitive to surface oil and is usable in all weather, day Figure 1. Top: Moderate Resolution Imaging Spectroradiometer (MODIS) ‘true-color’ image depicting the offshore entrainment of the Deepwater Horizon oil toward the Loop Current front on 17May 2010. Middle: Radarsat-2 synthetic aperture radar (SAR) image also depicting the surface oil on 17May 2010. Bottom: Geostationary Operational Environment Satellite East (GOES-East) sea surface temperature image depicting the Loop Current and the large merged cyclone north of the Loop Current on 17–19 May 2010. Superimposed on the color-coded sea surface temperatures are the oiled area, traced from the