Continuing Results from the Submesoscale Experiments and the February 2013 Campaign
Holt, Benjamin1; Baschek, Burkard2; Molemaker, Jeroen3; Marmorino, George4; Miller, W.D.5; Smith, Geoffrey B.4; Ohlmann, Carter6; Gierach, Michelle1; Gade, Martin7; Horstmann, Jochen8
1Jet Propulsion Laboratory, UNITED STATES; 2Helmholtz-Zentrum Geesthacht, GERMANY; 3University of California Los Angeles, UNITED STATES; 4Naval Research Laboratory, UNITED STATES; 5Naval Research Laboratory, UNITED KINGDOM; 6University of California Santa Barbara, UNITED STATES; 7University of Hamburg, GERMANY; 8NATO Undersea Research Center, ITALY
In order to truly resolve the small scales of submesoscale eddies and fronts, we have collected fine-resolution (1-15m) in situ and aerial data during the first submesoscale experiment SubEx1 in April 2011 and now during SubEx2 in February 2013. Both experiments took place near Catalina Island in the Southern California Bight, an area known to have extensive small-scale eddies and frontal features. Rapid measurements enabled us to observe significant changes over very short time scales and to investigate the longer-term evolution of the features. Measurements were taken in a collaborative effort with infrared, hyperspectral, and SAR imagery from three aircraft, as well as in situ measurements using a Towed Instrument Array (TIA), drifters, acoustic Doppler current profiler, as well as measurements of surfactants and water-column optical measurements. In addition, satellite observations were obtained from Envisat ASAR (SubExI), TerraSAR-X and Radarsat2 (SubEx2), plus the ASTER and MODIS sensors. The temperature and salinity data collected with the TIA, having 1- to 5-m resolution over a 35-m depth covering the upper 35m of the water column at a tow speed of 4-5m/s, demonstrate that the submesoscale features mostly occur within a shallow, 5-15m deep thermocline, and that fronts show temperature and density gradients of 0.5 to 1°C and 0.2kg/m3over 5m. The observed features evolve over the course of a few hours. Rotational and advective velocities are 0.2-0.4 m/s, consistent with a large Rossby number flow. This paper will focus on the repeat observations of small eddies and fronts obtained in SubEx2 by ASTER, TerraSAR-X, Radarsat2 and Modis. Small-scale eddies are detected by SAR in coastal environments by the appearance of surfactants which act as tracers of the underlying current field. Some of the imagery provided repeat observations of a less than an hour to a day, that will enable the tracking of the rapidly evolving eddy field and derivation of rotation velocity maps through feature tracking. These observations also included the detection of a recurring frontal feature off Catalina Island. This study will present preliminary results of eddy tracking from the combined SAR time series, and an interpretation of the surface features when compared with coincident high-resolution ocean surface temperatures, measured through airborne infrared observations, and in situ temperature transects. The new results will be compared with eddy image-pairs collected in SubEx1 using UAVSAR and Envisat ASAR.