Automatic Identification and Characterization of the Loop Current Deepak Cherian Summer Intern Indian Institute of Technology, Kharagpur

Outline Motivation Characterization Result Validation Discussion Future Work References

Motivation Gulf of Mexico Caribbean Sea Hand drawn contours

Motivation Hand drawn contours Gulf of Mexico Caribbean Sea Loop Current (LC) Caribbean Sea Hand drawn contours

Motivation Hand drawn contours Method of Identification Limitations Manual front analysis at Naval Oceanographic Office (NAVO) Temperature contours High res Multi Channel Sea Surface Temperature data Limitations Not at all time instants Constrained by seasonal heating and cloud cover Discontinuous contour Lot of effort

Automatically Identified contours Motivation Automatically Identified contours Method of Identification Use a chosen threshold Many possible choices 17 cm SSH contour : Leben (2005) 20 degree Celsius isotherm at z = -150m : Oey et al. (2001) Based on the high velocity gradients that characterize the edge of the current Subjective Possibility of prediction when applied to model output (eg. HYCOM)

Automatically Identified contours Characterization Automatically Identified contours Leben (2005) identified various possible metrics Maximum westward extent Maximum northward extent Length of contour Area Circulation along contour Volume

Characterization Metrics Explained Northward Extent Westward Extent

Result

Validation

Validation Correlations Temperature SSH Max W 0.2072 0.2209 Max N 0.2621 0.2305 RMS Error Temperature SSH Max W 1.7902 2.0780 Max N 1.5377 1.4649

Validation Correlations Temperature SSH Max W 0.2072 0.2209 Max N 0.2621 0.2305 RMS Error Temperature SSH Max W 1.7902 2.0780 Max N 1.5377 1.4649

Discussion Advantages Allows for extraction of a Loop Current front during both summer and winter Automated Identification of eddy process through spikes and drops in metric time series When applied to HYCOM predicted data, allows prediction of Loop Current position RMSE errors are around 2 degrees and low correlations Could be reduced with a different contour Hand drawn contours needn’t be good enough Northward extent metric seems to be best

Future Work Validate with more hand contours Complete contours first Allows for validation across more metrics Experiment with different contours Possibility of better results Port to MATLAB Faster More accurate contour prediction

References Oey, L.-Y., T. Ezer, G. Forristall, C. Cooper, S. DiMarco, and S. Fan (2005), An exercise in forecasting loop current and eddy frontal positions in the Gulf of Mexico, Geophys. Res. Lett., 32, L12611, doi:10.1029/2005GL023253. Leben, R. R. (2005), Altimeter-derived loop current metrics, in Circulation in the Gulf of Mexico: Observations and Models, Geophys. Monogr. Ser., vol. 161, edited by W. Sturges and A. Lugo-Fernandez, pp. 181–201, AGU, Washington, D. C.