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

2. Outline Motivation Characterization Result Validation Discussion
Future Work
References

3. Motivation
Gulf of Mexico
Caribbean Sea
Hand drawn contours

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

5. 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

6. 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)

7. 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

8. Characterization Metrics Explained Northward Extent Westward Extent

9. Result

12. Validation

13. 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

14. 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

15. 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

16. 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

17. 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: /2005GL
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.