NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA DISSERTATION OBSERVATIONS AND MODELING OF THE INTERNAL TIDE IN A SUBMARINE CANYON by Emil T. Petruncio September, 1996 Dissertation Supervisors: Jeffrey D. Paduan - Leslie K. Rosenfeld Thesis P45853 Approved for public release; distribution is unlimited. r KNOX LIBRARY DUDLEY SCHOOL SMAVAL POSTGRADUATE SSKeREY CA 93943-5101 . REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1 204, Arlington. VA 22202-4302, and to the Office of Management and Budget Paperwork Reduction Project (0704-01 88) Washington DC 20S03 2. 3. 1 . AGENCY USE ONLY (Leave blank) REPORT DATE REPORT TYPE AND DATES COVERED September 1996. Doctoral Dissertation 4. TITLE AND SUBTITLE FUNDING NUMBERS OBSERVATIONS AND MODELING OF THE INTERNAL TIDE IN A SUBMARINE CANYON AUTHOR(S) Emil Thomas Petruncio 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) PERFORMING Naval Postgraduate School ORGANIZATION Monterey CA 93943-5000 REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER 1 1 . SUPPLEMENTARY NOTES The views expressed in this thesis are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government. 12a. DISTRTOUTION/AVAILABILnY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited. 13. ABSTRACT (maximum 200 words) Shipboard ADCP and CTD measurements were conducted in Monterey Submarine Canyon in April and October 1994 to determine the propagation characteristics and energy levels of the semidiurnal internal tide. The measurements reveal a bottom-intensified internal tide propagating energy upcanyon. The region of strongest motion is in a beam 150-200 m thick, centered approximately 150 m above the Canyon floor. Along-canyon baroclinic M2 currents are typically 15-20 cm s"\ an order of magnitude larger than the estimated barotropic tidal currents. In April 1994, the internal tidal beam is well described by a progressive wave, while in October 1994, the signal is standing along and perpendicular to the beam. The Princeton Ocean Model was used to study the generation and propagation of semidiurnal internal tides in submarine canyons and to investigate their sensitivity to canyon shape. Minor changes in floor slope are found to have a significant impact on the strength of internal tides in a canyon. The numerical experiments reproduce several features of the internal tide that are in qualitative agreement with the observations, including upcanyon energy propagation along the canyon floor, internal tide generation along the canyon rim, and tidal pumping of dense water up onto the shelf near the canyon head. 14. SUBJECT TERMS 15. NUMBER OF internal waves, tides, internal tides, Monterey Bay, Monterey Submarine Canyon, PAGES 192 submarine canyons, coastal ocean currents, POM, ocean modeling 16. PRICE CODE 17. SECURITY CLASSIFICA- SECURITY CLASSIFI- 19. SECURITY CLASSIFI- 20. LIMITATION OF TION OF REPORT CATION OF THIS PAGE CATION OF ABSTRACT ABSTRACT Unclassified Unclassified Unclassified UL NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Preserved by ANSI Std. 239-18 298-102 u Approved for public release; distribution is unlimited. OBSERVATIONS AND MODELING OF THE INTERNAL TIDE IN A SUBMARINE CANYON Emil T. Petruncio Lieutenant Commander, United States Navy B.S., United States Naval Academy, 1985 M.S., Naval Postgraduate School, 1993 Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY IN PHYSICAL OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL September. 1996 u > /O DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL MONTEREY CA 93943-5101 ABSTRACT Shipboard ADCP and CTD measurements were conducted in Monterey Submarine Canyon in April and October 1994 to determine the propagation characteristics and energy levels of the semidiurnal internal tide. The measurements reveal a bottom- intensified internal tide propagating energy upcanyon. The region of strongest motion is in a beam 150-200 m thick, centered approximately 150 m above the Canyon floor. 1 Along-canyon baroclinic M2 currents are typically 15-20 cm s* , an order of magnitude larger than the estimated barotropic tidal currents. In April 1994, the internal tidal beam is well described by a progressive wave, while in October 1994, the signal is standing along and perpendicular to the beam. The Princeton Ocean Model was used to study the generation and propagation of semidiurnal internal tides in submarine canyons and to investigate their sensitivity to canyon shape. Minor changes in floor slope are found to have a significant impact on the strength of internal tides in a canyon. The numerical experiments reproduce several features of the internal tide that are in qualitative agreement with the observations, including upcanyon energy propagation along the canyon floor, internal tide generation along the canyon rim, and tidal pumping of dense water up onto the shelf near the canyon head. VI TABLE OF CONTENTS I. INTRODUCTION 1 A. MOTIVATION 1 1. Coastal Tidal Current Prediction 1 2. Internal Tides In Monterey Bay 2 B. OBJECTIVES 3 1. The Field Study 3 2. The Modeling Study 4 II. REVIEW OF INTERNAL TIDE THEORY AND OBSERVATIONS 7 A. INTERNAL TIDE GENERATION AND PROPAGATION 7 1. Beam-like Propagation Of Internal Tides 8 2. Internal Wave Reflection From Sloping Bottoms 10 3. Internal Waves And Tides In Canyons 11 4. Internal Tides In Monterey Submarine Canyon 13 IE. THE HELD EXPERIMENTS 17 A. DATA COLLECTION AND PROCESSING 17 1. Shipboard Experiments 17 2. Sea Level Data 22 3. S-4 Current Meter and Thermistor 23 B. OBSERVATIONS AND ANALYSIS 23 1. Harmonic Analysis 24 2. Monterey Bay Tidal Heights Analyses 25 3. Along-canyon Observations Of The Density Field 27 4. Along-canyon Observations Of The Current Field 31 5. Cross Canyon Observations 40 6. Near Bottom Current And Temperature Oscillations 41 7. Energetics 46 C. DISCUSSION 50 1. Possible Internal Tide Generation Sites 50 2. Comparison To Wunsch's Modal Solutions For Standing Waves 53 D. SUMMARY 56 IV. THE MODELING EXPERIMENTS 61 A. MOTIVATION 61 B. MODEL DESCRIPTION 63 1. Previous Tidal Applications 65 2. Internal Tides Process Study 67 C. MODEL INITIALIZATION, FORCING, AND BOUNDARY CONDITIONS 69 1. External Mode Boundary Conditions 69 2. Internal Mode Boundary Conditions 72 3. Pressure Gradient Truncation Error Analysis 74 vii D. RESULTS 78 1. Overview Of Experiments 78 2. Internal Tide Generation On the Continental Slope and Shelf Break 79 3. Canyon Case 1 81 4. Summary of Canyon Case 1 Experiment 90 5. Canyon Case 2 - Floor Slope Variations 91 6. Canyon Case 3 - Width Variations 92 E. SUMMARY 94 V. CONCLUSIONS AND RECOMMENDATIONS 97 APPENDIX A. HARMONIC ANALYSIS 161 APPENDIX B. ERROR ESTIMATION OF THE TIDAL HEIGHTS ANALYSIS 163 APPENDIX C. ERROR ESTIMATION OF THE TIDAL CURRENTS ANALYSIS... 167 LIST OF REFERENCES 169 INITIAL DISTRIBUTION LIST 179 vni ACKNOWLEDGEMENTS This research was sponsored by the Office of Naval Research Graduate Fellowship program under which LCDR Emil T. Petruncio, USN has studied Operation of the R/V Point Sur was funded by the Commander, Naval Meteorology and Oceanography Command, and computing resources were provided by the Naval Postgraduate School. One of the most rewarding aspects of this research was the opportunity to work with and learn from a number of talented scientists. I would like to thank my "dream team" dissertation committee, Professors Ed Thornton, Bob Haney, Anthony Healey, and especially my dissertation supervisors, Professors Jeff Paduan and Leslie Rosenfeld for their encouragement, inspiration, and guidance. Thanks also to Professor Ly-Ngoc Le of NPS and Professor Geoff Vallis of U.C. Santa Cruz for their participation on the committee in the early stages of the project. Other members of the Oceanography faculty I would like to recognize for their contributions are Professors Mary Batteen, Peter Chu, Lin Jiang, and Julie McClean. I am grateful to the fine staffs of the NPS Oceanography Department and Computer Center for their help throughout the project; particularly Mr. Mike Cook for generously sharing his insight into computer programming and data visualization, Mr. Tarry Rago for his participation in data collection and CTD data processing, Mr. Paul Jessen for contributing his ADCP processing skills, Ms. Laura Ehret for her interest in the modeling work, and Ms. Hoda Salib for her excellent administrative support. I would also like to extend my thanks to CDR Rost Parsons, USN, who contributed his programs and ideas during his stay at NPS as an ONR Graduate Fellow. There are also many experts outside NPS who contributed to the success of this project. I would like to thank Captain Steve Bliss and the crew of the R/V Point Sur for their outstanding seamanship and teamwork, Mr. Gerry Hatcher of the Monterey Bay Aquarium Research Institute for his CTD data processing, Dr. Steve Gill and his colleagues at the National Ocean Service for providing sea level data, and Dr. Jim Lewis of Ocean Physics Research and Development for sharing his knowledge on ocean modeling. Another factor in the success of the modeling project was the interest of the "Monterey Bay Chapter" of the POM Users Group, which included Dr. Mike Clancy, Dr. Paul May, and Mr. Webb deWitt of the Fleet Numerical Meteorology and Oceanography Center, and Drs. Rich Hodur and Simon Chang of Naval Research Lab, Monterey. The following scientists also contributed to my understanding of internal waves and ocean modeling by sharing their considerable experience and insight: Drs.