Calhoun: The NPS Institutional Archive DSpace Repository Theses and Dissertations 1. Thesis and Dissertation Collection, all items 2013-09 Assessment of tropical cyclone structure variability Stenger, Robert A. Monterey, California: Naval Postgraduate School http://hdl.handle.net/10945/37723 Downloaded from NPS Archive: Calhoun NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA DISSERTATION ASSESSMENT OF TROPICAL CYCLONE STRUCTURE VARIABILITY by Robert A. Stenger September 2013 Dissertation Supervisor: Russell L. Elsberry Approved for public release; distribution is unlimited THIS PAGE INTENTIONALLY LEFT BLANK 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 Jeff erson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Offi ce of Management and Budget, Paperwork Reduction Project (0704-0188) Washington DC 20503. 1. AGENCY USE ONLY (Leave 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED blank) September 2013 Dissertation 4. TITLE AND SUBTITLE: 5. FUNDING NUMBERS ASSESSMENT OF TROPICAL CYCLONE STRUCTURE VARIABILITY 6. AUTHOR(S) Robert A. Stenger 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER Naval Postgraduate School Monterey, CA 93943-5000 9. SPONSORING/MONITORING AGENCY NAME(S) AND 10. SPONSORING/MONITORING ADDRESS(ES) AGENCY REPORT NUMBER N/A 11. SUPPLEMENTARY NOTES The views expressed in this dissertation are those of the author and do not refl ect the offi cial policy or position of the Department of Defense or the U.S. Government. 12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution unlimited A 13. ABSTRACT(maximum 200 words) The landfall of large hurricanes in densely populated areas has increased the awareness that tropical cyclone struc- ture plays an important role in the destructive potential of a storm. A unique set of H*Wind analyses of Atlantic tropical cyclones during the 2003-2005 seasons is studied to better understand the internal and external mechanisms that lead to signifi cant variability in surface wind structure. Secondary eyewall formation, asymmetric convection, land interaction, and environmental vertical wind shear were generally found to be mechanisms for radius of maximum wind increases, intensity decreases, and size of the radius of 34-kt wind increases. Two modes of size changes were documented that may lead to 100 km increases in 12-24 h, or near-zero size changes when a sharper than average outer wind structure profi les are generated. The statistical relationships among the radius of maximum wind, intensity, and outer-core wind structure from this sample may provide perturbed vortex initial conditions for an ensemble model to predict structure changes. 14. SUBJECT TERMS 15. NUMBER OF PAG ES Tropical Meteorology; Tropical Cyclone Structure; Tropical Cyclone Prediction; Western North Pacifi c Typhoons; Atlantic Hurricanes; H*Wind Analysis; H*Wind Analysis Tool; Ensemble 311 Modelling; Secondary Eyewall Formation; Asymmetric Convection; Land Interaction; Vertical Wind Shear 16. PRICE CODE 17. SECURITY 18. SECURITY 19. SECURITY 20. LIMITATION OF CLASSIFICATION OF CLASSIFICATION OF THIS CLASSIFICATION OF ABSTRACT REPORT PAG E ABSTRACT Unclassifi ed Unclassifi ed Unclassifi ed UL NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. 239-18 i THIS PAGE INTENTIONALLY LEFT BLANK ii Approved for public release; distribution is unlimited ASSESSMENT OF TROPICAL CYCLONE STRUCTURE VARIABILITY Robert A. Stenger Lieutenant Colonel, United States Air Force B.S., Texas A&M University, 1994 M.S., Air Force Institute of Technology, 2000 Submitted in partial fulfillment of the requirements of the degree of DOCTOR OF PHILOSOPHY IN METEOROLOGY from the NAVAL POSTGRADUATE SCHOOL September 2013 Author: Robert A. Stenger Approved by: RussellL.Elsberry Distinguished Research Professor of Meteorology Dissertation Supervisor WendellA.Nuss PatrickA.Harr Professor of Meteorology Professor of Meteorology Assistant Dissertation Supervisor Assistant Dissertation Supervisor Michael T. Montgomery Robert A. Koyak Professor of Meteorology Associate Professor of Operations Research Approved by: Wendell A. Nuss, Chair, Department of Meteorology Approved by: O. Douglas Moses, Associate Provost for Academic Affairs iii THIS PAGE INTENTIONALLY LEFT BLANK iv ABSTRACT The landfall of large hurricanes in densely populated areas has increased the awareness that tropical cyclone structure plays an important role in the destructive potential of a storm. A unique set of H*Wind analyses of Atlantic tropical cyclones during the 2003— 2005 seasons is studied to better understand the internal and external mechanisms that lead to significant variability in surface wind structure. Secondary eyewall formation, asymmetric convection, land interaction, and environmental vertical wind shear were generally found to be mechanisms for radius of maximum wind increases, intensity decreases, and size of the radius of 34-kt wind increases. Two modes of size changes were documented that may lead to 100 km increases in 12—24 h, or near-zero size changes when a sharper than average outer wind structure profiles are generated. The statistical relationships among the radius of maximum wind, intensity, and outer-core wind structure from this sample may provide perturbed vortex initial conditions for an ensemble model to predict structure changes. v THIS PAGE INTENTIONALLY LEFT BLANK vi TABLE OF CONTENTS Page I. INTRODUCTION .......................... 1 A. MOTIVATION ....................... 1 1. Definition of Inner and Outer Core ..... 2 2. Surface Wind Profiles .............. 2 3. Secondary Eyewall Scenario .......... 8 4. Annular Storm Structure ............ 10 5. Importance of Wind Structure ........ 12 B. RELATED RESEARCH AND BACKGROUND .. 14 1. Vortex Rossby Waves .............. 15 2. Spiral Rainbands ................. 16 3. Asymmetric Convection ............ 17 4. Environmental Influences ........... 18 5. Vertical Wind Shear ............... 19 6. Upper-tropospheric Trough Interaction ... 20 7. Other Effects on Wind Structure Change .20 C. RESEARCH OBJECTIVE ............... 20 II. METHODOLOGY ......................... 23 A. DATA SET ......................... 23 B. H*WIND ANALYSIS ROUTINE ........... 25 1. History of SFMR ................. 25 2. Data-processing Methodology ......... 26 3. SFMR Algorithm ................ 27 4. Verification of SFMR Winds ......... 32 5. H*Wind Algorithm Limitations ....... 34 6. Sensitivity Analysis ............... 35 C. ANALYSIS TOOL ..................... 36 III. VALIDATION AND CHARACTERIZATION ........ 39 A. VALIDATION ....................... 39 B. CHARACTERIZATION ................. 41 1. Definition of Life Cycle ............. 41 2. Variability in Time ............... 42 3. Observed Structure Change .......... 43 vii Page C. IMPLICATION FOR ENSEMBLE INITIAL CON- DITIONS .......................... 52 1. Overview ...................... 52 2. Variability of Outer Wind Structure ..... 54 3. Assessment of Key Vortex Parameters ... 57 IV. MECHANISMS FOR STRUCTURE CHANGE ....... 89 A. SECONDARY EYEWALL FORMATION ...... 89 1. Complete Replacement Cycle ......... 89 2. Partial Replacement Cycle ........... 136 3. Conclusions for Secondary Eyewall Forma- tion ......................... 152 B. ASYMMETRIC CONVECTION ........... 155 1. Fabian (2003) ................... 156 2. Isabel (2003) ................... 162 3. Jeanne (2004) ................... 171 4. Conclusions for Asymmetric Convection .. 178 C. LAND INTERACTION ................. 181 1. Peripheral Interaction .............. 181 2. Near-core Interaction .............. 192 3. Conclusions for Land Interaction ....... 201 D. VERTICAL WIND SHEAR ............... 206 1. Fabian (2003) ................... 206 2. Isabel (2003) ................... 211 3. Ophelia (2005) .................. 219 4. Conclusions for Vertical Wind Shear .... 225 V. CONCLUSIONS ........................... 229 A. SUMMARY ......................... 229 B. FUTURE WORK ..................... 243 APPENDIX A. LIST OF STORMS ................. 247 APPENDIX B. COMPUTING CRITICAL RADII ........ 249 APPENDIX C. TIME-WEIGHTED INTERPOLATION .... 251 APPENDIX D. ANOMALOUS KINETIC ENERGY DELTA .253 APPENDIX E. OBSERVED STRUCTURE VARIABILITY .. 255 viii Page LIST OF REFERENCES .......................... 263 INITIAL DISTRIBUTION LIST ..................... 275 ix THIS PAGE INTENTIONALLY LEFT BLANK x LIST OF FIGURES Figure Page 1. Tangential wind profiles with x = 0.4 in Eq. (1) for various radial extents Ro (the radius where tangential wind speed is zero) at 1 15◦ latitude. Threshold wind speeds of 17, 25, and 50 m s− are highlighted by horizontal dashed lines (From Carr and Elsberry 1997).................................. 3 2. Median tangential wind profiles for Atlantic (a) tropical storms (TS) versus Saffir-Simpson Category 1 (H1) hurricanes and (b) Category 3 (H3) and Category 4 (H4) hurricanes (From Kimball andMulekar2004).......................... 6 3. Modeled storm evolution through the simulation time