A SYNOPTIC APPROACH TO THE SOUTH ASIAN MONSOON CLIMATE A dissertation submitted to Kent State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy By Md Rafiqul Islam August 2020 © Copyright All rights reserved Except for previously published Materials Dissertation written By Md Rafiqul Islam B.Sc., University of Dhaka, 2008 M.S., University of Dhaka, 2010 Ph.D., Kent State University, 2020 Approved by Dr. Scott Sheridan , Chair, Doctoral Dissertation Committee Dr. Thomas Schmidlin , Members, Doctoral Dissertation Committee Dr. Cameron C. Lee , Dr. Javed Khan , Dr. Laura G. Leff , Accepted by Dr. Scott Sheridan , Chair, Department of Geography Dr. Mandy Munro Stasiuk , Interim Dean, College of Arts and Sciences TABLE OF CONTENTS Page Table of Contents…………………………………………………………………………… iii List of Tables ……………………………………………………………………………. vi List of Figures…………………………………………………………………………… vii Acknowledgements………………………………………………………………………. ix 1. CHAPTER ONE INTRODUCTION ........................................................................... 1 2. CHAPTER TWO BACKGROUND .............................................................................. 9 2.1. Monsoon Seasonality ......................................................................................................... 9 2.2. Monsoon Onset ................................................................................................................. 10 2.3. Monsoon Mechanism ....................................................................................................... 13 2.4. Synoptic Climatology ....................................................................................................... 14 2.5. Self-Organizing Maps (SOMs)........................................................................................ 16 2.6. Application of Self-Organizing Maps............................................................................. 18 3. CHAPTER THREE .......................................................................................................... 22 3.1. ABSTRACT ...................................................................................................................... 22 3.2. Introduction ...................................................................................................................... 23 3.3. Background ...................................................................................................................... 24 3.3.1. Synoptic climatology and Self-organizing maps (SOMs) ...................................... 24 3.4. Application of Self Organizing map techniques ............................................................ 26 3.5. Data and methods ............................................................................................................ 28 3.5.1. Data ............................................................................................................................ 28 3.5.2. SOM methodology .................................................................................................... 29 3.5.3. Seasonal Delineation ................................................................................................. 32 iii 3.6. Results and discussion ..................................................................................................... 34 3.6.1. Sea level pressure ...................................................................................................... 34 3.6.2. Wind ........................................................................................................................... 39 3.6.3. Temperature .............................................................................................................. 45 3.6.4. Relative Humidity ..................................................................................................... 51 3.6.5. Precipitation .............................................................................................................. 57 3.7. DISCUSSION ................................................................................................................... 62 3.7.1. Seasonal delineation ................................................................................................. 62 3.7.2. Synoptic validation ................................................................................................... 64 3.8. CONCLUSION ................................................................................................................ 67 4. CHAPTER FOUR ............................................................................................................ 68 4.1. ABSTRACT ...................................................................................................................... 68 4.2. INTRODUCTION............................................................................................................ 69 4.3. Data and Methods ............................................................................................................ 72 4.3.1. Data ............................................................................................................................ 72 4.3.2. Criteria for onset and withdrawal of seasons ........................................................ 74 4.4. Results and discussion ..................................................................................................... 75 4.4.1. Utility of SOMs and seasonal circulation patterns ................................................ 75 4.4.2. Seasonal Onset, length, and Circulation Pattern Climatology ............................. 77 4.4.3. Comparing SOM based onset of monsoon dates with other existing methods ... 87 4.5. CONCLUSION ................................................................................................................ 89 5. CHAPTER FIVE ............................................................................................................. 91 5.1. INTRODUCTION............................................................................................................ 91 5.2. Data and methods: ........................................................................................................... 97 5.2.1. Data ............................................................................................................................ 97 5.2.2. Seasonal delineation (Creation of SOMs) ............................................................... 98 5.3. Results ............................................................................................................................... 99 5.3.1. Pre-monsoon season ............................................................................................... 100 5.3.2. Pre-monsoon to Monsoon Transition ................................................................... 102 5.3.3. Monsoon Season ...................................................................................................... 105 5.3.4. Monsoon to post-monsoon Transition .................................................................. 111 5.3.5. Post-monsoon Season ............................................................................................. 114 5.3.6. Post-monsoon to winter transition ........................................................................ 116 iv 5.3.7. Winter Season ......................................................................................................... 118 5.3.8. Winter to Pre-monsoon Transition ....................................................................... 120 5.4. DISCUSSION AND CONCLUDING REMARKS ..................................................... 121 6. CHAPTER SIX DISCUSSION ............................................................................... 132 7. CHAPTER SEVEN CONCLUSION ....................................................................... 141 v LIST OF TABLES Table 3-1 :Initial Definition of Seasonal Month of a Year _____________________________ 32 Table 3-2: Mean precipitation (mm) by node associated with wind SOM. ________________ 45 Table 3-3: Mean precipitation (mm) by node associated with temperature SOM ___________ 51 Table 3-4: Mean precipitation (mm) by node associated with relative humidity SOM _______ 57 Table 3-5: Mean precipitation field per SOM node as depicted in Figure 1.2 ______________ 66 Table 3-6: Mean precipitation field per SOM node as depicted in Figure 1.11 _____________ 66 Table 4-1: Decadal Mean Seasonal Onset Trend, a positive slope indicates . ______________ 81 Table 4-2: Decadal Trend analysis of Seasonal Length _______________________________ 83 Table 4-3: SOM based monsoon onset dates for different atmospheric variables. __________ 83 Table 4-4: Decadal Trend of Monsoon Onset, SOM Based Vs Others. ___________________ 87 vi LIST OF FIGURES Figure 1-1. South Asian Domain .................................................................................................... 2 Figure 3-1: South Asia and two local regions of interest, Kerala and Bangladesh. ..................... 31 Figure 3-2: SOM lattice for sea-level pressure.. ........................................................................... 37 Figure 3-3: Associated with each of the SOM nodes in Figure 3-2:. ........................................... 38 Figure 3-4: Each map represents the mean…………. in SLP SOM in Figure 3-2. ..................... 38 Figure 3-5: SOM lattice for wind.................................................................................................