UNIVERSITY OF CALIFORNIA SAN DIEGO Mesoscale Dynamics of Atmospheric Rivers A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Oceanography by Reuben Demirdjian Committee in charge: F. Martin Ralph, Chair Joel Norris, Co-Chair Amato Evan Jan Kleissl Richard Rotunno Shang-Ping Xie 2020 Copyright Reuben Demirdjian, 2020 All rights reserved. The Dissertation of Reuben Demirdjian is approved, and it is acceptable in quality and form for publication on microfilm and electronically: _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ Co-chair _____________________________________________________________ Chair University of California San Diego 2020 iii DEDICATION For my family (friends included) iv EPIGRAPH “Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.” Carl Sagan “All things must pass.” George Harrison “Once there was a tree…” Shel Silverstein v TABLE OF CONTENTS Signature Page ..................................................................................................................... iii Dedication ............................................................................................................................ iv Epigraph ............................................................................................................................... v Table of Contents ................................................................................................................. vi List of Figures ...................................................................................................................... vii List of Supplemental Material ............................................................................................. xii List of Tables ....................................................................................................................... xii Acknowledgements .............................................................................................................. xiii Vita ...................................................................................................................................... xv Abstract of the Dissertation ................................................................................................. xvi Introduction .......................................................................................................................... 1 Chapter 1: Dropsonde Observations of the Ageostrophy within the Pre-Cold-Frontal Low-Level Jet Associated with Atmospheric Rivers ............................................ 4 1.1: Introduction........................................................................................................... 5 1.2: Methods ................................................................................................................ 8 1.2a: Dropsondes ................................................................................................ 8 1.2b: Reanalysis ................................................................................................. 11 1.2c: Gradient Wind ........................................................................................... 11 1.2d: Stationarity ................................................................................................ 12 1.3: Observations of the Ageostrophic Component of the LLJ .................................. 13 1.3a: Characterization ........................................................................................ 13 1.3b: Gradient Wind Imbalance ......................................................................... 16 1.3c: Comparison of Observations with ERA5 Reanalysis ............................... 17 1.4: Diagnostic Analysis for an AgLLJ Case study .................................................... 19 1.4a: Evolution of the AgLLJ ............................................................................ 19 1.4b: Diagnostics of the Ageostrophic Jet’s Forcing Mechanism ..................... 21 1.5: Conclusions and Discussion ................................................................................ 24 Acknowledgements ..................................................................................................... 26 Tables and Figures ...................................................................................................... 27 Supplemental Figures .................................................................................................. 37 Chapter 2: A Case Study of the Physical Processes Associated with the Atmospheric River Initial Condition Sensitivity from an Adjoint Model .................................. 38 2.1: Introduction .......................................................................................................... 39 2.2: Methods ................................................................................................................ 42 2.2a: Control and Adjoint Run Descriptions ...................................................... 42 2.2b: The Sawyer-Eliassen Transverse Circulation Model ................................ 44 2.2c: Air Parcel Trajectories .............................................................................. 45 2.3: Case Study Background ....................................................................................... 46 2.3a: Synoptic-Scale Overview .......................................................................... 46 2.3b: Initial Condition Perturbations .................................................................. 48 2.4: Results .................................................................................................................. 49 2.4a: Evolved Perturbations ............................................................................... 49 2.4b: The Transverse Circulation ....................................................................... 54 2.4c: Pseudo-Lagrangian Evolution of the Transverse Circulation ................... 56 vi 2.4d: Lagrangian Evolution of the Optimal Perturbations ................................. 58 2.5: Conclusion and Discussion .................................................................................. 60 Acknowledgements ..................................................................................................... 62 Tables and Figures ...................................................................................................... 64 Supplemental Figures .................................................................................................. 74 Chapter 3: The Circulation Response of a Two-Dimensional Frontogenetic Model to Optimized Moisture Perturbations ........................................................................ 75 3.1: Introduction .......................................................................................................... 76 3.2: Methods ................................................................................................................ 78 3.2a: Frontal Model ............................................................................................ 78 3.2b: Numerical Setup ........................................................................................ 80 3.2c: Optimal Perturbation Method ................................................................... 82 3.2d: COAMPS Model ....................................................................................... 84 3.3: Results .................................................................................................................. 84 3.3a: The Moist Control Simulation .................................................................. 84 3.3b: Dry vs. Moist Run ..................................................................................... 85 3.3c: Comparison with COAMPS ...................................................................... 86 3.3d: Optimal Perturbations ............................................................................... 88 3.4. Conclusions and Discussion ................................................................................. 91 Figures ......................................................................................................................... 95 Supplemental Figures .................................................................................................. 105 References ............................................................................................................................ 108 vii LIST OF FIGURES Figure 1.1: Northeast Pacific images of IVT (color fill; kg s-1 m-1) from