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Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model

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Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model University of Connecticut OpenCommons@UConn Doctoral Dissertations University of Connecticut Graduate School 2-15-2019 Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model Qiang Sun University of Connecticut - Storrs, [email protected] Follow this and additional works at: https://opencommons.uconn.edu/dissertations Recommended Citation Sun, Qiang, "Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model" (2019). Doctoral Dissertations. 2058. https://opencommons.uconn.edu/dissertations/2058 Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model Qiang Sun, PhD University of Connecticut, 2019 Rivers modify coastal and open ocean salinity, stratification, and biogeochemistry. It is challenging to resolve or represent riverine, estuarine, and coastal processes that influence the delivery and transport of river waters to the ocean in Earth system models. This study improves and examines performance of the Parallel Ocean Program (POP) within the Community Earth System Model (CESM) with respect to riverine freshwater and analyzes river influences throughout the global ocean. Applied improvements are: imposing river runoff as point sources, using local reference salinities when coupling runoff to the ocean, and parameterizing estuarine mixing and exchange with the newly developed Estuary Box Model (EBM). The EBM successfully represents outflow salinity and volume fluxes for the Columbia River test case. Intercomparison of CESM runs shows strong sensitivity to the treatment of rivers. Improved representation increases near-surface surface salinity and reduces stratification near river mouths. There also are significant regional and remote changes in near-surface salinities. To assess model skill, a new climatology is created by averaging salinity observations from the World Ocean Database directly onto the POP grid cells, avoiding larger-scale spatial filtering that create high salinity biases in coastal regions. Model skill scores relative to the new climatology show that Qiang Sun – University of Connecticut, 2019 improvement in near-surface salinity is primarily attributed to focusing runoff as point sources and applying local reference salinities. Improvements in near-surface salinity stratification are primarily due to the EBM. Skill improvements extend far offshore and increase with proximity to the coast, particularly approaching major river mouths. With the applied improvements, river waters are tracked through the ocean with passive tracers. River tracer concentrations are high near river mouths, the global coastal ocean, and throughout much of the near-surface Arctic and North Atlantic Oceans. Rivers strongly influence near-surface salinity stratification in these areas. Rivers have stronger stratification contributions than precipitation and sea-ice melt near river mouths and on the Eurasian Arctic continental shelf. River water residence times for continental shelves range from 1 to 15 years. In the open ocean, river waters also are drawn into ocean interior driven by NADW formation and reach the deep South Atlantic Ocean after four decades. Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model Qiang Sun B.E., Xi’an University of Architecture and Technology, China, 2004 M.S., Gottfried Wilhelm Leibniz Universität Hannover, Germany, 2012 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at the University of Connecticut 2019 Copyright by Qiang Sun 2019 ii APPROVAL PAGE Doctor of Philosophy Dissertation Improving the Treatment of Rivers and Assessing River Influences in the Global Ocean of the Community Earth System Model Presented by Qiang Sun, B.E., M.S. Major Advisor _________________________________________________________________ Michael M. Whitney Associate Advisor ______________________________________________________________ Frank O. Bryan Associate Advisor ______________________________________________________________ Penny Vlahos Associate Advisor ______________________________________________________________ Melanie Fewings University of Connecticut 2019 iii Acknowledgements First and foremost, I would like to thank my advisor Michael M. Whitney. I appreciate all his contributions of time, ideas, and funding to make my PhD experience productive and stimulating. The joy and enthusiasm he has for research was contagious and motivational for me, even during tough times in the PhD pursuit. He has been a tremendous help with invaluable guidance and continuous support to my professional development. I consider myself very fortunate to get the opportunity to work under his supervision. I would also like to express my gratitude to my committee members: Frank O. Bryan, Penny Vlahos, and Melanie Fewings, for their comments, suggestions, and assistance with my research, and for being there for me when I needed them throughout different stages of my graduate studies. I would like to thank my research group members -Yan Jia and Steven Deignan-Schmidt. Our group has been a source of friendships as well as good advice and collaborations. You made my life in UConn enjoyable and memorable. I would like to thank my parents Luping and Luqing, for showing faith in me and giving me liberty to choose what I desired. I salute you all for the selfless love, care, and sacrifice you did to shape my life. I would like to thank my wife Xinxuan, for her continued and unfailing love, support and understanding during my pursuit of my PhD. You were always around at times I thought that it was impossible to continue, you helped me to keep things in perspective. I appreciate my little Derek for abiding my ignorance and the patience he showed during my thesis writing. Words would never say how grateful I am to all of you. iv Table of Contents Chapter 1. Introduction and objectives ......................................................................................................... 1 Chapter 2. A Box Model for Representing Estuarine Physical Processes in Earth System Models ............ 4 2.1 Introduction ....................................................................................................................................... 5 2.2 Background ........................................................................................................................................ 6 2.3 Estuary Box Model development ...................................................................................................... 7 2.3.1 Configuration .............................................................................................................................. 7 2.3.2 Continuous governing equations ................................................................................................. 8 2.3.3 Estuary-integrated volume and density balances ........................................................................ 9 2.3.4 Estuary-integrated potential energy balance ............................................................................. 10 2.3.5 Vertical velocity, density distribution, and estuary length ........................................................ 11 2.3.6 Dimensional solution ................................................................................................................ 13 2.3.7 Implementation of EBM in Earth system models ..................................................................... 14 2.4 Columbia River test case ................................................................................................................. 19 2.4.1 Observational data..................................................................................................................... 19 2.4.2 Comparisons with observations ................................................................................................ 20 2.4.3 ROMS simulation data .............................................................................................................. 21 2.4.4 Comparison to the ROMS simulation ....................................................................................... 22 2.5 Applying the EBM globally ............................................................................................................ 24 2.6 EBM test in global climate model ................................................................................................... 25 2.6.1 CESM and EBM settings .......................................................................................................... 25 2.6.2 Interpretation of CESM results ................................................................................................. 27 2.7 Discussion........................................................................................................................................ 32 2.8 Summary.......................................................................................................................................... 33 Acknowledgements ................................................................................................................................. 34 Tables and Figures .................................................................................................................................. 35 Chapter 3. Assessing the skill of the improved
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