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

• Main Author: Sun, Qiang
• Format: Text
• Language: unknown
• Published: OpenCommons@UConn 2019
• Subjects: Climate modelling; riverine freshwater; estuarine processes; salinity; stratification; continental shelf; climatology; Arctic; NADW; North Atlantic; South Atlantic Ocean
• Online Access: https://opencommons.uconn.edu/dissertations/2058; https://opencommons.uconn.edu/cgi/viewcontent.cgi?article=8341&context=dissertations

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). To assess model skill, a new climatology is created by averaging salinity observations from the World Ocean Database directly onto the POP grid cells. Model skill scores relative to the new climatology show that 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. 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. River water residence times for continental shelves range from 1 to 15 years. In the open ocean, river waters are drawn into ocean interior driven by NADW formation and reach the deep South Atlantic Ocean after four decades.