IMPACT OF VERTICAL COORDINATE SYSTEMS ON THE ACCURACY OF SIMULATING THERMAL STRUCTURE AND SEASONAL CIRCULATION IN LAKE MICHIGAN-HURON

In hydrodynamic modeling, the choice of vertical coordinate system (VCS) directly influences vertical processes, including vertical mixing, density stratification, and overturning circulation. VCS choice is particularly important for steep bathymetry (e.g. continental slopes, rift lakes) and weak stratification, which is especially relevant for large freshwater lakes, like the Laurentian Great Lakes, where contemporary operational hydrodynamic models simulate overly diffuse metalimnions. This is problematic for simulating many key ecosystem processes, such as phytoplankton growth and hypolimnetic hypoxia, the latter of which is directly correlated with hypolimnetic water volume. This study uses the Modular Ocean Model version 6.0 (MOM6) to simulate the thermal structure and seasonal circulation of Lake Michigan-Huron. MOM6 applies vertical Lagrangian remapping, a type of Arbitrary Lagrangian Eulerian (ALE) algorithm, enabling flexibility in using various VCSs, including geopotential (z or z*), isopycnal, sigma, or hybrid configurations. This study tests z*, sigma, isopycnal, and hybrid coordinates to assess the strengths and limitations of these VCS for simulating thermal structure and vertical mixing in baroclinic simulations of large, seasonally stratified freshwater lakes, which are novel systems for MOM6 applications. A well-validated hydrodynamic model will aid in coupling with next-generation biogeochemical (COBALT), climate (CM4), and ecosystem (Atlantis) models, improving the understanding of lake-atmosphere interactions, carbon cycling, and ecosystem dynamics. 

Presentation Preference: Oral

Primary Presenter: Meena Raju, University of Michigan (meena1982@gmail.com)

Authors:

Meena Raju, Cooperative Institute for Great Lakes Research, University of Michigan  (meena1982@gmail.com)

David Cannon, Cooperative Institute for Great Lakes Research, University of Michigan  (djcannon@umich.edu)

Peter Alsip, NOAA Great Lakes Environmental Research Laboratory  (peter.alsip@noaa.gov)

He Wang, NOAA/Geophysical Fluid Dynamics Laboratory & University Corporation for Atmospheric Research  (he.wang@noaa.gov)

Joseph Langan, NOAA Great Lakes Environmental Research Laboratory  (joseph.langan@noaa.gov)

Jia Wang, NOAA Great Lakes Environmental Research Laboratory  (jia.wang@noaa.gov)

Robert Hallberg, NOAA/Geophysical Fluid Dynamics Laboratory  (robert.hallberg@noaa.gov)

Charles Stock, NOAA/Geophysical Fluid Dynamics Laboratory  (charles.stock@noaa.gov)