An investigation of the thermal response to meteorological forcing in a hydrodynamic model of Lake Superior

Abstract

Lake Superior, the largest lake in the world by surface area and third largest by volume, features strong spatiotemporal thermal variability due to its immense size and complex bathymetry. The objectives of this study are to document our recent modeling experiences on the simulation of the lake thermal structure and to explore underlying dynamic explanations of the observed modeling success. In this study, we use a three‐dimensional hydrodynamic model (FVCOM—Finite Volume Community Ocean Model) and an assimilative weather forecasting model (WRF—Weather Research and Forecasting Model) to study the annual heating and cooling cycle of Lake Superior. Model experiments are carried out with meteorological forcing based on interpolation of surface weather observations, on WRF and on Climate Forecast System Reanalysis (CFSR) reanalysis data, respectively. Model performance is assessed through comparison with satellite products and in situ measurements. Accurate simulations of the lake thermal structure are achieved through (1) adapting the COARE algorithm in the hydrodynamic model to derive instantaneous estimates of latent/sensible heat fluxes and upward longwave radiation based on prognostic surface water temperature simulated within the model as opposed to precomputing them with an assumed surface water temperature; (2) estimating incoming solar radiation and downward longwave radiation based on meteorological measurements as opposed to meteorological model‐based estimates; (3) using the weather forecasting model to provide high‐resolution dynamically constrained wind fields as opposed to wind fields interpolated from station observations. Analysis reveals that the key to the modeling success is to resolve the lake‐atmosphere interactions and apply appropriate representations of different meteorological forcing fields, based on the nature of their spatiotemporal variability. The close agreement between model simulation and observations also suggests that the 3‐D hydrodynamic model can provide reliable spatiotemporal estimates of heat budgets over Lake Superior and similar systems. Although there have been previous studies which analyzed the impact of the spatiotemporal variability of overwater wind fields on lake circulation, we believe this is the first detailed analysis of the importance of spatiotemporal variability of heat flux components on hydrodynamic simulation of 3‐D thermal structure in a lake.

Investigation of Water Temperature Variations and Sensitivities in a Large Floodplain Lake System (Poyang Lake, China) Using a Hydrodynamic Model

“…In the current study, although varying only one input parameter is not sufficient to represent the conditions of changing climate and hydrology, this modification approach is suitable to investigate the sensitivity of the hydrodynamic model to changes in external forcings, because the direct influence of each input parameter can be investigated separately [19]. In some lakes, topography plays an important role in inducing temperature gradients between deep and shallow areas [5,20]. In Poyang Lake, for example, there are extensive shallow floodplain areas and deep flow channels that vary in temperature from the main body of the lake.…”

“…In some lakes, topography plays an important role in inducing temperature gradients between deep and shallow areas [5,20]. In Poyang Lake, for example, there are extensive shallow floodplain areas and deep flow channels that vary in temperature from the main body of the lake.…”

“…The hydrology of Poyang Lake varies seasonally under the combined effects of catchment river inflows and interactions with the Yangtze River [28,41]. These result in the water surface area varying from <1000->3000 km 2 each year in response largely to the water level fluctuations of 8-22 m [20]. Differences in water surface elevations can reach up to approximately 5 m in dry seasons, whereas the water surface is almost horizontal during flood seasons [42].…”

“…They found that the most sensitive reactions of the water temperature in the lake are the air temperature and wind speed. A 3D hydrodynamic model FVCOM (Finite Volume Community Model) was also adopted to predict the water temperature changes of the Lake Superior (USA-Canada border), which indicates that the physical model can be used to provide reliable spatiotemporal estimates of water temperature in complex lake systems [20]. These previous studies of water temperature demonstrate that hydrodynamic modeling has been used for a wide variety of lake systems.…”

A Hybrid Lagrangian-Eulerian Particle Model for Ecosystem Simulation

“…The unstructured 395 grid can be designed to provide a customized variable resolution to both coastline and 396 bathymetry. With the merits of ideal geometric fitting and local refinement of mesh 397 resolution, FVCOM has been used in numerous applications to estuaries, coastal oceans, 398 and the Great Lakes [Yang et al, 2013;Xue et al, 2015;Anderson et al, 2016;Xue et al 399 2017; Khangaonkar et al, 2018, Ye et al, 2018. These characteristics make the model 400 well suited for the study of Sandusky Bay.…”