Precipitation impacts on lake ice and water temperature in the North American Great Lakes

Ayumi Fujisaki-Manome, University of Michigan Ann Arbor, Ann Arbor, MI, United States; Cooperative Institute for Great Lakes Research, Ann Arbor, MI, United States, Eric J Anderson, Great Lakes Environmental Research Laboratory (GLERL), National Oceanic and Atmospheric Administration (NOAA), Ann Arbor, United States, James Andrew Kessler, NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, United States, Philip Chu, NOAA, United States, Jia Wang, NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, United States and Andrew Gronewold, University of Michigan, School for Environment and Sustainability, Ann Arbor, United States; University of Michigan Ann Arbor, School for Environment and Sustainability, Ann Arbor, MI, United States
Abstract:
Ice cover in the North American Great Lakes (hereafter the Great Lakes) plays critical roles in regional climate, weather, water levels, and waves. In addition, it has direct socioeconomic impacts on commercial shipping and navigation safety. Multiple studies demonstrated the high year-to-year variability of ice cover in the Great Lakes, which makes accurate forecasting challenging. A key factor to improve the capability to forecast changing Great Lakes ice cover at various time scales, from a few days to seasons, would be accurate representation of air-ice-lake interactions. In this context, this study examined precipitation impacts on ice cover and water temperature in the Great Lakes using state-of-art ice-hydrodynamic models based on the Finite Volume Community Ocean Model coupled with the unstructured grid version of Los Alamos Sea Ice model. Numerical experiments were conducted for the recent anomalously cold (2014-2015) and warm (2015-2016) winters that were accompanied high and low ice coverage over the lakes, respectively. In the numerical experiments, snow cover on the ice, which is the manifestation of winter precipitation, reduced the total ice volume (or mean ice thickness) in all of the Great Lakes, shortened the ice duration, and allowed earlier warming of water surface. The reduced ice volume was due to the thermal insulation of snow cover. The surface albedo was also increased by snow cover, but its impact to delay the melting of ice was overcome by the thermal insulation effect. During major snowstorms, snowfall over the water caused notable cooling of water surface due to latent heat absorption when snow melting. Overall, the sensible heat flux from rain from spring to summer was found to have negligible impacts on the water surface temperature. Although uncertainties remain with snow parameterizations and over-lake precipitation, this study demonstrated that winter precipitation be an important contributor to determine the Great Lakes ice production and thermal conditions from late fall to spring.
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