Intellectual Merit: The effects of heterogeneous pack ice on lake thermo and hydrodynamics and on lake-air interactions over the Great Lakes are not well understood. In fact the impact of ice on basin-scale circulation in the Great Lakes is almost completely unknown. This knowledge gap is an impediment to any ecological study that requires data on winter circulation. In addition, these deficiencies often are obstacles in forecasting lake-effect snowstorms and in modeling lake-atmosphere interaction. The overall objective of this project is to develop a basic understanding of Lake Erie (and other Great Lakes) winter hydrodynamics, including circulation, evolution of thermal structure, ice cover and heat exchange with atmosphere. The research will address the following questions: (1) What is the impact of ice on lake circulation pattern? (2) What is the impact of ice on spatial heterogeneity of lake-atmosphere heat flux? (3) What is the impact of ice on mixing and lake thermal structure? The following hypotheses are proposed: (1) During winters with little ice cover, the central basin of Lake Erie exhibits classic wind-driven two-gyre circulation pattern typical for ice-free conditions, but during winters when ice cover is extensive, the single anticyclonic gyre circulation prevails due to the effect of momentum flux vorticity. Additional hypotheses state that due to prevailing westerly-northwesterly winds and related ice drift, there is north-south gradient in ice concentration and thickness (less ice in the northern half of the lake, more ice in the southern half) and in near-surface current speed (due to retardation of momentum by ice). (2) Drifting ice creates significant spatial heterogeneity of lake-atmosphere heat flux with maximum fluxes in the northern part of the lake (due to decreased ice concentration and thickness) and minimum fluxes in the southern part of the lake (due to increased ice concentration and thickness). (3) Decreased ice concentrations in the northern part of Lake Erie lead to lower water temperatures and uniform vertical temperature profiles due to enhanced wind-generated mixing and heat exchange with atmosphere, while increased ice concentrations in the southern part of Lake Erie lead to higher water temperatures and weak vertical temperature stratification due to reduced mixing and heat exchange with atmosphere.
The field program will include measurements of currents, temperature and ice thickness at several moorings in the central basin of Lake Erie during two winters, complemented with helicopter surveys of ice concentration and thickness, and remote sensing observations of ice concentration. Modeling component will include applying and validating a newly developed ice-lake model to historic and field year winters, along with idealized case studies. Proposal hypotheses will be then tested by means of idealized case studies, realistic model runs, model sensitivity studies and observations.
Broader Impacts: In addition to a MS student supported by the project, several graduate students will be involved in this study through a joint NOAA GLERL/University of Michigan summer research program. Project results will be disseminated broadly through journal articles, presentations at scientific conferences, and a dedicated website. Direct ice thickness measurements will be a true breakthrough in limnological studies, as this technology has not yet been used by Great Lakes researchers. The ice model will be useful for many practical and scientific studies of the Great Lakes, Arctic and sub-Arctic lakes and seas with seasonal ice cover. The calibrated model will be transferred to GLERL and incorporated into Great Lakes Coastal Forecasting System to produce operational ice forecasts for the first time. This information will be invaluable for regional weather forecasting of lake-effect snow. Obtained data will be of also of great importance to biological sciences, helping understanding of development of phytoplankton blooms in winter, fish recruitment research and ecological forecasting.
