The Estimation of the Surface Energy Balance of the North American Laurentian Great Lakes Using Satellite Remote Sensing and MERRA Reanalysis

The Surface Energy Balance (SEB) of the Great Lakes (GL) is a key to understanding the effects of climate change on the GL. There is a high possibility of underestimating the SEB of the GL when using existing methodologies with inputs from near-shore and land-based meteorological data. This study provides the first technique to investigate the SEB over the GL from July 2001 to December 2014 using a combination of data from satellite remote sensing, reanalysis data sets, and direct measurements. The pixel-based Great Lake Surface Temperature (GLST) under all-sky conditions were well correlated with the in situ observations (R2 = 0.9102) with a cool bias of -1.10 °C and a root mean square error (RMSE) of 1.39 °C. Contrary to expectations, the long-term trends of GLST decreased slightly due to the impact of an anomalously cold winter in 2013-2014. The components of the surface radiation budget estimated from the proposed method showed a good statistical agreement. Monthly spatial variations of net shortwave radiation varied with cloud cover and surface albedo while net longwave radiation varied with the temperature difference between the water surface and the atmosphere. We evaluated the feasibility of three different techniques for the estimation of the turbulent heat fluxes over the GL: i) the Bowen Ratio Energy Balance method; ii) the bulk aerodynamic approach and; iii) turbulent fluxes from MERRA (Modern Era Retrospective Analysis). Turbulent heat fluxes from those methods were compared with the direct eddy covariance measurements. The best statistical agreement amongst the three approaches was the bulk aerodynamic approach. Turbulent fluxes estimate from MERRA were not recommended due to the poor statistic agreement with the direct measurements. Using the bulk aerodynamic or direct eddy covariance measurements, the over-lake evaporation peaked during winter. From MERRA, the over-lake precipitation is uniformly spread throughout the year. The Great Lakes Net Basin Supply (NBS) shows one-month temporal lag with the GL water level. The correlation between teleconnection indices and NBS showed a positive correlation with the Arctic Oscillation and the North Atlantic Oscillation while over-lake evaporation showed a negative correlation with Pacific Decadal Oscillation and Niño 3.4 Indies