Surface Energy Fluxes on the Great Lakes Based on Satellite-Observed Surface Temperatures 1992 to 1995

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Accurate estimates of surface energy exchange components are critical for understanding many physical processes of large lakes and their atmospheric environment. In this paper, the seasonal cycle of latent, sensible, and total heat flux from the surface of the Great Lakes is estimated. Lake surface temperatures derived from the NOAA/AVHRR satellite, along with meteorological data from surface station observations are incorporated in order to estimate spatial distributions of fluxes. Several well-known features are evident. Among these are the very high outgoing fluxes of latent and sensible heat during the late fall and early winter, which drive strong cooling of the lake surface and consequent convective mixing within the lake column. Another is greater seasonal variation of surface temperature and fluxes in shallower waters than in deeper waters. Due to strong static stability of the overlying atmospheric boundary layer during the spring, both the magnitude and the spatial variations of latent and sensible heat fluxes are small during the spring and, to a lesser degree, during the summer. The annual cycles of latent and sensible heat flux over the Great Lakes are roughly opposite in phase to the same fluxes over land, indicating a large exchange of energy via atmospheric advection between the lake and land surfaces. A major weakness of the method used here is that heat fluxes are calculated on the basis of an ice-free surface, making the derived fluxes for January through March roughly estimated.