The hydrodynamics of Lake Michigan and Lake Baikal were delineated using surface temperatures (SST) derived from the Advanced Very High Resolution Radiometer (AVHRR) aboard NOAA satellites. Lake Michigan data were obtained through the NOAA CoastWatch Program from May 1990 to July 1993. Images of Lake Baikal were collected between June 1990 and September 1991. AVHRR SST data showed the spatial and temporal dynamics of seasonal temperature cycles, thermal fronts, upwelling, and the interaction between the lakes and their bays and tributaries.

Thermal fronts in southern Lake Michigan typically formed in early May, but in 1991 fronts were first observed in mid-April. Fronts remained 5-30 km offshore for several weeks before rapidly migrating northward. By early June, water at temperatures <4 deg C was isolated in the northern basin. In 1992 and 1993, the northward migration was briefly reversed as the 5 deg C isotherm moved south before resuming its northward progression. The influence of the Grand and Milwaukee Rivers on spring warming was not observed in SST images. Water exchange between Green Bay and Lake Michigan occurred through the Sturgeon Bay Canal and at the mouth of the bay. Extensive upwelling was also observed in this area along the Door Peninsula.

The range of SST in the lake was small in winter and summer indicating relatively uniform thermal conditions as compared to spring and fall when temperatures rapidly responded to seasonal change. The maximum whole-lake median SST in 1991 was 23.8 deg C which was >4 deg C higher than in the other years studied. Minimum median SST ranged from 2.5 deg C in 1991 to 4.2 deg C in 1993.

Lake Baikal was ice-free in early June. The Selenga, Barguzin, and Upper Angara Rivers were significant sources of heat to the surface waters. The southern and middle basin warmed more quickly than the northern basin, however, the relatively shallow northern basin reached higher summer temperatures of about 16 deg C. Thermal fronts were generally associated with topographic features such as sills, coastal wetlands, bays, and river deltas. Upwelling in Lake Baikal was not clearly depicted using AVHRR SST data. Bands of relatively warm water persisted near shore throughout the lake in summer.

AVHRR SST provide a means of linking thermal structures, hydrodynamics, and biogeochemical processes in large lakes. Systematic changes in thermal structures may serve as indicators of regional or global climate change.