Pressure Effects on Great Lakes Vertical Control

This study investigated the warping effects of atmospheric pressure fields on the assumed level geopotential Great Lakes water surfaces during the 28-month period used in establishing the 1955 International Great Lakes Datum. The hydrostatic analysis used in the study indicated variations in lake water surface elevations of up to 4 cm during the study period. These variations were compared with computed gravitational effects similar to those included in the 1955 International Great Lakes Datum establishment. The atmospheric pressure effects were found to be of the same order of magnitude as those resulting from the nonuniform gravitational forces. Thus, the assumption that the water surfaces of the Great Lakes are level geopotential surfaces is erroneous and atmospheric pressure corrections should be included when establishing and revising the vertical control on the Great Lakes.