Effects of the Cowling Approximation on Predictions of Glacial Isostatic Adjustment

The vast majority of previous studies of glacial isostatic adjustment (GIA) consider the response of spherically symmetric, viscoelastic Earth models. In the normal mode theory traditionally applied in these studies perturbations in gravitational potential are coupled to perturbations in the density field through Poisson's Equation. Recently, an effort has been initiated by several independent groups to develop numerical methods to solve for the response of laterally varying Earth models. In these efforts it is advantageous to use the Cowling approximation. In this approximation the effects of the zeroth order potential field on displacements are included without simultaneously solving for the associated potential perturbation. In this poster, we investigate the effects of the Cowling approximation on a large suite of GIA predictions using spherically symmetric, rotating Earth models with Maxwell rheology. We compare the solutions obtained with and without the Cowling approximation both on global scale observations, such as ˙ {J}₂, and on local observations, such as relative sea level predictions. These results bound the error introduced by the Cowling approximation and thus serve as a guide to the development of numerical methods for 3-D GIA.