Analysis of grid imprinting on geodesic spherical icosahedral grids

Numerical grid imprinting errors have often been observed in global atmospheric models on icosahedral grids. In this paper we analyse the sources of grid imprinting error related to the usual finite volume discretization of the divergence operator. We introduce the concept of alignment of computational cells, and establish that convergence of second order is attained on aligned cells. Moreover, we present strong evidence that grid imprinting errors are caused by the slow convergence on badly aligned cells. The analysis presented is not restricted to icosahedral grids, being valid for any geodesic spherical grid.