Item

Abstract

By analysing real time model runs performed with the Ocean Model for Circulation and Tides (OMCT) with various forcing conditions, the impact of non-barotropic ocean dynamics on the time variable Earth's gravity field is estimated. The applied global ocean model is capable of simulating the three-dimensional thermohaline, wind- and pressure-driven circulation as well as lunisolar tidal dynamics and takes into account several so-called secondary effects, e.g., loading and self-attraction of a baroclinic water column, mass variations associated with sea-ice dynamics, and nonlinear interactions between tides and circulation which are commonly neglected in global numerical ocean models. In order to get insight into typical spatiotemporal patterns of ocean mass redistribution and consequently to identify oceanic regions of high impact on gravity changes, causative physical processes are separated and corresponding ocean bottom pressure fields reflecting the ocean's influence on the gravity field are analysed. Although monthly mean variabilities of ocean mass distributions are only slightly affected by loading and self-attraction and nonlinear interactions, instantaneously these secondary effects are responsible for anomalies in geoid heights up to about 1 mm, i.e., near the level of GRACE measurement noise. The baroclinic simulations suggest that ocean mass redistribution temporarily affect monthly mean gravity estimates obtained from GRACE down to horizontal scales of ~ 450 km.