Jet Alignment in a Two-Layer Quasigeostrophic Channel Using One-Dimensional Grid Warping

Abstract

Because of position errors traditional methods of data assimilation can broaden and weaken jets or other flow structures leading to reduced forecast skill. Here a technique to assimilate properties of coherent structures is developed and tested. Focusing on jets, the technique identifies jets in both the modeled and observed fields and warps the model grid so that the jet positions are better aligned prior to further assimilation of observations. The technique is tested using optimal interpolation on the flow in a two-layer quasigeostrophic channel. The results show that a simple and fast jet position correction algorithm can significantly improve the skill of a 12-h forecast. Furthermore, the results indicate that this method of position correction maintains its utility when observations become sparse.

Assimilation of ocean sea-surface height observations of mesoscale eddies

“…18,19 Our approach is based on the idea that since vortices dominate the dynamics, it should be possible to obtain good results at a fraction of the cost by only assimilating observations of the vortices. Our approach is also related to the coherent-structure-based approach of Beechler et al; 20 in that approach, the structure of interest was a jet rather than coherent vortices, and the assimilation algorithm included an extra grid-warping step not used here.…”

Spatial Error Metrics for Oceanographic Model Verification

“…Spatial error metrics have since advanced in a number of studies (Casati et al 2008;Gilleland et al 2009Gilleland et al , 2010aAhijevych et al 2009;Marzban et al 2009). More recent developments include an alignment method by Beechler et al (2010) only operating along one dimension. Clark et al (2010) searches for the best matching point within a predefined window size.…”