Forecasting of the dynamics and composition of the 2004-2005 Arctic vortex

This paper will examine and discuss the performance of a coupled meteorology and constituent forecasting system in the northern stratospheric winter of 2004-2005. The meteorological component of the system is the Goddard Earth Observation System, Version 4 (GEOS-4) data assimilation and forecasting system. For this work, a complete middle atmospheric chemistry module, developed in the Atmospheric Chemistry and Dynamics Branch at NASA GSFC has been implemented on-line in the GEOS-4 general circulation model. During the Polar Aura Validation Experiment, a trial project was run, in which the operational GEOS-4 analyses produced in near-real time were used to constrain a parallel model run, which included the chemistry package. These combined meteorology-chemistry “analyses” were used to generate ten day forecasts, initialized twice each day. In order to accommodate the real-time throughput, horizontal resolution was degraded from one to two degrees in the chemical system. This paper will examine in some detail three aspects of the results. First, the integrity of the analyses will be examined, in comparison to independent data. Second, measures of forecast skill will be presented; these will include “traditional” quantities such as anomaly correlation analyses, but also some quantities more suited to quantifying the dyncamical-chemical state of the middle atmosphere. Third, some reprocessing runs will be examined, in which the horizontal resolution of the dynamical-chemical system is changed: this analysis will focus on the impacts of increased (one-degree) resolution on our ability to represent mixing events around the vortex edge.