GMI Home > About GMI > The GMI Philosophy

The GMI Philosophy: Process-Oriented Evaluation

One of the goals of the Global Modeling Initiative is to reduce uncertainty in assessment calculations and in chemistry-climate model predictions. The GMI modular chemistry and transport models (CTMs) allow sensitivity testing of various aspects of model implementation. Early GMI studies investigated the sensitivity to numerical transport schemes (Rotman et al. [2001]) and evaluated transport characteristics of the GMI-CTM to input meteorological fields (Douglass et al. [1999]).

Understanding model sensitivities to the representation of physical processes is only part of process of reducing uncertainties. Physically based model evaluation is essential for model credibility, thus the value of an assessment calculation depends on strongly on a model’s demonstrated realistic behavior. That demonstration comes from the application of observationally-based tests to model simulations. In the late 1990's, GMI assessed the effects of aircraft exhaust on lower stratospheric ozone. To that end, the GMI science team developed 'objective grading criteria', that is, semi-quantitative, objective, observation-based tests that were used to grade the behavior of simulations. To assess the effects of a supersonic aircraft fleet flying mostly in the northern hemisphere, the tests focused primarily on northern hemisphere lower stratospheric temperature and transport characteristics. Three simulations using different meteorological data sets (from GISS, MACCM2, and GEOS-Strat) were objectively graded to determine which one was the most realistic [Douglass et al., 1999].

To date, GMI has developed tests that include temperature, barrier formation, and meridional transport in the stratosphere, including the UT/LS. Some of these tests have become part of the evaluations used in the Chemistry-Climate Model Validation Activity (CCMVal) for SPARC (Stratospheric Processes and their Role in Climate). More information on GMI transport and chemistry tests can be found in publications by Douglass et al. [1999], Strahan and Douglass [2004], Douglass et al. [2004], Strahan and Polansky [2006], and Strahan et al. [2007].

GMI will continue to work with groups involved in the study of chemistry-climate coupling by testing modules with observations in a CTM framework. As an example, GMI team members have used a wide range of existing observations to evaluate the GMI “Combo” chemistry, deposition and emission modules. Their successful evaluation has resulted in incorporation of these modules into the GEOS-5 GCM system as part of an ongoing chemistry-climate evaluation effort.

| Top of Page|