AN EVALUATION AND INTERCOMPARISON OF 4 NEW ADVECTION SCHEMES FOR USE IN GLOBAL CHEMISTRY MODELS

The need to use a higher spatial resolution and to include more chemic al species in global atmospheric chemistry models has led to a demand for efficient advection schemes with high accuracy. We test four newly developed three-dimensional advection schemes named Mol-rg, Split-u, Split-us, and Split-rg. We compare the new schemes with the existing s chemes Slopes and Second Moments, both implemented on a uniform grid. Mol-rg and Split-rg make use of a reduced grid. Split-us is an uncondi tionally stable scheme on a uniform grid. Two tests are performed with all schemes: a solid-body rotation test and a radon transport test. T he radon transport test is performed with the off-line global tracer m odel TM2. The solid-body rotation test shows that none of the new sche mes generates undershoot and overshoot and that all of them are mass c onservative. Slopes and Second Moments both generate small undershoot and overshoot at all resolutions. The accuracy of the new and old sche mes for rotation of a smooth profile is similar for the horizontal res olutions studied. Since the new schemes are slightly more diffusive th an the old schemes, they perform worse for rotation of a. cone. The ra don test shows that the errors related to the numerical schemes are mu ch smaller than other model errors. The main advantage of the new sche mes is that they use: 75% and 90% less memory than Slopes and Second M oments, respectively. At horizontal resolutions higher than 5 degrees x 5 degrees Split-us and Split-rg are the most efficient of the scheme s in terms of cpu time. The new advection schemes are available throug h Internet.