An evaluation and intercomparison of four new advection schemes for use in global chemistry models

Abstract

The need to use a higher spatial resolution and to include more chemical 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 schemes 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 unconditionally stable scheme on a uniform grid. Two tests are performed with all schemes: a solid‐body rotation test and a radon transport test. The radon transport test is performed with the off‐line global tracer model TM2. The solid‐body rotation test shows that none of the new schemes generates undershoot and overshoot and that all of them are mass conservative. Slopes and Second Moments both generate small undershoot and overshoot at all resolutions. The accuracy of the new and old schemes for rotation of a smooth profile is similar for the horizontal resolutions studied. Since the new schemes are slightly more diffusive than the old schemes, they perform worse for rotation of a cone. The radon test shows that the errors related to the numerical schemes are much smaller than other model errors. The main advantage of the new schemes is that they use 75% and 90% less memory than Slopes and Second Moments, respectively. At horizontal resolutions higher than 5° × 5° Split‐us and Split‐rg are the most efficient of the schemes in terms of cpu time. The new advection schemes are available through Internet.