Evaluation of the atmospheric transport in a GCM using radon measurements: sensitivity to cumulus convection parameterization

[摘要] The radioactive species radon (²²²Rn) has long been used as atest tracer for the numerical simulation of large scale transportprocesses. In this study, radon transport experiments are carriedout using an atmospheric GCM with a finite-difference dynamicalcore, the van Leer type FFSL advection algorithm, and twostate-of-the-art cumulus convection parameterization schemes.Measurements of surface concentration and vertical distribution ofradon collected from the literature are used as references in modelevaluation.

The simulated radon concentrations using both convection schemesturn out to be consistent with earlier studies with many othermodels. Comparison with measurements indicates that at the locationswhere significant seasonal variations are observed in reality, themodel can reproduce both the monthly mean surface radonconcentration and the annual cycle quite well. At those sites wherethe seasonal variation is not large, the model is able to give acorrect magnitude of the annual mean. In East Asia, where radonsimulations are rarely reported in the literature, detailed analysisshows that our results compare reasonably well with theobservations.

The most evident changes caused by the use of a different convectionscheme are found in the vertical distribution of the tracer. Thescheme associated with weaker upward transport gives higher radonconcentration up to about 6 km above the surface, and lower valuesin higher altitudes. In the lower part of the atmosphere resultsfrom this scheme does not agree as well with the measurements as theother scheme. Differences from 6 km to the model top are evenlarger, although we are not yet able to tell which simulation isbetter due to the lack of observations at such high altitudes.

[学科分类] 大气科学