15:30 〜 17:00
[AAS05-P06] Implementation of the radiative transfer model Mstrn11 on MIROC6 and initial validation by aquaplanet experiments
キーワード：放射伝達モデル、水惑星
The radiative transfer model MstrnX has been used in MIROC6 and NICAM. Recently, an excess of incident solar radiation was recognized as a problem. The new radiation scheme, Mstrn11 has been developed and shown to successfully improve the accuracy of the radiation calculation. However, it has not been studied yet how the model atmosphere changes when Mstrn11 is implemented in a global climate model. In this study, as the first trial of the Mstrn11 evaluation in a realistic simulation, aqua-planet experiments were conducted using the new and old radiation schemes in MIROC6 and changes in the model atmosphere are documented.
When the experiment was conducted using the standard L81 setting for the vertical layer with the Mstrn11 implementation, the model did not run stably and a 3.5-year integration was not completed. The reason for this behavior was that the absorption coefficients, given as a database in the bivariate space of pressure and temperature, were extrapolated outside the range of the given bivariate space. To avoid this problem, this study conducted comparisons using an L40 setting for the vertical layer.
Comparing the results of the experiments with MstrnX and Mstrn11, the incoming surface shortwave radiation was reduced. This is an expected result of the update of the radiation scheme. We can expect that the excess of incoming shortwave radiation at the surface will be mitigated when Mstrn11 is used in a climate model. The experiments with using the SST distribution close to reality showed a relaxation of the double-ITCZ trend of the model. Unfortunately, however, similar results were not obtained for when the SST gradient was steeper compared to the reality. The Hadley circulation was weakened by about 11% in the evaluation using the mass stream function, which is consistent with the weakening of the latent heat heating near the equator, and the weakening of eddy momentum transport and thermodynamic forcing in the upper troposphere.
When the experiment was conducted using the standard L81 setting for the vertical layer with the Mstrn11 implementation, the model did not run stably and a 3.5-year integration was not completed. The reason for this behavior was that the absorption coefficients, given as a database in the bivariate space of pressure and temperature, were extrapolated outside the range of the given bivariate space. To avoid this problem, this study conducted comparisons using an L40 setting for the vertical layer.
Comparing the results of the experiments with MstrnX and Mstrn11, the incoming surface shortwave radiation was reduced. This is an expected result of the update of the radiation scheme. We can expect that the excess of incoming shortwave radiation at the surface will be mitigated when Mstrn11 is used in a climate model. The experiments with using the SST distribution close to reality showed a relaxation of the double-ITCZ trend of the model. Unfortunately, however, similar results were not obtained for when the SST gradient was steeper compared to the reality. The Hadley circulation was weakened by about 11% in the evaluation using the mass stream function, which is consistent with the weakening of the latent heat heating near the equator, and the weakening of eddy momentum transport and thermodynamic forcing in the upper troposphere.