11:45 AM - 12:00 PM
[AAS03-10] How can the double-ITCZ problem be alleviated in climate models?
Keywords:ITCZ, climate model, cloud
The double-ITCZ problem is a common and longstanding bias in climate models and the cause has been discussed for many years. How can the double-ITCZ problem be alleviated in climate models?
The radiation bias, especially over the Southern Ocean, was terribly bad in MRI-CGCM3 that was used for CMIP5 simulations. However, the bias is significantly reduced in MRI-ESM2 (Yukimoto et al. 2019) that is used for CMIP6 simulations by various modifications related to clouds (Kawai et al. 2019). On the other hand, the double-ITCZ problem is also alleviated in the MRI-ESM2. Is the reduction in the radiation bias the cause of alleviation of the double-ITCZ problem?
Each modification that contributed to the reduction of the radiation bias in the MRI-ESM2 was progressively reverted to the corresponding older treatment in order to examine their individual impacts on the double-ITCZ problem. Results show that the double-ITCZ problem worsens almost monotonically when the excessive shortwave insolation over the Southern Ocean increases (Kawai et al. 2021). This result implies that the double-ITCZ problem in climate models can be alleviated by reducing the Southern Ocean radiation bias, at least, to some extent.
The radiation bias, especially over the Southern Ocean, was terribly bad in MRI-CGCM3 that was used for CMIP5 simulations. However, the bias is significantly reduced in MRI-ESM2 (Yukimoto et al. 2019) that is used for CMIP6 simulations by various modifications related to clouds (Kawai et al. 2019). On the other hand, the double-ITCZ problem is also alleviated in the MRI-ESM2. Is the reduction in the radiation bias the cause of alleviation of the double-ITCZ problem?
Each modification that contributed to the reduction of the radiation bias in the MRI-ESM2 was progressively reverted to the corresponding older treatment in order to examine their individual impacts on the double-ITCZ problem. Results show that the double-ITCZ problem worsens almost monotonically when the excessive shortwave insolation over the Southern Ocean increases (Kawai et al. 2021). This result implies that the double-ITCZ problem in climate models can be alleviated by reducing the Southern Ocean radiation bias, at least, to some extent.