Simulations of climate, including atmospheric chemistry and carbon cycle, are conducted for the period from 1850 through 2100 with a new earth system model (ESM) of the Meteorological Research Institute (MRI), MRI-ESM1. This model has been developed as an extension of the atmosphere-ocean coupled general circulation model, MRI-CGCM3, by adding chemical and biogeochemical processes. The dynamic and thermodynamic processes are entirely the same in both models. The horizontal resolution of MRI-ESM1 is higher than that of the ozone model that handles chemical processes which require high computational cost. In the control experiment, it is confirmed that the climatic drift of the model is insignificant with regard to surface air temperature (SAT), the radiation budget, and trace gas (carbon dioxide (CO2) and ozone) concentrations. Compared with a control experiment by MRI-CGCM3, SAT is slightly higher because of a higher tropospheric ozone concentration. The performance of MRI-ESM1 is validated by conducting a historical experiment. Overall, MRI-ESM1 simulates well observed historical changes in SAT and trace gas concentrations. However, increases in the SAT and atmospheric CO2 concentration are underestimated, associated with a positive feedback process through soil respiration. Namely the underestimation of atmospheric CO2 increase causes weak SAT rise which makes soil respiration inactive, and then the excess of net land surface CO2 uptake suppresses increase of the atmospheric CO2 concentration. The simulated present-day climate states of SAT, radiation fluxes, precipitation, and trace gas concentrations are also in good agreement with observations although there are errors of radiations, precipitation, and ozone concentration especially over the southern tropical Pacific in the simulation. These errors appear to be originated from the excess of convective activity: so-called double ITCZ (intertropical convergence zone). Both MRI-ESM1 and MRI-CGCM3 are similarly able to reproduce the present-day climatology. In future projections, the global mean SAT rise at the end of the 21st century relative to the pre-industrial era is 3.4°C in the experiment using the Representative Concentration Pathways 8.5 (RCP8.5) by MRI-ESM1, whereas it is 4.0°C in the MRI-CGCM3 experiment. The atmospheric CO2 concentration projected by MRI-ESM1 for the end of the 21st century is about 800 ppm, which is lower by 130 ppm than that prescribed in the RCP8.5 experiment with MRI-CGCM3. This difference is consistent with the above-mentioned difference in the SAT rise between MRI-ESM1 and MRI-CGCM3. The global mean total column ozone increases by about 25 DU during the period from 2000 to 2100, which is comparable to that prescribed in the experiment with MRI-CGCM3. It is also investigated how aerosols simulated with a newly introduced aerosol-chemistry process influence weak SAT rise at the end of the 20th century in MRI-ESM1.
The impact of principal component (PC) temporal and regional dependency on the performance of atmospheric retrieval from hyperspectral infrared sounder observation was investigated. The investigation was conducted for retrieval of temperature and water content vertical distribution from AIRS radiance data using the one-dimensional variation method (1D-Var). Simulation results indicated that by using a suitable number of the leading PCs, we can achieve the same level of retrieval accuracy as all the original 185 channels independently of season and region with much fewer channels. An experiment using real observational data showed that no significant difference in retrieval accuracy due to seasonal and regional variation of PC could be seen, which supported simulation study, but the retrieval using more PCs does not always achieve better accuracy, which was different from the results of the simulation study.