Climate simulations using MRI-ESM2 with 60 km resolution atmosphere and data assimilated ocean

To explicitly represent short-term atmosphere-ocean interactions while adequately simulating long-term regional-scale climate, climate simulations from the mid-20th century to the present were performed using the Meteorological Research Institute Earth System Model version 2 (MRI-ESM2), with the atmosphere of 60 km horizontal resolution and assimilating ocean observation. A monthly objective analysis of the ocean temperature and salinity were assimilated with a relaxation time of 10 days. Short time-scale atmosphere-ocean interactions, such as precipitation variations that lag behind sea-surface temperature (SST) variations, and SST decreases due to the passage of intense tropical cyclones, are represented in a manner similar to a fully coupled model. In addition, the performance of the model in reproducing climate over long time scales is comparable to our previous atmosphere-only simulations with prescribed observed SSTs, both over the global scale and over East Asia. The overestimation of intense tropical cyclones at mid-latitudes, which was seen in the atmosphere-only simulations, has been improved. The seasonal progression of the East Asian monsoon is also well simulated. These results are expected to contribute to reducing the uncertainty in the assessment of global warming impact, especially for extreme events in the Asian region.