Abstract
We conducted global warming projections using the Meteorological Research Institute-Atmospheric General Circulation Model Version 3.2 with a 60-km grid size (MRI-AGCM3.2H). For the present-day climate of 21 years from 1983 through 2003, the model was forced with observed historical sea surface temperature (SST). For the future climate of 21 years from 2079–2099, the model was forced with future SST projected by conventional couple models. Twelve-member ensemble simulations for three different cumulus convection schemes and four different SST distributions were conducted to evaluate the uncertainty of projection. Annual average precipitation will increase over the equatorial regions and decrease over the subtropical regions. The future precipitation changes are generally sensitive to the cumulus convection scheme, but changes are influenced by the SST over the some regions of the Pacific Ocean. The precipitation efficiency defined as precipitation change per 1° surface air temperature warming is evaluated. The global average of precipitation efficiency for annual average precipitation was less than the maximum value expected by thermodynamical theory, indicating that dynamical atmospheric circulation is acting to reduce the conversion efficiency from water vapor to precipitation. The precipitation efficiency by heavy precipitation is larger than that by moderate and weak precipitation.
Highlights
Uncertainty in future climate change projected by climate models originates from four main factors: emission scenario, model structure, internal natural variability and initial condition and external forcing and boundary condition [1]
Threedistributions, different cumulus convection of more see [31].sea surface temperature (SST). With these four as different as well as three schemes, cumulus we can evaluate the spread of the response, as the kind of different convection schemes, we model can evaluate thewhich spreadcan of be theinterpreted model response, which reliability information onkind future change. on future precipitation change
Aerosol and stratospheric ozone distributions simulated by the MRI-ESM and MRI-Chemical Transport Model (CTM) assuming the RCP8.5 scenario were not available at the time when we started a set of global warming projections in this study
Summary
Uncertainty in future climate change projected by climate models originates from four main factors: emission scenario, model structure, internal natural variability and initial condition and external forcing and boundary condition [1]. One of the striking advantages of time-slice experiment is that we can increase the horizontal resolution of atmospheric part, because we can save computer resources allocated for the ocean part Another advantage is that the present-day climatology simulated by an atmospheric model tends to be better than that by an AOGCM, because SST prescribed in the present-day climatology is observation. Tropical cyclone simulated by the atmospheric model tends to show overestimation of intensity [17] and erroneous northward shift of the existence area in mid-latitudes [18], owing to the lack of cooling by mixing of the ocean surface layer Despite this weakness in the time-slice experiment, we selected the option to use the higher horizontal resolution version of the atmospheric global model, which enables us to project the small spatial scale structure of future climate change without any dynamical downscaling using regional climate models. We will investigate how the conversion rate of precipitation from water vapor depends on the metrics of precipitation, the cumulus convection scheme and SST
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