Abstract
In estimates of climate sensitivity obtained from global models, the need to represent clouds introduces a great deal of uncertainty. To address this issue, approaches using a high-resolution global non-hydrostatic model are promising: the model captures cloud structure by explicitly simulating meso-scale convective systems, and the results compare reasonably well with satellite observations. We review the outcomes of a 5-year project aimed at reducing the uncertainty in climate models due to cloud processes using a global non-hydrostatic model. In our project, which was conducted as a subgroup of the Program for Risk Information on Climate Change, or SOUSEI, we use the non-hydrostatic icosahedral atmospheric model (NICAM) to study cloud processes related to climate change. NICAM performs numerical simulations with much higher resolution (about 7 km or 14 km mesh) than conventional global climate models (GCMs) using cloud microphysics schemes without a cumulus parameterization scheme, which causes uncertainties in climate projection.The subgroup had three research targets: analyzing cloud changes in global warming simulations with NICAM with the time-slice approach, sensitivity of the results to the cloud microphysics scheme employed, and evaluating circulation changes due to global warming. The research project also implemented a double-moment bulk cloud microphysics scheme and evaluated its results using satellite observation, as well as comparing it with a bin cloud microphysics scheme. The future projection simulations show in general increase in high cloud coverage, contrary to results with other GCMs. Changes in cloud horizontal-size distribution size and structures of tropical/extratropical cyclones can be discussed with high resolution simulations. At the conclusion of our review, we also describe the future prospects of research for global warming using NICAM in the program that followed SOUSEI, known as TOUGOU.
Highlights
The representation of clouds is widely regarded as the largest source of uncertainty in estimates of climate sensitivity obtained by global climate models (GCMs) (Boucher et al 2013; Soden and Held 2006; Dufresne and Bony 2008; Vial et al 2013; Schneider et al 2017; Zelinka et al 2017)
non-hydrostatic icosahedral atmospheric model (NICAM) can be used with an explicit cloud microphysics scheme and without a convective parameterization scheme to realistically reproduce the structure of meso-scale convective systems which compare reasonably well with satellite observations (Hashino et al 2013, 2016)
This article reviews the outcomes of the NICAM subgroup of the 5-year SOUSEI program, which aimed to reduce the uncertainty in climate models due to cloud processes using a global non-hydrostatic model
Summary
The representation of clouds is widely regarded as the largest source of uncertainty in estimates of climate sensitivity obtained by global climate models (GCMs) (Boucher et al 2013; Soden and Held 2006; Dufresne and Bony 2008; Vial et al 2013; Schneider et al 2017; Zelinka et al 2017). Yamada et al (2017) further analyzed the structural changes in TCs and showed that the horizontal scale of TCs increased with warming when compared between TCs of the same categories in the two climates Using these simulation results, Satoh et al (2015) analyzed convective mass flux associated with TCs and proposed a constraint for a future decrease in the number of TCs. Future changes in extra-tropical cyclones are examined by Kodama et al (2014) using the aqua planet experiments conducted by Yoshizaki et al (2012). LW cloud radiative warming is slightly increased around the poleward and eastward sides of the cyclone center These changes in SW and LW cloud radiative effects resemble changes in the liquid and ice water paths, respectively (not shown), which are consistent with the results of the aqua planet experiments (Kodama et al 2014). As the jet shifts poleward, the anomaly of the LW cloud radiative effect becomes positive in the
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