CAM6 simulation of mean and extreme precipitation over Asia: sensitivity to upgraded physical parameterizations and higher horizontal resolution

Abstract

Abstract. The Community Atmosphere Model version 6 (CAM6), released in 2018 as part of the Community Earth System Model version 2 (CESM2), is a major upgrade over the previous CAM5 that has been used in numerous global and regional climate studies. Since CESM2–CAM6 will participate in the upcoming Coupled Model Intercomparison Project phase 6 (CMIP6) and is likely to be adopted in many future studies, its simulation fidelity needs to be thoroughly examined. Here we evaluate the performance of a developmental version of the Community Atmosphere Model with parameterizations that will be used in version 6 (CAM6α), with a default 1∘ horizontal resolution (0.9∘×1.25∘, CAM6α-1∘) and a high-resolution configuration (approximately 0.25∘, CAM6α-0.25∘), against various observational and reanalysis datasets of precipitation over Asia. CAM6α performance is compared with CAM5 at default 1∘ horizontal resolution (CAM5-1∘) and a high-resolution configuration at 0.25∘ (CAM5-0.25∘). With the prognostic treatment of precipitation processes and the new microphysics module, CAM6α is able to better simulate climatological mean and extreme precipitation over Asia, better capture the heaviest precipitation events, better reproduce the diurnal cycle of precipitation rates over most of Asia, and better simulate the probability density distributions of daily precipitation over Tibet, Korea, Japan and northern China. Higher horizontal resolution in CAM6α improves the simulation of mean and extreme precipitation over northern China, but the performance degrades over the Maritime Continent. Moisture budget diagnosis suggests that the physical processes leading to model improvement are different over different regions. Both upgraded physical parameterizations and higher horizontal resolution affect the simulated precipitation response to the internal variability of the climate system (e.g., Asian monsoon variability, El Niño–Southern Oscillation – ENSO, Pacific Decadal Oscillation – PDO), but the effects vary across different regions. For example, higher horizontal resolution degrades the model performance in simulating precipitation variability over southern China associated with the East Asian summer monsoon. In contrast, precipitation variability associated with ENSO improves with upgraded physical parameterizations and higher horizontal resolution. CAM6α-0.25∘ and CAM6α-1∘ show an opposite response to the PDO over southern China. Basically, the response to increases in horizontal resolution is dependent on the CAM version.

Reversed impacts of the Arctic oscillation on the precipitation over the South China Sea and its surrounding areas in October and November

“…Then we can distinguish the contributions from different time and spatial scales to climatology . More details can be found from the literatures (Yao et al 2017;Chen et al 2018;Lin et al 2019). Coupled Model Intercomparison Project phase 6 (CMIP6) (Eyring et al 2016;Simpkins 2017;Zhao et al 2018) data are archived by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) (https ://esgf-node.…”

Multiscale Simulation of Precipitation Over East Asia by Variable Resolution CAM‐MPAS

“…Global climate models (GCMs) are fundamental tools for studying the precipitation climate over East Asia and its interaction with large‐scale circulations (Chen & Frauenfeld, 2014; Huang et al., 2013; Xin et al., 2020; Yao et al., 2017; Zhang & Chen, 2016). However, traditional low‐resolution GCMs have large deficiencies in reproducing the East Asian precipitation in terms of temporal evolution, spatial pattern, intensity distribution, etc., partly due to the insufficient resolution to resolve the complex terrain and its interaction with synoptic‐scale systems over East Asia (Boos & Hurley, 2013; Lin et al., 2019; Yao et al., 2017). High‐resolution GCMs can improve the East Asian summer monsoon (EASM) and precipitation simulations (Bacmeister et al., 2014; Kitoh & Kusunoki, 2007; Lin et al., 2019; Yao et al., 2017).…”

“…However, traditional low‐resolution GCMs have large deficiencies in reproducing the East Asian precipitation in terms of temporal evolution, spatial pattern, intensity distribution, etc., partly due to the insufficient resolution to resolve the complex terrain and its interaction with synoptic‐scale systems over East Asia (Boos & Hurley, 2013; Lin et al., 2019; Yao et al., 2017). High‐resolution GCMs can improve the East Asian summer monsoon (EASM) and precipitation simulations (Bacmeister et al., 2014; Kitoh & Kusunoki, 2007; Lin et al., 2019; Yao et al., 2017). For example, high‐resolution GCMs better simulate the East Asian summer monsoon (EASM) rain belt by improving the eastward‐propagating barotropic Rossby wave downstream of the TP, enhancing the stationary eddy meridional flow convergence, and consequently strengthening the moist energy transport from the tropic to the mid‐latitude (Yao et al., 2017).…”

Whether the CMIP5 Models Can Reproduce the Long-Range Correlation of Daily Precipitation?

“…Global climate models are widely used to reproduce the current climate and project future climate change (Zhou and Yu, 2006;Xu and Xu, 2012; Knutson et al, 2013;Kumar et al, 2013;Dong et al, 2018;He et al, 2019). It's crucial to evaluate and investigate the models' performance in simulating daily precipitation for developing adaptation strategies to reduce uncertainties of projecting precipitation in the future (Jiang et al, 2007;Jiang et al, 2009;Wang and Chen, 2013;Li et al, 2015;Li et al, 2018;Lin et al, 2019).…”