Global Mean Climate and Main Patterns of Variability in the CMCC‐CM2 Coupled Model

Abstract

Euro-Mediterranean Centre on Climate Change coupled climate model (CMCC-CM2) represents the new family of the global coupled climate models developed and used at CMCC. It is based on the atmospheric, land and sea ice components from the Community Earth System Model coupled with the global ocean model Nucleus for European Modeling of the Ocean. This study documents the model components, the coupling strategy, particularly for the oceanic, atmospheric, and sea ice components, and the overall model ability in reproducing the observed mean climate and main patterns of interannual variability. As a first step toward a more comprehensive, process-oriented, validation of the model, this work analyzes a 200-year simulation performed under constant forcing corresponding to present-day climate conditions. In terms of mean climate, the model is able to realistically reproduce the main patterns of temperature, precipitation, and winds. Specifically, we report improvements in the representation of the sea surface temperature with respect to the previous version of the model. In terms of mean atmospheric circulation features, we notice a realistic simulation of upper tropospheric winds and midtroposphere geopotential eddies. The oceanic heat transport and the Atlantic meridional overturning circulation satisfactorily compare with present-day observations and estimates from global ocean reanalyses. The sea ice patterns and associated seasonal variations are realistically reproduced in both hemispheres, with a better skill in winter. Main weaknesses of the simulated climate are related with the precipitation patterns, specifically in the tropical regions with large dry biases over the Amazon basin. Similarly, the seasonal precipitation associated with the monsoons, mostly over Asia, is weaker than observed. The main patterns of interannual variability in terms of dominant empirical orthogonal functions are faithfully reproduced, mostly in the Northern Hemisphere winter. In the tropics the main teleconnection patterns associated with El Niño-Southern Oscillation and with the Indian Ocean Dipole are also in good agreement with observations. CMCC-CM2 represents the base for a family of configurations responding to the different climate needs and applications, including the coupled Climate-Carbon cycle studies through the setup of an Earth System Model (CMCC-ESM 2), a twin set of configurations (CMCC-CM2-HR4 and CMCC-CM2-VHR4), specifically developed for the HighResMIP protocol (Haarsma et al., 2016), and the seasonal prediction system and its CHERCHI ET AL.

Description of the resolution hierarchy of the global coupled HadGEM3-GC3.1 model as used in CMIP6 HighResMIP experiments

“…The mean net eastward transport of 155, 90 and 125 Sv, respectively, for LL, MM and MH models compares to the recent observational range of 173 ± 11 Sv (Donohue et al, 2016), with earlier estimates lacking a robust barotropic component (e.g. 137±8 Sv; Cunningham et al, 2003). Using the former measure, LL is closest to the observational range, while MM is only 40 % of it.…”

Impact of model resolution on Arctic sea ice and North Atlantic Ocean heat transport

“…The fourth model is version 2 of the Euro-Mediterranean Centre on Climate Change Climate Model (CMCC-CM2; Cherchi et al 2018). It is composed of version 4 of the Community Atmosphere Model (CAM; Neale et al 2013), NEMO3.6 for the ocean, CICE4.0 for sea ice, and version 4.5 of the Community Land Model (CLM, Oleson et al 2013).…”

The typhoon-induced drying of the Maritime Continent

“…In order to demonstrate the role of TCs in drying the Maritime Continent, we also exploited GCM experiments. Although the CMCC-CM2 fully coupled model demonstrates a reasonable representation of the tropical mean climate and variability in both low (HR 110 km, CMIP5-like horizontal resolution) and high (28,16) [VHR 25 km, HighResMIP CMIP6like resolution (46,47)] resolution, the main difference between the two is the weakness of the lower-resolution model in representing the number and intensity of TCs (SI Appendix, Fig. S1).…”

“…We found that a net eastward water transport anomaly in the equatorial region of the west North Pacific (WNP), induced by TCs developing in the basin, may be responsible for a significant moisture flux divergence over the Maritime Continent, thus reducing the local precipitation during the onset of the dry season. We investigated this process using Japanese 55-y Reanalysis (JRA-55) (26) and conducted numerical experiments based on low-and highresolution versions of the Centro Euro-Mediterraneo per i Cambiamenti Climatici Climate Model 2 (CMCC-CM2) General Circulation Model (GCM) (16,27,28). Our findings suggest that forecasting TC activity in the WNP might also help in predicting the onset of the dry season over the Maritime Continent.…”