Changes in clouds and atmospheric circulation associated with rapid adjustment induced by increased atmospheric CO2: a multiscale modeling framework study

• Published in: Climate dynamics Vol. 55; no. 1-2; pp. 277 - 293
• Main Authors: Xu, Kuan-Man, Li, Zhujun, Cheng, Anning, Hu, Yongxiang
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2020; Springer Nature B.V
• Subjects: Atmospheric circulation; Atmospheric models; Boundary layer turbulence; Boundary layers; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Circulation; Climate models; Climatology; Cloud climatology; Cloud cover; Clouds; Computer simulation; Convection; Convective clouds; Cooling; Cooling effects; Earth and Environmental Science; Earth Sciences; Energy transport; Entrainment; Frameworks; Geophysics/Geodesy; Global climate; Global climate models; Heating; Levels; Masking; Modelling; Multiscale analysis; Ocean circulation; Oceanography; Oceans; Optical analysis; Planetary boundary layer; Radiative cooling; Radiative heating; Short wave radiation; Subsidence; Temperature; Turbulence; Water depth; Water vapor; Water vapour; forcing; Cloud radiative effects; Rapid adjustment; Multiscale modeling framework; CO; Low-level clouds
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-018-4401-2

The radiative heating increase due to increased CO 2 concentration is the primary source for the rapid adjustment of atmospheric circulation and clouds. In this study, we investigate the rapid adjustment resulting from an instantaneous doubling of CO 2 and its physical mechanism using a multiscale modeling framework (MMF). The cloud-resolving model component of this MMF includes a sophisticated third-order turbulence closure and the MMF simulates realistic shallow and deep cloud climatology and boundary layer turbulence. Although the simulated cloud adjustment and its mechanism generally agree with earlier studies with conventional global climate models and another MMF with a lower-order turbulence closure, this MMF simulates an increase in the global-mean shortwave and net cloud radiative cooling and a negative cloud radiative effect change due to cloud adjustment. This result is related to the large increase in low-level clouds over the extratropical and subtropical oceans, resulting from reduced cloud-top entrainment implied from strengthened inversion. The downshift of planetary boundary layer and low-level clouds is generally weaker than that simulated by other models, which is due to reduction of shallow cumulus in the ascending and weak subsidence circulation regimes but to increase of stratocumulus in the strongest subsidence regime. Optically thicker stratocumulus compensates for reduced cooling by shallow cumulus. The reduced strength of all oceanic circulation regimes, which may be contributed by weakened energy transport resulting from water vapor and cloud CO 2 masking effects, not only reduces optical depth of convective clouds but also shifts cloud coverage to lands where deep convection is enhanced.