Modeling water vapor and clouds as passive tracers in an idealized GCM

Yi Ming, Isaac M. Held

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


This paper introduces an idealized general circulation model (GCM) in which water vapor and clouds are tracked as tracers, but are not allowed to affect circulation through either latent heat release or cloud radiative effects. The cloud scheme includes an explicit treatment of cloud microphysics and diagnoses cloud fraction from a prescribed subgrid distribution of total water. The model is capable of qualitatively capturing many large-scale features of water vapor and cloud distributions outside of the boundary layer and deep tropics. The subtropical dry zones, midlatitude storm tracks, and upper-tropospheric cirrus are simulated reasonably well. The inclusion of cloud microphysics (namely rain re-evaporation) has a modest but significant effect of moistening the lower troposphere in this model. When being subjected to a uniform fractional increase of saturated water vapor pressure, the model produces little change in cloud fraction. A more realistic perturbation, which considers the nonlinearity of the Clausius-Clapeyron relation and spatial structure of CO2-induced warming, results in a substantial reduction in the free-tropospheric cloud fraction. This is reconciled with an increase of relative humidity by analyzing the probability distributions of both quantities, and may help explain partly similar decreases in cloud fraction in full GCMs. The model provides a means to isolate individual processes or model components for studying their influences on cloud simulation in the extratropical free troposphere.

Original languageEnglish (US)
Pages (from-to)775-786
Number of pages12
JournalJournal of Climate
Issue number2
StatePublished - Jan 1 2018
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Atmospheric Science


  • Cloud cover
  • Cloud microphysics
  • Cloud radiative effects
  • Water vapor


Dive into the research topics of 'Modeling water vapor and clouds as passive tracers in an idealized GCM'. Together they form a unique fingerprint.

Cite this