Using a cloud-resolving model to study the effects of subgrid-scale variations in relative humidity on direct sulphate-aerosol forcing
Article first published online: 19 DEC 2006
Copyright © 2001 John Wiley & Sons, Ltd
Quarterly Journal of the Royal Meteorological Society
Volume 127, Issue 577, pages 2385–2394, October 2001 Part A
How to Cite
Petch, J. C. (2001), Using a cloud-resolving model to study the effects of subgrid-scale variations in relative humidity on direct sulphate-aerosol forcing. Q.J.R. Meteorol. Soc., 127: 2385–2394. doi: 10.1002/qj.49712757710
- Issue published online: 19 DEC 2006
- Article first published online: 19 DEC 2006
- Manuscript Revised: 9 APR 2001
- Manuscript Received: 9 OCT 2000
- Climate model;
Cloud-resolving model simulations over a tropical ocean and a mid-latitude continental region have been used to investigate the influence of subgrid-scale variations of relative humidity on the direct radiative forcing of sulphate aerosols. Offline radiation calculations based on output from a cloud-resolving model, with and without sulphate aerosol included, are used to calculate the direct radiative forcing of the aerosol. This forcing is compared with results from single-column radiation calculations typical of those produced by a climate model.
The results from this idealized study show that a typical climate model can underestimate the direct radiative forcing of aerosols by up to 80%. The errors in a climate-model calculation are largest when the mean relative humidity is high or there are moist regions within a drier domain; this is usually reflected in a larger standard deviation of the relative humidity. Over the more humid tropical ocean, a climate model may underestimate the direct radiative forcing of sulphate aerosols by 43%, on average (ranging between 30% and 80%). Over the drier continental mid-latitude region the average error is only 10%, but instantaneous values can exceed 50% during times when both the mean relative humidity and its standard deviation are large; this is typically close to convective events.