Aerosol-cloud interactions: emerging issues and tasks
The conventional understanding of aerosol-cloud interactions, so-called Twomey and Albrecht effects, only focuses on microphysical modifications of clouds by aerosols with no consideration of dynamic responses to aerosols. Numerous recent studies have shown that aerosol-induced changes in feedbacks between aerosol and cloud dynamics can outweigh the effect of the instantaneous microphysical modification of clouds by aerosols in the response of cloud radiative properties and precipitation to aerosols. Associated with these recent studies, there are newly emerging imminent major issues we need to resolve to reduce uncertainties by aerosol-cloud interactions in the prediction of climate change. These major issues are:
1. Aerosol-induced invigoration of convective clouds.
2. Overestimation of aerosol indirect effects in climate models.
3. Effect of aerosol on open- and closed-cell structures in stratocumulus clouds.
4. Effect of aerosol on the mixed-phase clouds in the Arctic.
Understanding aerosol-induced invigoration of convective clouds is important, since convective clouds form the cloud regime that produces most of the precipitation on a global average basis, and so are important for determining the relationship between aerosol and precipitation and thus the effect of the relationship on global hydrologic circulations and spatial patterns and associated global flooding and drought patterns.
Recent studies show climate model tends to over-estimate aerosol indirect effects. Climate model is the only tool that is able to provide quantitative information on climate change. Hence, resolving the issue of the over-estimation will bring better, confident quantitative assessment of climate change, which helps society gear up for climate change in a more practical way.
Open- and closed-cell structures have a significant impact on the albedo of stratocumulus clouds which form the cloud regime that determines a significant portion of the reflected solar radiation from clouds and so are important for determining the possible cooling by aerosol-cloud interactions. Mixed-phase clouds in the Arctic affect the Arctic-ice areal extent by modulating solar radiation incident on the Arctic. The variation of the Arctic-ice areal extent has a substantial impact on the Earth’s albedo. Hence, gaining the better understating of aerosol effect on the open- and closed-cell structures and the Arctic mixed-phase clouds will improve our estimation of aerosol effect on the Earth’s albedo and associated climate change. My studies have been focusing mostly on the issues of the invigoration of convective clouds and overestimation of aerosol indirect effects in climate models, which are less traveled by aerosol community than the other two issues.