Review: Cloud invigoration by aerosols—Coupling between microphysics and dynamics

• A review paper about the invigoration effect of convective clouds by aerosols
• Observational and numerical evidence are summarized.
• A chain of processes that leads to cloud invigoration is suggested.
• Possible climate consequences of the invigoration effect are discussed.

The cloud invigoration effect refers here to the link between an increase in aerosol loading and deepening of convective clouds. The effect can be reflected also in a larger cloud fraction and an increase in the condensate mass that is distributed higher in the atmospheric column. Identifying the invigoration effect by aerosols requires attributing certain changes in cloud dynamics to changes in cloud microphysics. More than 10 years of extensive research using data collected in field experiments, analysis of satellite measurements and the employment of state-of-the-art numerical models have been used in an attempt to study this elusive phenomenon. Despite these intensive efforts, the validity of the invigoration effect and the possibility of climate responses to this effect are still considered to be open questions. In this review observational evidence and modeling results for cloud invigoration are discussed. Studies that indicate convective cloud invigoration effects, as well as studies that suggest no or even opposite effects are summarized. A coherent physical mechanism that describes a chain of processes that takes place under the proper conditions in the core of a convective cloud provides explanation for the “ideal” case of invigoration reported by observations and numerical modeling, while the competition between core-based vs. margin-based processes explains the cases that deviate from the “ideal”. Because convective clouds play a key role in the Earth's radiation balance, in the water cycle and atmospheric circulations, invigoration implies possible consequences at scales ranging from a single cloud up to the global.