Impact of aerosols on convective clouds and precipitation

Abstract

[1] Aerosols are a critical factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. Current research suggests that aerosol effects on clouds could further extend to precipitation, both through the formation of cloud particles and by exerting persistent radiative forcing on the climate system that disturbs dynamics. However, the various mechanisms behind these effects, in particular, the ones connected to precipitation, are not yet well understood. The atmospheric and climate communities have long been working to gain a better grasp of these critical effects and hence to reduce the significant uncertainties in climate prediction resulting from such a lack of adequate knowledge. Here we review past efforts and summarize our current understanding of the effect of aerosols on convective precipitation processes from theoretical analysis of microphysics, observational evidence, and a range of numerical model simulations. In addition, the discrepancies between results simulated by models, as well as those between simulations and observations, are presented. Specifically, this paper addresses the following topics: (1) fundamental theories of aerosol effects on microphysics and precipitation processes, (2) observational evidence of the effect of aerosols on precipitation processes, (3) signatures of the aerosol impact on precipitation from large-scale analyses, (4) results from cloud-resolving model simulations, and (5) results from large-scale numerical model simulations. Finally, several future research directions for gaining a better understanding of aerosol-cloud-precipitation interactions are suggested.

Time-dependent, non-monotonic response of warm convective cloud fields to changes in aerosol loading

“…Despite the extensive research conducted in the last few decades and the fact that clouds have an important role in the Earth's energy balance (Trenberth et al, 2009), clouds are still considered to be one of the largest sources of uncertainty in the study of climate and climate change (Forster et al, 2007;Boucher et al, 2013).…”

“…The invigoration mechanism, which refers to deeper and larger clouds with larger mass that develop under polluted conditions, was studied mainly in deep convective clouds (Andreae et al, 2004;Koren et al, 2005;Rosenfeld et al, 2008;Tao et al, 2012;Fan et al, 2013;Hazra et al, 2013a;Altaratz et al, 2014). Our focus here is on warm-cloud fields for which previous observational studies reported an invigoration effect or a non-monotonic response of the clouds to an increase in aerosol loading.…”

Observations of aerosol‐induced convective invigoration in the tropical east Atlantic

“…Several studies [Andreae et al, 2004;Khain et al, 2005;Koren et al, 2005;van den Heever et al, 2006;van den Heever and Cotton, 2007;Lee et al, 2008a;Li et al, 2008;Rosenfeld et al, 2008;Lebo and Seinfeld, 2011;van den Heever et al, 2011;Storer and van den Heever, 2013;Fan et al, 2013] suggest that increased aerosol concentrations will lead to the invigoration of deep convective storms; however, there is still no clear consensus on this effect, as recently summarized in Tao et al [2012]. It is generally established that in a polluted environment, or one which contains higher number concentrations of aerosols that can act as cloud condensation nuclei (CCN), collision and coalescence in deep convective systems will be less effective due to the increased numbers of smaller cloud droplets, thus leading to a reduction in warm rain production.…”

“…This leaves higher amounts of liquid water in cloud that can be lofted to form ice, providing an additional source of latent heating which can increase the buoyancy of an updraft. These changes can lead to stronger storms with higher cloud tops, greater ice mass, and heavier surface precipitation [Andreae et al, 2004;Khain et al, 2005;Koren et al, 2005;van den Heever et al, 2006;Li et al, 2008;Rosenfeld et al, 2008;Storer et al, 2010;Tao et al, 2012;Storer and van den Heever, 2013].…”

Vertical distributions of aerosol optical properties during the spring 2016 ARIAs airborne campaign in the North China Plain

“…Aerosols modify the local and regional radiation budget and climate by absorbing and scattering solar radiation through the aerosol direct effect (Charlson and Hofmann, 1992) and impact photochemistry (Dickerson et al, 1997). Aerosols can also affect cloud-precipitation processes and aerosol-cryosphere interactions through indirect and semi-direct effects (Twomey,8996 F. Wang et al: Vertical distributions of aerosol optical properties that the magnitude of precipitation is strongly correlated to aerosol concentration Li et al, 2011;Tao et al, 2012), through various mechanisms as summarized most recently in Li et al (2017b). Precipitation frequency and intensity are also altered by the long-term impacts of aerosols (Guo et al, 2016(Guo et al, , 2017.…”