The aerosol-cyclone indirect effect in observations and high-resolution simulations

Abstract

Abstract. Aerosol-cloud interactions are a major source of uncertainty in predicting 21 st century climate change. Using highresolution, convection-permitting global simulations we predict that increased cloud condensation nuclei (CCN) interacting 10 with midlatitude cyclones will increase their cloud droplet number concentration (CDNC), liquid water (CLWP), and albedo.For the first time this effect is shown with 13 years of satellite observations. Causality between enhanced CCN and enhanced cyclone liquid content is supported by the 2014 eruption of Holuhraun. The change in midlatitude cyclone albedo due to enhanced CCN in a surrogate climate model is around 70% of the change in a high-resolution convection-permitting model, indicating that climate models may underestimate this indirect effect. 15

Strong Dependence of Atmospheric Feedbacks on Mixed‐Phase Microphysics and Aerosol‐Cloud Interactions in HadGEM3

“…In other words, the fact that a model has an ECS within the range provided by independent estimates (e.g., Stevens et al, ) does not imply that the model is representing all the feedbacks correctly. From the model‐development perspective, our efforts as a community should focus on improving understanding of the underlying processes and finding observational process‐based metrics that are capable of constraining the processes that control the models' radiative feedbacks, expanding on the recent work on feedback proxies, both in the midlatitudes (e.g., Ceppi et al, ; Gordon & Klein, ), and in the tropics (e.g., McCoy et al, ; Myers & Norris, ; Qu et al, ). Of course, the assumption here is that the relationship between these processes and the long‐term feedbacks holds in the real world.…”

Predicting decadal trends in cloud droplet number concentration using reanalysis and satellite data

“…Aerosol indirect effects can be grouped into two categories: the first indirect effect, or Twomey effect (Twomey, 1977), by which enhanced concentrations of cloud condensation nuclei (CCN) enhance CDNC (for a fixed liquid water content), leading to an increase in cloud albedo; and the lifetime, or Albrecht effect (Albrecht, 1989), by which enhanced CDNC suppresses precipitation and leads to thicker or more persistent clouds and higher cloud albedo. The first indirect effect has been supported by numerous empirical studies relating remotely sensed aerosol properties to remotely sensed CDNC Gryspeerdt et al, 2016;Patel et al, 2017;Quaas et al, 2008Quaas et al, , 2009Matsui et al, 2006;Nakajima et al, 2001;Sekiguchi et al, 2003), although whether aerosol affects cloud lifetime is still debated (McCoy et al, 2017b;Malavelle et al, 2017;Gryspeerdt et al, 2016;Mace and Avey, 2016). Studies have utilized the natural laboratory provided by transient degassing volcanoes to study cloud responses to changes in aerosol (Mace and Abernathy, 2016;Gassó, 2008;Yuan et al, 2011;Malavelle et al, 2017; Mc-…”

Predicting decadal trends in cloud droplet number concentration using reanalysis and satellite data

“…For the analysis presented in this paper we adopt the technique used in previous studies (Gassó, 2008;Mace and Abernathy, 2016;Yuan et al, 2011;McCoy and Hartmann, 2015;McCoy et al, 2017b;Malavelle et al, 2017) and examine the response of cloud properties to volcanic sulfate sources. We support this analysis by examining the systematic change in 30 anthropogenic sulfur emissions from Asia and North America due to emissions controls , as in previous studies (Bennartz et al, 2011), although our data record extends over a period of enhanced emissions controls in East Asia and thus we anticipate a decrease in CDNC in contrast to Bennartz et al (2011).…”

“…al., 2006;Nakajima et al, 2001;Sekiguchi et al, 2003), although whether aerosol affects cloud lifetime is still debated (McCoy et al, 2017b;Malavelle et al, 2017;Gryspeerdt et al, 2016). Studies have utilized the natural laboratory provided by transient degassing volcanoes to study cloud responses to changes in aerosol (Mace and Abernathy, 2016;Gassó, 2008;Yuan et al, 2011;McCoy et al, 2017b;Malavelle et al, 2017). In this vein, McCoy et al (2017a) used aerosol reanalysis to provide additional information regarding aerosol speciation and vertical structure.…”