Constraining cloud lifetime effects of aerosols using A‐Train satellite observations

Abstract

[1] Aerosol indirect effects have remained the largest uncertainty in estimates of the radiative forcing of past and future climate change. Observational constraints on cloud lifetime effects are particularly challenging since it is difficult to separate aerosol effects from meteorological influences. Here we use three global climate models, including a multiscale aerosol-climate model PNNL-MMF, to show that the dependence of the probability of precipitation on aerosol loading, termed the precipitation frequency susceptibility (S pop ), is a good measure of the liquid water path response to aerosol perturbation (l), as both S pop and l strongly depend on the magnitude of autoconversion, a model representation of precipitation formation via collisions among cloud droplets. This provides a method to use satellite observations to constrain cloud lifetime effects in global climate models. S pop in marine clouds estimated from CloudSat, MODIS and AMSR-E observations is substantially lower than that from global climate models and suggests a liquid water path increase of less than 5% from doubled cloud condensation nuclei concentrations. This implies a substantially smaller impact on shortwave cloud radiative forcing over ocean due to aerosol indirect effects than simulated by current global climate models (a reduction by one-third for one of the conventional aerosolclimate models). Further work is needed to quantify the uncertainties in satellite-derived estimates of S pop and to examine S pop in high-resolution models. Citation: Wang, M., et al. (2012), Constraining cloud lifetime effects of aerosols using A-Train satellite observations, Geophys. Res. Lett., 39, L15709,

On the relationship between cloud contact time and precipitation susceptibility to aerosol

“…Until climate models are able to resolve clouds and convection, this approach may be worth pursuing. Alternatively, the multimodel framework [e.g., Wang et al, 2012] or new probability distribution function approaches to representing subgrid turbulence [Larson and Golaz, 2005] may prove useful.…”

A Community Atmosphere Model With Superparameterized Clouds

“…As shown in Figure 1, Wang et al [2011a] replaced the very simple representation of cloud droplets and ice crystals of the original SP-CAM with a more general treatment that allows the number of droplets and crystals in clouds to respond more realistically to changes in aerosol particles produced by human activities, and the aerosol particles are now allowed to respond to cloud updrafts, chemical processing in droplets, and removal from the atmosphere by precipitation explicitly simulated by CRM (through a subsidiary model called Explicit Clouds and Parameterized Pollutants (ECPP)). These changes permit estimates of the impact of cloud-aerosol-precipitation interactions on the global energy balance [Wang et al, 2011b] that have been shown to be significantly more realistic than previous estimates [Wang et al, 2012].…”

Estimating precipitation susceptibility in warm marine clouds using multi-sensor aerosol and cloud products from A-Train satellites

“…Precipitation susceptibility has been proposed to evaluate aerosol-cloud-precipitation interactions and to further constrain the cloud water response to aerosol perturbations in cli-mate models (Feingold and Siebert, 2009;Terai et al, 2012;Wang et al, 2012). It was first proposed by Feingold and Siebert (2009) and was defined as…”

“…Sorooshian et al (2009) further estimated S 0 by replacing CDNC with aerosol index (AI). Wang et al (2012) proposed an alternative metric, the precipitation frequency susceptibility, defined as…”