A Parameterization of Interstitial Aerosol Extinction and Its Application to Marine Cloud Brightening

[ayesha iqbal]

https://journals.ametsoc.org/configurable/content/journals$002fatsc$002f79$002f11$002fJAS-D-22-0047.1.xml

Authors 

Fabian Hoffmann, Bernhard Mayer and Graham Feingold

Online Publication: 18 Oct 2022

Print Publication: 01 Nov 2022

DOI: https://doi.org/10.1175/JAS-D-22-0047.1

Abstract

Marine cloud brightening (MCB) is a geoengineering approach to counteract climate change by the deliberate seeding of sea salt aerosol particles that, once they activated to cloud droplets, directly increase cloud reflectance and hence global albedo. However, a large fraction of the seeded aerosol may remain interstitial, i.e., unactivated particles among cloud droplets. Because the consideration of interstitial aerosol optical properties usually requires computationally expensive simulations of the entire particle spectrum and direct Mie calculations, we develop a simple parameterization to be used with computationally efficient bulk and even bin cloud microphysical schemes that do not treat the unactivated aerosol explicitly. Using parcel and large-eddy simulations with highly detailed Lagrangian cloud microphysics and direct Mie calculations as a reference, we show that the parameterization captures the variability in the interstitial aerosol extinction successfully. By applying the parameterization to typical MCB cases, we find that the consideration of interstitial aerosol extinction is important for the assessment of MCB in shallow clouds with weak updrafts, in which only a small fraction of aerosol particles is activated to cloud droplets.

Source: Journal of the Atmospheric Sciences

[Stephen Salter]

Hi All

The Hoffmann paper seems to be a convincing argument to treat regions where there has just been rain to clean the air and to use a mono-disperse spray to get a high nucleation fraction. We do not want the bigger nuclei to grab water vapour and starve the smaller ones.  

Advice on the optimum size would be welcome. Is 0.8 micron sensible? How narrow should the spread be? Has there been any climate modelling of spread width?

Stephen

 

Emeritus Professor of Engineering Design

School of Engineering

University of Edinburgh

Mayfield Road

Edinburgh EH9 3DW

Scotland

0131 650 5704 or 0131 662 1180

YouTube Jamie Taylor Power for Change

 

 

 

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Subject: [geo] A Parameterization of Interstitial Aerosol Extinction and Its Application to Marine Cloud Brightening

 

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