Microphysical, macrophysical, and radiative responses of subtropical marine clouds to aerosol injections

[ayesha iqbal]

https://www.researchgate.net/publication/367410630_Microphysical_macrophysical_and_radiative_responses_of_subtropical_marine_clouds_to_aerosol_injections 

Authors 

Je-Yun Chun, Robert Wood, Peter Blossey and Sarah J. Doherty

25 January 2023

Citation: Chun, J. Y., Wood, R., Blossey, P., & Doherty, S. J. (2022). Microphysical, macrophysical and radiative responses of subtropical marine clouds to aerosol injections. Atmospheric Chemistry and Physics Discussions, 1-38.

Abstract 

Ship tracks in subtropical marine low clouds are simulated and investigated using large-eddy simulations. Five variants of a shallow subtropical stratocumulus-topped marine boundary layer (MBL) are chosen to span a range of background aerosol concentrations and variations in free-tropospheric moisture. Idealized time-invariant meteorological forcings and approximately steady-state aerosol concentrations constitute the background conditions. We investigate processes controlling cloud microphysical, macrophysical, and radiative responses to aerosol injections. For the analysis, we use novel methods to decompose the liquid water path (LWP) adjustment into changes in cloud and boundary-layer properties and to decompose the cloud radiative effect (CRE) into contributions from cloud macro- and microphysics. The key results are that (a) the cloud-top entrainment rate increases in all cases, with stronger increases for thicker than thinner clouds; (b) the drying and warming induced by increased entrainment is offset to differing degrees by corresponding responses in surface fluxes, precipitation, and radiation; (c) MBL turbulence responds to changes caused by the aerosol perturbation, and this significantly affects cloud macrophysics; (d) across 2 d of simulation, clouds were brightened in all cases. In a pristine MBL, significant drizzle suppression by aerosol injections results not only in greater water retention but also in turbulence intensification, leading to a significant increase in cloud amount. In this case, Twomey brightening is strongly augmented by an increase in cloud thickness and cover. In addition, a reduction in the loss of aerosol through coalescence scavenging more than offsets the entrainment dilution. This interplay precludes estimation of the lifetime of the aerosol perturbation. The combined responses of cloud macro- and microphysics lead to 10–100 times more effective cloud brightening in these cases relative to those in the non-precipitating MBL cases. In moderate and polluted MBLs, entrainment enhancement makes the boundary layer drier, warmer, and more stratified, leading to a decrease in cloud thickness. This LWP response offsets the greatest fraction of the Twomey brightening in a moderately moist free troposphere. This finding differs from previous studies that found larger offsets in a drier free troposphere, and it results from a greater entrainment enhancement of initially thicker clouds, so the offsetting effects are weaker. The injected aerosol lifetime in cases with polluted MBLs is estimated to be 2–3 d, which is much longer than estimates of typical ship track lifetimes from satellite images.

Source: ResearchGate

[Stephen Salter]

Hi All

 

This paper is heavy going for engineers outside the climate physics community but if, my understanding is correct, the conclusions for marine cloud brightening are encouraging. 

 

I would like to point out to the climate physics community that hydrofoil vessels have very low wave-making drag.  When are they not spraying they can travel at extremely high speed. Autonomous wind-driven vessels have no problems about fuel, food or water.  The wide range of effectiveness covered in the paper  does not matter if intelligent fleet controllers with continuous satellite information and ginormous quantum computers, can give instant forecasts of the results of any treatment pattern.  We can then cherry pick the optimum times and places for treatment to get results that our dear political leaders request. 

 

With the exception of the  work by Stjern et al. ( https://acp.copernicus.org/articles/18/621/2018/acp-18-621-2018-supplement.pdf ) who increased the condensation nuclei concentration by 50% in ocean regions with low cloud, much of the marine cloud brightening has used a boring strategy of a steady injection, all the year round, rain or shine,  between low latitudes, usually 30 S to 30 N. 

 

The short life of aerosol, seen as a disadvantage by ignorant objectors, is actually highly desirable.  At the very least we want to migrate with the seasons. For a short time at midsummer there is more solar heat going into the poles than the equator.  Accurate forecasts are now available to more than a week ahead.  I argue that we want to operate under clear blue skies in places where there has been recent rain to clean the air.  We want time for this to spread widely and later get to regions with higher humidity to give cloud formation.  We can target El Niño events and reduce warm sea surface areas to moderate typhoons and steer the Indian Ocean dipole.

 

The engineering design of spray vessels is well advanced. In mass production the annual cost of owning a  fleet will be cheap enough, below  one Cop conference,  to have them on standby as a rapid reaction force.  Please tell us the places where and when the force will be most effective and how fast you need us to get there.  Instead of being passive observers you can become active controllers. 

 

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] Microphysical, macrophysical, and radiative responses of subtropical marine clouds to aerosol injections

 

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