After a volcanic eruption, together with SO2, there’s also a large amount of ash injected in the upper troposphere that might favor heterogeneous nucleation against homogeneous. This is mostly the reason why after volcanic eruption a slight increase in citrus coverage is found. On the other hand in a geoengineering simulation, the lack of this effect combined with a dynamical response of a continuous injection would produce a difference response.
We briefly discuss in the conclusion of our study the differences between an eruption and a SG scenario. //////////////////////////////////////////////////////////// Daniele Visioni PhD Student Dipartimento di Scienze Fisiche e Chimiche, Universita' dell'Aquila Via Vetoio, 67100 - Coppito, L'AQUILA e-mail: daniele.visi...@aquila.infn.it //////////////////////////////////////////////////////////// > On 13 Feb 2018, at 04:54, Andrew Lockley <andrew.lock...@gmail.com> wrote: > > Hasn't observational data from Pinatubo constrained this variable reasonably > well? It would be surprising if there was "hidden" cooling of such magnitude. > This would also presumably apply to Tambora, etc. which have left temperature > (measured and proxy) and ash records. > > A > >> On 5 Feb 2018 18:28, "Daniele Visioni" <daniele.visi...@aquila.infn.it> >> wrote: >> Hi Andrew, thank you. >> >> No, you did not misunderstand our paper. If by particle rain-out you are >> referring to sulfate particles settling from the stratosphere to the upper >> troposphere and thus affecting freezing >> by increasing the number of available IN for homogeneous freezing, what we >> found, in agreement with Cirisan et al. (2013), is that this is a negligible >> effect (some mW/m^2), expecially compared to the thermo-dynamical response >> that we show in our paper. >> >> Best, >> Daniele >> >> //////////////////////////////////////////////////////////// >> Daniele Visioni >> PhD Student >> Dipartimento di Scienze Fisiche e Chimiche, Universita' dell'Aquila >> Via Vetoio, 67100 - Coppito, L'AQUILA >> e-mail: daniele.visi...@aquila.infn.it >> Check out our latest published paper: >> https://www.atmos-chem-phys.net/17/11209/2017/acp-17-11209-2017.html >> //////////////////////////////////////////////////////////// >> >> >> >> >> >> >> >> >> >>> On 5 Feb 2018, at 10:42, Andrew Lockley <andrew.lock...@gmail.com> wrote: >>> >>> Poster's note: this is very important paper, as it constrains a key >>> side-effect of SAI. I may misunderstand the paper, but I don't think it's >>> looking at particle rain-out - which may provide a further mechanism >>> >>> Upper tropospheric ice sensitivity to sulfate geoengineering >>> Daniele Visioni1,2, Giovanni Pitari1, and Glauco di Genova2 >>> 1Department of Physical and Chemical Sciences, Universitá dell'Aquila, >>> 67100 L'Aquila, Italy >>> 2CETEMPS, Universitá dell'Aquila, 67100 L'Aquila, Italy >>> Received: 30 Jan 2018 – Accepted for review: 02 Feb 2018 – Discussion >>> started: 05 Feb 2018 >>> Abstract. Aside from the direct surface cooling sulfate geoengineering (SG) >>> would produce, the investigation on possible side-effects of this method is >>> still ongoing, as for instance on upper tropospheric cirrus cloudiness. >>> Goal of the present study is to better understand the SG thermo-dynamical >>> effects on the homogeneous freezing ice formation process. This is done by >>> comparing SG model simulations against a RCP4.5 reference case: in one case >>> the aerosol-driven surface cooling is included and coupled to the >>> stratospheric warming resulting from aerosol absorption of longwave >>> radiation. In a second SG perturbed case, surface temperatures are kept >>> unchanged with respect to the reference RCP4.5 case. Surface cooling and >>> lower stratospheric warming, together, tend to stabilize the atmosphere, >>> thus decreasing turbulence and water vapor updraft velocities (−10 % in our >>> modeling study). The net effect is an induced cirrus thinning, which may >>> then produce a significant indirect negative radiative forcing (RF). This >>> would go in the same direction as the direct effect of solar radiation >>> scattering by the aerosols, thus influencing the amount of sulfur needed to >>> counteract the positive RF due to greenhouse gases. In our study, given a 8 >>> Tg-SO2 equatorial injection in the lower stratosphere, an all-sky net >>> tropopause RF of −2.13 W/m2 is calculated, of which −0.96 W/m2 (45 %) from >>> the indirect effect on cirrus thinning (7.5 % reduction in ice optical >>> depth). When the surface cooling is ignored, the ice optical depth >>> reduction is lowered to 5 %, with an all-sky net tropopause RF of −1.45 >>> W/m2, of which −0.21 W/m2 (14 %) from cirrus thinning. Relatively to the >>> clear-sky net tropopause RF due to SG aerosols (−2.06 W/m2), the cumulative >>> effect of background clouds and cirrus thinning accounts for −0.07 W/m2, >>> due to close compensation of large positive shortwave (+1.85 W/m2) and >>> negative longwave adjustments (−1.92 W/m2). When the surface cooling is >>> ignored, the net cloud adjustment becomes +0.71 W/m2, with the shortwave >>> contribution (+1.97 W/m2) significantly larger in magnitude than the >>> longwave one (−1.26 W/m2). This highlights the importance of including all >>> dynamical feedbacks of SG aerosols. >>> >>> >>> Citation: Visioni, D., Pitari, G., and di Genova, G.: Upper tropospheric >>> ice sensitivity to sulfate geoengineering, Atmos. Chem. Phys. Discuss., >>> https://doi.org/10.5194/acp-2018-107, in review, 2018. >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "geoengineering" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to geoengineering+unsubscr...@googlegroups.com. >>> To post to this group, send email to email@example.com. >>> Visit this group at https://groups.google.com/group/geoengineering. >>> For more options, visit https://groups.google.com/d/optout. >> -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com. 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