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 geoengineering@googlegroups.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. To post to this group, send email to geoengineering@googlegroups.com. Visit this group at https://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
