Hi all, *On Tuesday, February 13, 2018 at 3:21:28 PM UTC+1, dvisioni wrote:* > > *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.* >
I don't think there is any scientific agreement on the response of cirrus to the volcanic eruptions. Neither from observations (e.g. Meyer et al. 2015 <http://onlinelibrary.wiley.com/doi/10.1002/2015JD023326/full>), nor from the model side. I wouldn't expect the ash to make a significant impact on the global scale, as it falls out out the atmosphere too quickly to significantly change the cirrus radiative forcing (looking from the global modeller's perspective) (+don't forget that a shift from homogeneous to heterogeneous freezing could additionally thin the cirrus and decrease further their warming effect, i.e. cirrus seeding effect) Best, Blaz > > > On 13 Feb 2018, at 04:54, Andrew Lockley <andrew....@gmail.com > <javascript:>> 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...@aquila.infn.it > <javascript:>> 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...@aquila.infn.it <javascript:> >> 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....@gmail.com >> <javascript:>> 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 geoengineerin...@googlegroups.com <javascript:>. >> To post to this group, send email to geoengi...@googlegroups.com >> <javascript:>. >> 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.
