If I understand from the email below , you used aerosols with no fall speed. Are experiments planned to simulate aerosol descent?
Andrew On Mon, 16 Dec 2019, 05:43 Govindasamy Bala, <bala....@gmail.com> wrote: > Andrews, > > We did not do experiments with aerosols above 22 km. It is likely that the > cooling effect will be larger when aerosols are at 25 km. Beyond that it is > likely that the additional cooling benefits disappear. We need more > experiments to confirm this. > > The sensitivity to height in our paper arises mainly because of the > increases in stratospheric water vapor (which partly offsets the cooling > efficiency of the aerosols) that is associated with the stratospheric > heating by the aerosols. This increase in stratospheric water vapor is > largest when the aerosols (and the heating) is close to the tropopause. > > In our paper, we have isolated the effect of just one factor. As Doug has > pointed out, the sedimentation effect would also lead to more cooling if > aerosols are injected at higher altitudes... > > Best, > Bala > > On Sun, Dec 15, 2019 at 9:05 PM Douglas MacMartin <dgm...@cornell.edu> > wrote: > >> This is a great study to understand the effectiveness per unit mass **in >> the stratosphere**. Also keep in mind that there’s an additional >> factor, that at lower altitudes it takes higher injection rates to achieve >> the same burden in the stratosphere (i.e., lower lifetime at lower injected >> altitude). >> >> >> >> If the only thing you cared about was cost, then since there are existing >> studies demonstrating that you can design an aircraft to get to ~20-21km, >> we roughly know that it could be done, but higher altitude injection means >> less total sulfur injected and hence smaller side effects, and should be >> better understood both on the modeling and implementation cost as the trade >> may well be worth it. >> >> >> >> doug >> >> >> >> *From:* geoengineering@googlegroups.com <geoengineering@googlegroups.com> >> *On Behalf Of *Govindasamy Bala >> *Sent:* Saturday, December 14, 2019 9:38 PM >> *To:* Andrew Lockley <andrew.lock...@gmail.com> >> *Cc:* geoengineering <geoengineering@googlegroups.com> >> *Subject:* Re: [geo] Climate system response to stratospheric sulfate >> aerosols: sensitivity to altitude of aerosol layer >> >> >> >> Dear Andrew, >> >> Thanks for the posting. The heights studied were 16, 19 and 22 km, height >> that are relevant to solar radiation modification problem.. The final >> paragraph in the paper is worth reading to get more quantitative >> information from this modeling study. >> >> >> >> "To summarize, for the same mass, the efficiency (defined >> >> as changes in surface temperature per Tg S) of volcanic >> aerosol is less when it is prescribed at lower altitudes in the >> stratosphere (Fig. 9). For example, in our simulations, there is >> a surface cooling of 0.44K for each teragram of sulfur placed >> in the stratosphere at about 16 km altitude (100 hPa). There >> is an additional surface cooling of 0.15K per Tg S when the >> prescribed altitude is increased from about 16 km to about >> 22 km (37 hPa)." >> >> >> >> On Sat, Dec 14, 2019 at 12:55 AM Andrew Lockley <andrew.lock...@gmail.com> >> wrote: >> >> Poster's note : this has significant implications for the engineering of >> delivery systems. I can't do the pressure altitude conversion in my head, >> but it's a lot higher than what's generally been planned for. We're gonna >> need a bigger boat. >> >> >> >> >> >> https://www.earth-syst-dynam.net/10/885/2019/ >> >> >> >> Climate system response to stratospheric sulfate aerosols: sensitivity to >> altitude of aerosol layer >> >> *Krishna-Pillai Sukumara-Pillai Krishnamohan et al. *Received: 01 May >> 2019 – Discussion started: 23 May 2019 – Revised: 24 Oct 2019 – Accepted: >> 08 Nov 2019 – Published: 13 Dec 2019 >> >> Abstract >> >> top <https://www.earth-syst-dynam.net/10/885/2019/#top> >> >> Reduction of surface temperatures of the planet by injecting sulfate >> aerosols in the stratosphere has been suggested as an option to reduce the >> amount of human-induced climate warming. Several previous studies have >> shown that for a specified amount of injection, aerosols injected at a >> higher altitude in the stratosphere would produce more cooling because >> aerosol sedimentation would take longer. In this study, we isolate and >> assess the sensitivity of stratospheric aerosol radiative forcing and the >> resulting climate change to the altitude of the aerosol layer. We study >> this by prescribing a specified amount of sulfate aerosols, of a size >> typical of what is produced by volcanoes, distributed uniformly at >> different levels in the stratosphere. We find that stratospheric sulfate >> aerosols are more effective in cooling climate when they reside higher in >> the stratosphere. We explain this sensitivity in terms of effective >> radiative forcing: volcanic aerosols heat the stratospheric layers where >> they reside, altering stratospheric water vapor content, tropospheric >> stability, and clouds, and consequently the effective radiative forcing. We >> show that the magnitude of the effective radiative forcing is larger when >> aerosols are prescribed at higher altitudes and the differences in >> radiative forcing due to fast adjustment processes can account for a >> substantial part of the dependence of the amount of cooling on aerosol >> altitude. These altitude effects would be additional to dependences on >> aerosol microphysics, transport, and sedimentation, which are outside the >> scope of this study. The cooling effectiveness of stratospheric sulfate >> aerosols likely increases with the altitude of the aerosol layer both >> because aerosols higher in the stratosphere have larger effective radiative >> forcing and because they have higher stratospheric residence time; these >> two effects are likely to be of comparable importance. >> >> -- >> 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 view this discussion on the web visit >> https://groups.google.com/d/msgid/geoengineering/CAJ3C-04wbNfg0E3q_8GtwXay88n_2r%2BhzYfVfrNPjq9SpJd9pg%40mail.gmail.com >> <https://groups.google.com/d/msgid/geoengineering/CAJ3C-04wbNfg0E3q_8GtwXay88n_2r%2BhzYfVfrNPjq9SpJd9pg%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> >> >> >> -- >> >> With Best Wishes, >> >> ------------------------------------------------------------------- >> G. Bala >> Professor >> Center for Atmospheric and Oceanic Sciences >> Indian Institute of Science >> Bangalore - 560 012 >> India >> >> Tel: +91 80 2293 3428; +91 80 2293 2505 >> Fax: +91 80 2360 0865; +91 80 2293 3425 >> Email: gb...@iisc.ac.in; bala....@gmail.com >> Web:http://dccc.iisc.ac.in/dr_govindasamy_bala_profile.html >> ------------------------------------------------------------------- >> >> >> >> -- >> 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 view this discussion on the web visit >> https://groups.google.com/d/msgid/geoengineering/CAD7fhV%3Dc5Q4XVod8rAide3VNOmN1uyPbp6B6TCRKij474F_Meg%40mail.gmail.com >> <https://groups.google.com/d/msgid/geoengineering/CAD7fhV%3Dc5Q4XVod8rAide3VNOmN1uyPbp6B6TCRKij474F_Meg%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > > > -- > With Best Wishes, > > ------------------------------------------------------------------- > G. Bala > Professor > Center for Atmospheric and Oceanic Sciences > Indian Institute of Science > Bangalore - 560 012 > India > > Tel: +91 80 2293 3428; +91 80 2293 2505 > Fax: +91 80 2360 0865; +91 80 2293 3425 > Email: gb...@iisc.ac.in; bala....@gmail.com > Web:http://dccc.iisc.ac.in/dr_govindasamy_bala_profile.html > ------------------------------------------------------------------- > > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-05QM63AG%3DxNEWoj_bTryjqpcZxph3bQKa_11ziO4WxfCw%40mail.gmail.com.
