26 km is probably not going to add any more benefit compared 25 km if you consider the effect identified in our paper but it is better when sedimentation effect is considered. More experiments with the NCAR WACCM model would be good to precisely nail this down.
On Tue, Dec 17, 2019 at 2:10 PM Andrew Lockley <andrew.lock...@gmail.com> wrote: > Is 26k less good than 25? > > On Tue, 17 Dec 2019, 08:37 Govindasamy Bala, <bala....@gmail.com> wrote: > >> Andrew, >> >> Sedimentation effect works in the same direction as the effect we >> identified in our study. Therefore, higher the altitude of injection, the >> better. My judgement: 25 km would be good. >> >> On Mon, Dec 16, 2019 at 8:54 PM Andrew Lockley <andrew.lock...@gmail.com> >> wrote: >> >>> So what's your judgement on the ideal injection altitude? >>> >>> Andrew >>> >>> On Mon, 16 Dec 2019, 10:36 Govindasamy Bala, <bala....@gmail.com> wrote: >>> >>>> Andrew, >>>> Many modeling groups (e.g. Tilmes and others) have already performed >>>> simulations that inject aerosols at different heights and thus have >>>> included the sedimentation effects and many many other effects. These >>>> studies simulate the NET effects and hence hard to interpret and quantify >>>> the individual effects. The strength of our ESD paper is that it changes >>>> only one variable and identifies its individual contribution to the total >>>> problem. >>>> >>>> What we have learnt during the course is that there are too many >>>> variables in the aerosol SRM problem (transport, location of injection, >>>> aerosol-cloud interaction, aerosol-radiation interaction, aerosol micro >>>> physics and the resulting size distribution of the aerosols, etc.) and the >>>> resulting uncertainties could be too large. This is of course known to many >>>> of us for a long time...... >>>> >>>> On Mon, Dec 16, 2019 at 3:41 PM Andrew Lockley < >>>> andrew.lock...@gmail.com> wrote: >>>> >>>>> 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 >>>>>> ------------------------------------------------------------------- >>>>>> >>>>>> >>>> >>>> -- >>>> 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 >>>> ------------------------------------------------------------------- >>>> >>>> >> >> -- >> 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 >> ------------------------------------------------------------------- >> >> -- 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/CAD7fhVmmi%3DBiq01-YMWgB%3DaxqTLZKNL5mvC5Lpg866hU0NO1rQ%40mail.gmail.com.
