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 ------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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