Is 26k less good than 25? On Tue, 17 Dec 2019, 08:37 Govindasamy Bala, <[email protected]> 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 <[email protected]> > wrote: > >> So what's your judgement on the ideal injection altitude? >> >> Andrew >> >> On Mon, 16 Dec 2019, 10:36 Govindasamy Bala, <[email protected]> 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 <[email protected]> >>> 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, <[email protected]> >>>> 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 <[email protected]> >>>>> 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:* [email protected] < >>>>>> [email protected]> *On Behalf Of *Govindasamy Bala >>>>>> *Sent:* Saturday, December 14, 2019 9:38 PM >>>>>> *To:* Andrew Lockley <[email protected]> >>>>>> *Cc:* geoengineering <[email protected]> >>>>>> *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 < >>>>>> [email protected]> 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 [email protected]. >>>>>> 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: [email protected]; [email protected] >>>>>> 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 [email protected]. >>>>>> 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: [email protected]; [email protected] >>>>> 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: [email protected]; [email protected] >>> 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: [email protected]; [email protected] > 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-06o%3Dkw4Xi_QgGva513_%3Dzgt_m05vGqx%2Bu67HhcP9B5CQw%40mail.gmail.com.
