Dear Olivier, Stephen and Douglas, I highly appreciate your responses. Olivier’s point 1/, that the sulfate aerosol geoengineering forcing depends on the preexisting radiation, made me realise that the there should be a latitude-dependence of the green house forcing too. I believe Stephen’s comment relates to this. However, I do better appreciate now, as Douglas emphasized, that rather different forcing distributions can result in similar response in terms of e.g. the temperature field. This is quite a surprising fact.
Best wishes, Tamas > On 18 Feb 2020, at 12:07 AM, Douglas MacMartin <[email protected]> wrote: > > Agreed that the pattern of response isn’t as inhomogeneous as the forcing is, > though it is still true that a uniform aerosol layer will overcool the > tropics and undercool the poles, and that choosing your injection locations > so that the aerosol layer is not perfectly uniform does actually maintain > temperature gradients better. (But the undercooling of the poles of course > is still small compared to the warming that would be there without > geoengineering.) > > doug > > From: [email protected] <[email protected]> On > Behalf Of Olivier Boucher > Sent: Monday, February 17, 2020 4:19 AM > To: [email protected] > Subject: Re: [geo] sulfate aerosol geoengineering modelled by solar dimming > > Hi Stephen, > > you're correct and I'd think the negative SW RF is more offset by the > positive LW RF in the tropics than in the high latitudes (alike the pattern > of RF by WMGHG). But again, the pattern of a not-too-inhomogeneous forcing is > only moderately important. > > Regards > > Olivier > > Hi All > > But you also have to consider outgoing long wave radiation especially in > winter. > > Stephen > > Emeritus Professor of Engineering Design. School of Engineering, University > of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland [email protected] > <mailto:[email protected]>, Tel +44 (0)131 662 1180 > WWW.homepages.ed.ac.uk/shs <http://www.homepages.ed.ac.uk/shs>, YouTube Jamie > Taylor Power for Change > On 17/02/2020 08:35, Olivier Boucher wrote: > Dear Tamas, > > there are typically 3 effects that govern RF by stratospheric aerosols as a > function of latitude for a given aerosol burden. Let's think in terms of > solar zenith angle (one has then to integrate over SZA which is a function of > latitude and season) > > 1/ insolation decreases with SZA as cos(theta) where theta is the SZA > > 2/ air mass increases with SZA as 1/cos(theta), of course the effect this > has breaks down at some point because of multiple scattering > > 3/ upscattering function also increases with SZA (because more forward > scattering contributes to upscattering). > > You could assume 1/ and 2/ cancel each other at first approximation, so > because of 3/ there is indeed more RF at larger SZA. In fact there is an > optimum around SZA=60° but that depends on the AOD and how much multiple > scattering there is. > > Now life is a bit more complicated, as transport and aerosol size varies also. > > In any case, the climate response is not a copy-paste of the spatial > distribution of the RF. It matters but not too much. And it matters more for > rapid adjustments than for feedbacks. See eg > https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013JD021110 > <https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013JD021110> > Regards, > > Olivier > > > Dear All, > > I would like to ask for some useful references about sulfate aerosol > geoengineering. Assuming some uniform aerosol coverage around the globe, at > some height, with a certain vertical layer thickness, i would imagine that at > higher latitudes the radiative forcing exerted by the aerosols is larger due > to the longer distance of travel of sun rays through the aerosol "cloud". As > a consequence, the latitude-dependence of the downward-directed radiative > forcing should have an even larger gradient than solar irradiance. Therefore, > I’m wondering how big mistake it is to model such a geoengineering scenario > by dimming the sun. > > Any feedback or reference would be much appreciated. > > Thank you, > > Tamas > > -- > -- > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/47fba577-d1ff-de51-6636-f87c391fc1bb%40lmd.jussieu.fr > > <https://groups.google.com/d/msgid/geoengineering/47fba577-d1ff-de51-6636-f87c391fc1bb%40lmd.jussieu.fr?utm_medium=email&utm_source=footer>. > -- > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/2ecbd308-7da2-acab-e310-f4fff1932114%40ed.ac.uk > > <https://groups.google.com/d/msgid/geoengineering/2ecbd308-7da2-acab-e310-f4fff1932114%40ed.ac.uk?utm_medium=email&utm_source=footer>. > > > The University of Edinburgh is a charitable body, registered in > Scotland, with registration number SC005336. > > -- > -- > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/dca880ff-00b6-ac6e-1315-36440bbd4971%40lmd.jussieu.fr > > <https://groups.google.com/d/msgid/geoengineering/dca880ff-00b6-ac6e-1315-36440bbd4971%40lmd.jussieu.fr?utm_medium=email&utm_source=footer>. > > -- > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/BL0PR04MB47073A2914A7AE638E8A4B8C8F160%40BL0PR04MB4707.namprd04.prod.outlook.com > > <https://groups.google.com/d/msgid/geoengineering/BL0PR04MB47073A2914A7AE638E8A4B8C8F160%40BL0PR04MB4707.namprd04.prod.outlook.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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