Droplet size may affect chemistry because of surface tension. At sufficiently small scales, a high-curvature surface isn't the same chemically as a lower-curvature surface.
My impression is that the Brewer Dobson circulation is the net circulation after east-west wind is canceled out, since the zonal circulation goes in circles of fairly homogeneous air and thus doesn't contribute to net long-term transport. But I don't actually know any more about it than you do. On May 9, 9:11 pm, Andrew Lockley <[email protected]> wrote: > A few comments on that:1) Droplet size shouldn't affect chemistry. Both > surface area and the cross sectional area are proportional to the square of > the radius. Volume affects residence time, and is proportional to the cube > of the radius. Big droplets are shorter-lived, and hence more controllable, > but less mass-efficient. > 2) The Brewer Dobson circulation drives aerosol transport and predominantly > acts towards the poles. I am not aware of East-West winds in the > stratosphere (but that's probably because I know sweet FA about such things, > not cos they don't exist) In the absence of EW circulation, what will force > aerosols to India? > 3) Release into the high stratosphere would remove the need to release > precursor at the equator, as lifting from the BDC would not be needed. > What's the peak height of the balloons? > 4) On a more general point, should we start a 'wish list' of research papers > that need to be done. Eager young PhD students will hopefully come along > and pick these up for us. Or is that just fantasy? > > A > > 2009/5/10 Alvia Gaskill <[email protected]> > > > This depends on the objective. For a global aerosol program designed to > > stop the warming of the entire planet, the answer is no. In this case, we > > want the aerosol to stay suspended as long as possible to get the maximum > > amount of sunlight scattering and to minimize the quantity of precursor that > > has to be transported to the stratosphere. The longer lived aerosol would > > also tend to be less of a problem in ozone depletion as the surface area > > would be reduced relative to larger shorter lived droplets. > > > If the aerosol precursor is released in the tropical stratosphere, it will > > circle and cover the entire globe, including India. Releases outside the > > tropics could be attempted, but this would create uneven warming of a > > different kind and a good portion of India and all of China is outside the > > tropics anyway. > > > In the case of an Arctic only aerosol program, the aerosol size issue is > > probably the same, but the supporters have set as criteria releasing the > > precursor in the upper troposphere (around 45,000 ft) in the spring with the > > goal of having it all gone by the end of the summer. This would minimize > > any ozone depletion as the aerosol would have to be present in the winter > > for the "dark" reactions to take place. Having the aerosol active only > > during the summer might lessen or have no impact on monsoons or other > > seasonal rainfall patterns. There is no data to support this one way or the > > other. > > > Note also that the limited modeling done to date in addition to the > > resolution of regional impacts issue mentioned earlier today also has > > focussed almost entirely on high loading of aerosol precursor to simulate > > that required to offset a doubling of CO2 from pre-industrial. While these > > extreme conditions may actually be required at some point decades from now, > > a more likely scenario is one of a gradual incremental increase in the > > aerosol to match GHG forcing or to offset loss of tropospheric aerosols. In > > such cases, the climate system may adjust and there may be no impact on > > monsoonal flows or precipitation or the effect may be very gradual and so > > can be dealt with by adaptation. The point is we simply don't know because > > these studies haven't been done. Thus the risk questions posed by John > > Nissen represent work that needs to be done. > > > ----- Original Message ----- > > *From:* Andrew Lockley <[email protected]> > > *To:* John Nissen <[email protected]> > > *Cc:* Alvia Gaskill <[email protected]> ; [email protected] ; > > [email protected] ; [email protected] ; [email protected]; > > [email protected] ; [email protected] ; > > [email protected] ; [email protected] > > *Sent:* Saturday, May 09, 2009 8:01 PM > > *Subject:* Re: [geo] Re: Balancing the pros and cons of geoengineering > > > Can't we modify the aerosol size, and deployment patterns, to make sure > > they fall out quickly and don't go anywhere near India? > > A > > > 2009/5/9 John Nissen <[email protected]> > > >> Very good discussion. > > >> I'm trying to get a balance of pros (benefits B1-B7) and cons (specific > >> fears S1-S21). What I'd like out of our discussion is some kind of risk > >> assessment for the possible downside of a weaker monsoon, as this is > >> considered the biggest risk in the regional effects (S1). And we could > >> make this reasonably pessimistic, to be on the safe side - i.e. be cautious > >> with the application of geoengineering. On the other hand, we might be > >> able > >> to reduce this risk, e.g. by neutralising sulphate aerosol; if there's a > >> good chance of this working, then we can factor that into the calculation. > >> Or the risk might be offset by a benefit in that region, e.g. improved > >> summer water supply from Himalayan glaciers? > > >> So, what kind of impact would a weaker monsoon (ISM) have on India? What > >> is the probability of stratospheric aerosols deployed in the Arctic would > >> produce a weaker monsoon? Can this risk be significantly countered? Can > >> it > >> be significantly offset? > > >> Note that the risk on benefit side might be measured in terms of a risk, > >> without geoengineering, of millions or even billions of lives being lost > >> (especially if massive methane release adds several degrees of global > >> warming, B4). Alternatively we could measure in GDP lost - current global > >> GDP (aka GWP) is about $60 trillion I believe. > > >> Cheers, > > >> John > > >> ----- Original Message ----- From: "Alvia Gaskill" <[email protected]> > >> To: <[email protected]>; <[email protected]> > >> Cc: <[email protected]>; "Andrew Lockley" < > >> [email protected]>; <[email protected]>; <[email protected]>; < > >> [email protected]>; <[email protected]>; < > >> [email protected]>; <[email protected]> > >> Sent: Saturday, May 09, 2009 4:50 PM > >> Subject: Re: [geo] Re: Balancing the pros and cons of geoengineering > > >> Stephen makes a good point that leads to a more general one. If there are > >>> precipitation reductions associated with sunlight blocking schemes, > >>> consideration should also be given to mitigating these, analogous to the > >>> medications given to patients with Type II diabetes to combat the side > >>> effects of the primary drug. > > >>> This is an oversimplification, but the way summer monsoons work is that > >>> in the summer the land gets warmer than the ocean faster, creating a low > >>> pressure area and this causes on shore flow as air moves from high to low > >>> presssure. For some reason, Laki caused this to be muted. There were no > >>> aerosols from Laki over India and it has been suggested there was a > >>> teleconnected response (see the paper Stephen attached) although in paleo > >>> climate the authors say the effects were direct, but don't give specifics. > >>> In the case of Pinatubo, both the land and sea were cooled by the aerosol > >>> and the land simply didn't heat up fast enough to generate the on shore > >>> flow. > > >>> If the Arctic only aerosol geoengineering does cause a reduction in the > >>> ISM (Indian Summer Monsoon as there are other monsoons that affect India, > >>> but this is the most important one), use of the cloud whitening to restore > >>> at least some of the temperature differential should be considered. > >>> Likewise, in a global aerosol scheme, with a global aerosol spread similar > >>> to that of Pinatubo, the cloud whitening could also be used to create a > >>> temperature differential, but at some point it becomes a race to the > >>> bottom, > >>> with the land temperature simply too cool to initiate the low pressure > >>> area. > >>> In this case, reducing the depth of the aerosol layer over the land may > >>> be > >>> the most effective way to restore the dynamics. > > >>> I previously suggested using ammonia released from either planes or > >>> balloons to react with the sulfate aerosol and drop them out as ammonium > >>> sulfate. This idea as well as Stephen's could be applied to other > >>> locations > >>> such as the Amazon, Eastern China and Africa where models indicate > >>> unacceptable reductions in precipitation are a result of either aerosol > >>> geoengineering or global warming. Of course, the ammonia wouldn't be of > >>> any > >>> value in a global warming/no aerosol scenario. > > >>> I said in one the earliest papers I wrote on geoengineering that > >>> eventually we were going to have to learn how to manipulate the climate to > >>> our advantage. That includes both gross scale and fine tuning. > > >>> In a related issue, last year I posted a link from a group in the UK that > >>> was carrying out some 130 different models of aerosol geoengineering. It > >>> was a volunteer effort among universities. If they have done even a > >>> fraction of the modeling, this work should be taken into account in > >>> designing new studies such as Rutgers is proposing. Anyone have an > >>> update? > > >>> You may recall also that we spent some time last year discussing the > >>> significance of the "little brown blotches" in absolute terms and now Ken > >>> also raises the issue of their resolution. > > >>>http://en.wikipedia.org/wiki/Monsoon > > >>> Monsoons are caused by the larger amplitude of the seasonal cycle of land > >>> temperature compared to that of nearby oceans. This differential warming > >>> happens because heat in the ocean is mixed vertically through a "mixed > >>> layer" that may be fifty meters deep, through the action of wind and > >>> buoyancy-generated turbulence, whereas the land surface conducts heat > >>> slowly, with the seasonal signal penetrating perhaps a meter or so. > >>> Additionally, the specific heat capacity of liquid water is significantly > >>> higher than that of most materials that make up land. Together, these > >>> factors mean that the heat capacity of the > > ... > > read more » --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
