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], Tel +44 (0)131 662 1180 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
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
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