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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