understand
that to have world-wide impact, the event would need to be in the
tropical/sub-tropical belt? However, would be glad to be corrected if
anyone has got more on this.

ISTR HH Lamb saying that in "Climate, History and the Modern World."
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Found this on the CRU site which might help .... they imply that for
*maximum* effect such activity should be at lower latitudes etc.

I think the idea is that tho tropical eruptions cause cooling at the surface,aerosol injection
causes heating in the stratosphere thus enhancing the equator pole temperature gradient.Sulphur is
the key aerosol ingredient.In NH winter a stronger polar vortex results -ie +ve NAO/AO mode and
continental warming.This 'advective' effect outweighs the radiative cooling at low latitudes and in
the summer.
Injection into the stratosphere at high latitudes (presumably dispersion by the jet wld be rapid)
causes high latitude heating and a reduced meridional temperature gradient.ie -ve NAO/AO mode and
continental cooling.
..IIRC the 1980 eruption was largely confined locally at the surface causing strong daytime cooling
(and conversely high night time temps locally)-as much as 10C (?),

--
regards,
david
(add 17 to waghorne to reply)