[Godzilla]

Maybe 70,000 years ago....Today, with prevailing winds, the jet stream etc, the ash would be blown mostly eastbound, before it ever reached the "upper atmosphere" as you say.

Please note, the top of the eruption column has reached the upper atmosphere in this picture.

I know the following may be a little complicated for you, but here is a example showing the upper air flow paths.

[dragnet2]

The top pics looks just like a fire in S.Cal...Wind dictates where da smoke goes....lol

Ya notice your weather chart shows everything moving EAST from Cal?

lol.....

[dragnet2]

Here is what you're suggesting....heheheh...

"Smoke/ash direction is not dependent on wind direction"

I'm getting that movie movie felling again....lol