H 'n' H,
Thanks for the clarification. No, my only reasoning was thinking that a jet core travelling at 200 kts will then affect the air in near proximity to it, and so on and so forth. 'My' theory was that if this process happens over, for example, 30 nms or so (laterally speaking) then although the change would be noticeable, it would cause no caffeine spillages as you said! But as I suspected, I do stand corrected!
Mind you, I'm sure that, like universal black holes, jetstreams come in all shapes and sizes, some 'shallower' than others so to speak. After all, as wxjedi mentioned, it was a smooth ride for him
Rainboe, thank you for your enlightening contribution also
Cheers, Jack