The MH extinction comes from another reason: The arc heats up the gas, the heated gas expands, so becomes lighter than the surrounding. Because of the gravity acceleration, the less dense gas rises against the rest, forming a gas flow, bowing the arc upwards, so against the acceleration vector. That is well known, so obvious to anyone at least somehow familiar with high pressure discharges.
What is not that obvious: Any bump is in fact a surge of very high acceleration. And the same as gravity, this acceleration moves the gasses of different density in similar manner. Because the bump may easily be way greater in it's peak acceleration level than the gravity, it yields way faster gas flows within the arctube. And this faster gas flow then bows the arc in a way greater extend and even quite likely just blows it off, so the arc extinguish as a result.
By the way this is one of the factors, why a simple mirror optics never catch up with HID automotive lighting: The vibration cause the arc to move wildly around it's position and that would make the beam shaking in the same way. The projection technique with dedicated rigid shield was the only viable way around the problem, even though the vibration still does modulate the light intensity. But at least it does not cause glare...
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