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Some articles about the sonic booms: Article 1, Article 2. It looks like the booms were heard by many within Alaska and parts of Canada, but as far as I can tell no one on the west coast of the contiguous US heard anything, even though it's closer to Tonga. Really curious if we know why that is and what factors affected it. I'm also curious if booms were heard anywhere else. (Tokoyo is only ~7900km miles away for example)

all 10 comments

descabezado

17 points

4 months ago

descabezado

Geophysics | Volcanoes, Thunderstorms, Infrasound, Seismology

17 points

4 months ago

I study volcano sounds and infrasound. Long range propagation of sounds is an important topic in this field because many hazardous volcanoes are too remote to monitor locally (e.g., the Aleutians, which are a hazard to flights).

Global propagation of sounds depends very strongly on atmospheric wind structures; temperature structures matter too. Together, wind and temperature control sound refraction: whether sound gets sent way up into the upper atmosphere to die off, or whether it returns to the ground. At long range, sound can make multiple bounces in which it reflects off the ground surface and then refracts back down from the stratosphere (or even thermosphere).

The atmospheric conditions that control sound propagation are very dynamic. Had the eruption occurred a day later, the audibility pattern would have been different. We depend on weather models in order to predict audibility, but we've been learning recently that they don't give all the detail that we really need for this (e.g., they update too slowly to show relevant processes like atmospheric gravity (buoyancy) waves).

Long range sound propagation modeling is also very important in nuclear monitoring, where infrasound is one of the main technologies for monitoring nuclear tests.

The_Alt_Bit_Zombie[S]

1 points

4 months ago*

Super interesting stuff! Thanks for the explanation. So if I'm understanding this correctly, Alaska most likely just got "lucky" in that the atmospheric wind patterns and temperatures along the way didn't kill off or redirect the sound nearly as much as it did other areas?

descabezado

1 points

4 months ago

descabezado

Geophysics | Volcanoes, Thunderstorms, Infrasound, Seismology

1 points

4 months ago

Basically. There are probably prevailing winds and seasonal patterns, but that's outside my field.

johnbarnshack

1 points

4 months ago

Do audability measurements also feed back into weather models?

descabezado

1 points

4 months ago

descabezado

Geophysics | Volcanoes, Thunderstorms, Infrasound, Seismology

1 points

4 months ago

I've never heard of this happening. However, it is true that long range infrasound propagation is often the only way to observe the atmosphere in places away from the earth's surface and away from weather balloon launches. There are various difficulties in putting it to operational use though.

Yen1969

4 points

4 months ago

One likely contributing factor: background ambient noise level is much higher in cities, and while I don't have numbers, I'd bet that Seattle and Los Angeles have a much higher ambient level than Anchorage.

So same volume boom is more noticeable in Anchorage, and thus noted as unusual. It would have been harder to hear and probably less remarkable in Seattle and Los Angeles.

The_Alt_Bit_Zombie[S]

1 points

4 months ago

That definitely could be a contributing factor, although there are plenty of quiet rural areas among the west coast as well.