Pressure wave from Pacific volcanic eruption

[Freddie]

First wave just after 1900 UTC Saturday (approx. 15 hours after the eruption), and a second artefact just before 0200 UTC Sunday.

-- 
Freddie
Alcaston
Shropshire
148m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/statistics/alcaston/latest.xlsx

[Nick Gardner]

My air pressure recordings at 5 minute resolution.

 --
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk  

[Graham Easterling]

Thanks for that, very interesting.

Graham

penzance

[Brian Wakem]

-- Brian Wakem Lower Bourne, Farnham, Surrey http://www.brianwakem.co.uk/weather Live obs @ 16:40:37 : 6.5C, DP 5.6C, RH 94%, 0.4 mm

On Sunday, 16 January 2022 at 09:24:30 UTC Freddie wrote:

[jack.h...@gmail.com]

 The Tonga volcano was big but not on the scale of Krakatoa or Tambora.  So what is the speculation about the pressure spike from a supervolcano on the other side of the planet?  

[Len W]

Had a couple of spikes on my barograph. 1.5 mb at 1930hr, 2 mb 6hrs later at 0130hrs.

Why two pulses?

Tonga 175°W, right the other side of earth. Earth circumference about 40,000 km.

Speed of sound at 20°C 344 m per sec, but must have been supersonic.

Wind must have had an effect?

Is anybody else during the math as the americans say?

Len

Wembury

[Len W]

32 hrs to go round earth, 16 hrs to half way round.

Eruption 0400 UTC, shock wave arrives Europe 1900 UTC.

i.e. 15 hrs. The maths agrees approximately.

But the secord shockwave?

Len

[Paul (Once of Dawlish)]

Really interesting. Freddie, or anyone; why was there a second, negative pressure wave on the Sunday?  

[Paul Knightley]

The second was the wave from the ‘other way’…in fact, if you check barographs today you should be able to see both waves…one around 0700 and one not far from 1400…this is evidence of both waves having gone around the Earth a second time…pretty amazing stuff.

[Len W]

I thought this might be the case. The second wave took 6 hrs longer for pretty much the same distance. Was this the one going west?

In which case it might have been affected by a westerly air flow, at least in mid lats.

It is not as simple as the analogy of a stone dropped into water giving ripples.

Here we have shockwaves moving away on a sphere in air that is already moving in places.

Len

Wembury

[Graham Easterling]

I thought this might be the case. The second wave took 6 hrs longer for pretty much the same distance. Was this the one going west?

In which case it might have been affected by a westerly air flow, at least in mid lats

Would the rotation of the Earth been an influence on the wave's travel relative to the ground? 

Graham 

Penzance - Cloudy today.

[Len W]

Not sure what you mean Graham. Atmosphere moves with the rotating earth. If faster a westerly wind, if slower an easterly wind

The rotation though gives us a turning effect (Coriolis) on the motion.

Len

[Paul Knightley]

The second wave took longer as the UK is not at the antipode of Tonga…thus it had further to travel. Winds and pressure patterns would have some effect, but as the wave is travelling at close to the speed of sound, probably not a huge amount. The 2 waves were detected a second time yesterday crossing the UK, by the way.

[Graham Easterling]

It wasn't the Coriolis affect I was thinking about. It was the fact that the shock wave was travelling at the speed of sound, very different to normal movements in the atmosphere where the Coriolis force is so important. I just wondered if, at that speed, the rotation of the Earth would have some effect on it's apparent speed on the ground.

I'm way out of my comfort zone here, just asking.

Graham

On Tuesday, 18 January 2022 at 20:01:37 UTC Len W wrote:

[Graham Easterling]

Just read Paul's reply. should have read it first, thanks for that

Graham

[Paul (Once of Dawlish)]

I see, thank you. it is, as you say, amazing stuff.

On Monday, January 17, 2022 at 5:52:15 PM UTC Paul Knightley wrote: