January 2022 Archives

Mon Jan 17 09:39:05 CET 2022

Hunga Tonga affected the air pressure in my apartment

Hunga Tonga–Hunga Haʻapai was a volcanic island in Tonga. Was (past tense) because a volcano erupted there a few dats ago on 14 Jan 2022, and probably destroyed most of the island, as well as sent a tsumani across the Pacific ocean, and a wave of pressure through the atmosphere, detectable all the way around the world.
Jeremy Cole reported seeing two pressure waves from the eruption arrive in Nevada. (The first was the shorter way around the planet, and the second was the longer way.) For the longer path, the speed calculated is 689 mph, or 1108 kph. (It was a little faster for the shorter path.) Google maps tells me the distance from Hunga Tonga to Berlin, DE is 16,375 kilometers, the shortest path (heading North and West).

16,375 km / 1,108 kph = 14 hours and 47 minutes.

The time of the eruption reported in the graphic supplied by Jeremy Cole is 04:14:45 UTC. So 04:14 + 14 hours and 47 minutes is 19:01, Berlin is UTC+1, so add another hour and i'd expect to see the first wave arrive around 20:00.

I don't recall noticing the change in air pressure, but i think the Airthings Wave Plus sensor in my apartment did:


... beginning about 20:10, there's a sharp increase and then recovery, which matches the shape of the first wave in the chart for Nevada.

Google Maps and Google Earth only seem to want to give me the shortest path between two points, but maybe i can work out the longer path with a bit of math. Wikipedia says the circumerence of the Earth is 40,075 km around the Equator, and 40,008 at the poles, so just splitting the difference between the two that's 40,047 km. (I imagine one can compute the distance across the surface of a slightly imperfect sphere-shaped object, but i do need to start my day job soon...)
So we subtract the short path from the (averaged) circumference, and...: 40,047 - 16,375 = 23,672 km.

23,672 km / 1,108 kph = 21.36 hours.

04:14 UTC + 21 hours and 22 minutes + 1 hour (Berlin is UTC+1) = 02:35 Sunday morning, which is about 10 minutes earlier than the 2nd wave shows up. Maybe it was slower than the 1,108 kph observed in Nevada -- perhaps it loses some speed the further it travels.


Posted by johan | Permanent link