Tonga volcano shockwave signature in air pressure records in Germany

The explosive eruption of the Tonga volcano on Jan 15, 2022, 04:15 (UTC) created a shockwave which travelled around the world. E.g. it is seen nicely in the air pressure record from Unkeroda (50.934N, 10.269E) in Thuringia. Below is a graph of the record:

Two events are clearly seen (the record has a time resolution of 5′ only): a first at Jan 15, 2022 20:20 CET, and a second at Jan 16, 2022 02:00 CET.

The circular shockwave emanating from the eruption is nicely seen in remote sensing data of midlevel water vapour (GOES-17). After expanding over the hemisphere it converged on the other side of the planet arriving in Germany after 20:00 CET. The speed of the wave can be calculated from the arrival in Unkeroda:

The distance from the Tonga volcano (20.56S, 175.37W) to Unkeroda is 16’598 km (calculated on the reference ellipsoid); the time difference from the eruption until the first event is 14hours 45Minutes, which gives a speed of 312.5 m/s. This is close to a typical speed of sound in the upper troposphere.

Theoretically, assuming a perfectly spherical Earth, the sound wave would have converged at the antipode point of the Tonga volcano (i.e. at 20.56N, 4.53E). This point lies about 3406 km south of Unkeroda. Using the speed calculated above, it should have arrived at the antipode point at about Jan 15, 2022, 23:01 CET. Subsequently, the shock wave should have dispersed again in circular form from the antipode point, reaching Unkeroda again three hours later – this is exactly the time of the second event seen above (i.e. at 02:00 CET on Jan 16). The map below shows the path of the wave crossing Unkeroda (black) and then on to the antipode point and back (pink). The red circle shows the wave at the time of the first and the second event in Unkeroda.

An interesting question is, what happened at the antipode point. Theoretically, assuming a perfect sphere, no attenuation in the atmosphere and no vertical broadening of the wave, the original sound of the eruption could have been heard at the location. Since this not the case, clearly the signal will have been quite distorted. Still, a sizeable pressure signal should have been picked up by local measurements. Unfortunately, the antipode point lies close to the southern border in Algeria, about 240km SSW from the city of Tamanrasset. The METAR data from Tamanrasset airport are unfortunately only available at hourly resolution and thus do not show a convincing signal.

In case you want to ‘hear’ the sound of the eruption as recorded in Estonia: Steffen Noe has resampled the high resolution pressure record from his SMEAR station and turned it into a sound file…

Addition (Jan 24, 2022):

Diego Aliaga from University of Helsinki, Finland, has made an analysis of the shockwave as seen in IR radiation from two geostationary satellites (GEOS16, GEOS17). In his Twitter tweet you can see an animation of the IR brightness anomaly. The circular wave moving from Tonga to the antipode and back, several times, is clearly visible.

Addition (Jan 25, 2022):

Yet another animation of satellite data: this time from EUMETSAT data, made by Mathew Barlow of University of Massachusetts Lowell. It shows nicely the shock wave around the antipode point. As anticipated, it is not converging perfectly, but already somewhat distorted.

Addition (Jan 26, 2022):

More articles on the effects of the Tonga shockwave are appearing: Science has a nice piece on small tsunamis seen at the coast of Japan and also in the Caribbean. In Japan these small tsunamis were seen earlier than the actual ocean surface wave tsunami from Tonga; they were locally generated by the pressure shockwave which travels much faster. EOS contains an interesting commentary with more animations, model simulations and observations of the atmospheric shock wave.


About Little Science Blog

Director Emeritus, Max-Planck-Institute for Biogeochemistry, Jena, Germany Research Director, Division of Atmospheric Sciences, Department of Physics, University of Helsinki, Finland
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s