On the morning of January 17 Japan time, my daughter and grandson were in a park near our home in Yokohama when she noticed that the clouds looked very unusual. She took some photos [1]. We speculated that the clouds might have been affected by the shockwave from the Tonga eruption.
Other people in Yokohama posted similar photos to Twitter [2, 3, 4].
After. The tsunami had arrived in several waves over about a twelve-hour period a day and a half earlier. A page in Japanese with the arrival times and peak wave heights at various locations is here:
The waves observed being not merely compression (sound) waves, but gravity waves, in which the air column itself is transported vertically.
Implications and impacts of this are as yet unknown, but the results might include mixing between atmospheric regions, impacts on satellites (increased drag for very-low-orbiting craft), the speed at which the waves propagate (atmospheric gravity waves should be slower than compression blast waves), cloud patterns (lifted humid air would tend to condense out, then re-vaporise, at it is lifted and lowered).
What's changed in particular is our ability to observe, from multiple instruments and points of view, events of this magnitude. New sensors -> new observable phenomena.
In long distance rf communication, radio waves are bounced (sometimes several times) off different regions in the ionosphere (https://www.electronics-notes.com/articles/antennas-propagat...). Since the waves caused by the eruption apparently reached the ionosphere, (some) radio bands may be affected.
When were were learning Bessel functions in college, the prof told us Bessel discovered them when trying to figure out why buildings in England fell down when Krakatoa blew up on the other side of the world.
(Bessel functions tell you what happens when you hit a sphere with a hammer.)
'It was not until October that the first plausible explanation for “The Year without a Summer” was suggested. Friedrich Bessel, a German astronomer, reported seeing thick clouds of dust in the upper atmosphere. He theorized that these dust particles screened portions of Earth from the warming rays of the sun. It was discovered that in April 1815, Mount Tambora, an Indonesian volcano, had erupted with such force that it had sent an estimated 100 cubic miles of fine dust into the atmosphere. Witnesses to the eruption reported that the sky remained dark for two days. The dust then rose high into the stratosphere, where it encircled the world for several years to come.'
'Skeptics in 1816 doubted that a faraway volcano could steal their summer. However, most present-day researchers believe Bessel’s explanation to be generally correct, demonstrating the global nature of weather. The dust in the atmosphere eventually settled, and the spring of 1817 was back to normal.'
I’m a private pilot. I was taking off when it happened and the tower radioed me to check my altimeter once more because they weren’t sure if they were having an equipment malfunction. I looked back and it was the exact time of the expected pressure wave picked up by the official readings at the time. So I definitely noticed but figured it was just a general error, it was only after I checked the history did I realize it was probably the volcano !
I counted 6 passes of the wave(s) on my home sensor, and maybe 7, but I have to go check neighboring sensors in the next state over to verify that the bump really is from the eruption.
I heard that the waves were going to converge at the antipode of the explosion which was supposed to be in Algeria I think. Any interesting data or observations from that incident?
Translation: «Antipodes are also animated with METEOSAT-11. The propagation speed seems to be different depending on the route, and the timing of coming to the antipodes is slightly different»
Airplane altimeters are adjusted according to a radio announced local pressure or a default(29.92 inHg). That make altitudes inaccurate but ensure separation between planes flying directly above and below. So shouldn't matter as long as pressure changes are nonapocalyptic.
It's amazing to me all the data we have collected on this. Academically I know we have satellites, sensors, cameras, models, effectively infinite storage, and mind boggling compute resources. But this event specifically it has really clicked for me how much we actually know now, and our capacity to learn. It's the first time I have been excited by technology in a long time.
Climate change implications are interesting, I think a net negative in the long-term for all the greenhouse gases released, but an unknown short-term global cooling trend expected. Was the recent snow storm in Eastern US affected by the Tonga eruption?
I wonder if they can estimate how much water was converted to steam in the explosion. I just read today that the power of this was equivalent to Pinatubo at its peak, the big difference is that it just lasted 10-20 minutes where Pinatubo ran for a week or more.
The blast yield has been given as equivalent to 6 MT TNT,[1] equivalent to a large nuclear weapon. This estimate itself is probably based on shockwave, ejecta volume and velocity, or similar effects,[2] so I'm somewhat working backwards to the estimation basis, but let's roll with that.
6 megaton TNT is about 11,100 billion * 2260 J
2260 J is the latent heat of vaporisation of water (the energy required to turn 1g of 100C water to steam).
If the ocean water were at 100C before vapourisation, that works out to about 11 million m^3 (or 11 million tonnes) of seawater vapourised, about 0.011 km^3.
The actual amount would be less than this, as the seawater would have been heated from below 100C (at 4.18 joules/(g*degreeC)), and some of the heat would likely have been dissipated in other modes (e.g., kinetic energy).
But that's an upper bound.
Since steam occupies about 1,000 the volume of liquid water, that 11 million tonnes would have displaced 11 km^3 of atmosphere, or a cube 2.2 km on a side, or a sphere with a radius of about 1.37 km.
Which makes me wonder what the specific blast geometry would have been, and how that might have affected blast and gravity wave generation. A narrow column jetting straight up might have a much more pronounced gravity-wave effect than a generalised, say, hemispheric, blast.
As before: not a geologist.
Edit: It's also helpful to remember that that volume of steam has mass and momentum. Once it starts moving, it's going to take some resistive force to stop it, and atmospheric resistance and gravity are pretty much all we've got to work with. But 11 million tonnes moving at a good clip (up to around 600--1,100 kph, based on other estimates of the shockwave) has a significant stopping distance.
Another difficulty is that you're essentially estimating boiling a blob of water away but that's not what takes place - the process is explosive, quickly dumping lots of 'excess' energy elsewhere. It also doesn't stop heating the water once it hits 100c vapour.
The nature of rough physics back-of-the-envelope (or quick on-the-shell) estimation is to get a rough idea of values and quantities involved. My expectation is that my estimate is somewhere within an order of magnitude of actual values, and suspect it's well on the high side.
Modelling the specific events and characteristics of seawater infiltration to magma vents and chambers is well beyond my pay grade. I'm not representing to any extent that I've done this realistically. I'm simply showing what the maximimum potential vaporisation magnitude might be given a 6 MT energy input using a very naive heat of vaporisation conversion.
I'd noted the circularity in my note --- I'm estimating vapourisation effects and consequent blast yield using estimations of energy release which are based on the observed blast characteristics. Circular circularity is circularly circular.
The Axios article ... provides minimal insight on NASA's estimation methods. Though the comment on kinetic (blast) energies does suggest modeling based on the size, and probably rate of expansion, of the steam and ash plume. A forensic analysis of the 2020 Beiruit explosion discusses how total explosive force is estimated by blast diameter (see: https://forensic-architecture.org/investigation/beirut-port-...).
On thermal vs. blast effects: my estimate is based on the conversion of applied thermal energy into blast energy through vapourisation of water into steam. The 1,000-fold volumetric expansion provides that blast capability. It would then be much of the observed blast that the original 5--6 MT erruption energy is based on. My understanding is that "thermal effects" would refer to additional heat radiated from the erruption, exclusive of that heat which triggered the steam explosion itself.
FWIW, claims are now that the blast may have been 50 MT equivalent or larger. That's at least as large as the Tsar Bomba (50 MT) yield, the largest nuclear weapon ever detonated.
Nicely done! Agree the blast dynamics would likely have a substantial effect on the effect. If you watch the satellite view you can see oscillations at the ceiling of the cloud, almost like ripples in water. I wonder if that is what triggered the ripples being reported.
Gravity waves? The way you described this in your other post as "in which the air column itself is transported vertically", did you mean pressure waves, as in a change in air pressure?
I'm not a geologist, so don't take my incredulity for anything suggesting scientific fact, here.
I'm not a geologist (or meteorologist) either, so salt accordingly.
One 'splainer I've seen[1] described the volcanic erruption as the result of seawater infiltrating a magma chamber or vent, flash-vaporising, and basically blowing straight up to a height of about 30km (roughly 100,000 ft). Think of this not simply as a pressure wave blasting upwards, but as a bolus of air (and steam / water vapour) punching up through the atmosphere. It's analogous to a water wave spiking up out of fluid --- after it rises up, it will collapse back down, then rebound up, repeating this several times.
The spike also both propogates out and creates a gravity-wave front which propagates outward, again creating a vertical wave across the top of the atmosphere.
We're used to gravity waves in water largely because water isn't compressible. Sound travels through water, but shock waves tend to have limited reach since water itself doesn't compress --- a water shock is rapidly transformed into a water gravity wave, with a surge and collapse. (How much energy is transmitted through either wave mode I don't know, though someone versed in fluid dynamics could probably say.)
Air is compressible, so a major part of the effect of an explosion is shock. That said, you can get gravity waves in air as well, and the Tonga erruption is apparently a demonstration of this.
Wikipedia has the 'splainer for you[1]. There are good satellite examples online[2]
But basically it has to do with buoyancy. A cloud or other layering of the atmosphere has a stable place in the vertical column. If the atmosphere passes over a mountain range that displaces the column vertically, the column returns to its normal position. In returning, the atmosphere overcorrects repeatedly and "bounces" back into position much like a single jump onto a mattress.
In water, surface waves operate principally under the effects of surface tension (small waves such as you'd find in a ripple tank, to about 0.1s period), or gravity, where the mass and inertia of the water moving up and down dominante.
There are also pressure waves, which are the result of compression and expansion of a medium. Water compresses poorly, whilst air compresses quite well and elastically. Sound is largely a phenomenon of pressure waves.
With the development of very sensitive instruments, gravitational waves in which the geometryof space-time itself is altered can now be detected. Despite the similarity in terms, "gravity waves" and "gravitational waves" are very different phenomena, and we'd need events at the scale of neutron star collisions to be ablet to create readily-detectable gravitational waves. Tonga Hunga was somewhat below this threshold.
There are also electromagnetic waves, experienced as EMR (including visible light), AC electric power transmission, and magnetic waves. Again, different phenomena, though the same underlying wave equations describe this behaviour.
Material Wave might be a less confusing term than 'Gravity Wave' which at least outside of this field sounds like what someone in the field might call a 'gravitational wave'.
Though that too should be subject to re-definition if a better and more easily communicated understanding of the density of space / time / gravity (as we know it today) makes the term outdated.
Compression (sound) waves are also material waves, so that term would generate its own ambiguity.
We could instead call the more recently detected gravitational waves "spacetime waves". Though I suspect someone might step in and make some observations about EMR in that context.
They are waves in a density gradient caused by gravity - it's unfortunate, but essentially there are two things with the same name - English is like that some times
Other people in Yokohama posted similar photos to Twitter [2, 3, 4].
[1] http://gally.net/miscellaneous/20220117_Yokohama_clouds/inde...
[2] https://twitter.com/hiboshi045/status/1482884882837966853
[3] https://twitter.com/mimikaki75/status/1483037087213375488
[4] https://twitter.com/YasuA_Yokohama/status/148287894217674752...