The shock wave that emanated from the Tonga volcanic eruption was evident in infrared and visual satellite imagery. Just wondering if the observed wave is perhaps due to the condensation of water in the atmosphere or perhaps due to the refraction/diffraction of light?
See the visual and infrared animations here:
https://www.ausmarinescience.com/marine-science-basics/waves/tonga-eruption-and-tsunami/
Prof. Daryl Metters
The shock wave from the Tonga eruption was measured in hectopascal units, quite impressive for a physics lab *.
* https://twitter.com/BOM_WA/status/1482563705695084550
Best Regards.
The eruption generated several types of waves in the atmosphere; the list includes infrasound waves, Lamb waves, and acoustic-gravity waves.
Propagation of the volcanic shock wave across the Pacific Ocean could be followed in GOES-17 (GOES-West) Mid-level Water Vapor (6.9 µm)
https://cimss.ssec.wisc.edu/satellite-blog/archives/44252
The problem of the interaction between a shock wave and condensation is very well known and was documented in the past; for some additional information please consult
https://www.nature.com/articles/259190a0
and
https://academic.oup.com/gji/article-abstract/222/2/735/5834547
Concerning the question: “Just wondering if the observed wave is perhaps due to the condensation of water in the atmosphere or perhaps due to the refraction/diffraction of light?” I think that both effects are important and that they relative significance was dependent on the distance from the eruption site.
According to this excerpt from a timely article (please see below), by the time the tsunami reaches land, it is less of a wave and more of an inundation, that is, a huge wall of ocean that sweeps into the land:
"When tsunamis get to shore, they often do not crest and break like a typical ocean wave. Instead, they are more like a large wall of water that can inundate land near the coast. It is as if sea level were to suddenly rise by a few feet or more. This can cause flooding and very strong currents that can easily sweep people, cars and buildings away."
SOURCE LINK: https://theconversation.com/what-causes-a-tsunami-an-ocean-scientist-explains-the-physics-of-these-destructive-waves-175213
"On Jan. 15, 2022, coastal areas across California were placed under a tsunami warning. Gado via Getty Images
January 19, 2022 8.45am EST
"What causes a tsunami? An ocean scientist explains the physics of these destructive waves"
Author: Sally Warner, Assistant Professor of Climate Science, Brandeis University
Disclosure statement Sally Warner has received funding from the National Science Foundation and the Office of Naval Research.
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On Jan. 15, 2022, the Hunga Tonga-Hunga Ha’apai volcano in Tonga erupted, sending a tsunami racing across the Pacific Ocean in all directions.
As word of the eruption spread, government agencies on surrounding islands and in places as far away as New Zealand, Japan and even the U.S. West Coast issued tsunami warnings. Only about 12 hours after the initial eruption, tsunami waves a few feet tall hit California shorelines – more than 5,000 miles away from the eruption.
I’m a physical oceanographer who studies waves and turbulent mixing in the ocean. Tsunamis are one of my favorite topics to teach my students because the physics of how they move through oceans is so simple and elegant.
Waves that are a few feet tall hitting a beach in California might not sound like the destructive waves the term calls to mind, nor what you see in footage of tragic tsunamis from the past. But tsunamis are not normal waves, no matter the size. So how are tsunamis different from other ocean waves? What generates them? How do they travel so fast? And why are they so destructive?
Learn moreWe believe good journalism is good for democracy and necessary for it.
When the Hunga Tonga-Hunga Ha'apai volcano erupted, it launched ash into the atmosphere, created a powerful shock wave and displaced a huge amount of water, generating a tsunami that raced across the ocean. Japan Meteorological Agency via Wikimedia Commons, CC BY📷
Deep displacement
Most waves are generated by wind as it blows over the ocean’s surface, transferring energy to and displacing the water. This process creates the waves you see at the beach every day.
Tsunamis are created by an entirely different mechanism. When an underwater earthquake, volcanic eruption or landslide displaces a large amount of water, that energy has to go somewhere – so it generates a series of waves. Unlike wind-driven waves where the energy is confined to the upper layer of the ocean, the energy in a series of tsunami waves extends throughout the entire depth of the ocean. Additionally, a lot more water is displaced than in a wind-driven wave.
Imagine the difference in the waves that are created if you were to blow on the surface of a swimming pool compared to the waves that are created when someone jumps in with a big cannonball dive. The cannonball dive displaces a lot more water than blowing on the surface, so it creates a much bigger set of waves.
Earthquakes can easily move huge amounts of water and cause dangerous tsunamis. Same with large undersea landslides. In the case of the Tonga tsunami, the massive explosion of the volcano displaced the water. Some scientists are speculating that the eruption also caused an undersea landslide that contributed to the large amount of displaced water. Future research will help confirm whether this is true or not.
This simulation from the National Oceanic and Atmospheric Administration shows how tsunami waves propagated away from an earthquake that occurred about 600 miles from Tonga in 2021.
Tsunami waves travel fast
No matter the cause of a tsunami, after the water is displaced, waves propagate outward in all directions – similarly to when a stone is thrown into a serene pond.
Because the energy in tsunami waves reaches all the way to the bottom of the ocean, the depth of the sea floor is the primary factor that determines how fast they move. Calculating the speed of a tsunami is actually quite simple. You just multiply the depth of the ocean – 13,000 feet (4,000 meters) on average – by gravity and take the square root. Doing this, you get an average speed of about 440 miles per hour (700 kilometers per hour). This is much faster than the speed of typical waves, which can range from about 10 to 30 mph (15 to 50 kph).
This equation is what oceanographers use to estimate when a tsunami will reach faraway shores. The tsunami on Jan. 15 hit Santa Cruz, California, 12 hours and 12 minutes after the initial eruption in Tonga. Santa Cruz is 5,280 miles (8,528 kilometers) from Tonga, which means that the tsunami traveled at 433 mph (697 kph) – nearly identical to the speed estimate calculated using the ocean’s average depth.
Many tsunamis, including the 2011 Tsunami in Japan, move inland and can flood areas far from the coast. U.S. Air Force photo/Staff Sgt. Samuel Morse via Wikimedia / Commons📷
Destruction on land
Tsunamis are rare compared to ubiquitous wind-driven waves, but they are often much more destructive. The 2004 Indian Ocean tsunami killed 225,000 people. More than 20,000 lost their lives in the 2011 Japan tsunami.
What makes tsunamis so much more destructive than normal waves?
As waves approach shore, they get pushed upward by the rising seafloor. Régis Lachaume via Wikimedia Commons, CC BY-SA📷
In the open ocean, tsunami waves can be small and may even be undetectable by a boat at the surface. But as the tsunami approaches land, the ocean gets progressively shallower and all the wave energy that extended thousands of feet to the bottom of the deep ocean gets compressed. The displaced water needs to go somewhere. The only place to go is up, so the waves get taller and taller as they approach shore.
When tsunamis get to shore, they often do not crest and break like a typical ocean wave. Instead, they are more like a large wall of water that can inundate land near the coast. It is as if sea level were to suddenly rise by a few feet or more. This can cause flooding and very strong currents that can easily sweep people, cars and buildings away.
[Get fascinating science, health and technology news. Sign up for The Conversation’s weekly science newsletter.]
Luckily, tsunamis are rare and not nearly as much of a surprise as they once were. There is now an extensive array of bottom pressure sensors, called DART buoys, that can sense a tsunami wave and allow government agencies to send warnings prior to the arrival of the tsunami.
If you live near a coast – especially on the Pacific Ocean where the vast majority of tsunamis occur – be sure to know your tsunami escape route for getting to higher ground, and listen to tsunami warnings if you receive one.
The eruption of the Hunga Tonga-Hunga Ha’apai volcano severed the main communication cable that connects the people of Tonga to the rest of the world. While the science of tsunamis can be fascinating, these are serious natural disasters. Only a few deaths have been reported so far from Tonga, but many people are missing and the true extent of the damage from the tsunami is still unknown."
https://theconversation.com/what-causes-a-tsunami-an-ocean-scientist-explains-the-physics-of-these-destructive-waves-175213
There are differences between a wave caused by an earthquake and a tsunami caused by an underwater volcanic eruption:
https://www.cnn.com/2022/01/15/asia/tsunami-warning-tonga-volcano-intl-hnk/index.html
"Tsunami advisories lifted in US after waves hit Tonga following volcanic eruption
By Alex Stambaugh, Laura Smith-Spark, Rhea Mogul, Sophie Jeong and Dakin Andone, CNN
Updated 1:53 AM ET, Mon January 17, 2022
(CNN)An underwater volcano in the South Pacific erupted violently on Saturday, causing tsunamis to hit Hawaii, Japan, and Tonga's largest island, Tongatapu -- sending waves flooding into the capital.
The Hunga-Tonga-Hunga-Ha'apai volcano, about 30 kilometers (18.6 miles) southeast of Tonga's Fonuafo'ou island, first erupted on Friday and a second time on Saturday around 5:26 p.m. local time, according to CNN affiliate Radio New Zealand (RNZ).The eruptions sent a plume of ash, gas and steam 20 kilometers (12.4 miles) into the air, according to RNZ. Satellite imagery showed a massive ash cloud and shockwaves spreading from the eruption. Ash was falling from the sky in the Tonga capital, Nuku'alofa, Saturday evening and phone connections were down.
The eruption caused a severe tsunami on Tongatapu, where the capital is located, with waves flowing onto coastal roads and flooding properties on Saturday.
So far, New Zealand authorities have not received any reports of deaths or injuries in Tonga related to the eruption, Prime Minister Jacinda Ardern said at a news conference on Sunday.📷 Expert explains what's happening in 'jaw-dropping' eruption video 02:12The tsunami had a "significant impact" on Nuku'alofa, with boats and large boulders washed ashore, and shops along the coast damaged, she added.
RNZ reported that residents fled for higher ground as waves swept the waterfront, main street and grounds of Tonga's Royal Palace. Though it was early evening, videos show the sky already dark from the ash cloud.
Tonga's King Tupou VI was evacuated from the palace, RNZ said, citing local media reports of a convoy of police and troops rushing the monarch to a villa at Mata Ki Eua.
Telecommunications were affected, though it's not clear how widespread the damage is yet, Ardern said, adding that the main undersea cable has been impacted likely due to loss of power.
The New Zealand government has committed an initial $340,000 in relief supplies, technical support, and supporting local responses, with the country's Defence Force sending assistance to Tonga, Ardern said.
She added that while conditions in the area seem stable, further eruption activity cannot be ruled out.
Impact in Japan The eruption also had effects across the Pacific, as tsunami warnings and advisories were issued from parts of New Zealand and Japan to the United States and Canada's British Columbia.
Per the National Weather Service, a tsunami warning means those nearby should get inland or seek higher ground immediately, while an advisory means they should stay away from the shore and out of the water.
Japan's Meteorological Agency issued a tsunami advisory for the country's coastal areas early Sunday morning, with the northeastern prefecture of Iwate seeing waves as high as 2.7 meters (9 feet). Multiple smaller tsunamis were reported in numerous other locations, according to public broadcaster NHK.
By Sunday afternoon, all tsunami advisories had been lifted, the meteorological agency said. Weather agency officials ruled out the possibility of further tsunamis across the country, but said there might be some tidal fluctuations.
Japan's coast guard was out assessing damage, but so far none had been reported, NHK said, noting it was still dark and more waves were expected. Officials continued to ask people to stay alert and away from beaches.
Footage shared on NHK from a viewer in Setouchi town, on Amami Oshima Island, showed bumper-to-bumper traffic as cars evacuated to higher ground. Other footage showed people sleeping on floors in evacuation centers in Iwate.📷A tsunami has hit Tonga's largest island, Tongatapu.
Elsewhere, Australia's Bureau of Meteorology said it recorded a tsunami wave of 1.2 meters (about 4 feet) near Nuku'alofa at 5:30 p.m. local time on Saturday. And the Pacific Tsunami Warning Center said tsunami waves of 2.7 feet (0.8 meters) were observed by gauges at Nuku'alofa and waves of 2 feet at Pago Pago, the capital of American Samoa, Reuters reported.
The nearby island of Fiji also issued a public advisory asking people living in low-lying coastal areas to "move to safety in anticipation of the strong currents and dangerous waves." Footage from the ground shows people fleeing to higher ground in Suva, the capital of Fiji, as large waves hit the coast.
In Samoa, another Pacific island nation, a tsunami watch is in effect for all low-lying coastal areas, the Samoa Meteorological Service said, with residents and visitors advised to stay away from beach areas.
An earlier tsunami advisory for the Pacific island nation of Vanuatu was discontinued, with the country's National Disaster Management issuing an "all clear." The office had earlier advised residents to move away from the coastline and seek higher ground.📷📷📷📷📷📷📷📷📷📷📷📷Isla Hunga-Tonga-Hunga-Ha'apaiTongatapu Island📷📷📷📷📷📷Keyboard shortcuts
Map data ©202220 km / Terms of Use
Waves seen in the US The eruption also sent waves to the US West Coast, with some exceeding 3 and 4 feet in height, according to the National Weather Service office in San Diego.
The highest waves recorded were in Port San Luis, California (4.3 feet); King Cove, Alaska (3.3 feet); Area Cove, California (3.7 feet); Crescent City, California (3.7 feet); and Port Reyes, California (2.9 feet).The first tsunami waves were felt on the West Coast early Saturday morning, according to Dave Snider, the tsunami warning coordinator at the National Weather Service's National Tsunami Warning Center in Palmer, Alaska.A wave as high as 1.2 feet had been observed in Nikolski, Alaska, he told CNN via telephone, while waves as tall as 1 foot were observed in Atka, Adak and King Cove, Alaska.
"This may not be the largest wave as this is coming in yet," Snider told CNN, saying the event was not over.📷Ash rises into the air after a powerful underwater volcanic eruption in the South Pacific.
The initial coastal tsunami advisory included the states of California, Oregon, Washington and Alaska, according to the National Tsunami Warning Center. All of the advisories had been lifted by early Sunday morning, according the Tsunami Warning Center.The Pacific Tsunami Warning tweeted no damage was reported thus far from the tsunami observed in the Hawaiian Islands. A tsunami advisory for Hawaii was canceled by the agency Saturday morning.
Adam Weintraub, a spokesperson for the Hawaii Emergency Management Agency, told CNN there were "no reports of major damage so far," though the effects had been felt across multiple islands. Officials were still assessing the damage.
The impacts were the equivalent of a "high King Tide," Weintraub said earlier, telling CNN there had been flooding in parking lots and harbor areas he characterized as "nuisance flooding."
Speaking by telephone, Snider said, "We don't have a really good forecast because this event is based on a volcano rather than an earthquake."
Nonetheless, the National Weather Service in Seattle urged caution along the US Pacific Coast on Saturday. "Move off the beach and out of harbors and marinas in these areas," NWS Seattle tweeted.
The city of Laguna Beach, California, closed all beaches, boardwalks, harbors and piers until further notice in response to the tsunami advisory early Saturday morning, telling residents, "please stay out of the water and away from the shore.
"Santa Cruz, California, also experienced some "minor flooding" at the harbor, city manager Elizabeth Smith told CNN.📷High tide comes into a harbor in Santa Cruz, California, seen in this still image from a video obtained by CNN. The water quickly drained out, Brad Anderson -- the person that provided the video -- said.The waves came right at high tide, Fire Chief Rob Young said. The initial wave occurred at approximately 7:40 a.m. local time, he said, bringing with it a 1 to 2-foot wave right at the peak of high tide. The largest wave came in at about 8:49 a.m. local time, prompting a surge of about 7 feet at the harbor. A subsequent surge just after 10 a.m. was "diminished."
"When it comes, it comes quickly," he said. "Not just a 1-foot wave, but it comes in a surge because it draws all the water out first, and then it comes in."
There was some damage in the harbor and to some docks, he said. There was also "light flooding" on the beaches and up to the city's first surface street, Young said.
All beaches and the harbor will be closed until at least noon local time, Smith said, and people were evacuated from nearby stores and the area near the harbor, though no one has been evacuated from their homes. A surf contest has been postponed and is expected to resume later Saturday.
New Zealand on alert A tsunami advisory was also issued for coastal areas on the north and east coast of New Zealand's North Island and the Chatham Islands, where "strong and unusual currents and unpredictable surges at the shore" were expected, according to New Zealand's National Emergency Management Agency.
New Zealand's official weather service said its weather stations across the country had observed "a pressure surge" on Saturday evening from the eruption.📷A satellite image taken by Himawari-8, a Japanese weather satellite, and released by the agency, shows an undersea volcano eruption at the Pacific nation of Tonga Saturday, January 15, 2022.Scientist Emily Lane, of New Zealand's National Institute of Water and Atmospheric Research, told the New Zealand Science Media Centre it was a "very significant" eruption.
"The shock wave from it is clearly visible in satellite imagery and there are reports of the eruption being heard at least as far away as New Zealand," she said. "The tsunami from the eruption has reached over 2,500 kilometers being recorded on gauges over all of Aotearoa.
"Tsunamis generated by volcanoes are much less common than tsunamis from underwater earthquakes, Lane said.
A smaller eruption in late 2014 and early 2015 built up the crater of the volcano to above the surface of the water, Lane added, but it's not yet clear exactly how Hunga-Tonga-Hunga-Ha'apai erupted on this occasion. "When we see what is left of the island after this eruption is over we can start to put together the pieces of what happened," she said.
Professor Shane Cronin, from the School of Environment at the University of Auckland, told the New Zealand Science Media Centre research into historical eruptions by the same volcano suggested the current eruption episode could last for weeks or months "and further similar-sized eruptions to the 15 January 2022 event are possible."
"The eruption is likely to result in significant ash fall (up to 10 centimeters) in Tongatapu as well as the Ha'apai group of islands," he said. "Help will be needed to restore drinking water supplies. People of Tonga must also remain vigilant for further eruptions and especially tsunami with short notice and should avoid low-lying areas."
An earlier tsunami warning issued for American Samoa has since been canceled, according to the NWS Pacific Tsunami Warning Center.
There is no tsunami threat to Guam and the Commonwealth of the Northern Mariana Islands from a "distant eruption," according to the Pacific Tsunami Warning Center.
The volcano had been active from December 20, but was declared dormant on January 11, according to RNZ.CNN's Dave Alsup, Jennifer Hauser, Junko Ogura, Emiko Jozuka and Haley Brink contributed to this report."
SOURCE LINK: Tsunami advisories lifted in US after waves hit Tonga following volcanic eruption
https://www.cnn.com/2022/01/15/asia/tsunami-warning-tonga-volcano-intl-hnk/index.html
Of the two choices, i.e., (1) condensation of water in the atmosphere; and (2) refraction or diffraction of light, it seems more likely that the satellite imaging of the Tonga shock wave, which was a distinctive feature of the undersea volcanic eruption evident in infrared and visual satellite imagery, was due to (2) refraction or diffraction of light. The reason for my answer to this ResearchGate discussion thread question stems from a somewhat analogous scenario in the manner by which shock waves may be seen to power an exploding star:
https://asd.gsfc.nasa.gov/blueshift/index.php/2017/09/05/shock-waves-power-an-exploding-star/
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Shock Waves Power an Exploding Star
- By Raleigh McElvery
- September 5, 2017
- Comments Off on Shock Waves Power an Exploding Star
Roughly 50 times each year, a star nearing the end of its life accretes too much material from a close companion star and erupts in a violent display of light — shedding its outer surface and propelling shock waves into our galaxy — only to recover and smolder as it did before. This event is called a ‘nova.’
This ability to “reprocess” sets novae apart from their rare supernovae counterparts, which occur only several times per century and self-destruct amid an even greater celestial outburst. And yet, it’s the more common novae that could hold the answers to essential questions regarding our universe.
📷
As this nova illustration shows, when a white dwarf accretes too much material from its companion star, it ejects material in two district winds. Shock waves are created as the two winds collide, producing gamma rays (magenta). Research now suggests this may be the primary source of visible light as well. Credit: NASA’s Goddard Space Flight Center/S. Wiessinger
Given that these events usually occur thousands of light years away, I went to discuss their significance with two more accessible sources: Laura Chomiuk and Kwan Lok Li of Michigan State University. Both scientists recently allied with Columbia University and the ASAS-SN project (of which Chomiuk is a key member) in hopes of untangling the fundamental processes underlying the lifecycle of stars.
They have turned their attention to one classical nova in particular, ASASSN-16ma, located within the “archer” constellation Sagittarius. Their paper, recently published in Nature Astronomy, suggests a novel source for the nova’s post-outburst glow — offering insight into other outer-space explosions.
The authors explained that ASASSN-16ma is among the brightest novae ever detected by the Fermi Large Area Telescope — a satellite instrument built to observe cosmic events releasing a high-energy form of light called gamma rays. The Fermi Mission, spearheaded by NASA’s Goddard Space Flight Center, also discovered back in 2010 that novae generate these high-energy rays.
Gamma rays are emitted as material is ejected from the star in two distinct winds or “outflows.” A slow burst is followed by a faster one, which then crashes into the first and creates a shock wave. Visible light also radiates from the same explosion, although until now most scientists believed it stemmed from nuclear reactions on the surface of the star.
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This animation shows the first nova outburst, from a white dwarf called V407 Cygni, detected by Fermi’s Large Area Telescope (LAT) back in 2010. Gamma rays (magenta) arise when accelerated particles in the explosion’s shock wave crash into the red giant’s stellar wind. Credit: NASA/Conceptual Image Lab/Goddard Space Flight Center
But something wasn’t right about the traditional explanation. Novae shouldn’t have enough power to produce gamma rays — nor release as much visible light as they do given their calculated luminosity limit.
This inherent contradiction confounded astrophysicists and theorists alike, until last year when Chomiuk requested that Fermi focus on ASASSN-16ma for an extended duration to collect more sensitive data. As luck would have it, Fermi was already observing another nova in the same neighborhood, so Goddard’s team was more than happy to oblige, tilting their telescope slightly. When scientists began to sift through the data transmitted from the cosmos to Earth, one specific trend became abundantly clear.
“Our results were telling us our previous assumption that all the luminosity comes from the surface of the star was flawed,” Chomiuk explained to me from her office in East Lansing. “A lot of it actually comes from the same place as the gamma rays,” she continued. That is, the colliding shock waves.
Seeking an outsider’s perspective, I made my way to the second floor of Goddard’s astrophysics building to chat with one of the center’s Fermi aficionados, David Thompson. Eager to lend guidance, Thompson presented his miniature replica of the spacecraft, and indicated the boxy Large Area Telescope seated atop the winged satellite. “We’ve been seeing similar novae for years, but this was unexpected,” he said. “The authors have enough detail in their data to challenge the conventional wisdom about what makes novae bright.”
But I soon learned these ideas weren’t entirely unprecedented. During every interview I conducted, one name kept coming up: collaborator and lead theorist, Brian Metzger of Columbia University. Metzger had been crunching the numbers on novae for several years, but lacked substantive data to bolster his hypotheses. That is, until now.
“Novae have been observed by the naked eye since well before the modern era,” Metzger told me, “and yet our view of what is producing these bright outbursts continues to change.”
📷
The Fermi LAT 60-month image, constructed from front-converting gamma rays with energies greater than 1 GeV. The most prominent feature is the bright band of diffuse glow along the map’s center, which marks the central plane of our Milky Way galaxy. Image credit: NASA/DOE/Fermi LAT Collaboration
Fermi’s Deputy Project Scientist, Elizabeth Hays, said Metzger’s paradigm had already garnered some buzz throughout the scientific community, although at the time the universe had yet to reveal an event that clearly reflected his calculations. Now, thanks to ASASSN-16ma, she affirmed his conjectures may expose what powers these nova outbursts — processes which might also extend to other kinds of stellar explosions, like dazzling supernovae as well as star mergers.
“We’ve been ignoring this whole piece of the puzzle,” she said. “When we come across high-energy processes like these novae, it becomes clear just how much more work we have left to do.”
Understanding novae shock and gamma ray production could also explain certain properties of accelerating particles traveling close to the speed of light, as well as the subsequent magnetic fields.
When I asked Li what was next, he said he plans to continue using Fermi data to monitor nearby novae. Ultimately, he hopes to pinpoint similarly strong correlations between gamma ray and visible light emissions within additional novae. “We’re always looking for new sources to test our model, and ensure it truly and accurately describes gamma-ray phenomena in classical novae,” he added.
Back at Goddard, Thompson repositioned his Fermi model on the shelf among his books, and agreed a single example alone does not constitute proof. But it’s certainly a good place to start. “These results prompt us to think about things in a new way,” he said, “and that’s what science is about.”
SOURCE LINK: https://asd.gsfc.nasa.gov/blueshift/index.php/2017/09/05/shock-waves-power-an-exploding-star/
Prof. Janusz Pudykiewicz
Thank you for pointing out the Nature paper, now I understand that the cloud condensation occurs only for a very short time (picture 1a - 1c) of Nature paper.
I thought it propagates with the shock wave thousand of Kms away, but it is more as a first-order transition on site due to the explosion.
Best Regards to all.
Dear Professor Pedro L. Contreras E.
Thank you for this comment. I would like to add that the shock wave generated initially by the most powerful volcanic eruption after travelling a certain distance is becoming an acoustic wave:
>>One characteristic of explosive volcanoes is the formation of atmospheric shock waves. These shock waves can travel significant distances from the volcanic vent, as shown by Morrissey and Chouet [1997], carrying important information about the dynamics of the eruption. When energy is suddenly released into the atmosphere, a sound wave is generated. If the energy released is large enough, such as in some volcanic eruptions, a shock wave is generated instead. A shock wave differs from a sound wave in that it is traveling faster than the speed of sound. As the shock wave propagates, it gradually loses speed until the velocity is equal to the speed of sound, at which point it becomes a sound wave.
Thank you again, Prof. Janusz Pudykiewicz
These volcano shock waves have a lot of interesting physics, new phenomena.
https://scientificrussia.ru/articles/vliyanie-vulkanicheskogo-pepla-na-stoyachuyu-udarnuyu-volnu
Best Regards to all.
https://www.nytimes.com/2022/01/19/climate/scientists-tonga-volcano-eruption-effects.html,kindly check this link.
https://www.rmets.org/metmatters/tongan-eruption-sends-atmospheric-shockwaves-around-world,u can follow this link.
https://www.washingtonpost.com/weather/2022/01/16/hunga-tonga-volcano-tsunami-eruption/,this link may be useful.
https://amp.france24.com/en/live-news/20220117-shock-waves-landslides-may-have-caused-rare-volcano-tsunami-experts,kindly check this link
https://www.sciencedaily.com/releases/2014/06/140630164508.htm,this link may be useful.
http://gamma.cs.unc.edu/SHOCK/sewall-sca08.pdf,also this link may be useful.
Thank you to all that have contributed to my discussion. To summarize the discussion:
(1) The supposed shock wave was most likely (or turned into) a pressure wave as it moved away from the eruption site
(2) Acoustic waves can cause atmospheric condensation
(3) Shock waves from Nova create refraction/diffraction of light.
I would like to postulate an alternative answer: the pressure wave compressed then decompressed the atmosphere (see attached atmospheric pressure from Shorncliffe on the east coast of Australia) as it travelled from the eruption site, could this change in density of the atmosphere have caused refraction/diffraction of light?
I Have also attached a plot of the atmospheric pressure at nuku'alofa tonga, about 65 km from the eruption site. This plot shows a sudden fall in pressure of around 20 hPa followed by a sudden rise of around 25 hPa, (opposite to the Shorncliffe pressure steps) the question is: could the nuku'alofa pressure change be an initial shock wave that Prof Janusz-Pudykiewicz has mentioned and the Shorncliffe pressure change a pressure wave?
Also note that the Pressure wave speed to Shorncliffe is around 1044 km/hr (< Mach 1). I am yet to determine the wave speed to Nuku alofa as the actual explosion time is unclear/inaccurate.
Daryl Metters
Dear Daryl Metters and Readers,
The suggested role of the shock wave in creation of the refraction/diffraction of light is definitely plausible. Furthermore, shadowgraph methods are commonly used for the study of various shock waves, as we can see in the images available at:
https://en.wikipedia.org/wiki/Shadowgraph
The shadowgraphs available for this volcanic eruption are difficult to interpret exactly because they show a combined effect of condensation, changes of air density, and corresponding changes of the concentration of aerosol particles affected by the shockwave.
https://www.rmets.org/metmatters/tongan-eruption-sends-atmospheric-shockwaves-around-world
https://www.researchsquare.com/article/rs-1513574/v1
What excited tsunami from Tonga 2022 eruption? Observation and theory
Y Nishikawa, MY Yamamoto, K Nakajima, I Hamama… - 2022
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