Did the Miyako earthquake affect Medium Wave broadcast reception on 9 November 2025?

Added: 2026-05-10

[00:00:01]All right. Next up, we have what I believe is a hybrid talk. And this is going to be from Satoshi Miyachi, JP1SCQ of Japan, and Nick Hall-Patch, VE7DXR from Canada. And so, let's see, who is here in person?

[00:00:23]It's all virtual. Okay.

[00:00:26]They got delayed in the airlines. So, if our AV people can help us switch over to a virtual configuration.

[00:00:33]Okay. So, let's start from here. Okay.

[00:00:37]So, I'm Satoshi Miyachi, JP1SCQ, radio amateur in JA, and I'm active on mostly on HF band, and I'm very happy to be here today. Thank you.

[00:00:47]>> [snorts] >> There was a very unusual medium wave signal attenuation observed on the day of 9th November 2025.

[00:00:58]Then, we received signals disappeared about 30 minutes. So, this is a report for the particular event happened on that day.

[00:01:08]All right. I [laughter] think Sorry.

[00:01:12]All right. So, you're seeing the next screen.

[00:01:16]Correct?

[00:01:18]So, um a little bit about the DX Edition that we had. It's It's It's in the Tohoku region. It's about 500 km northeast of Tokyo, 39 north, 141 east. And it's the place facing to the Pacific Ocean, then offers very, very nice view around the area.

[00:01:40]Um I changed the screen to the third page.

[00:01:44]Um although that many of us licensed radio amateurs, but this DX Edition was received only.

[00:01:52]And we used the SDR receivers such as Perseus Airspy HF Discoveries.

[00:01:59]Then, captured a whole medium wave whole spectrum onto our PC.

[00:02:08]The antenna looks like that this. We named it um We name it that the TDDF or the twisted double decker delta loop delta flag antenna. Um some of you may be more familiar with the receiving antenna D-Cat.

[00:02:26]And the base length of one triangle is 20 m. And it's It's like a two triangles put together. So, the total length base length is about 40 m or 130 ft long.

[00:02:40]The height is about 5 m, and direction Oh, sorry. I mean, the This is an antenna that low noise amplifier is a must.

[00:02:51]Then, this antenna is directed to northeast for target signals from North America.

[00:02:59]Right. I changed to the next one.

[00:03:03]Here are some of the the exciting catches from this location in 2018 2018 that we heard station from South America. Argentina and Uruguay, and 2021 was another exciting year that we we could hear the East Coast of the United States, WBC Boston, on 1030.

[00:03:24]And from the Pacific West Coast, KFBK 1530 is always very strong here. And it's like a local station, and it's very nice to hear the traffic report of Sacramento every 10 minutes.

[00:03:40]Okay. So, I'm starting from here, the analysis of the SDR files using the WebSDR Playback software.

[00:03:50]The vertical axis represent the time, and the horizontal axis show frequency.

[00:03:55]So, the left starting from 530 kHz to the uh 1 1700 kHz to the right-hand side.

[00:04:05]On this slide, the left one shows the 10 kHz spacing. That means that these are the signals from North America on that day. And the green portions means the signals are coming. Then, right-hand side of the screen is the showing the signals from Japan and around North China.

[00:04:28]Then, this one When I saw this 9 kHz imported WebSDR file, I was very surprised because um unusual attenuation, those black bars suddenly appear on the 7:15 UTC.

[00:04:45]So, those well-received signals disappeared nearly 30 minutes until 7:45.

[00:04:52]So, the area circled by yellow here, this made us to the project of this project for more analysis.

[00:05:04]Then, as one of the possibilities that we can think of was the something to do with the local sunset, but our quick answer was no.

[00:05:14]That is because that on the previous records of the previous day or previous years, there were no similar attenuation recorded.

[00:05:26]Then, there must be another reason that remembering that evening, there was a very, very strong earthquake happened, magnitude 6.9, and epicenter was only 140 km or 90 miles in the Pacific. Then, we also heard a tsunami alert on that day. So, we even thought at that time that some interesting things might be captured on this these records.

[00:05:56]By anyway, that possible relationship with the earthquake we questioned, but there were reports uh signal strength changes, especially in the very low frequency band, but um related noise before earthquake also.

[00:06:13]But we we heard of we haven't heard of such attenuation on the medium wave band.

[00:06:20]So, then I tried to identify the stations with two groups.

[00:06:26]Uh one is one in the blue is the no visible attenuation.

[00:06:31]And the red group for heavily attenuated things stations.

[00:06:37]Then, I put them onto the map of Japan here.

[00:06:40]Then, it's It's getting clear and that uh group signal the not affected signal stations were north of Japan. And attenuated ones south or southwest of Japan.

[00:07:00]Okay.

[00:07:02]Then, continuing continuing a little bit more analysis, not only the Japanese stations, but uh those stations signals from China, northeast of China.

[00:07:13]Then, identify those station and frequencies and plotted them on the Google Map again.

[00:07:19]Then, so it's like this. So, um that's the moment that I sent the SDR files to Nixon for further analysis. Then, Nixon then conducted various investigations to further analyze the signal strengths and determine the cause. So, now Nixon, I give the microphone to you.

[00:07:41]I will stop sharing right now.

[00:07:44]So, now we we we we we recognized the attenuations occurred before the earthquake itself occurred. But actually, it's pretty difficult to get indications of what was happening in in the landmass of Japan before the earthquake. So, we started by looking at the intensities of the earthquake on the landmass of Japan at the time of the earthquake, and we've got these two maps here comparing the the two of these with with our map. And in certainly, we can see that we had in the north part of Japan, the earthquake was not felt particularly strongly. And that was where we had no attenuations. However, if we look at the south part of Japan into the west, there was attenuations observed, but in the south part, the earthquake was not really felt at all.

[00:08:39]So, before we went much deeper into this, we thought, well, was there some more obvious cause of the signal dropouts that we had missed? And the first uh analysis was that in fact, some of the signals were 25 dB or more uh attenuations occurring quite suddenly.

[00:09:01]And we so we looked a little more carefully at those and realized that those were the signals that were actually further away from Tanohata.

[00:09:10]And so, this updated version of the Google Maps shows this with the yellow pins indicating signals that have been attenuated by 25 dB or more.

[00:09:22]So, we're now going to look at a couple of example signal strengths.

[00:09:26]One from Hiroshima, which is 1,000 km distance from Tanohata, and then also from Niigata, which is only 300 km away. And try and compare the signal intensities. And right now, we can see, okay, this is Hiroshima's signal.

[00:09:46]It dropped under 50 kHz. It dropped very, very deeply and quite suddenly.

[00:09:52]The signal from Niigata, in In although there was observed, it was much gentler and not nearly so deep. We also threw on this purple trace here, and that's indicating no attenuation of ground wave from signal that was only 5 km away. So, it looks as if these were skywave signals.

[00:10:15]All right, we better look again at the sunset terminator. Really, maybe that was more important than the time of the earthquake. And we put the we have put the sunset terminator on here, and you can see as as indicated before, the the lack of attenuation night time side daytime side is where the Indian attenuation served.

[00:10:38]Um, and so and then the more deeply what affected signals were further away from the daytime side.

[00:10:45]So, um, why would your distant signals on the daytime side of the terminator be attenuated more?

[00:10:51]What event would affect propagation signals at medium frequency in season from daytime side, but not the night time side?

[00:10:59]And thought, well, maybe a solar flare.

[00:11:02]And in fact, when we looked, there had been a 1.7 X1.7 solar flare observed by Japan's National Institute of Information and Communication, as well as by NOAA.

[00:11:13]And so, they actually did a report and CIT started by observing that there were a number of solar flares, but this one is the one we're interested in, 07:35 UTC.

[00:11:25]And uh the report stated that the the honestly, it's what it looked at was um some traces I I honest on traces from um from Okinawa, and at 07:10, we have here traces uh below 5 MHz is showing a nice trace from the E region. By 07:35, those traces had disappeared. Really, nothing much below 5 MHz. And the you can see the disappearance of this ionospheric echo.

[00:11:59]The report referred to this as a delegate phenomenon observed in Okinawa.

[00:12:04]It's better known in America as a radio blackout.

[00:12:07]Now, when when Griffith pointed out that we should look at the D region absorption product model provided by SWPC.

[00:12:16]The increased absorption in the D region due to solar X-rays and solar particles and the effect on radio propagation effect uh the rapidly increasing effect of the solar flares is seen in the heat map displayed in this video.

[00:12:32]We get to go.

[00:12:34]We can't.

[00:12:37]It's unfortunate.

[00:12:39]Oh.

[00:12:40]Not much time, so we better proceed on.

[00:12:43]Um, if we look at the detail, look back here, we can see the detail uh you know, that there is attenuation and definitely the D region is being affected quite a lot around Japan. So, we'll look a little more carefully. We compare on the left-hand side here is the 8th of November when there was no solar flare, and you can see that the heat map is showing very little absorption in the D region.

[00:13:12]On the other hand, on the 9th of November, there is a heck of a lot of absorption being indicated by the heat map.

[00:13:21]So, our sort of simulation of medium wave skywave propagation assumes that such signals are heavily absorbed during the daytime because of the solar illumination causing D region to absorb any signals from the daytime side, but in fact, as sunset approaches, the the D region begins to lose its absorptive capabilities because of the lower solar illumination. And so, we have a rough illumination rough illustration here of the D region somewhat artistic liberties taken, uh but the the the traces the ray traces from Hiroshima and Niigata to Tanohata are in in fact from the pro program, and you can see that there is would be some absorption of the upward going ray trace from Hiroshima on a normal day, and so it would be received in Tanohata, and Niigata there would be very little absorption at all.

[00:14:25]But in the next slide, we're going to observe observe that the D region is in fact much intensified, and so the signal from Hiroshima is being absorbed on the way up and being absorbed on the way down, and even the signals from Niigata are being absorbed somewhat here on the 9th of November. So, we then took the signal from signal trace from Hiroshima with its deep attenuation, and we overlaid it with the uh this blue blue trace here, which is the X-ray flux during the course of the solar solar flare, and you can see it maps very very nicely as as the X-ray flux increases, the signal from Hiroshima drops at 30 dB in 5 minutes.

[00:15:23]So, in conclusion, we definitely the the the DXers definitely absorbed temporarily attenuated signal broadcast signals, and during their DX session shortly afterwards, there was this earthquake, which really caused them to take a deeper look at what was taking place in signals.

[00:15:44]Um, however, even though the earthquake was obvious physical manifestation, uh it didn't seem to line up very well, and so we looked and found the X-ray flux and from the solar flare seems to have been much more likely to be the cause of the attenuation.

[00:16:06]So, thank you very much from both of us.

[00:16:10]It's a great fun figuring this out, and our final slide, we give you some YouTube shorts of what happened during the expedition, and also we have the something from the DXer circle in Japan, and they are they they were the ones who provided this particular all all the data from this one. So, thank you again.

[00:16:38]Thank you.

[00:16:39]>> [applause] >> Thank you so much, Satoshi. Thank you, Nick. That was a wonderful presentation, and I I thought it showed very nicely how a careful analysis is really important, and sometimes the thing that's drawing the most attention to us is not the thing that you really need to be paying attention to, at least in terms of this radio data.

[00:17:01]So, as our next speaker is coming up, we will take some additional questions, and I can ask the AV techs to reconfigure for an in-person presentation.

[00:17:12]Any questions for Satoshi and Nick Hall Patch?

[00:17:21]All right. Thank you so much. I really appreciate that wonderful presentation.