TWO MINUTES OF WONDER:

A LOOK AT NATURAL VLF RADIO EVENTS OF SEPTEMBER 26, 1993 - 1104 TO 1106 UTC

by Stephen P. McGreevy


After submitting the text of my article to Donald and also finishing Christmas cleanup, I now had more time to pursue other natural radio projects, such as getting more WR-3 and WR-3E whistler receivers shipped to customers. While working on these whistler receiver's, I usually enjoy playing many of my natural radio recordings made from all of my expeditions and camping trips over the past 5 years. I also enjoy listening to recordings made by other natural radio enthusiasts.

It turns out that the morning of Sunday, September 26, 1993 was a very notable day in natural radio listening as well as for me personally. In the late afternoon of September 25, and still rather excited at being in the Canadian Prairies, as well as having seen our first auroral display the night before, Gail and I were listening to CBK 540 from Watrous, Saskatchewan, a CBC powerhouse that was now playing a wonderful mix of ethnic instrumental music. We felt as though we were in the middle east or the great African steppes as we headed westward on Provincial Highway 51 west of Kerrobert, Saskatchewan.

About half an hour before sunset, we reached Alberta, and stopped briefly to snap a photograph of us standing next to the "Entering Alberta, Wild Rose Country" sign.

Photo of Gail West and myself in front of Alberta sign

Whew!, we had crossed into yet another huge and awesome province. Remembering that the next morning was "VLF Sunday" - a date arranged in advance by Michael Mideke to record natural VLF radio at a few pre-arranged times, we started looking for a back road off of what was now Alberta Provincial Highway 12. We were in a sparsely populated and rather hilly area near Kirriemuir and Monitor, AB, and hoped we could find a location to spend the night which was away from electric power-lines by at least a mile. As we drove down the highway, we tossed our heads left and right, spying a few interesting looking dirt and gravel roads on both sides of the main highway.

Braking to a halt on the empty highway, we did yet another of our multiple point turns in the van and headed back the other way. The first gravel road we chose ended up looking a bit too well-travelled and also not far enough from AC power-lines. The second choice couldn't have been better - a lightly rutted dirt (and mud) track into some low hills and trees next to an arroyo. The road terminated at what appeared to be ranch homestead with only a trailer and fallen-down windmill atop one of the small hills. A quick check with my WR-3 confirmed this level hill-top location was great for natural radio listening, being quite some distance from electric wires. With some trepidation - since we didn't like the idea of trespassing - we walked up to the trailer prepared to ask permission to park nearby. But, nobody was home and the place looked like it had been unoccupied for at least a week, so we elected to stay and set up the WR-4B VLF receiver's antenna mast then ate dinner while watching the perfectly clear sky turn colors as night approached. It felt like it was going to be a cold night, though the very dry air would make the cold bite less, and I hoped the aurora would return.

Mike Mideke was also preparing himself to tape natural radio on the following morning of September 26. Probably at the time Gail and I found the unoccupied trailer site, Mike was preparing his equipment for the short trip to Hannigan Pass near Mt. Baker. He had been up in Bellingham on family business and so was prepared to listen up in Washington state. His wife, Elea, was back home at their ranch homesite near San Simeon on California's Central Coast. Wisely, Mike left instructions for Elea to also record the whistler band at the appointed times, set for 1100 and 1200 UTC (4 a.m. and 5 a.m. PDT).

Back up in Alberta, Gail and I went to bed. At about 3 a.m. MDT, I awoke and looked out the van's rear doors, and was startled then joyous to see the northern sky filled with a green glow. Looking closer, I also spied faint bursts of green "splotches" moving ("squirting") in a left-to-right (west-to-east) direction! Wow, it was much better than the night before! Apparently, a minor magnetic storm was happening, though I really wasn't alerted to it since the geo-magnetic "indices" put out on shortwave time and frequency standard station WWV from Colorado was reporting only "unsettled" magnetic conditions. I quickly awoke Gail, who had missed out on seeing the fainter aurora the night before. The next thing I did was turn on the WR-4B whistler receiver and start up the tape recorder. I was instantly rewarded by a faint squawking sound of "chorus" as well as weird tones slowly rising then falling. When these weird "sliding tones" would appear, the aurora would slightly brighten and the "squirting green splotches" also seemed to speed up!

By this time, it was at or below freezing, and frost was rapidly building up on the outside of the van's windows though the air inside the van had been considerably warmer--at least until I threw open the back doors and began watching the auroral show while still tucked tightly in my sleeping bag. Gail borrowed the whistler receiver's headphones and listened to the weird VLF radio sounds coming forth, but sleepiness overcame her again and she dozed off. As the initial excitement wore off, I also felt very sleepy again and decided to doze for a while with the tape recorded still running--I at least wouldn't miss out on the great VLF radio sounds.

As the 1100 UTC period approached, I flipped the cassette over and prepared to tape the auroral radio chorus, which by this time was become quite vigorous. Alas, I waited until about 1104 UTC/5:04 a.m. Central Daylight Time to begin the taping, thinking the appointed monitoring time was to begin at 1105 UTC, when actually it began at 1100. I rolled the tape and taped an entire side of a C-90 (45 minutes) of the fantastic Alberta auroral chorus.

Back near Bellingham, WA, Mike also started his DAT recorder at 1100 UTC, taping the auroral chorus (which was almost as loud there as up in Alberta). Back at the Mideke's ranch homestead in California's Central Coast, Elea also began recording her tape. Because both Mike and Elea were taping for the coordinated monitoring session, they both stopped taping shortly after the appointed 1106 UTC stop-tape time, while I - enjoying the visual aurora as well its radio chorus emissions - kept the tape rolling for the next 45 minutes, falling asleep yet again. While I dozed, Gail awoke to find part of the aurora turning into various shades of red. She apparently woke me to tell me of it but, unfortunately, I drifted back asleep and missed seeing it as I was rather sleepy.

At around 1205 UTC (another time period to record), I rolled tape but found things had died down considerably. Farther south and west near Bellingham, Mike taped still more chorus and sliding tones plus an occasional whistler. Elea also did the same, catching the same weak whistlers and a very weak chorus. Up in Alberta as dawn approached, I found "dead band" conditions--nothing--no chorus or whistlers.

The three tapes made my Mike, Elea, and myself of the Sept. 26 chorus and whistlers would eventually form the basis of a fascinating simultaneous playback "stereo" natural radio tape which I would not produce until January 1995. What it revealed would be very fascinating sounding to me and the first diversity/stereo VLF recording I would hear.

Painstakenly synchronizing the two minutes of overlapping tape segments (1104 to 1106 UTC - I wish it were longer), I played them back into another stereo recorder making sure that the tapes stayed within 200 milliseconds of each other--and sometimes they were exactly on! This required dexterous tweeking of the "pitch" control on my Marantz tape recorder which was playing back Mike's and Elea's tape segments - my Alberta recording was in the other playback deck. An interesting VLF natural radio scenario becomes apparent:

September 26, 1993 - 1104 to 1106 UTC. "Whooping/squawking" chorus of medium strength but light density was being heard in Alberta, along with the strange sliding tones. They are also apparent on Mike's Washington tape, though weaker--especially the sliding tones--by several dB. In Washington, the lightning static and tweeks are slightly louder, but down in California, they are VERY loud. Interestingly, at around 1105 UTC a fast and fairly pure whistler happens, clearly audible both on Mike's Washington state tape and also on Elea's San Simeon, California recording, but NOT AT ALL heard in the Alberta tape, a rather interesting example of a strictly "West Coast whistler." The ongoing whoops and squawks of the auroral chorus so strong in Alberta and a tad less so in north-western Washington are also audible in California between the fierce static, but in California there also with several weak whistlers that are not heard in Washington or Alberta.

Directly comparing the Alberta and California tapes by playing them in synchronization is really quite fascinating. Repeating some commentary just offered above, California is experiencing fierce static, much of which is also heard in Alberta. But there are many bursts of moderate static in CA that are very weak in Alberta. The whoops, squawks of chorus and also strange sliding-tones dominate the Alberta tape segment, but some of those low-pitched squawks are simultaneously heard (but considerably weaker) in the California tape. California has quite a bit of weak whistlers, and the auroral- generated sliding-tones are very faint (or nil) under the big tweeks. Some of the tweeking lightning sferics are the same strength in Alberta as at San Simeon 1000 miles south in California.

It seems likely that the weak and fairly pure-tone whistlers heard in California were happening from lightning to the south or east of California, and these whistlers did not make it to Alberta, which was enjoying the VLF radio sounds of the auroral emissions. All of this makes for a truly fascinating "3-dimensional" stereo look (and now FEEL) for what the natural VLF radio band was doing over western North America for those two minutes on the morning of Sunday, September 26, 1993.

In the future, I would like to digitally synchronize to within 1 mS or less these tapes. Truly, hearing is understanding--it is fascinating enough to independently listen to natural radio tapes recorded from different locations at the exact same time, but to combine them into a "stereo holographic audio image" tells so much more!

Stephen P. McGreevy, January 1995


The audio recording of the "Alberta Auroral Chorus" can be heard at

http://www-pw.physics.uiowa.edu/mcgreevy/

(McGreevy Ground-based VLF recordings)

And also on the Irdial-Discs "Electric Enigma" CD, info at:

http://www.ibmpcug.co.uk/~irdial/vlf.htm

(Electric Enigma: The VLF recordings of Stephen P. McGreevy)

Special Thanks to Larry Granroth at the Univ. of Iowa Physics and Astronomy Department, and also to the Irdial-Discs webmasters.


1996 Solar-Minimum VLF Recording Expedition to Manitoba, Canada and Nevada, USA: Detailed report of VLF events between August 22 and September 23, 1996. Contains sound files, photographs, and the text body of the report.


Steve McGreevy
Contact Information


BACK TO THE NATURAL RADIO HOME PAGE AND OTHER LINKS