More MHz Auroral E
By Emil Pocock, W3EP RR 3 Box 70 (Rte 207) Lebanon, CT 06249
Since the announcement in December 1989 OST of the first-ever reported incidence of widespread auroral-E propagation on 144 MHz, which occurred earlier in the year on March 13-14, a second notable 144-MHz auroral-E event has been reported. This session took place during the early hours of August 15, 1989, along the Canadian-US border west of the Great Lakes. At least 25 contacts were known to have been made between 0615 and 0725 UTC, although one station reported a 144-MHz auroral-E contact as late as 0810. The number and extent of amateur contacts may have been limited by the time (0800 UTC was 2:00 AM local in the Central time zone) and the relative lack of 144-MHz stations in the western parts of the US and Canada.
The paths of all known contacts are plotted in Fig 1. The average distance spanned was about 1900 km, nearly the same as the longest contacts reported during the March event. The longest reported contact was made between WB7UZO (CN78) and VE3KNI (EN38) at about 2300 km; the shortest reported contact was about 1450 km, made by WB7UZO and VE5LY (D070). Signals were exceedingly strong (up to 60 dB over S9), clear, and free of Doppler effects, consistent with E-layer reflections near the maximum usable frequency (MUF). The approximate midpoints of all 25 known contacts (shown in Fig 2) lay within a discrete area, further suggesting that a very small region of enhanced E-layer ionization was responsible for the unusual propagation.
Associated ionospheric conditions were similar to those reported during the March event. A geomagnetic storm was in progress. The geomagnetic A index was 61 on August 15 (up from 54 the day before), while the K index reached 6 at 0000 UTC August 15 and held at that level until at least 0900. Aurora propagation was widely reported across the northern third of the country on the 50- and 144-MHz bands during the August 15-16 period. Auroral-E propagation on 50 MHz was widespread for more than an hour prior to 0615 and continued for at least an hour after evidence of auroralE on 144 MHz disappeared. Apparent double-hop 50-MHz auroral-E contacts were reported from the Pacific Northwest to the Canadian maritime provinces, New England, and the South. The aurora was visible across the northern tier of the United States.
Conclusions
Although this geomagnetic storm and associated aurora did not reach the magnitude of the March 1989 event, the two periods of auroral-E share common characteristics. Both took place during major to severe geomagnetic storms. Path midpoints, and thus the apparent location of unusual E-layer ionization, lay along the US-Canadian border. Strong aurora propagation on 144 MHz and widespread 50-MHz auroral-E conditions preceded the appearance of 144-MHz auroral-E. AuroralE was observed on 144 MHz for relatively short periods of time: 72 minutes during March and 70 minutes in August.
This latest event seems to substantiate earlier
Fig 1—Paths of 25 known 144-MHz auroral-E contacts, Aug 15, 1989, 0615-0725 UTC. The lines may represent more than one contact along the same path. Large dots show the locations of reporting stations.
Fig 2—Midpoints of 144-MHz auroral-E contacts are shown by dots. The shaded area encompasses the midpoints of all 25 contacts and thus indicates the known extent of an E-layer region with an MUF greater than 144 MHz.
May 1990 3
observations about auroral-E propagation. It behaves much like sporadic-E and appears to have a distinct MUF that rises and falls over time. Path distances fell within the E-layer single-hop range, although the 2300-km contact of WB7UZO and VE3KNI stretches that theoretical limit by about 100 km for E-layer reflections at 105 km. This suggests that ionization may have been a bit higher than average. It occurs during great auroras, but a K index of 6 may be sufficient to trigger auroral-E propagation as high as 144 MHz. Path midpoints during the August event (K = 6) were at a more northerly geographic latitude than path midpoints during the March event (K = 9) and at a considerably greater geomagnetic latitude, plotted as magnetic inclination. This is entirely consistent with long-term aurora observations, but suggests that 144-MHz auroral-E may be more common across Canada than previously suspected.
Prospects
Further episodes of 144-MHz auroral-E can be expected during the next two years as we go through the peak of solar cycle 22. Alert stations should monitor both 50 and 144 MHz for conditions that seem to precede 144-MHz auroral-E. Stations north of the Canadian-US border may wish to pay particular attention to this possibility whenever the K index exceeds 5.1 would be most grateful for any further reports of these or future auroral-E episodes. Send reports to Emil Pocock, RR3 Box 70 (Rte 207), Lebanon CT 06249.
Acknowledgements
This report was based on the logs and observation of NF7X, VE3KNI, VE4ABE, VE4AQ, W7FI, and WB7UZO. I appreciate their contribution to this study.
References
Pocock, Emil, "Auroral-E Propagation at 144 MHz," QST,
Dec 1989, pp 28-32. Preliminary Report arid Forecast of Solar Geophysical Data, 22 August 1989, NOAA-USAF Space Environment Services Center, Boulder, CO.
Johnson Space Flight Center to Host 1990 AMSAT Symposium
The 1990 AMSAT Space Symposium will be held at NASA's Johnson Space Center near Houston, Texas, on October 19-21. The Johnson Space Center Amateur Radio Club, W5RRR, will be this year's host.
Registration will open on Friday afternoon at the nearby King's Inn. Tours of the Center wiil be possible on Friday and Monday. The tour will include such areas as Mission Control, the Shuttle Mock-up facility, as well as the "Zero-G" Tank, a massive swimming pool used to train mission specialists for Shuttle Extra Vehicular Activities (rubber rafts are not allowed and space suits are not necessary).
The Symposium will take place on Saturday in the Visitor Center's Main Auditorium. It is sure to be a day packed with talks and presentations on various amateur satellites and related projects. The day will conclude with a Texas-style Bar-B-Que and the AMSAT Banquet.
Mark your calendar and make plans to attend this year's AMSAT Symposium. This is the "Year of the Amateur Satellite" and if you haven't gotten involved in the Amateur Space program, this would be an excellent way to find out what it's really all about. This is sure to be one of the most exciting Symposiums ever.
For more information, contact AMSAT at PO Box 27, Washington, DC 20044.—AMSAT News Service
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