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Smoothed Mean Sunspot Number (Rsm) for July 2000: 123.9

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Sudden Ionospheric Disturbance Report

Sudden Ionospheric Disturbances (SID) Recorded During January 2001

The events listed above meet at least one of the following criteria

Reported in at least two observer reports Visually analyzed with definiteness rating = 5 Reported by overseas observers with high definiteness rating

Solar Events

Once again the past month featured many lower C-Class flares punctuated with a smaller number of large M-Class flares. The most active periods were centered around the 15th and the 20th of January. Of the 191 X-Ray flares registered by the Goes-8 spacecraft, only 10 of them were M-Class and there were in fact no X-Class flares all month. Our observers monitored 8 of these large flares. A total of 45 events were reported for the month. The 15th was a noteable day for it consisted of two very large events, generated from a C9.4 at 1600 UT and a C4.9 at 1845 UT, both relatively small flares. On the 19th there was an M1 flare at 1625 and this resulted in a very long duration event that lasted most of the rest of the day. This was most curious, especially since not only was it a long slow event but it was followed by an abnormally low dip of signal strength afterwards. Unfortunately my signal was cut off by the sunset effect before it could show how the signal might have recovered. What we need here is an observer in Hawaii :) (We have Europe, eastern North America, and even South Africa, but no one farther west than Jerry Winkler in Houston, Texas.)

The 20th was another active day including the strongest flare of the month: an M7.7 that once again was cut off for me by the sunset pattern. The SID event was on a very steep rise when it abruptly stopped and leveled off, followed by a very sharp decline. I was struck by how very dependent the propagation of the signal is to the Ionosphere and how sensitive our receivers are - not just to the flares occurring on the sun, but also to the composition of a vital part of our atmosphere. It is always this sense of being able to measure the environment around me that makes SID monitoring so interesting. I'm sure many of our observers feel the same.

The most active day was on the 24th, a day on which observers monitored many significant events. Interestingly, in a similar manner with which the high flare activity for the month consisted mainly of a lot of smaller flares, all of the flares that day were lesser class flares. The average was only at a level of C4.5. Neverthless they all produced strong signal enhancements easily visible on my daily chart recording. Hopefully most of you check your charts or recorders every day. It is much easier to log the data for one day than for 7 days or worse yet 30 days. The side benefit, of course, is first hand knowledge of the days activity on the sun and in the Ionosphere. Good observing and of course Happy New Year and Happy New Millennium.

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SOLAR BULLETIN of the American Association of Variable Star Observers. Vol. 57, No. 1, January, 2001

Casper H. Hossfield, SID Sup. Editor PO Box 23 New Milford, NY 10959, USA

SUDDEN IONOSPHERIC DISTURBANCES RECORDED DURING January , 2001

capaavso@aol.com Fax 973 853 2588

Art Stokes has redesigned his Gyrator II receiver so it requires fewer parts and is easier to build. The new minimal design and Art's description of its advantages is shown here. Recently Al McWilliams of torsion magnetometer fame built a gyrator II receiver and ran some tests on it. He very loosely coupled the output of a precision function generator to the input of the gyrator II and stepped the frequency up and down 10 Hz and obtained a very well defined curve. At the center frequency (24000 Hz) the DC output was 13 volts. At about 70% of this voltage the frequency width is close to 160 Hz. Therefore the overall "Q" of the gyrator II is calculated to equal 150. I.e., the "bandwidth" is 160 Hz when tuned to 24000 Hz. The gyrator II was then tuned to 25.2 kHz to produce an output of 13 volts. When the receiver was tuned back to 24 kHz the signal voltage dropped to 0.8 volts, a factor of 16 from the 13 volts at 25.2 kHz. This seems to indicate an additional narrow bandpass filter would be required to receive the 24 kHz from Cutler, Maine in St. Cloud. The 25.2 kHz transmitter in La Moure, SD is only about 200 miles from St. Cloud, MN where Al lives. He measured drift over time and found it to be less than 5 Hz. A recording of an inverted SES on the 25. 2 signal is shown below. Another recording below shows Gyrator II has no problem, however, recording the much weaker 21.4 kHz signal from NPM in Hawaii. I do not know of anyone else who has successfully recorded NPM in Hawaii from the USA with a gyrator II receiver. Al uses a long wire antenna rather than the small indoor loop antenna others use. This may account for his success. These tests show that despite its simplicity Gyrator II is an excellent little receiver that is easy to build and set up to record solar flares. Its 160 Hz passband provides excellent selectivity that will separate the stations and with a good antenna it can pull in the weak signals like NPM in Hawaii.

The chart above records an inverted SES on the 25.2 kHz signal. Its transmitter distance from S. Cloud, MS is only 200 miles. For a nearby signal inverted SESs are not unusual and often provide excellent sensitivity to ionospheric disturbances.

The shaded areas in the chart above are the nightime part of the recording. Notice how the sunset rise of NPM on 21.4 kHz does not occur until about 4-hours after sunset in St. Cloud, MN. The signal still responds to flares after local sunset giving extra hours of coverage when recording a far westerly signal like NPM.

The Minimal Gyrator II VLF Receiver by Arthur J. Stokes.

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