The Great Magnetic Storm of March 8, 1970

This was one of the largest magnetic storms of Cycle 20, and the largest one that I had yet experienced since becoming licensed in late December of 1963. (1970/03/08 Ap=149) The solar flux for this event was not super high (c. 170) compared to other dates in Cycle 20 (and prior and later Cycles). The flare/CME that was responsible for it had occurred on Mar 5. In those days the best information available to the general public on solar-terrestrial events could be had by listening to the WWV GEOALERTS broadcast at 18 minutes after the hour (and usually revised but once a day) and the 4-times-a-day propcasts (for the North Atlantic). From my records of those from early March 1970 ... 02 08 14 20z 03-01-70 EEE U5 U6 U5 03-02-70 SEE N5 U5 U6 03-03-70 IEE U5 N6 U6 03-04-70 IEE N6 N6 U6 03-05-70 S N6 N6 N6 03-06-70 S N6 N6 03-07-70 EHH U5 U7 U6 03-08-70 IMU W5 W6 W4 03-09-70 EGP W3 W3 W5 03-10-70 EEE W4 U6 N6 03-11-70 EEE W5 N6 03-12-70 EEE N6 U6 N7 The very complex GEOALERT coding then in effect is detailed here in a 1968 WWV publication from which this has been arduosly abstracted. ============================================================================================= 1.7. Propagation Forecasts A forecast of radio propagation conditions is broadcast in International Morse Code during the last half of every fifth minute of each hour. On each of the standard frequencies from WWV. Propagation notices were first broadcast from WWV in 1946. The announcement each five minutes was commenced on November l5, 1963. The present type of propagation has been broadcast from WWV since July 1952. North Pacific forecasts were broadcast from WWVH from January 1954 until November 1964, but these are no longer available. The WWV forecast announcements refer to propagation along paths in the North Atlantic Area, such as Washington, D. C. to London or New York City to Berlin. The announcements are the short term forecasts prepared by the ESSA, Telecommunications Disturbance Forecast Center, Box 178, Fort Belvoir, Virginia 23060. The regular times of issue of the forecasts are 0500, 1100 (1200 from November 1-April 30), 1700, and 2300 GMT. The forecast announcement tells users the condition of the ionosphere at the regular time of issue and the radio quality to be expected during the next six hours. The forecasts are based on data obtained from a worldwide network of geophysical and solar observatories. These data include radio soundings of the upper atmosphere, short wave reception data, observations of the geomagnetic field, solar activity and similar information. Trained forecasters evaluate the information and formulate the forecasts using known sun-earth relationships. WWV broadcasts the forecast as a letter and a number. The letter portion identifies the radio quality at the time the forecast is made. The denoting quality are “N”, “U”, and “W”, signifying that radio propagation conditions are either normal, unsettled, or disturbed, respectively. The number portion of the forecast announcement from WWV is the forecast of radio propagation quality on a typical North Atlantic path during the six hours after the forecast is issued. Radio quality is based on the ITS 1 to 9 scale which is defined as follows: Disturbed Unsettled Normal grades(W) grade (U) grades (N) 1. useless 5. fair 6. fair-to-good 2. very poor 7. good 3. poor 8. very good 4. poor-to-fair 9. excellent If for example, propagation conditions are normal at the time the forecast is issued but are expected to become “poor-to-fair” during the next six hours, the forecast announcement would be broadcast as N4 in International Morse Code. 1.8. Geophysical Alerts Letter symbols indicating the current geophysical alert (Geoalert) as declared by the World Warning Agency of the International Ursigram and World Days Service (IUWDS) are broadcast in very slow International Morse Code from WWV and WWVH on each of the standard radio carrier frequencies. These broadcasts are made from WWV during the first half of the 19th min of each hour and from WWVH during the first half of the 49th min of each hour. Such notices have been broadcast since the International Geophysical Year, 1957-58, and have continued by international agreement. On January 1, 1968 a new coding system was instituted for broadcasting Geoalerts. This was necessary to make possible the dissemination of larger quantities of information resulting from improved techniques in observation and prediction of geophysical events. Previous codes were superseded. The symbols used indicate experimenters and researchers in radio, geophysical, and solar sciences the content of the IUWDS Geoalert message which is issued daily at 0400 GMT to identify days on which outstanding solar or geophysical events are expectedor have occurred in the preceding 24-our period. Geoalerts for a given day are first broadcast at 0418 GMT on station WWV, Fort Collins, Colorado, then at 0448 GMT on station WWVH, Maui, Hawaii. These broadcasts are repeated at hourly intervals until the new alert is issued. The new coding permits three types of information at each broadcast-each in the form of letters repeated three times in slow Inernational Morse Code. The first set concerns either FORECASTS a solar or geophysical event for the next day, and/or the observation of a stratospheric warming (STRATWARM). Letters which may occur in the first set and their meaning are as given in the table below The second and third sets of letters pertain to the occurrence of and approximate time of observed solar or geophysical events. The coding for the time and type of event is shown in the table given below. EEE ( . ) No alert (NIL) III ( .. ) FLARES expected SSS (... ) PROTON FLARE expected TTT ( -) MAGSTORM expected 1st letter UUU ( ..-) FLARES and MAGSTORM expected VVV (..._) PROTON FLARE and MAGSTORM expected HHH (....) STRATWARM observed DDD (-.. ) STRATWARM plus FLARES expected BBB (-...) STRATWARM plus PROTON FLARE expected MMM (-- ) STRATWARM plus MAGSTORM expected ______________________________________________ Day before that of issue Day of NIL (hours GMT) issue ______________________________________________ 00-06 06-12 12-18 18-24 00-04 _______________________________________________________________ 2nd letter set: MMM TTT HHH SSS III EEE PROTON EVENT (--) (-) (....) (...) (..) (.) _______________________________________________________________ 3rd letter set: UUU AAA BBB DDD NNN EEE GEOMAGNETIC STORM (..-) (.-) (-...) (-..) (-.) (.) _______________________________________________________________ For example, the following message (in In- EEE = No PROTON EVENT between 0000 ternational Morse Code) GMT yesterday and 0400 GMT today signifies:GEO SSS EEE DDD DDD = GEOMAGNETIC STORM occurred (began) GEO = Solar geophysical message between 1800 and 2400 GMT yesterday SSS = PROTON FLARE expected ============================================================================================ Now, with that out of the way ... March 7 had a total solar eclipse which tracked from southern Mexico up to the Florida panhandle and then up the east coast of the US. Several expeditions had been set up along the path of totality and, among other data, some collected ionospheric effects. To be able to differentiate the eclipse effects data is also collected for a few days before and after the event so more than normal scrutiny was being exercised when the magnetic storm struck on Sunday afternoon. As for me, on Saturday morning it started to get overcast (the after effects from a strong frontal passage and storms on Friday). That presented a snap decision - whether to stay put and hope for clearing or to head south and look for better skies with less cloud coverage. That resulted in an automobile run (with a 3" f/10 Newtonian reflector) eventually down IH-37 almost half way to Corpus Christi - with stops along the way to make quick snapshots of the projected solar disk (and coming across at least one other observer doing the same pursuit!) Meanwhle, the ionospheric effects on the AM broadcast band were obvious as it filled with Mexican stations now propagating due to the weakening of the absoprtive D-layer along the eclipse shadow path to the south of here. (As a side note, the 620 ASA 125 film was processed at a drug store - luckily they had made prints before they accidentally shreded the original negatives! They made other negatives from those prints.) Now to the Sunday storm. 35-MHz paging stations from the east coast were noted via F2 and had faded out at their "normal" time. However, by late afternoon they had returned (a classic indicator of a magnetic storm onset) as had faint 50-MHz F2 backscatter from Louisiana. I took a brief step outside to use up the remaining frames on the film spool from the prior day's solar eclipse - returning to find a greatly expanded event. In all between 2220z and 0010z some 16 states were heard via backscatter resulting in these contacts (Swan 250 to 3-el Cushcraft c. 20' AGL) WA5TTH 1970-03-08 19:07:00 6M SSB LA K4QKR 1970-03-08 22:40:00 6M SSB FL audio K6QEH 1970-03-08 22:44:00 6M SSB CA audio K5WWQ 1970-03-08 22:52:00 6M SSB TX (Austin the hard way!) K5VRY 1970-03-08 23:20:00 6M SSB TX K9EQA 1970-03-08 23:32:00 6M SSB IL KP4DCY 1970-03-08 23:45:00 6M SSB PR WA5NOB 1970-03-09 00:03:00 6M SSB AR Note the Puerto Rican - that was direct F2 (and some 30 db louder than the backscatter). It was at this time that I made a quick check of Ch 2 on the TV - a jumbled mass of signals (with audios!) rivaling the most intense Es events while Ch 3 was nil. Clearly F2 with a sharp MUF cutoff and likely a mix of Latin America direct F2 and US F2 backscatter. As any idents were hopeless (c. 2350z) I went back to 50-MHz. The largest magnetic storm of Cycle 20 (Ap=182) occurred in early August 1972 - a time of the year that was less beneficial for F2 enhancements than the smaller event of Mar 1970 had produced. WA5IYX exceprt of Mar 11, 1970 letter to W5KHT
page created: Mar 9, 2010 modified: Jul 4, 2012