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Propagation Forecast Bulletin 51 ARLP051-23
SB PROP @ ARL $ARLP051 ARLP051 Propagation de K7RA ZCZC AP51 QST de W1AW Propagation Forecast Bulletin 51 ARLP051 From Tad Cook, K7RA Seattle, WA December 22, 2023 To all radio amateurs SB PROP ARL ARLP051 ARLP051 Propagation de K7RA The Winter Solstice, the shortest day of the year in the Northern Hemisphere occurred at 0327 UTC on December 22. It is the start of summer in the Southern Hemisphere. Solar activity increased over the last reporting week (December 14-20), with eleven new sunspot groups emerging. One new sunspot group appeared on December 15, four more on the following day, another on December 17, three more on December 18, and two more in December 19-20. Average daily sunspot number rose from 110.3 to 137.4, solar flux from 129.8 to 162.7, planetary A index 5.6 to 18.4, and middle latitude A index from 4.6 to 13.7. The most active day was Sunday, December 17 when the planetary A index was 36, and Alaska's college A index was 88. The cause was what Spaceweather.com reported as the strongest flare of the current solar cycle, an X2.8 class, and it caused a radio blackout. Here is a video of the brief flash: https://bit.ly/3RP3xCw Spaceweather.com reported on Wednesday that another flare is coming from sunspot group AR3529, and here is a movie they posted: https://bit.ly/3tipAbr Predicted solar flux is 190, 188 and 186 on December 22-24, then 182, 180, 170 and 165 on December 25-28, 145 on December 29-30, 150 on December 31, then 145, 140 and 138 on January 1-3, 2024, then 136 on January 4-5, then 140, 145 and 148 on January 6-8, 145 on January 9-12, then 150, 147, 145, 140, and 138 on January 13-17, 136 on January 18-19, then 140, 145 and 148 on January 20-22, then 145 on January 23-26, then 150, 145, 140 and 138 on January 27-30. Predicted planetary A index is 5, 12 and 8 on December 22-24, 5 on December 25-29, 8 on December 30-31, then 10 and 8 on January 1-2, 2024, 5 on January 3-7, 10 on January 8-9, 8 on January 10, 5 on January 11-13, 15 on January 14, 12 on January 15-16, and 8 on January 17-19, then 5 on January 20-25, and 8 on January 26-27. Jon Jones, N0JK wrote, from Kansas: "Some winter 6 meter Es December 18-19. N7BHC (EL15) and KD5CAF (EL18) into EM28 for me on FT8 around 0100 UTC December 19. Earlier stations in Colorado, Kansas, and Missouri had ZL7DX in on 6 meters at 2200 UTC December 18." Here is a new, long video from Dr. Tamitha Skov, WX6SWW, from earlier this week: https://bit.ly/3GPRYET Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - December 21, 2023 from F.K. Janda, OK1HH: "Astronomical winter began in the Northern Hemisphere at the moment of the Winter Solstice: December 22 at 0327 UTC. On this day is the longest night and, of course, the shortest day. The total effect of solar X-ray and ultraviolet radiation on the ionosphere of our hemisphere was thus relatively the smallest of the entire year, and the effects of changes in the solar wind were all the more effective. This is also one of the reasons why, despite relatively high solar activity, the shortwave propagation conditions are worse than we would like and then we expected. "Over the next six months, the length of the day will increase until the Summer Solstice on June 20. Slowly at first, then faster, fastest around the Spring Equinox on March 20. It is certain that then the propagation conditions will be significantly better than now. It is even possible that the maximum of the eleven-year cycle will occur as early as next year, although it would be better for us if it did not occur until 2025. "Although we have not observed any particularly large sunspot groups in recent weeks, there were always one or two active regions among them, whose magnetic configuration allowed the development of a medium-sized eruption, possibly even with a CME - after all we observed several of these. The exception was the X2.8 class eruption on December 14 at 1702 UTC, the strongest so far since the beginning of the 25th solar cycle, or since the major disturbances in September 2017. "The eruption originated in AR3514, which was approaching the western limb of the Sun. Even though it hurled a fast-moving CME into space, it was relatively unlikely to cause strong geomagnetic storms here on Earth. Eventually, the CME either missed Earth or hit so weakly that it was not detected by satellite sensors. "During the rise of the solar flux from 126 on December 12 to 195 on December 20, with the corresponding increase in solar X-ray radiation, shortwave propagation improved only slightly, actually fluctuating, which was expected. "The last geomagnetically quiet day was December 13, after which the Earth's magnetic field was unsettled to active (more precisely: active around last weekend). However, most days until the end of this year should be geomagnetically quieter, while the solar flux will remain elevated. Therefore, we can expect slightly better propagation." Here are a number of articles about a Big Flare: https://bit.ly/3RQG4Rb https://bit.ly/3RRzBpe https://bit.ly/48tJtuH https://bit.ly/3TAeybV https://bit.ly/48pIpbo https://bit.ly/488c88X https://bit.ly/3tymsrK https://bit.ly/3RwJzLh https://bit.ly/3RThBuQ https://bit.ly/3RRzzh0 An article about Radio Blackout: https://bit.ly/3v5b5Il Send your tips, reports, observations, questions and comments to k7ra@arrl.net. When reporting observations, don't forget to tell us which mode you were operating. For more information concerning shortwave radio propagation, see http://www.arrl.org/propagation and the ARRL Technical Information Service web page at, http://arrl.org/propagation-of-rf-signals . For an explanation of numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere . An archive of past propagation bulletins is at http://arrl.org/w1aw-bulletins-archive-propagation . More good information and tutorials on propagation are at http://k9la.us/ . Also, check this article about understanding solar indices: https://bit.ly/3Rc8Njt Instructions for starting or ending email distribution of ARRL bulletins are at http://arrl.org/bulletins . Sunspot numbers for December 14 through 20, 2023 were 126, 130, 163, 129, 137, 144, and 133, with a mean of 137.4. 10.7 cm flux was 155.1, 144.3, 149, 154.6, 161.4, 179.3, and 195.3, with a mean of 162.7. Estimated planetary A indices were 16, 12, 14, 36, 28, 12, and 11, with a mean of 18.4. Middle latitude A index was 13, 8, 10, 32, 16, 10, and 7, with a mean of 13.7. NNNN /EX
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