“Geomagnetic Storm Season” is Over

June and July bring frequent 6-meter DX openings via long-distance sporadic-E propagation and persistent quiet geomagnetic conditions. These 2 months are well known to North American 6-meter DXers as the most productive time of year for DX up to 8,700 miles.

“The quiet geomagnetic season during June and July typically has only about half as many geomagnetic storms compared to March and April,” says contester and solar observer Frank Donovan, W3LPL. The planetary Kp index is usually about two points lower than during March and April, and severe (Kp = 8 or 9) storms are very infrequent, but the quiet geomagnetic season doesn’t mean the end of geomagnetic storms. Two of the most severe (Kp = 8+) geomagnetic storms during Solar Cycle 24 occurred on June 22 and 23, 2015.

Storms during June and July are not as frequent, strong, or as long lasting as they are during the geomagnetic storm seasons of March/April and September/October, but even the most severe storms (Kp = 8 or 9) can occur at any timewith little warning.

We’ve had two moderate (Kp = 6) storms so far in 2021, both during March. We also had eight minor (Kp = 5) storms: five in March and one each in January, February, and April.

“June and July 2020 were exceptional for 6-meter DX via sporadic E, and these normally geomagnetically quiet months were exceptionally quiet — the quietest since 1996,” Donovan said. “I made more than 500 European QSOs during June and July, more than 100 QSOs with stations in Japan (11,000 kilometers) during June, and one very unexpected QSO with UN3GX (10,500 kilometers) in mid-June.”

Donovan noted that no geomagnetic storms occurred in June and July 2020; the last time this occurred was June and July 1996. Only four brief geomagnetically active (Kp = 4) periods occurred in 2020 (June 7 and July 14, 24, and 25). The rest of 2020 was also exceptionally quiet with only one moderate storm in late September — and eight minor storms, he said. “June and July 2019 had two minor storms — on June 8 and July 9 and 10. There were only two moderate storms in 2019 — in May and August — and 15 minor storms.”

June and July 2018 saw three minor storms — June 1 and 25/26 and July 5. Just two moderate storms happened in 2018 — in May and August — and 16 minor storms, Donovan said.

“Coronal mass ejections (CMEs) caused 2017 to be much more geomagnetically active. June and July 2017 had two moderate storms on July 16 and 17 and three minor storms on June 11 and 16 and July 9,” Donovan said. “Three strong-to-severe (Kp = 7 to 8) storms occurred in September and May, with 12 moderate storms, and at least 33 minor storms occurred throughout the year.”

Donovan observed that Earth-directed CMEs are just beginning to cause occasional geomagnetic storms now that Solar Cycle 25 is somewhat more active. “During the next few years, CMEs will become the dominant cause of moderate-to-severe geomagnetic storms,” he said. “Geomagnetic storms caused by CMEs usually develop more quickly, are more long lasting, and are more severe than the typically brief, minor storms caused by coronal hole high-speed streams during the approximately 4 years near solar minimum.”

SOURCE:ARRL