Our Sun has been very active this past week, with the average solar flux rising nearly 12 points to 155.5, while the average daily sunspot numbers dropped nearly 41 points to 96.1. This implies fewer, but more intense, sunspots. Sunspot numbers for September 22-28 were 86, 90, 88, 108, 103, 82 and 116, with a mean of 96.1. The 10.7 cm flux was 150.8, 158.2, 190.4, 168.8, 148.2, 139 and 133.4, with a mean of 155.5. The estimated planetary A indices were 3, 3, 4, 4, 67, 30 and 24, with a mean of 19.3. The estimated mid-latitude A indices were 2, 2, 3, 4, 20, 22 and 13, with a mean of 9.4.
A huge sunspot group numbered 1302 emerged on September 22. This was the source of a coronal mass ejection that triggered an immense geomagnetic storm. The planetary A index peaked at 67 on September 26, followed by 30 the next day and 24 on September 28. The planetary K index reached 8 for two of the three-hour reporting periods on September 26, indicating an intense geomagnetic storm. The resulting aurora was observed in many places, including Maine, Massachusetts, Michigan, Minnesota, New York, North Dakota and South Dakota. On September 22, there was a major X1.4 class solar flare at 1100 UTC, with a large CME, but this was when sunspot 1302 was just coming over the horizon, so it wasn’t Earth-directed. On September 24 sunspot group 1302 produced a larger X1.9 flare, and today the group is just past the point where it is directly facing Earth, but still in the middle of the visible solar disc. It could still produce more flares.
Source Link: arrl.org/news