Space weather, week 37 of 2026.
·Week 37 of 2026, September 7, 2026 to September 13, 2026, 7 of 7 days recorded. Earth's magnetic field reached storm level on 1 day; the most disturbed day was September 8, 2026, with the Kp index (0 to 9, storm at 5 and above) peaking at 5, minor geomagnetic storm (G1). The Sun let off 12 small (C-class) flares over the week.
One section per complete UTC day, written by the daily data run from NOAA's feeds: the planetary Kp index every three hours, the GOES X-ray flare list, NOAA's daily sunspot number and 10.7 cm flux, and hourly solar wind at L1. Nothing here is edited by hand. The record index explains each figure, and the same numbers are in the open data file.
Monday, September 7, 2026
Earth's magnetic field was active conditions, no storm: the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 4.3 in the 21:00 to 24:00 UTC window and averaged 3.2 for the day. Aurora reached only the far north, Alaska, northern Canada, and northern Scandinavia. The Sun let off 1 small (C-class) flare; the biggest was C1.0 at 19:35 UTC, too small to notice on Earth. The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 426 km per second, a normal pace, and peaked at 572. Its magnetic field swung strongly southward for a time (Bz down to -14.1 nT), the direction that lets energy into Earth's field and drives storms.
Kp through the day, one value per three hours from midnight UTC: 1.3, 2, 3.3, 4, 3, 3.7, 4, 4.3.
Tuesday, September 8, 2026
Earth's magnetic field was minor geomagnetic storm (G1): the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 5 in the 06:00 to 09:00 UTC window and averaged 4 for the day. Aurora could reach the northern US states, Scotland, and Scandinavia. The Sun let off 6 small (C-class) flares; the biggest was C3.4 at 23:39 UTC, too small to notice on Earth. The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 523 km per second, fast, and peaked at 663. Its magnetic field tipped southward for a time (Bz down to -6.5 nT), the direction that feeds storms.
Kp through the day, one value per three hours from midnight UTC: 4.3, 4, 5, 4.3, 3.7, 4.7, 3, 3.
Wednesday, September 9, 2026
Earth's magnetic field was unsettled: the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 3 in the 15:00 to 18:00 UTC window and averaged 2.5 for the day. Aurora stayed up near the poles. The Sun let off 2 small (C-class) flares; the biggest was C3.2 at 10:32 UTC, too small to notice on Earth. The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 429 km per second, a normal pace, and peaked at 506. Its magnetic field tipped southward for a time (Bz down to -6.9 nT), the direction that feeds storms.
Kp through the day, one value per three hours from midnight UTC: 2.7, 1.3, 2.3, 2.7, 2.7, 3, 3, 2.7.
Thursday, September 10, 2026
Earth's magnetic field was quiet: the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 2.7 in the 00:00 to 03:00 UTC window and averaged 2.1 for the day. Aurora stayed up near the poles. The Sun let off 2 small (C-class) flares; the biggest was C1.6 at 17:12 UTC, too small to notice on Earth. The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 447 km per second, a normal pace, and peaked at 502. Its magnetic field stayed mostly northward (Bz no lower than -4.6 nT), the direction that keeps storms away (23 of 24 hours recorded).
Kp through the day, one value per three hours from midnight UTC: 2.7, 2.7, 2, 2.3, 2.3, 1.3, 1, 2.7.
Friday, September 11, 2026
Earth's magnetic field was unsettled: the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 3 in the 03:00 to 06:00 UTC window and averaged 2 for the day. Aurora stayed up near the poles. The Sun produced no flares worth recording (nothing reached C class, the smallest size NOAA lists). The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 420 km per second, a normal pace, and peaked at 488. Its magnetic field tipped southward for a time (Bz down to -5.1 nT), the direction that feeds storms.
Kp through the day, one value per three hours from midnight UTC: 1.3, 3, 1.7, 2.7, 2.3, 1.7, 1, 2.
Saturday, September 12, 2026
Earth's magnetic field was unsettled: the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 3 in the 06:00 to 09:00 UTC window and averaged 1.8 for the day. Aurora stayed up near the poles. The Sun let off 1 small (C-class) flare; the biggest was C5.8 at 17:20 UTC, too small to notice on Earth. The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 403 km per second, a normal pace, and peaked at 469. Its magnetic field tipped southward for a time (Bz down to -6.3 nT), the direction that feeds storms (23 of 24 hours recorded).
Kp through the day, one value per three hours from midnight UTC: 1.3, 2.3, 3, 2.3, 2, 1.3, 1, 1.
Sunday, September 13, 2026
Earth's magnetic field was unsettled: the Kp index, a 0 to 9 scale where 5 and above counts as a geomagnetic storm, peaked at 3 in the 03:00 to 06:00 UTC window and averaged 1.4 for the day. Aurora stayed up near the poles. The Sun produced no flares worth recording (nothing reached C class, the smallest size NOAA lists). The sunspot count for this day arrives from NOAA the following afternoon and is added on the next run. The solar wind, the stream of particles flowing past Earth, averaged 398 km per second, a normal pace, and peaked at 504. Its magnetic field tipped southward for a time (Bz down to -6.7 nT), the direction that feeds storms.
Kp through the day, one value per three hours from midnight UTC: 2.3, 3, 2, 0.7, 1.3, 1, 0.3, 0.7.
What do these numbers mean?
Four things are tracked each day. The Kp index says how disturbed Earth's magnetic field was, on a 0 to 9 scale measured every three hours; 5 and above is a geomagnetic storm, and the higher it goes the farther south the aurora reaches. Flares are sudden flashes on the Sun, sorted by size: C-class is small and harmless, M-class is medium and can briefly fade shortwave radio, X-class is large. The sunspot count is NOAA's daily tally of dark spots, weighted so that groups count more than lone spots; it runs from 0 on a blank Sun to 150 or more near the peak of a solar cycle. The radio output is the Sun's brightness at a 10.7 cm radio wavelength, a second activity gauge that does not depend on counting spots; 70 is quiet, 200 very active. The solar wind is the stream of particles flowing past Earth, measured about 1.5 million km upstream; its speed and the north-south direction of its magnetic field (Bz) decide whether a storm follows, because a southward field lets the wind's energy into Earth's field.