Space weather, week 41 of 2026.
·Week 41 of 2026, October 5, 2026 to October 11, 2026, 1 of 7 days recorded. Earth's magnetic field reached storm level on 1 day; the most disturbed day was October 5, 2026, with the Kp index (0 to 9, storm at 5 and above) peaking at 5.3, minor geomagnetic storm (G1). The Sun let off 1 medium (M-class) and 4 small (C-class) flares over the week. The daily sunspot count ran from 58 to 58, averaging 58, a quiet Sun for this stage of the cycle.
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, October 5, 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 5.3 in the 03:00 to 06:00 UTC window and averaged 3.6 for the day. Aurora could reach the northern US states, Scotland, and Scandinavia. The Sun let off 1 medium (M-class) and 4 small (C-class) flares; the biggest was M1.0 at 18:48 UTC, enough for a brief shortwave radio fade on the daylit side. NOAA's sunspot count was 58, a quiet Sun for this stage of the cycle (0 is no spots at all; 150 to 200 is typical at the peak of a cycle); 1 new sunspot group appeared. The Sun's radio output, a second gauge of its activity that does not depend on counting spots, read 100, moderate (about 70 for a quiet Sun, 200 or more for a very active one). The solar wind, the stream of particles flowing past Earth, averaged 565 km per second, fast, and peaked at 656. Its magnetic field tipped southward for a time (Bz down to -9 nT), the direction that feeds storms.
Kp through the day, one value per three hours from midnight UTC: 4, 5.3, 2.3, 3.3, 2.7, 3.7, 3.7, 4.
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.