Space weather is the changing conditions in space caused by the Sun — flares, particle storms and magnetic storms — that can disturb satellites, radio, GPS and power grids.
On Earth, weather means rain, wind and heat. In space, the weather comes from the Sun. The Sun constantly blows out a stream of charged particles called the solar wind, and sometimes it erupts much more violently. When that energy and material reach Earth, they disturb its magnetic field and upper atmosphere, with effects on power lines, GPS, radio and satellites. This is space weather.
The US National Oceanic and Atmospheric Administration (NOAA) rates space weather on three five-step scales:
Level 1 is minor and level 5 is extreme. In an average 11-year solar cycle NOAA expects about 1,700 minor (G1) geomagnetic storm events, but only about 4 extreme (G5) ones.
On 2 September 2023 ISRO launched Aditya-L1 on PSLV-C57. On 6 January 2024 it entered a halo-orbit around the Sun–Earth L1 point, about 1.5 million km from Earth. From there it watches the Sun without ever being eclipsed.
Four of its seven payloads look at the Sun: VELC (the corona), SUIT (ultraviolet), SoLEXS (soft X-rays) and HEL1OS (hard X-rays). Three measure the space around the spacecraft: ASPEX and PAPA sample solar-wind particles, and a magnetometer measures the magnetic field. Together they study how flares and coronal mass ejections begin and how the solar wind drives space weather.
Solar Cycle 25 has been stormy. ISRO's 2024 report counts 18 strong (G3), 20 severe (G4) and 2 extreme (G5) geomagnetic storms that year, which sped up the orbital decay of low satellites. A record 2,095 catalogued objects re-entered the atmosphere in 2024.
Find 6 January 2024 on the mission timeline — the day Aditya-L1 entered its halo orbit around L1 and began India's full-time watch on the Sun. Follow Aditya-L1
NOAA's G scale is tied to the Kp index, a measure of how disturbed Earth's magnetic field is: G1 = Kp 5, G2 = Kp 6, G3 = Kp 7, G4 = Kp 8 (including 9−), G5 = Kp 9. The expected frequency per 11-year cycle falls steeply with level — G1 about 1,700 events (about 900 days), G2 about 600 (360 days), G3 about 200 (130 days), G4 about 100 (60 days), G5 about 4 (4 days).
A cycle has about 11 × 365 ≈ 4,000 days. So minor storm conditions occur on about 900 / 4,000 ≈ 22% of days, while extreme ones occur on about 4 / 4,000 = 0.1% of days.
The R scale follows flare X-ray brightness: R1 = M1 (10⁻⁵ W/m²), R2 = M5, R3 = X1 (10⁻⁴ W/m²), R4 = X10, R5 = X20. The S scale steps by factors of ten in the flux of particles above 10 MeV, from S1 (10) to S5 (10⁵).
Why watch from L1? Coronal mass ejections travel at speeds from under 250 km/s to nearly 3,000 km/s. Material passing L1, 1.5 million km out, still has that distance to cover before reaching Earth:
This is in line with NOAA's statement that a shock's arrival typically gives 15 to 60 minutes of warning. Aditya-L1's in-situ instruments sit in exactly that early-warning position.
R for radio blackouts from solar flares, S for solar radiation storms, and G for geomagnetic storms. Each runs from 1 (minor) to 5 (extreme).
A spacecraft in a halo orbit around L1 sees the Sun continuously, with no eclipses, and samples the solar wind before it reaches Earth.
It can increase atmospheric drag, which makes the satellite lose height faster and drift from its predicted position, and it can cause surface charging.