Solar wind now
A spacecraft about 1.5 million km upstream measures the solar wind roughly 30 to 60 minutes before it reaches Earth. Three numbers matter most for the aurora: Bz, speed and density.
2.9Bz, nT (south is negative)
4Bt, total field, nT
352speed, km/s
5.8density, p/cm³
10-minute averages at build time (October 29, 2026), from NOAA's real-time solar wind feed.
Last 24 hours
Bz (nT): negative is good for aurora
Speed (km/s)
Density (protons per cubic cm)
What the numbers mean
- Bz: the north-south direction of the magnetic field carried by the solar wind. When it points south (negative) for an hour or more, energy flows into Earth's magnetic field and the aurora brightens. A Bz of -10 nT or lower held for a while often comes with storms.
- Speed: a quiet solar wind blows at about 300 to 400 km/s. Fast streams from coronal holes reach 500 to 700 km/s, and strong coronal mass ejections can pass 1,000 km/s.
- Density: how many particles the wind carries. A jump in density and speed together usually marks the arrival of a shock.
None of these numbers alone decides the night. They show what is coming in the next hour; the Kp index shows what the magnetic field is doing now.
Source: NOAA SWPC real-time solar wind (magnetometer and plasma data from the spacecraft NOAA uses at the L1 point), public domain. Unofficial copy.
Page built: October 29, 2026.