520 km/sEnhancedBz -1 nT
The solar wind is running quicker than usual— watch the Bz: a sustained southward turn is what lights up the aurora.
Speed520 km/s
Density4.4 /cm³
IMF Bz-1 nT (south)
IMF Bt3.1 nT
SUN · SOLAR WIND
Solar Wind, Right Now
The Sun doesn't just shine — it blows. A constant stream of charged particles, the solar wind, races outward past Earth at hundreds of kilometres a second. When it speeds up and its magnetic field turns southward, it couples to our planet and lights up the aurora. These are the live numbers behind tonight's forecast.
LIVE · Solar wind (DSCOVR, real time)Updated Jul 25, 1:23 PM UTC
Source: NOAA SWPC / NASA DSCOVR at L1, propagated to Earth arrival · a southward Bz (negative) is what couples the wind to Earth and drives the aurora · refreshes ~every few minutes.
The two numbers that matter
Speed usually sits around 300–400 km/s; a fast stream (500–800+ km/s) delivers more energy. But the decisive number is Bz— the north–south tilt of the wind's embedded magnetic field, measured in nanotesla. When Bz turns negative(southward), it links up with Earth's own field like two bar magnets snapping together, pouring energy into the upper atmosphere. A sustained, strongly southward Bz is what turns a quiet night into an aurora night — often more so than the headline Kp number.
Where this reading comes from
These values are measured by NASA's DSCOVRspacecraft, parked at the L1 point about 1.5 million kilometres sunward of Earth — far enough upstream that it sees the wind roughly 15–60 minutes before it reaches us. That short lead time is exactly why an aurora forecast is only confident an hour or so ahead: watch the live Bz, then check whether it's enough to see the lights from your location.
Field guides
THE WHOLE STAR
Flares, the solar wind, sunspots and eclipses — the Sun, all on one canvas.