Space Weather
Proton density — live and explained
How "thick" the stream of solar particles hitting Earth is right now — a supporting factor that amplifies geomagnetic response when combined with fast wind and a southward Bz.
Live Proton Density
Updated every 10 minutes from live NOAA data.
Telemetry: DSCOVR Spacecraft / ACE
Why it matters
Density combines with solar wind speed to determine dynamic pressure — how hard the solar wind is physically pushing against Earth's magnetosphere. High density paired with high speed compresses Earth's magnetic field more, which can amplify a geomagnetic storm's effects and is one of the signatures forecasters use to identify when a CME has actually arrived.
Normal range
Typical quiet solar wind density runs 1-5 p/cm³. Values in the 10-20 p/cm³ range are elevated and often mark a CME's dense sheath region; occasionally density briefly spikes above 50 p/cm³ during unusually dense events.
What today's value means
Waiting for live data to interpret…
What is proton density?
Proton density measures how many protons occupy each cubic centimeter of the solar wind — essentially how "thick" or concentrated the stream of particles is. A typical baseline is around 1-10 particles per cm³. On its own, density has a modest effect on geomagnetic activity, but it matters more in combination: higher density paired with fast solar wind speed and a southward IMF Bz delivers a stronger overall push into Earth's magnetosphere, since more particles are carrying that energy inward. A sudden spike in density is also one of the classic signatures of a coronal mass ejection's leading edge arriving at Earth.
Recent history
The last 24 hours of observed proton density.
FAQ
What's a high proton density reading?
Baseline solar wind typically runs 1-10 particles/cm³. Readings above 15-20 often indicate a CME's dense plasma sheath has arrived, and are worth watching alongside speed and Bz for signs of an active geomagnetic storm.
Does high density alone cause aurora?
Not by itself. Density amplifies the effect of an already-favorable setup — fast wind and southward Bz — rather than driving activity on its own.