How to Read the Solar Wind
Solar wind is the continuous stream of charged particles flowing outward from the Sun's corona. Real-time solar wind data from the DSCOVR and ACE satellites arrives roughly 15–60 minutes before the same plasma reaches Earth, giving forecasters short-fuse warning.
The Three Numbers That Matter
Speed (km/s), density (particles/cm³), and temperature (K) together describe the wind hitting Earth's magnetosphere. Baseline slow wind runs around 300–400 km/s at 5–10 p/cm³. High-speed streams from coronal holes push 500–700 km/s. CME arrivals often show a sharp density spike and a sudden speed jump above 800 km/s.
Why Density and Speed Multiply
Solar wind pressure on the magnetosphere scales with density times velocity squared. That means a modest CME with high density and high speed can compress the magnetosphere as much as a much faster but thinner high-speed stream.
Reading the Traces
On a live plot, look for a sudden vertical jump across all three panels at once — that's a shock front. If Bz turns strongly negative at the same time, expect a geomagnetic storm within hours.
Frequently Asked Questions
What speed counts as 'fast' solar wind?
Anything above about 500 km/s is considered fast. Above 700 km/s typically indicates a strong high-speed stream or a CME arrival.
Where does the data come from?
The DSCOVR and ACE satellites at the L1 Lagrange point, roughly 1.5 million km sunward of Earth.