What Is Solar Wind?
The solar wind is a continuous stream of charged particles — mostly protons and electrons — flowing outward from the Sun's corona at speeds typically between 300 and 800 km/s. It carries the Sun's magnetic field out through the Solar System, and its interaction with Earth's own magnetic field is what shapes the magnetosphere and, ultimately, drives space weather.
Key Facts
Typical speed: roughly 300–500 km/s in slow wind, up to 700–800+ km/s in fast streams. Fast streams often originate from coronal holes on the Sun. It's composed mainly of protons and electrons, with trace heavier ions, at a density typically of a few particles per cubic centimeter near Earth.
How We Watch It Coming
The solar wind is continuously measured at the L1 point by spacecraft like DSCOVR and ACE, giving roughly 30–60 minutes of warning before it reaches Earth.
Why It Matters
Solar wind speed, density, and — combined with Bz — its magnetic orientation together determine how much energy gets coupled into Earth's magnetosphere. A fast, dense stream with a southward field is the classic recipe for an active aurora night.
Frequently Asked Questions
Where does the solar wind come from?
It flows continuously outward from the Sun's corona, accelerated by the Sun's extreme coronal temperature. Faster streams typically originate from coronal holes — regions of open magnetic field where solar material escapes more easily.
How much warning does solar wind data give before it reaches Earth?
Spacecraft at the L1 Lagrange point, about 1.5 million km sunward of Earth, typically give roughly 30 to 60 minutes of advance warning before a given parcel of solar wind reaches Earth's magnetosphere.
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