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Solar Wind

Flares and CMEs get the dramatic headlines, but they're not the only thing the Sun sends toward Earth. There's a steady, continuous stream of charged particles flowing outward from the Sun in every direction, at every moment — the solar wind. It never really stops. What changes is its speed, density, and the orientation of the magnetic field it carries, and those changes are what decide whether a given day is geomagnetically calm or restless.

What Solar Wind Is

Solar wind is a continuous outflow of charged particles — mostly protons and electrons — escaping the Sun's outer atmosphere fast enough to overcome its gravity. Speeds range roughly from 250 to 800 km/s depending on where it originates, and it carries the Sun's magnetic field out with it, stretching it into a rotating spiral shape as the Sun turns — a structure often compared to the skirt of a twirling ballerina, called the interplanetary magnetic field (IMF).

Where It Comes From: Fast Wind vs. Slow Wind

Not all solar wind is equal. Its speed depends on the region of the Sun it left from:
  • Fast solar wind (500–800 km/s) streams from coronal holes — cooler, darker patches in the corona where the magnetic field opens outward into space instead of looping back to the surface, letting particles escape freely. Coronal holes are largest and most persistent at the Sun's poles, but they can also form and drift through the equatorial region, especially as solar maximum transitions toward the cycle's declining phase.
  • Slow solar wind (~400 km/s) flows from the more structured, closed-field regions near the Sun's equator, forming what's known as the heliospheric current sheet — a folded, rotating boundary that separates regions of opposite magnetic polarity.

Because the Sun rotates roughly every 27 days, a persistent coronal hole sends the same fast stream past Earth again and again on a repeating schedule — these recurring encounters are called corotating interaction regions (CIRs), and they're one of the more predictable sources of mild, recurring geomagnetic activity.

What Forecasters Actually Watch




Three numbers, measured continuously by satellites positioned about 1.5 million km upstream of Earth, determine how much impact incoming solar wind will have:

Parameter What it tells forecasters
  •  Speed (km/s)  | Higher speed streams hit the magnetosphere harder
  •  Density (particles/cm³)  | Combined with speed, determines dynamic pressure on the magnetosphere
  •  Bz (IMF north-south component, nT)  | The single most important number — southward (negative) Bz opens the door to geomagnetic storms; northward Bz mostly shields Earth

A fast, dense stream with a strongly southward Bz is the recipe for a geomagnetic storm. The same stream with a northward Bz can arrive at Earth and barely register.

Solar Wind vs. Flares vs. CMEs

It's easy to blur these together, but they're distinct phenomena on different timelines. A solar flare is a flash of radiation reaching Earth in about 8 minutes. A coronal mass ejection is a discrete eruption of plasma taking 1–3 days to arrive. Solar wind, by contrast, isn't an event at all — it's the constant background flow, occasionally organized into a faster stream by a coronal hole, typically taking 2–4 days to reach Earth once that stream forms.

How Solar Wind Triggers Geomagnetic Activity

When solar wind — whether it's a steady fast stream or the leading edge of a CME — carries a southward-pointing magnetic field, it connects with Earth's own field through magnetic reconnection, opening a channel for energy to flow into the magnetosphere. This intensifies the ring current and can trigger geomagnetic storms, typically in the G1–G2 range for a strong coronal hole stream, with the potential for stronger storming in rarer cases, particularly when a CIR arrives alongside or shortly after a CME.

Established Effects

Solar wind's main confirmed effects mirror those of the geomagnetic storms it helps trigger: fluctuations in power grid currents, degraded GPS accuracy, disrupted high-frequency radio, and — most visibly — aurora, pushed to lower latitudes when a southward Bz opens the door for energy to pour in.

Possible Effects on Human Health

Because sustained coronal hole streams can keep the geomagnetic field mildly disturbed for several days at a stretch — longer than a single storm from an isolated CME — some people report a similar pattern of fatigue, headaches, or disrupted sleep during these extended active periods as during sharper storms. The evidence here follows the same pattern as elsewhere in this wiki: a widely reported correlation, without yet a confirmed biological mechanism to explain it.

Solar Wind in 2026

Recurring coronal hole streams have been a regular feature of 2026's space weather, arriving every 27 days or so as the same holes rotate back into an Earth-facing position, typically pushing conditions to G1–G2 storm levels for a day or two before waning. These streams frequently interact with CMEs arriving from the Sun's ongoing high flare output during Solar Cycle 25's extended maximum, making some stretches of geomagnetic disturbance the product of both sources arriving close together rather than either one alone.

What is solar wind?
Solar wind is a continuous stream of charged particles, mostly protons and electrons, flowing outward from the Sun at speeds between roughly 250 and 800 km/s. It carries the Sun's magnetic field with it, shaped into a rotating spiral as the Sun turns.
What is the difference between fast and slow solar wind?
Fast solar wind (500-800 km/s) comes from coronal holes, where the Sun's magnetic field opens outward and lets particles escape freely. Slow solar wind (around 400 km/s) comes from more structured regions near the Sun's equator.
What is Bz and why does it matter for geomagnetic storms?
Bz is the north-south component of the magnetic field carried by solar wind. A southward (negative) Bz connects with Earth's magnetic field through reconnection, opening a channel for energy to trigger geomagnetic storms; a northward Bz mostly shields Earth from that energy.
What is a corotating interaction region (CIR)?
A CIR is the recurring encounter between Earth and a fast solar wind stream from a persistent coronal hole, arriving roughly every 27 days as the Sun rotates the same hole back into an Earth-facing position. CIRs are a predictable source of mild, recurring geomagnetic activity.
How is solar wind different from a coronal mass ejection?
Solar wind is the Sun's continuous background particle flow, while a coronal mass ejection is a discrete eruption of plasma that takes 1-3 days to reach Earth. A fast solar wind stream from a coronal hole typically takes 2-4 days to arrive.
Can solar wind activity affect how people feel?
Some people report fatigue, headaches, or disrupted sleep during extended periods of fast solar wind and mild geomagnetic disturbance, similar to reports around geomagnetic storms generally. A confirmed causal mechanism hasn't been established, though the correlation is widely reported.