---
source: https://iinventedlight.com/library/notes/solar-wind.md
title: "The solar wind and coronal holes"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NOAA, Solar Wind, US government work, public domain; NOAA, Coronal Holes, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "space: space weather"
tags: ['space-weather', 'sun', 'solar-wind']
sources:
  - id: S1
    title: "Solar Wind"
    publisher: NOAA
    url: https://www.swpc.noaa.gov/phenomena/solar-wind
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Coronal Holes"
    publisher: NOAA
    url: https://www.swpc.noaa.gov/phenomena/coronal-holes
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# The solar wind and coronal holes

**Answer:** The solar wind is a constant outflow of plasma, mainly protons and electrons, carrying the Sun's magnetic field. Slow wind (about 400 km/s) dominates near the Sun's equator; fast wind (500 to 800 km/s) streams from coronal holes, and fast streams can trigger minor to moderate geomagnetic storms.

## Speeds and structure

Because the Sun rotates every 27 days, fast and slow streams form a spiral that NOAA compares to a twirling ballerina's skirt. Where fast wind overtakes slow wind it piles up into a corotating interaction region (CIR) of higher density and stronger field.

## Coronal holes

Coronal holes look dark in extreme ultraviolet and X-ray images because they are cooler and less dense, with open magnetic field lines that let wind escape easily. They are most common around solar minimum, are steadiest at the poles, and can persist for several rotations.

## Space weather effects

High-speed winds bring geomagnetic storms while slow winds bring calm conditions. Strong CIRs and fast streams typically cause G1 to G2 storms, sometimes stronger.

## Claims
- id: C1
  claim: The solar wind consists mainly of protons and electrons as plasma.
  source: S1
  evidence: "The solar wind continuously flows outward from the Sun and consists mainly of protons and"
- id: C2
  claim: Coronal holes produce high-speed wind of 500 to 800 km/s.
  source: S1
  evidence: "Coronal holes produce solar wind of high speed, ranging from 500 to 800 kilometers per"
- id: C3
  claim: High speed winds bring geomagnetic storms; slow winds bring calm.
  source: S1
  evidence: "High speed winds bring geomagnetic storms while slow speed winds bring calm space weather."
- id: C4
  claim: Coronal holes are cooler, less dense regions with open magnetic fields.
  source: S2
  evidence: "They appear dark because they are cooler, less dense regions than the surrounding plasma"
- id: C5
  claim: Coronal holes are more common around solar minimum.
  source: S2
  evidence: "are more common and persistent during the years around solar minimum"

## Sources
- [S1] Solar Wind. NOAA. https://www.swpc.noaa.gov/phenomena/solar-wind . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Coronal Holes. NOAA. https://www.swpc.noaa.gov/phenomena/coronal-holes . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).