Solar Wind Origin

TL;DR

This paper reviews the origin of the solar wind, discussing historical theories, current understanding, unresolved questions, and recent advances in observations and modeling that enhance our knowledge of solar and space weather phenomena.

Contribution

It provides a comprehensive overview of solar wind origin theories, recent observational and computational advancements, and highlights ongoing research challenges and insights into solar and space weather.

Findings

Solar wind is driven by gas pressure from the hot solar corona.

Recent observations and simulations are improving understanding of solar wind acceleration.

Unresolved questions remain about coronal heating and wind acceleration mechanisms.

Abstract

The Sun continuously expels a fraction of its own mass in the form of a steadily accelerating outflow of ionized gas called the "solar wind." The solar wind is the extension of the Sun's hot (million-degree Kelvin) outer atmosphere that is visible during solar eclipses as the bright and wispy corona. In 1958, Eugene Parker theorized that a hot corona could not exist for very long without beginning to accelerate some of its gas into interplanetary space. After more than half a century, Parker's idea of a gas-pressure-driven solar wind still is largely accepted, although many questions remain unanswered. Specifically, the physical processes that heat the corona have not yet been identified conclusively, and the importance of additional wind acceleration mechanisms continue to be investigated. Variability in the solar wind also gives rise to a number of practical "space weather" effects on human life and technology, and there is still a need for more accurate forecasting. Fortunately, recent improvements in both observations (with telescopes and via direct sampling by space probes) and theory (with the help of ever more sophisticated computers) are leading to new generations of predictive and self-consistent simulations. Attempts to model the origin of the solar wind are also leading to new insights into long-standing mysteries about turbulent flows, magnetic reconnection, and kinetic wave-particle resonances.