Study finds ions in solar flares may be far hotter than thought
Researchers at the University of St. Andrews report ions in solar flares could reach temperatures more than 6.5 times earlier estimates, a finding that may affect space weather forecasting
Scientists say ions in solar flares can reach temperatures more than 6.5 times higher than previous estimates, a result that could change how researchers model flare energy release and forecast space weather.
The findings, published recently in the Astrophysical Journal Letters by a team at the University of St. Andrews in Scotland, indicate that ions within some parts of solar flares may reach temperatures above 117 million degrees Fahrenheit — far higher than prior estimates of roughly 18 million degrees Fahrenheit. Solar flares are sudden, intense bursts of energy in the Sun’s outer atmosphere that heat surrounding plasma and can, at times, damage satellites, cause radio blackouts, disrupt power grids and produce vivid auroras on Earth.
"Solar physics has historically assumed that ions and electrons must have the same temperature. However, redoing calculations with modern data, we found that ion and electron temperature differences can last for as long as tens of minutes in important parts of solar flares, opening the way to consider super-hot ions for the first time," said Dr. Alexander Russell, a lecturer at the University of St. Andrews, in a statement accompanying the paper.
The paper ties recent discoveries about a process called magnetic reconnection — in which opposing magnetic field lines break and reconnect, converting magnetic energy into particle heating and motion — to flare physics. Previous work had shown magnetic reconnection can heat ions roughly 6.5 times more than electrons in near-Earth space, in the solar wind and in computer simulations. The St. Andrews team said those results had not previously been connected directly to conditions inside solar flares.
If ions are substantially hotter than electrons for sustained periods, that imbalance could affect how energy is partitioned and radiated during flares, which in turn influences a flare’s brightness, color and apparent size in different wavelengths. The researchers said accounting for super-hot ions may help resolve longstanding questions about why some flares appear broader or more brilliant than models predict.
Understanding these temperature differences could also have operational consequences. Forecasters at agencies such as the National Oceanic and Atmospheric Administration use scales and models to rate solar activity and predict geomagnetic storms; researchers say improved knowledge of ion heating and energy distribution could lead to more accurate space weather forecasts. Geomagnetic storms driven by intense solar activity can last several days and interfere with satellite operations, GPS navigation and terrestrial power grids.
The study relies on reanalysis of observational data combined with results from simulation work and prior near-Earth measurements. The authors caution that their conclusions concern ion temperatures in key parts of flares and do not imply a uniform temperature increase across all flare regions.
The team called for further observational and modeling work to test how widespread the effect is across different flare types and to determine how best to incorporate ion-electron temperature differences into predictive models. Such follow-up will be needed before the new results can be translated into operational forecasting tools.
The paper was peer-reviewed and appears in the Astrophysical Journal Letters. The authors said the link between reconnection-driven ion heating and flare structure points to a previously underappreciated mechanism that may be important for solar and space physics research going forward.