In the realm of solar physics and space weather, a team of researchers from the University of California, Berkeley, and the University of Michigan has been delving into the mysteries of the solar wind. Led by Jack D. Collard, this group has been leveraging data from the Solar Orbiter mission to better understand the origins of the solar wind, particularly the slow solar wind, whose source has remained uncertain. Their findings, published in the journal Astronomy & Astrophysics, offer a new way to classify solar wind source regions, which could have implications for space weather forecasting and understanding the Sun’s influence on the heliosphere.
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. It comes in two main types: fast and slow. While the fast solar wind is known to originate from coronal holes, the source of the slow solar wind has been less clear. To investigate this, the researchers turned to compositional metrics, specifically the charge state ratio of oxygen ions (O7+/O6+), which can provide insights into the solar wind’s source regions. However, measuring these charge states has typically been limited to distances of 1 astronomical unit (AU) and beyond, until the launch of the Solar Orbiter.
The researchers used data from the Solar Orbiter’s Heavy Ion Sensor and Proton and Alphas Sensor, which cover distances from 0.28 to 1 AU. They found a strong anti-correlation between proton specific entropy and the oxygen charge state ratio that persists over a broad range of distances in the inner heliosphere. Proton specific entropy is a measure of the disorder or randomness in the proton population of the solar wind. By categorizing the observed solar wind into fast solar wind, slow Alfvenic solar wind, and slow solar wind, they identified clear distinctions in specific entropy values and charge state ratios across these types.
This relationship between proton specific entropy and the oxygen charge state ratio can be used as a proxy to identify the solar wind source region, even in the absence of in-situ charge state measurements. This is particularly useful for missions like the Parker Solar Probe, which ventures much closer to the Sun than the Solar Orbiter. By establishing this relationship and quantifying its radial dependence, the researchers have provided a new tool for understanding the solar wind’s origins and behavior throughout the heliosphere.
For the energy sector, particularly space-based solar power or satellite operations, understanding the solar wind and its sources can help in predicting space weather events. These events can impact satellite operations, power grids, and communication systems on Earth. By providing a new way to classify solar wind source regions, this research could contribute to improved space weather forecasting, helping to protect these critical infrastructures.
In summary, the researchers have demonstrated that proton specific entropy can serve as a reliable proxy for the oxygen charge state ratio, offering a new method to classify solar wind source regions. This finding not only advances our understanding of the solar wind but also has practical applications for space weather forecasting and the protection of space-based and ground-based energy infrastructures.
This article is based on research available at arXiv.