# Proton-proton collisional age to order solar wind types

**Authors:** Verena Heidrich-Meisner, Lars Berger, Robert F. Wimmer-Schweingruber  
**arXiv:** [2003.10851](https://arxiv.org/abs/2003.10851)  
**Date:** 2020-03-24  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2003.10851v1/

## Key points

- The study explores the properties of a solar wind stream and how they are determined by its source region and transport effects.
- Proton-proton collisional age is considered as an ordering parameter for the solar wind at 1AU and investigated in relation to the solar wind classification scheme developed by Xu & Borovsky (2015).
- A simplified solar wind classification scheme based solely on the proton-proton collisional age is proposed, called PAC solar wind classifier.
- The three basic solar wind types from this categorization cover different regimes in terms of proton-proton collisional age $a_{col,p-p}$.
- Sector-reversal plasma is a combination of particularly slow and dense solar wind and most stream interaction boundaries.
- The study shows that the solar wind is well ordered by the proton-proton collisional age, implying underlying intrinsic relationships between plasma properties, especially proton temperature and magnetic field strength in each plasma regime.
- Most solar wind parameters such as magnetic field strength B and oxygen charge state ratio $n_{O^{7+}}$/$n_{O^{6+}}$ change with the solar activity cycle. Therefore, all solar wind categorization schemes based on threshold values need to be adapted to the solar activity cycle as well.
- The proposed PAC classifier offers a simplified approach for classifying different types of solar winds based on their proton-proton collisional age.

## Summary

The study titled "Proton-proton collisional age to order solar wind types" by Verena Heidrich-Meisner, Lars Berger, and Robert F. Wimmer-Schweingruber explores the properties of a solar wind stream and how they are determined by its source region and transport effects. The authors consider the proton-proton collisional age as an ordering parameter for the solar wind at 1AU and investigate its relation to the solar wind classification scheme developed by Xu & Borovsky (2015). They propose a simplified solar wind classification scheme based solely on the proton-proton collisional age, which they call PAC solar wind classifier. This alternative scheme does not require explicit magnetic field information and leads to a classification that is very similar to the full Xu & Borovsky (2015) scheme. The authors observe that the three basic solar wind types from this categorization cover different regimes in terms of proton-proton collisional age $a_{col,p-p}$. They argue that sector-reversal plasma is a combination of particularly slow and dense solar wind and most stream interaction boundaries. The study shows that the solar wind is well ordered by the proton-proton collisional age, implying underlying intrinsic relationships between plasma properties, especially proton temperature and magnetic field strength in each plasma regime. The authors note that most solar wind parameters such as magnetic field strength B and oxygen charge state ratio $n_{O^{7+}}$/$n_{O^{6+}}$ change with the solar activity cycle. Therefore, all solar wind categorization schemes based on threshold values need to be adapted to the solar activity cycle as well. Overall, this study provides valuable insights into understanding how different types of solar winds can be classified based on their properties without requiring explicit magnetic field information. The proposed PAC classifier offers a simplified approach for classifying different types of solar winds based on their proton-proton collisional age.