Polytropic Behavior in Corotating Interaction Regions: Evidence of Alfv\'enic Heating

TL;DR

This study examines the polytropic behavior of different regions in corotating interaction regions (CIRs) using Wind spacecraft data, revealing Alfvénic heating effects and variable polytropic indices across regions.

Contribution

It provides new insights into the polytropic indices in CIRs and demonstrates the role of Alfvénic wave dissipation in plasma heating within these structures.

Findings

Compressed regions show increased polytropic index due to heating.

Uncompressed fast solar wind exhibits high {b3} correlated with Alfve9n wave activity.

Results support Alfve9nic heating as a key process in CIR plasma dynamics.

Abstract

Corotating Interaction Regions (CIRs) are recurring structures in the solar wind, characterized by interactions between fast and slow solar wind streams that compress and heat plasma. This study investigates the polytropic behavior of distinct regions in and around CIRs: uncompressed slow solar wind, compressed slow solar wind, compressed fast solar wind, and uncompressed fast solar wind. Using Wind spacecraft data and an established methodology for calculating the polytropic index ({\gamma}), we analyze 117 CIR events. Results indicate varying {\gamma} values across regions, with heating observed in compressed regions driven by Alfv\'en wave dissipation originating from fast streams. In the uncompressed fast solar wind, {\gamma} exceeds adiabatic values the most and correlates well with strong Alfv\'enic wave activity.