Thermodynamic Evolution of Plumes

TL;DR

This study investigates the thermodynamic evolution of solar coronal plumes using multi-wavelength observations, revealing their formation processes, thermal structure, and dynamic properties, which are crucial for understanding their role in solar wind generation.

Contribution

It provides detailed observational insights into the formation, thermal structure, and dynamics of coronal plumes, enhancing understanding of their evolution and influence on solar wind.

Findings

Plume formation is preceded by small-scale jets at its base.

Plumes exhibit multi-thermal nature with internal temperature structures.

Outflow velocities are significant and sometimes comparable to sound speeds.

Abstract

Plumes are considered to play an important role in the origin of solar wind. However, an understanding of their thermodynamic evolution is not complete. Here, we perform a detailed study of a plume inside a coronal hole throughout its lifetime, using the observations from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI). We find that the plume's formation is preceded by frequent occurrences of small-scale jets and jet-lets at its base, leading to the gradual development of plume haze. The plume rapidly developed within the first six hours into its well-known morphology. Light curves from all EUV channels exhibit a similar profile, suggesting its multi-thermal nature and intensity modulation over its lifespan. Moreover, the photospheric magnetic field dynamics at the plume's base are highly correlated with its light curve in 171~{\AA}. We calculate outflow velocities, observed prominently in the 171~{\AA} passband and mildly in the 193~{\AA} and 211~{\AA} passbands, with median speeds lower in higher temperature bands but occasionally comparable to the respective sound speeds. When data is averaged over larger spatial scales, the plume appears iso-thermal along its length, with constant temperature throughout its lifetime. However, an analysis of the differential emission measure at full resolution reveals the presence of higher-temperature plasma, indicating internal temperature structures within the plume. These results provide new insights into the formation, dynamics, and thermal properties of coronal plumes, placing tighter constraints on models to understand their thermodynamic evolution and potential role in the solar wind.