Contribution of polar plumes to fast solar wind

TL;DR

This study analyzes SOHO/UVCS data to determine the physical properties of solar polar plumes, revealing their significant contribution to the fast solar wind and their dynamic nature.

Contribution

It provides a self-consistent analysis of plume outflow speeds and densities, quantifying their contribution to the solar wind for the first time using UVCS data.

Findings

Plumes expand with outflow speeds similar to interplumes in most cases.

Plumes contribute approximately 20% to the polar solar wind.

Plume contributions vary with their stage of evolution.

Abstract

Context. Several physical properties of solar polar plumes have been identified by different published studies, however such studies are rare and sometimes in disagreement. Aims. The purpose of the present work is to analyze a set of SOHO/UVCS data dedicated to the observation of plumes and to obtain a picture of the physical properties of plumes in the intermediate solar corona through a self-consistent analysis. Methods. We applied the Doppler Dimming technique to data acquired by SOHO/UVCS in April 1996, which was during the very early phases of the mission. From this we derived outflow speeds and electron densities. We used SOHO/LASCO images as context data in order to better identify plume and interplume regions in the UVCS field of view. Results. The results we obtain demonstrate that in three cases out of four plumes expand with outflow speeds comparable to those of interplumes, and in a single case with lower speeds. We estimate that the contribution of plumes to the wind coming from the solar poles is about 20%, and that different plumes provide a different contribution, possibly according to different stages of their evolution. Conclusions. We conclude that plumes are not static structures, and that they contribute significantly to the wind coming from the solar poles.