Connecting the Low to High Corona: Propagating Disturbances as Tracers of the Near-Sun Solar Wind

TL;DR

This study tracks propagating disturbances from the low corona to extended regions, revealing distinct classes with different speeds and behaviors, enhancing understanding of the solar wind acceleration process during solar minimum.

Contribution

The paper introduces a new method for generating nonradial height-time profiles of propagating disturbances, providing detailed velocity profiles and classifications of these disturbances during solar minimum.

Findings

Identification of slow and fast propagating disturbances with distinct speed profiles.

Slow disturbances accelerate from ~16 km/s to ~200 km/s from 1.5 to 7.5 solar radii.

Periodic brightness variations correlate with disturbance propagation, consistent with solar wind speeds.

Abstract

We revisit a quiet 14-day period of solar minimum during January 2008 and track sub-streamer propagating disturbances (PDs) from low heights in STEREO/EUVI to the extended corona through STEREO/COR1 and into STEREO/COR2 along nonradial paths that trace the structure of the underlying streamers. Using our recently developed method for generating nonradial Height-Time profiles of outward PDs (OPDs) and inward PDs (IPDs), we obtained their velocities along the radial and position angle directions. Our analysis of 417 unique OPDs revealed two classes: slow and fast OPDs. Slow OPDs form preferentially at $\approx$1.6 $R_\odot$ closer to the streamer boundaries, with asymmetric occurrence rates, and show speeds of $16.4_{-8.4}^{+26.6}km/s$ at 1.5 $R_\odot$ and accelerate up to $200.1_{-57.9}^{+71.1}km/s$ at 7.5 $R_\odot$. Fast OPDs form preferentially at $\approx$ 1.6 $R_\odot$ and at $\approx$3.0 $R_\odot$ both at the streamer boundaries and slightly more often within them. They show speeds of $87.8_{-24.8}^{+59.1}km/s$ at 1.5 $R_\odot$ up to $197.8_{-46.7}^{+61.8}km/s$ at 7.5 $R_\odot$. IPDs are observed forming at $\approx$1.8 $R_\odot$ with speeds of tens of $km/s$, mostly concentrated in the aftermath of a CME eruption. We present an example in which we show that periodic brightness variations related to OPDs remained in the range of 98 to 128 min, down to $\approx$2.0 $R_\odot$, well within the field of view of COR1. The velocity profiles of slow OPDs for heliocentric height below 3.0 $R_\odot$ show good agreement with speeds more closely related to the bulk solar wind obtained via interplanetary scintillation.