The temporal and spatial scales of density structures released in the slow solar wind during solar activity maximum

TL;DR

This study uses heliospheric imagery to analyze the spatial and temporal scales of density structures released in the slow solar wind during solar maximum, revealing cyclic activity and contributions to mass flux.

Contribution

It provides new insights into the timing, size, and distribution of density structures in the slow solar wind, linking remote sensing with in-situ measurements.

Findings

Density structures are released approximately every 19.5 hours.

Structures have a typical radial size of about 12 solar radii.

The global heliospheric current sheet is dominated by blobs and flux ropes.

Abstract

In a recent study, we took advantage of a highly tilted coronal neutral sheet to show that density structures, extending radially over several solar radii (Rs), are released in the forming slow solar wind approximately 4-5 Rs above the solar surface (Sanchez-Diaz et al. 2017). We related the signatures of this formation process to intermittent magnetic reconnection occurring continuously above helmet streamers. We now exploit the heliospheric imagery from the Solar Terrestrial Relation Observatory (STEREO) to map the spatial and temporal distribution of the ejected structures. We demonstrate that streamers experience quasi-periodic bursts of activity with the simultaneous outpouring of small transients over a large range of latitudes in the corona. This cyclic activity leads to the emergence of well-defined and broad structures. Derivation of the trajectories and kinematic properties of the individual small transients that make up these large-scale structures confirms their association with the forming Slow Solar Wind (SSW). We find that these transients are released, on average, every 19.5 hours, simultaneously at all latitudes with a typical radial size of 12 Rs. Their spatial distribution, release rate and three-dimensional extent are used to estimate the contribution of this cyclic activity to the mass flux carried outward by the SSW. Our results suggest that, in interplanetary space, the global structure of the heliospheric current sheet is dominated by a succession of blobs and associated flux ropes. We demonstrated this with an example event using STEREO-A in-situ measurements.