Constraints on the variable nature of the slow solar wind with the Wide-Field Imager on board the Parker Solar Probe

TL;DR

This study uses simulations and observations from the Parker Solar Probe's WISPR instrument to constrain the properties and release mechanisms of slow solar wind transient density structures near the solar equator.

Contribution

It introduces four new simulation scenarios to analyze the release and propagation of transient density structures in the slow solar wind, providing constraints on their properties and detectability.

Findings

Simulated density structures range from 2-8 Rs in size.

Approximately 35-45 structures per day are released from the solar equatorial plane.

Density structures covering 1-20% of perihelion could be detected by PSP.

Abstract

In a previous work we analysed the white-light coronal brightness as a function of elongation and time from Wide-Field Imager (WISPR) observations on board the Parker Solar Probe (PSP) mission when PSP reached a minimum heliocentric distance of ~ 28 Rs. We found 4-5 transient outflows per day over a narrow wedge in the PSP orbital plane, which is close to the solar equatorial plane. However, the elongation versus time map (J-map) analysis supplied only lower limits on the number of released density structures due to the small spatial-scales of the transient outflows and line-of-sight integration effects. In this work we place constraints on the properties of slow solar wind transient mass release from the entire solar equatorial plane. We simulated the release and propagation of transient density structures in the solar equatorial plane for four scenarios: (1) periodic release in time and longitude with random speeds; (2) corotating release in longitude, periodic release in time with random speeds; (3) random release in longitude, periodic release in time and speed; and (4) random release in longitude, time, and speed. The simulations were used in the construction of synthetic J-maps, which are similar to the observed J-map. The four considered scenarios have similar ranges (35-45 for the minimum values and 96-127 for the maximum values) of released density structures per day from the solar equatorial plane and consequently from the streamer belt, given its proximity to the solar equatorial plane during the WISPR observation. Our results also predict that density structures with sizes in the range 2-8 Rs, covering 1-20 % of the perihelion could have been detectable by PSP in situ observations during that interval.