Speaker: Marco Velli
Affiliation: EPSS, UCLA

Abstract:
It has been established since the Helios epoch and confirmed by Ulysses and SOHO that the sources of fast solar wind streams at solar minimum are the polar coronal holes, while slower solar wind streams have contributions from different sources. The larger than expected filling factor of slow solar wind has been attributed to flows coming from coronal hole boundaries, i.e., regions with large expansion factors, or from regions where the mapping of the magnetic field from the photosphere into the heliosphere is complex, as identified for example by the squashing factor, and known as the S-Web.
The observations by Parker Solar Probe that much of the solar wind, independently of speed, is dominated by Alfvénic fluctuations, and the frequent observation of slow Alfvénic solar wind, previously observed relatively rarely in Helios and Wind data, provide evidence for a picture of solar wind origins that incorporates both the expansion factor and S-web paradigms: both coronal holes with large expansion and S-Web regions act as slow solar wind sources, with the difference that highly expanding coronal holes provide Alfv.nic slow streams, while the S-web wind is unlikely to exhibit strong Alfvénic correlations.
As far as the fast solar wind is concerned, we focus on a new aspect associated with the interaction of spherically polarized Alfvén waves and the background wind. It arises from the continuous presence of spherically polarized Alfvénic fluctuations, in the form of switchbacks and patches of switchbacks, that lead the solar wind to be formed of multitudes of one-sided jets. We call the average effect of such jets the Gosling boost, as Jack Gosling was the first to recognize such one-sided jets over the baseline unperturbed solar wind expansion. Here we show how the Gosling boost provides direct empirical evidence for the acceleration of the wind by Alfvénic fluctuations and discuss the more general question
of the origin and acceleration of Alfvénic solar wind streams.

Zoom/Meeting Link: https://ucla.zoom.us/j/97828298609?pwd=kbJEOQ2YHlxZifxQW1uT7SQkiBmchT.1

Submitted by: Omar Abuassaf (oabuassaf@yahoo.com)