Center for Astrophysics Research and Technologies Seminar Series
Mapping the Solar Wind from Source to Spacecraft
Presented by Samantha Wallace (UNM)
For the past 25+ years, the magnetic expansion factor (f_s) has been a parameter used in the calculation of terminal solar wind speed (v_sw) in the Wang-Sheeley-Arge (WSA) coronal and solar wind model. The magnetic expansion factor measures the rate of flux tube expansion in cross section between the photosphere out to 2.5 solar radii (i.e., source surface), and is inversely related to v_sw (Wang & Sheeley, 1990). Since the discovery of this inverse relationship, the physical role that f_s plays in solar wind acceleration has been debated. In this study, we investigate whether f_s plays a causal role in determining terminal solar wind speed or merely serves as proxy. To do so, we identify pseudostreamers, which occur when coronal holes of the same polarity are near enough to one another to limit field line expansion. Pseudostreamers are of particular interest because despite having low f_s, spacecraft observations show that solar wind emerging from these regions have slow to intermediate speeds of 350-550 km/s (Wang et al., 2012). In this work, we develop a methodology to identify pseudostreamers that are magnetically connected to spacecraft (i.e., ACE, STEREO-A & B) using WSA output derived with synchronic ADAPT input maps. We utilize this methodology to track the parcel of solar wind that left the pseudostreamer and obtain the spacecraft-observed solar wind speed for those field lines. We then compare the magnetic expansion factor of the last open field line on either side of each pseudostreamer cusp with the observed solar wind speed from spacecraft magnetically connected to the region. We identified 37 pseudostreamers and performed a statistical analysis to determine the correlation of f_s at pseudostreamer cusps and the terminal speed of the emerging solar wind. Our results show that there appears to be no correlation between f_s and v_sw at pseudostreamer cusps. Future work will involve looking at the compositional signatures of the solar wind for each pseudostreamer, and will explore the role of f_s in modulating the fast solar wind along continuously open field lines using Ulysses observations deep inside coronal holes.
2:00 pm, Thursday, March 21, 2019
PAIS-2540, PAIS
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