Center for Astrophysics Research and Technologies Seminar Series
Solar Wind Acceleration in the Open Field Corona
Presented by Samantha Wallace (UNM)
This dissertation work involves two projects that investigate how the solar wind is accelerated along continuously open solar magnetic field lines. The first project involves determining the role played by the magnetic expansion factor in solar wind acceleration. For the past 25+ years, the magnetic expansion factor (fs) has been a parameter used in the calculation of terminal solar wind speed (vsw) in the Wang-Sheeley-Arge (WSA) coronal and solar wind model. It measures the rate at which a magnetic flux tube on the Sun expands in cross section between the solar surface (1 Rs ) and 2.5 Rs , and is inversely related to vsw. Since the discovery of this inverse relationship, the physical role that fs plays in solar wind acceleration has been debated. In this study, we investigate whether fs plays a causal role in determining terminal solar wind speed or merely serves as proxy. To do so, we study pseudostreamers, which occur when 2 coronal holes (i.e., concentrated regions of unipolar flux tubes) of the same polarity are near enough to one another to limit magnetic field line expansion, and thus have low fs. Pseudostreamers are of particular interest because despite having low expansion factors, spacecraft observations show that solar wind emerging from these regions have slow to intermediate speeds of 350-550 km/s. In this work, we develop a methodology to identify pseudostreamers that are magnetically connected to satellites using WSA output. We use this methodology to identify several cases (~20 - 30) where spacecraft are magnetically connected to pseudostreamers, and perform a statistical analysis to determine the correlation of fs within pseudostreamers and the terminal speed of the solar wind emerging from them. Future work will explore the role of fs in modulating the fast solar wind and will involve a similar analysis for cases where spacecraft are deep within coronal holes. The second project makes use of global radial solar wind outflow maps derived via Doppler dimming (Bemporad et al., 2017). These maps specify the global solar wind speed from ~2-5 Rs. We will use these maps, along with WSA output and in-situ spacecraft observations to determine acceleration profiles for the solar wind emerging from continuously open magnetic field lines. This will be accomplished by connecting the Doppler dimming determined speeds along the WSA specified magnetic field lines from 2 - 5 Rs with in-situ observations at 1 AU where we have the measured speed, elemental composition, and charge states of the solar wind from ACE. The elemental composition and charge state information will help to ensure that we are working with boundary and high speed solar wind and not slow or transient wind. We will explore whether these acceleration profiles are function of fs or other coronal parameters.
2:00 pm, Thursday, November 16, 2017
PAIS-2540, PAIS
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