Using Stereoscopic Observations of Cometary Plasma Tails to Infer Solar Wind Speed

<p>Detection of the solar wind speed near the Sun is significant in understanding the heating and acceleration of the solar wind. Cometary plasma tails have long been used as natural probes for solar wind speed; previous solar wind speed estimates via plasma tails, however, were based on comet images from a single viewpoint, and the projection effect may influence the result. Using stereoscopic observations from the Solar Terrestrial Relations Observatory and the Solar and Heliospheric Observatory, we three-dimensionally reconstruct the plasma tails of three comets C/2012 S1 (ISON), C/2010 E6, and C/2011 W3 (Lovejoy) and infer the ambient solar wind speed. The first comet is located between 3.5 and 6 solar radii (Rs) away from the Sun at high latitudes; the estimated solar wind speed is about 300-500 km s<sup>-1</sup>. The second comet is located within 10 Rs and about 20\textdegree away from the ecliptic; the estimated solar wind speed is about 200-320 km s<sup>-1</sup>. The third comet is also located at low latitudes but farther (\&gt;20 Rs) away from the Sun; the estimated solar wind speed is about 100-600 km s<sup>-1</sup>. For comets near the ecliptic, our results are close to those predicted by MHD models, whereas for the comet at high latitudes, the deviation between our estimate and the model results is notable. This consistency and difference could be used to constrain and improve solar wind models. We will seek opportunities to apply the method to comet 322P, whose tail may sweep the Parker Solar Probe.</p>
Year of Publication
The Astrophysical Journal
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Date Published