Using Single-view Observations of Cometary Plasma Tails to Infer Solar Wind Speed

Abstract

Abstract A comet plasma tail is a product of the interaction between the solar wind and the comet’s coma, and has long been studied as a natural probe of the solar wind condition. We previously developed a method to derive the solar wind speed from dual-view observations of comet plasma tails. Here we improve the method to use single-view observations by assuming a radially propagating solar wind and apply it to two comets, C/2011 W3 (Lovejoy) and C/2012 S1 (ISON) observed by coronagraphs on board the Solar and Heliospheric Observatory and STEREO. We compare the results to the solar wind simulations and tomography and to the results from our previous dual-view method, and find they are generally consistent, especially when the comets were far away from the Sun or far away from the ecliptic plane and when the observer is high above the comet’s orbital plane. Meanwhile, we notice that this method may suffer from a large error for comets near the ecliptic plane and close to the Sun, where a nonradial component of the solar wind is significant. Using the observations from the first seven orbits of the Parker Solar Probe, we show that the solar wind deviates from a radial direction significantly within around 35 R s. We also notice that, when the nonradial solar wind component is presented, the error may be even larger if the observer is closer to the comet’s orbital plane. This method provides a potentially useful tool to estimate the solar wind speed around comets from only single-view imaging observations.