Solar Wind Velocities at Comets C/2011 L4 Pan‐STARRS and C/2013 R1 Lovejoy Derived Using a New Image Analysis Technique

Abstract

The ion tails of bright comets have long been considered as a natural tracers of the solar wind (SW) near these objects. Studies of comets and their ion tails allow inexpensive monitoring of key SW structures in the inner heliosphere, much of which is otherwise only accessible by in situ SW spacecraft measurements. Here, we present a novel technique to mine the rich archive of amateur, professional and spacecraft observations of cometary ion tails. To demonstrate this, we focus on Near‐Sun comet C/2011 L4 (Pan‐STARRS) during Carrington Rotations (CR) 2134 and 2135 and comet C/2013 R1 (Lovejoy) during CR 2118. We outline the technique’s shortcomings, including its geometric limitations, and present a catalog of radial SW velocities derived in the near‐comet environment and information on the heliospheric conditions inferred from the measured SW. Complementary measurements, derived from folding ion rays and a velocity profile map built from consecutive images, are provided as an alternative means of quantifying the SW ‐cometary ionosphere interaction. We find that comets are generally good indicators of SW structure, but the quality of the results is strongly dependent on the observing geometry.

Fine-scale structure in cometary dust tails II: Further evidence for a solar wind influence on cometary dust dynamics from the analysis of striae in comet C/2011 L4 Pan-STARRS

“…However, the given speeds of 600 km s −1 to which particles are supposedly accelerated is far larger than the values for the solar wind speed given around the comet from this model. The interpretation of the clumpy tail as an ion tail given by Ramanjooloo (2015) and Ramanjooloo and Jones (2022) was used to derive solar wind speeds that lay between 200 and 400 km s −1 , which is much more in agreement with the CORHEL simulated results. Before a conclusion can be drawn on the most likely interpretation, the orientation of the short straight tail must also be considered, as the interpretation of both tails depends somewhat on each other; they of course cannot both be ion tails.…”

“…From all the evidence in the temporal maps of both the clumpy tail and short straight tail, and the CORHEL simulation results, the conclusion by Ramanjooloo (2015), Ramanjooloo and Jones (2022) by far seems the most probable. This interpretation gives the clumpy tail as a disparate ion tail, with the short straight tail appearing to be some kind of elemental tail.…”

“…The HI-1 dataset was previously analysed by Raouafi et al (2015) to investigate a phenomena they named High-Velocity Evanescent Clumps (HVECs), material that the authors suspected to be charged dust particles picked up by the solar wind or neutral atoms accelerated by radiation pressure with 𝛽 𝑟 > 50. However, other analyses have speculated that these clumps are simply the comet's ion tail (Ramanjooloo (2015), Ramanjooloo and Jones (2022)). Fig.…”

“…Right of this is another short straight tail. Raouafi et al (2015) labels these two tails as the HVEC tail and ion tail respectively, whereas Ramanjooloo (2015), Ramanjooloo and Jones (2022) identify them as the ion tail and elemental iron tail respectively. The correct interpretation may be discernible by creating temporal maps of the area surrounding each tail (see Section 4.2).…”

“…In order to help resolve the dilemma between sources that differ on what to label the other tails of C/2011 L4, temporal maps of these two additional tail regions have been created. The clumpy tail describes the region given by Raouafi et al (2015) as the HVEC tail and by Ramanjooloo (2015) and Ramanjooloo and Jones (2022) as the ion tail.…”