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

Yudish Ramanjooloo,Geraint H Jones

doi:10.1029/2021ja029799

Yudish Ramanjooloo, Geraint H Jones

Open Access

https://doi.org/10.1029/2021ja029799

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Abstract

AbstractThe 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.

Highlights

The cometary ion tail is an induced magnetotail structure, pointing approximately along the anti-sunward direction but lagging the true anti-solar direction by a few degrees
We obtained 109 vswr estimates from 36 fully processed images out of 123 am475 ateur images with a detectable ion tail. 7 solar wind estimates did not pass the rejection process and 43 of the remainder are measurements of a sinuous and variable ion tail that were too challenging to interpret with sufficient confidence
The amateur images amassed for this time period were supplemented by our own observations undertaken at the Isaac Newton Telescope in January 2014, presenting a unique opportunity to validate the quality of amateur images using high quality observations from an established scientific observing facility

Summary

Introduction

The cometary ion tail is an induced magnetotail structure, pointing approximately along the anti-sunward direction but lagging the true anti-solar direction by a few degrees. This aberration angle arises from a combination of the comet’s orbital velocity and the local solar wind velocity, vsw. With a favourable observing geometry, comets with a suitably bright ion tail, can contribute towards increasing our understanding of the variability in vsw. The first hints of the solar wind’s existence came from observations of comets’ ion tails (Hoffmeister, 1943; Biermann, 1957).

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