The structure of the inner heliosphere as revealed by amateur astronomers' images of comets

Y. Ramanjooloo (1, 2), G. H. Jones (1,2), A. J. Coates (1,2) (1) Mullard Space Science Laboratory, Department of Space & Climate Physics, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK, (yr2@mssl.ucl.ac.uk) (2) The Centre for Planetary Science at UCL/Birkbeck, Gower Street, London, WC1E 6BT, UK. Comets' plasma (type I) tails have been studied as natural probes of the solar wind since the mid-20th century. The appearance, structure, and orientation of a comet's plasma tail are primarily controlled by local solar wind conditions. When the observing geometry is ideal, the direction and dynamics of the plasma tail can reveal temporal and spatial variations in the solar wind flow local to the comet. The plasma tail is generally oriented away from the solar radial direction due to the comet's orbital motion. Many tail features, such as condensations, kinks, and disconnection events can usually be directly related to changes in the local solar wind. Amateur images of comets obtained with modern equipment and sensors are arguably better in quality than professional images obtained only 2-3 decades ago. We have studied amateur images of several comets, primarily using images of comet C/2001 Q4 (NEAT), from December 2003 to December 2004, and comet C/2004 Q2 (Machholz), between September 2004 and June 2005. For these comets, we compared the aberration angle of their plasma tails with observed and modelled values of near-Earth solar wind data and other heliospheric events. The changing orientation and disturbances in the plasma tail of comet Machholz, NEAT and other comets are used to test the validity of amateur images of comets as a diagnostic tool to understand the temporal and spatial variability of the solar wind in the inner heliosphere. We summarise the results of the study. This analysis technique also offers an opportunity to investigate historical images of comets, thus providing snapshots of the variability of solar wind conditions over past solar cycles, e.g. latitudinal variations of the solar wind, heliospheric current sheet sector boundaries and the boundaries of transient features, such as coronal mass ejections and corotating interaction regions. We demonstrate the application of the analysis technique to historical data obtained by both amateurs and professionals.