| Authors : | Susanta Kumar Bisoi (National Institute of Technology, Rourkela – 769008, India),
Dipti Rajan Rout (GFZ German Research Centre for Geosciences, Potsdam, Germany),
Janardhan, P. (Physical Research Laboratory, Navrangpura, Ahmedabad – 380009, India),
Fujiki, K. (Institute for Space-Earth Environmental Research, Nagoya University, Japan),
and Charkarabarty, D. (Physical Research Laboratory, Navrangpura, Ahmedabad – 380009, India).
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| Abstract : | The solar wind flow is primarily radial in nature. However, non-radial flows have been observed on several occasions, which are usually geo-effective and also have consequences on space weather. Despite that the exact origin of the non-radial flows has not yet been addressed. Here, I will present our detailed investigations of 25 such non-radial events during the period 1995-2017. All the events of interest present highly non-radial solar wind cases with the azimuthal flow angle exceeding > 6 degree for a period of one day or more and are selected during the period when no coronal mass ejection and/or co-rotating interaction regions were seen. For most of the events, the near-Earth solar wind density was < 5 cm^−3 for periods of more than one day, similar to the well-known “solar wind disappearance events” wherein an unusual drop of the near-Earth solar wind density < 1 cm^−3 for prolonged periods (>1 day) was typically noticed. Based on the significant increase seen in the charge state ratio of O7+/O6+ at 1 AU for most of the events, we traced them back to the Sun and found their source regions to be originated in around active region and coronal hole (AR-CH) pairs located at the central meridian. Further, examining the dynamical evolutions in their source regions using Extreme ultra-violet Imaging Telescope (EIT) and Michelson Doppler Imager (MDI) data, a clear reduction in CH area accompanied by the formation of new coronal loops and the emergence of new magnetic flux regions were observed for all the events. The evolutions taking place in AR-CH boundaries eventually disturb the stable CH configurations, and thereby, leading to the extremely non-radial solar wind outflows. I will discuss, based on our results, a possible causative mechanism of the origin of the highly non-radial solar wind flows.
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