On the multi-scale dynamics and energy flow near reconnection regions in the magnetopause and magnetotail using the MMS, Cluster and THEMIS observations during the geomagnetic storm of 31 December 2015

Abstract

Magnetic reconnection is a very important energy conversion process that plays a vital role in solar wind-magnetosphere coupling. This study presents a unique analysis of the coordinated observations from MMS, Cluster and THEMIS spacecraft during a geomagnetic storm on 31 December 2015. The analyses are aimed to understand the intricacies of the short-scale processes during 4 different short (20 min) encounters and a long duration (8 h) traversal of all the satellites covering the main and the recovery phase of the storm. The main results show that at the reconnection sites in the magnetotail, the FAC density is majorly contributed by the electrons moving anti-parallel to the magnetic field. Significantly, the FACs estimated from the Curlometer method and plasma (or local) method agree well and authenticate the interpretations. The majority of the electron population is found to shift towards the mid (0.2–2 keV) and high-energy (2–30 keV) range during the reconnection, wherein higher (∼one order more) ion and electron energy flux is observed under the effect of the intense storm compared to non-storm cases. The Hall electric field is found to be the major contributor to the total electric field during magnetic reconnection whereas, we observe the growing significance of the pressure divergence term during later phases of the storm. Longer duration (8-hour) continuous observations from the unique alignment of the four spacecrafts show a dominance of magnetic (plasma) properties over plasma (magnetic) properties in the magnetotail (magnetopause). The magnetotail (magnetopause) is found to be highly dynamic with higher (lower) levels of the electric and magnetic field, ion and electron temperature, and simultaneous lower (higher) levels of plasma density, energy flux, and FACs. The drastic enhancements of the plasma and field parameters happen in the sun-earth plane and during different crossings at the magnetopause and magnetotail. The simultaneous observations from magnetopause and magnetotail during a moderate geomagnetic storm indicate further needful coordinated investigations on the nature of reconnections on the day and night side and variations during the intense category of storms.