Presentation #105.02 in the session Multi-scale physics of Earth’s magnetotail.
Understanding the effects of multi-scales on the onset of collisionless magnetic reconnection in the earth’s magnetotail during substorms requires the understanding of the balance between local and global processes and how these processes are affected by the presence of the heavier O+ ions of ionospheric origin. The presence of ionospheric oxygen ions (O+) changes the dynamics of the Earth’s magnetotail during the growth and expansion phases of a substorm. For example, the mass loading of the reconnection inflow region due to the O+ ions, abundantly present in the lobes during storm times, leads to the reduction of the reconnected flux rate. However, in a realistic magnetosphere, the higher O+ content is highly correlated with the more disturbed conditions. During these conditions, together with the increase in the O+ content, the lobe magnetic field and the tail pressure are also substantially modified, and the synergy of these multi-scale effects can lead to the suppression of the reduction effect of O+ in the reconnection rate. In this study we use Cluster and MMS observations of reconnection X-line encounters to estimate the local reconnection rate for a range of conditions. In order to evaluate these observations and assess the role of global and meso scales in the substorm onset and development, we use for the first time 3D global hybrid simulations (HYPERS code) to study the build-up of the O+ ions in the magnetotail by launching O+ outflows. A comparative study is performed between a magnetosphere without ionospheric outflows and a magnetosphere where outflows are launched from the dayside and/or the nightside.