The role of O+ in the local, mesoscale and global dynamics of the earth’s magnetotail

Abstract:

The ionospheric oxygen ions (O⁺) can change the dynamic of the Earth’s magnetotail during the substorm phases. It is shown that the mass loading of the reconnection inflow region should lead to the reduction of the reconnected flux rate [Shay and Swisdak, 2004; Karmimabadi et al, 2011; Tenfjord et al., 2019]. In a realistic magnetosphere the higher O⁺ content is highly correlated with more disturbed conditions, therefore the lobe magnetic field and overall the tail pressure is substantially modified. A recent statistical study using Cluster observations showed that a higher O⁺ content during the substorm growth phase makes the substorm more difficult to trigger, while during the substorm expansion phase the magnetotail unloading rate is faster when the O⁺ content is higher [Liu et al, 2013]. Analyzing Cluster and MMS observations of X-line encounters in the Earth’s magnetotail we find that while the normalized reconnection rate is independent of the mass density in the plasma sheet, the rate of reconnected flux does increase with the density of O⁺. This result is in agreement with the [Liu et al, 2013] results and it suggests that during disturbed events, the higher tail pressure can overcome the reduction of the reconnection rate due to the presence of O⁺ and will result in a faster rate of reconnected flux.