Scaling of Ion Outflow Speed and Ion Bulk Heating in Lobe Reconnection and Their Relations to Shear Flow

Abstract

Magnetic reconnection at the high-latitude magnetopause is accompanied by velocity shear due to the tailward flow of the magnetosheath. This study investigates 24 high-latitude magnetopause reconnection events observed by the Cluster satellites and examines how ion outflow speed and ion bulk heating depend on the upstream Alfvénic parameters and shear flow speed. We find that the ion outflow speed and ion bulk heating scale well with the hybrid asymmetric Alfvén speed ($V_{\text{A}L,\text{asym}}$) and the inflowing magnetic energy per particle ($m_i{V}_{\text{A}L,\text{asym}}^2$), respectively, calculated using the upstream magnetic field and plasma density on both the magnetosheath and lobe sides. This is the first observational evidence that the Alfvénic scaling relationships, previously known for reconnection in the solar wind and at the low-latitude magnetopause, also hold true for reconnection at the high-latitude magnetopause. We also find that both the ion outflow speed and ion bulk heating show a positive correlation with shear flow speed. These results imply that as shear flow speed increases, the magnetic field and plasma density in the magnetosheath near the lobe reconnection region may adjust in a way that increases $V_{\text{A}L,\text{asym}}$.