Effects of Solar Wind Dynamic Pressure on Plasma Characteristics and Location of the Near-Earth Reconnection Point

Solar wind dynamic pressure controls the size of Earth's magnetosphere. When the dynamic pressure increases, the magnetopause and magnetotail contract. This contraction moves the magnetic reconnection point in the current sheet closer to Earth than during lower dynamic pressure conditions. As a result, periods of high dynamic pressure are expected to produce stronger responses in magnetotail plasma than periods of low dynamic pressure. The Wind satellite, located at ~220RE upstream of Earth, monitors the solar wind density, velocity, and the interplanetary magnetic field (IMF). Meanwhile, the Magnetospheric MultiScale (MMS) spacecraft spent two three-month spans observing the magnetotail at two different apogees from Earth (May to July 2016 at ~12 RE and June to August 2017 at ~25 RE). We examine these data when magnetic reconnection in the current sheet observed by MMS coincided with elevated dynamic pressure observed by Wind and propagated to 20 RE upstream. Because the location of the X-line in the tail also varies with IMF Bz strength and orientation, we bin events according to the concurrent IMF Bz orientation. We also bin events according to the observed X-line location with respect to the spacecraft and the observed trajectory of the X-line in the GSM-X direction because the motion of the X-line points to a change in the mechanisms dominating the dynamics of the plasma sheet region. With these binned events, we make two primary comparisons. First, we compare the locations of tail reconnection events at high solar wind dynamic pressure to those of reconnection events at low solar wind dynamic pressure. Second, we compare ambient plasma sheet characteristics such as plasma density, magnetic field strength, and current density of reconnection observations ranging from ~10RE to 25RE down-tail. These analyses help us further understand how substorms can vary their effects on the magnetospheric plasma.