Ion Moment Variability Across Substorm Phases: Statistical Insights

Abstract

In this study, we analyze 5 years of THEMIS and MMS mission data to statistically investigate the distribution of earthward and tailward ion flows during three substorm phases in Earth's magnetotail plasma sheet. The average flow patterns reveal primarily slow sunward and occasional fast tailward convection throughout all substorm phases. Most earthward flows in the plasma sheet had speeds around 35 km/s within the region $X>-15R_E$, as observed by THEMIS, while peak velocities reached up to 350 km/s in areas where , as observed by MMS-1. Tailward flows showed velocities near 30 km/s earthward of $X\approx -15$, according to THEMIS, with peak velocities of 300 km/s in the region $X>-15R_E$, based on MMS-1 data. Dusk-dawn $\left(V_{\perp y}\right)$ flows exhibit duskward motion in the premidnight and midnight regions and dawnward motion in the postmidnight sector. A dawn-dusk density and pressure asymmetry was observed, with higher density and pressure on the dawn side of the near-Earth plasma sheet throughout the growth to recovery phases. Plasma sheet temperatures were generally lower during the growth and late expansion phases compared to the recovery phase, especially near midnight compared to the flanks. A Student's t-test revealed a statistically significant asymmetry in ion flows and plasma parameters between the dawn and dusk sectors.