A global comparison of O⁺ upward flows at 850 km and outflow rates at 6000 km during nonstorm times

Abstract

.[1] There has been recent progress in understanding the sources and consequences of energetic O + in the ring current and other regions of the magnetosphere. Various energization mechanisms that depend on geomagnetic activity, altitude, magnetic local time, and relative position within the auroral oval acting on O + have been proposed. Our understanding of the altitude and magnetic local time variation of these processes has not proceeded as rapidly, however. Contemporary magnetosphere models now include species-dependent dynamics. These models will benefit from improved spatial and altitudinal knowledge of O + energization processes. Here we present a global view of O + upward flows observed at DMSP (850 km) compared to outflow rates observed by Polar (5000-7000 km) during nonstorm times in the framework of dynamic auroral boundary coordinates. This study considers observational proxies for heating and energization mechanisms and shows that these proxies set useful boundaries on their efficacy. This study indicates that during nonstorm times (1) energization between 850 km and 5000-7000 km is predominantly transverse, (2) the efficiency of ion energization is often not focused at the boundaries of the auroral zone, and (3) auroral zone acceleration above DMSP is relatively more important in the cusp than at midnight.

Dawnward shift of the dayside O+ outflow distribution: The importance of field line history in O+ escape from the ionosphere

“… Redmon et al [2012] have compared thermal upwelling O + fluxes observed on DMSP to energetic escaping O + fluxes observed near 2 R E (geocentric) by the Polar satellite and found that auroral zone acceleration processes above DMSP are more important on the dayside morning hours. In particular, Redmon et al [2012] found that above DMSP altitudes wave or transverse heating is the most important energization process. On the dayside, Kasahara et al [2001] and Chaston et al [2007]have shown that, on average, dayside wave power is associated with and focused at the cusp.…”

“…Integrals of the flux over magnetic latitudes (red asterisks) and the auroral zone in boundary coordinates (black +'s) are shown as a function of MLT. The latitude‐integrated flux in magnetic latitude coordinates is larger because, as discussed by Redmon et al [2010, 2012], not all upwelling ions observed by DMSP are in the auroral zone. The color insets in both coordinate systems show a peak flux (ions/s‐m 2 ) in the dayside upwelling in the noon sector.…”

“…Chen et al found a similarly sharp ramp in increasingly positive O + velocities near sunrise and a peak in diffusive flux nearer noon. The present study analyzes O + fluxes at 850 km and integrated over much higher auroral zone latitudes, which form the seed population for the energization processes acting at higher altitudes, resulting in ion outflows [e.g., Redmon et al , 2012 and references therein].…”

CASSIOPE Enhanced Polar Outflow Probe (e-POP) Mission Overview

“…Yau et al (2011) reviewed the different aspects of thermal and suprathermal ion outflows, including the polar wind (Yau et al 2007). Both ion outflow categories are strongly influenced by the solar EUV irradiance and solar wind energy input (Cully et al 2003) and the state of the magnetosphere-ionosphere-thermosphere, and both exhibit significant seasonal variations (Redmon et al 2012;Yau et al 1985). Compared with H + and He + , O + exhibits a much stronger dependence on magnetic and solar activity, the active-to-quiet time and solar maximum-to-minimum ratios of the energetic O + ion outflow rate being ∼ 20 and ∼ 5, respectively (Yau et al 1988).…”

Imaging and Rapid-Scanning Ion Mass Spectrometer (IRM) for the CASSIOPE e-POP Mission

“…Strangeway et al 2005), including direct heating of ions by plasma waves (Andre et al 1998), frictional heating and subsequent mirroring, and ambipolar outflow driven by photoelectrons (Abe et al 1993) or by heated ionospheric electrons resulting from soft auroral precipitating electrons (Redmon et al 2012).…”