On the presence and properties of cold ions near Earth's equatorial magnetosphere

Abstract

Plasma flows related to magnetospheric convection or ULF waves often increase cold ions' kinetic energy sufficiently above the spacecraft potential energy so that these ions can be detected by charged particle instrumentation. Other detection methods also reveal the presence of cold ions even in the absence of flows. By applying such methods to complementary data sets obtained from particle, electric field, and magnetic field measurements by the multiple Time History of Events and Macroscale Interactions during Substorms spacecraft, we study the occurrence rates of cold ions and properties-composition, densities, and temperatures-of the dominant species (H + , He + , and O + ) near the equatorial magnetosphere. As plasma flows occur at all magnetic local time (MLT) sectors, predominantly outside the plasmasphere, they enable studies of cold ion occurrence and properties as functions of geocentric distance (up to 13 R E ) and MLT. Of the dominant cold ions, protons are most abundant on the dayside and coldest almost everywhere. By comparison, the heavier ions show evidence of larger abundance on the nightside and higher temperatures at most locations: median n He+ /n H+ is ≤0.1 in the afternoon, ≥1.0 on the nightside, and near 0.5 at dawn; median n O+ /n H+ exceeds 1 throughout the nightside and around dawn at smaller geocentric distances but varies from 0.0 to 0.1 in the afternoon; and T O+ > T He+ everywhere. By isolating the convective particle drift component of measured ion flows, we deduce that nightside/dawn/prenoon cold ions are components of the warm plasma cloak while cold ions near noon/afternoon are likely of mixed origin, including nightside/cusp outflow, plasmaspheric plumes, and the solar wind.

Subpacket structures in EMIC rising tone emissions observed by the THEMIS probes

“…These parameters in Table 1 are consistent with the particle data of THEMIS observation and those reported by Lee and Angelopoulos [2014]. The time evolution of the emission is controlled mostly by the nonlinear growth rate and optimum amplitude, which are determined by the density and average perpendicular velocity of energetic protons [Omura et al, 2010, equation (54); Shoji and Omura, 2013, equation (22)].…”

Previously hidden low-energy ions: a better map of near-Earth space and the terrestrial mass balance

“…Plumes are usually found in the afternoon and last for days, but weaken in density, width and flux with time (Chandler et al 1999, Borovsky and Denton 2008, Darrouzet et al 2008, Moore et al 2008, Spasojevic and Sandel 2010. Low-energy ions are found just inside the magnetopause, not only in plasmaspheric plumes (Matsui et al 1999, André and Lemaire 2006, Lee and Angelopoulos 2014, and indications of a cold 'plasmaspheric wind' have been found (Dandouras 2013). However, as for the high latitude case, observations of low-energy ions onboard a sunlit, and charged spacecraft have been rare.…”

The Earth: Plasma Sources, Losses, and Transport Processes

“…Nightside equatorial cold ions were sampled using the ULF wave technique by Lee and Angelopoulos (2014) out to ∼13 R E during predominantly quiet times (observation interval between 2008 and 2013). They used the THEMIS satellites to sample cold ions during intervals of enhanced bulk plasma flows (convection or ULF waves) that accelerated ambient cold ions above the spacecraft potential so they could be detected by the particle instruments carried by the three inner THEMIS spacecraft (low inclination, 1.5 by 13 R E ).…”

“…These nightside equatorial observations support the interpretation by Engwall et al (2009b) that the outflowing LEP observed with Cluster II were likely energized above the energy needed to form a wake at locations near the plasma sheet. Lee and Angelopoulos (2014) used the heavy ion density ratios and higher temperatures on the nightside to also infer a major ionospheric source of LEP at L < 13 R E . They noticed another trend: the median temperatures of all three species were quite warm (10-100s eV) and traced out a path from pre-midnight through the dawn side, consistent with particles in the warm plasma cloak, with evidence of another path of the nightside warm ions along the dusk side.…”

“…Hamilton et al (1988) showed that during a very large storm, ionospheric O + became the dominant contributor to the plasma pressure at the peak of the main phase. Greenspan and Hamilton (2002) Kistler et al 1989Kistler et al , 1999Jordanova et al 2001Jordanova et al , 2003Jordanova et al , 2010 have shown that particle drift from the near-earth plasma sheet, with a large convection electric field bringing the ions into the inner magnetosphere, and then a reduced convection electric trapping the ions in the inner magnetosphere, is able to explain Lee and Angelopoulos (2014) the observed ring current spectra. The complex, non-maxwellian energy spectra observed in the ring current result from the competition between gradient curvature and E × B drifts in the inner magnetosphere, combined with loss processes along the drift path.…”