The plasma environment inside geostationary orbit: A Van Allen Probes HOPE survey

The two full precessions in local time completed by the Van Allen Probes enable global specification of the near-equatorial inner magnetosphere plasma environment. Observations by the Helium-Oxygen-Proton-Electron (HOPE) mass spectrometers provide detailed insight into the global spatial distribution of electrons, H+, He+, and O+. Near-equatorial omnidirectional fluxes and abundance ratios at energies 0.1-30 keV are presented for 2 ≤ L ≤ 6 as a function of L shell, magnetic local time (MLT), and geomagnetic activity. We present a new tool built on the UBK modeling technique for classifying plasma sheet particle access to the inner magnetosphere. This new tool generates access maps for particles of constant energy for more direct comparison with in situ measurements, rather than the traditional constant μ presentation typically associated with UBK. We present for the first time inner magnetosphere abundances of O+ flux relative to H+ flux as a function of Kp, L, MLT, and energy. At L = 6, the O+/H+ ratio increases with increasing Kp, consistent with previous results. However, at L < 5 the O+/H+ ratio generally decreases with increasing Kp. We identify a new "afternoon bulge" plasma population enriched in 10 keV O+ and superenriched in 10 keV He+ that is present during quiet/moderate geomagnetic activity (Kp < 5) at ~1100-2000 MLT and L shell 2-4. Drift path modeling results are consistent with the narrow energy and approximate MLT location of this enhancement, but the underlying physics describing its formation, structure, and depletion during higher geomagnetic activity are currently not understood.

Assessing the role of oxygen on ring current formation and evolution through numerical experiments

Low O⁺/H⁺ ratio produced stronger ring currentInclusion of physics-based ionospheric outflow leads to a reduction in the CPCPOxygen presence is linked to a nightside reconnection point closer to the Earth.

Ionospheric redistribution during geomagnetic storms

[1]The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dst<-100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation but follows it by 3-6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.

An investigation of the magnetosphere–ionosphere response to real and idealized co-rotating interaction region events through global magnetohydrodynamic simulations

This study investigates the role of interplanetary magnetic field (IMF) B z fluctuations periodicity in the transfer of solar wind mass and energy to the magnetosphere during the co-rotating interaction region/high-speed stream event of 10 November 2003 through global modelling simulations using the space weather modelling framework. To do so, we used both solar wind observations and a variety of idealized inputs as upstream boundary conditions, describing different solar wind configurations for which relative contribution of the peak-to-noise ratio in the input B z power spectrum to the periodicity transfer is examined. Fast Fourier transforms of both input to and the response of the magnetosphere reveal that the transfer of IMF B z periodicity to the magnetosphere is unaltered by other solar wind parameters, although the size of the peak-to-noise ratio of the input signal is the controlling factor that determines this transfer. The global magnetosphere simulation suggests that a threshold amount of power (peak-to-noise ratio) of approximately 10 in the input signal is needed for the magnetosphere to react to the periodicity in the input B z , while for the cross-polar cap potential, the threshold amount is significantly smaller.