On the fibrous structure of currents in the magnetosphere

Fibrous structure of current system in earth magnetospher

Instantaneous Aspects of Sq-currents According to Data on the Equinox Season During the IGY

Sq-field dynamics determined from IGY dat

The UT /Universal Time/ component in Sq variations, according to data obtained during the second season MPG

Universal time component in geomagnetic variations, according to International Geophysical Year dat

On the predominance of oblique disturbances in the supersonic shear flow instability of the geomagnetic tail boundary

A study is made of the influence of the longitudinal magnetic field and density inhomogeneity on the supersonic shear flow instability at the magnetospheric tail boundary. It is shown that the most unstable are slow oblique (3D) disturbances, with a phase velocity approaching at a sufficiently large angle (with respect to the flow direction) the magnetosonic velocity. Their growth rate and spectral width are much larger than those of the usually considered longitudinal (2D) supersonic disturbances. The magnetic field reduces the compressibility effect and, unlike the subsonic case, has a noticeable destabilizing effect on the excitation of oblique disturbances

Seasonal variations of medium-latitude Sq currents according to MGG data /IGY/

Seasonal variations of medium latitude Sq ionospheric currents determined from IGY dat

On the Existence of Ionospheric Feedback Instability in the Earth’s Magnetosphere-Ionosphere System

The ionospheric feedback instability (IFI) has been considered one of the main generation mechanisms for large-amplitude ultralow frequency waves and small-scale field-aligned currents in the auroral and subauroral regions for more than 40 years. Sydorenko and Rankin (2017, https://doi.org/10.1002/2017GL073415) have recently challenged the very existence of the IFI for any realistic geophysical conditions in the Earth\u27s ionosphere-magnetosphere system. Because this conclusion contradicts numerous theoretical, numerical, and experimental works successfully used IFI to explain and predict results from observations for more than four decades, it deserves special attention. We show that this conclusion is mainly based on the specific ionospheric density profile and boundary conditions used in two runs of simulations presented in Sydorenko and Rankin (2017), and the generalization of this result is not justified. The effect of the collisions between ionospheric ions and neutrals on the development of the instability has been well studied since 1981, and these studies demonstrate that it does not prevent the development of the instability. Furthermore, excellent agreement of the theoretical and numerical results with observations verify without doubt the IFI existence and significance in the Earth\u27s magnetosphere-ionosphere system

Ultralow Frequency Electrodynamics of Magnetosphere-Ionosphere Interactions Near the Plasmapause During Substorms

Ultra low frequency (ULF) electromagnetic waves have been regularly observed by the CRRES, Cluster, and Van Allen Probes satellites near the plasmapause during substorms. Frequently, the small-scale waves are detected together with a large-scale quasi-stationary electric field collocating with mesoscale plasma flows penetrating into the plasmasphere. These observations suggest that the plasmapause plays an important role in the conversion of the kinetic energy of energetic particles moving toward the Earth from the reconnection site in the magnetotail into a large-scale electric field. The field penetrates along the magnetic field into the ionosphere and generates small-scale, shear Alfvén waves and field-aligned currents. These waves can form a standing pattern between the hemispheres, and under certain conditions, they can be amplified by interactions with the ionosphere. This scenario is verified in the paper by reproducing with simulations structure and amplitude of the ULF waves observed by the Van Allen Probe-A satellite near the plasmapause on 17 March 2015. The simulations are based on the reduced two-fluid MHD model describing generation of ULF Alfvén waves and field-aligned currents by the ionospheric feedback instability driven by the large-scale electric field. Simulations demonstrate good, quantitative agreement between spatial structure, frequency, and amplitude of the simulated waves and the observations

Toward the Unified Theory of SAID-Linked Subauroral Arcs

We present a unified approach to subauroral arcs within intense subauroral ion drifts (SAID), which explains the observed transition of a precursor Stable Auroral Red (SAR) arc into Strong Thermal Emission Velocity Enhancement (STEVE). This approach is based on the short-circuiting concept of fasttime SAID as an integral part of a magnetospheric voltage generator between the innermost boundaries of the freshly injected plasma sheet electrons and ring current ions. Here, enhanced plasma turbulence rapidly heats the bulk plasma and accelerates suprathermal non-Maxwellian “tails.” Heat and suprathermal electron transport rapidly elevate the ionospheric electron temperature—the source of a bright SAR arc. Through a substorm, the density altitude profile within the evolving ionospheric SAID channel transforms into a “fresh” F-region trough with the E-region valley. The ionospheric feedback instability within the depleted-density SAID channel generates small-scale, field-aligned currents with parallel electric fields sufficient to produce the suprathermal electron population, exciting the STEVE and Picket Fence emissions. This approach also explains the inner electromagnetic structure of intense SAID, which is consistent with fine optical structures in STEVE and Picket Fence

Ionospheric Feedback and ULF Quarter-Waves

This paper presents results from the numerical investigation of nonlinear feedback interactions between ULF field-aligned currents (FACs) and the ionospheric plasma in the global magnetospheric resonator with a non-symmetrical distribution of the plasma density in the conjugate hemispheres. The density asymmetry is enhanced by the introduction of the ionospheric valley in the hemisphere where the plasma density is already lower. The main result from this study is that in the non-symmetrical resonator, the ionospheric feedback mechanism, driven by the electric field with the maximum amplitude of 50 mV/m, develops nonlinear, intense, small-scale upward currents with a characteristic quarter-wavelength structure along the ambient magnetic field. The frequency of these waves is two times less than the fundamental frequency of the symmetrical resonator. The ionospheric valleys, which are depletions of the plasma density between the ionospheric E and F regions, enhance this effect, by reducing the effective ionospheric conductivity. This effect is important for the interpretation of ground, satellite, and sounding rocket observations of ULF waves and FACs in the auroral and subauroral geospace