Field Localization and Density Cavitation in Low-Beta Plasmas

In the present paper, filamentous structure formation, associated turbulent spectrum, and density cavity formation phenomena have been investigated for low- β plasma β ≪ m e / m i applicable to the auroral region. A set of dimensionless equations governing the dynamics of three dimensionally propagating inertial Alfvén wave (3D-IAW) and perpendicularly propagating magnetosonic wave (PMSW) has been developed. Ponderomotive force due to 3D-IAW has been included in the dynamics of the PMSW. Numerical simulation has been performed to study the nonlinear coupling of these two waves. From the obtained results, we found that the field intensity localization takes place which may further lead to the additional dissipation/turbulence process for particle heating and acceleration in space plasma. The associated turbulent spectrum is obtained with scaling nearly k − 4.28 at smaller scales (in the dissipation range). Relevance of the obtained results with the observations reported by various spacecrafts such as Hawkeye and Heos 2 has been discussed. Also, density fluctuations (depletion) of ∼ 0.10 n 0 are calculated, which are consistent with the FAST spacecraft observation reported.

Electric Field Multifractal Features in the High-Latitude Ionosphere: CSES-01 Observations

In the polar ionosphere, the electric field is characterized by broadband and power law spectral densities at small/short spatio-temporal scales, which support a possible turbulent nature of the electric field fluctuations. Here, we investigate the multifractal character of the full three-dimensional electric field in the polar ionosphere as recorded on board the first Chinese Seismo-Electromagnetic Satellite (CSES-01). The results of our analysis prove a clear different degree of multifractality of the electric field fluctuations approaching either the polar cap trailing edge or the auroral region. The observed differences in the multifractal character are interpreted in terms of the different natures of the particle precipitation in the polar cap and in the auroral region. A possible link between the multifractal nature of electric field fluctuations, parallel to the geomagnetic field, and filamentation of field aligned currents (FACs) is established.

Solar activity and its impact on the mid-latitude trough during geomagnetic storms

<p>Mid-latitude trough (MIT) is the distinct structure observed in Earth’s ionosphere at high latitudes especially at the nighttimes. The phenomenon is observed at both hemispheres. As it resides at the topside ionosphere in the sub-auroral region, its behaviour and properties are highly sensitive to the solar and geomagnetic activity. Generally as the geomagnetic activity is more pronounced the MIT is observed at lower latitudes, it also deepens and becomes much more distinct in comparison to the low magnetic activity periods. MIT responds as well to the rapid changes in geomagnetic conditions, as are the geomagnetic storms, mainly caused by the CMEs. </p><p>Based on the observations gathered by DEMETER data between 2005 and 2010 years  we present a set of geomagnetic storm cases and how the MIT properties has been changing as the storm evolves. We also discuss how it corresponds to the current solar activity and their evolutionary history  described by a set of different parameters.</p>

Farley Buneman instabilities in the Auroral region: Continuous kinetic and hybrid simulations.

<p>Farley-Buneman instabilities generate a spectrum of field-aligned plasma density irregularities in the E region. Although fully kinetic particle-in-cell simulations offer a comprehensive description of the underlying physics, its computational cost for studying non-local phenomena is tremendous. New methods based on hybrid and continuous approaches have to be explored to capture non-local physics.</p><p>In this work, we present new developments on a continuous solver of Farley-Buneman waves. We compare the performance of fully kinetic (continuous), hybrid, and fluid models. Furthermore, we investigate phase speed saturation, wave turning effects, and dominant wavelengths and assess how well these correspond to radar measurements. Finally, we describe some initial attempts at constructing simple surrogate models to capture the dominant microphysics of these simulations.</p>

Observational evidence for heat transfer from Jupiter's polar auroral region to lower latitudes

<p>Jupiter, Saturn and Uranus have non-auroral ionospheres that are measurably 100s of Kelvin hotter than models can explain by solar heating alone. This problem has existed for many decades and is generally termed in literature as the "energy crisis". One way to cause heating in the non-auroral ionosphere is to redistribute heat from the auroral ionosphere at the poles down to lower latitudes (the auroral region itself is heated thermally by collisions as a result of the auroral mechanism). Most models of global circulation suggest that heat within the polar/auroral is confined there by Coriolis forces, such that auroral energy cannot be communicated to lower latitudes, but until now there have been no high spatial resolution observations of temperature in the auroral region simultaneous with non-auroral regions to confirm it. Today we will present ground-based observations of Jupiter's ionospheric H3+ temperature at high spatial resolution (~1000km per pixel). H3+ is a major ion at Jupiter, considered in quasi-thermodynamic equilibrium with its surroundings, and therefore a good proxy for energy balance of the ionosphere. These observations, taken by the 10-meter Keck telescope on April 14, 2016 and Jan 25, 2017, strongly suggest heat from the auroral region is spreading to lower latitudes, such that the missing heat source causing the "energy crisis" may ultimately be auroral in nature.</p>

Influence of seasonal changes on the mid-latitude trough properties

<pre>The sub-auroral region of the main ionospheric trough is a very unique area strongly affected by different type of instabilities coming from both the bottom (Earth's atmosphere) and the top (Earth's magnetosphere) neighbouring regions. The main ionospheric trough’s general characteristics as well as the detailed features change accordingly to the time of day, season, solar cycle and many others. The location of MIT in the latitude-longitude coordinate system throughout the year reflects seasonal changes. Annual variations are observed also in the shape and intensity of the structure. Despite the representation of the structure in the geomagnetic coordinate system, northern and southern trough are not symmetric in the same local season. However some similarities have also been observed. In particular for both hemispheres the structure appears the deepest and well developed during local winter, whereas during local summer the structure becomes hardly visible. Observations show that the MIT tends to shift equatorward for some longitudes in both hemispheres. MIT properties for this study have been derived from DEMETER and COSMIC/FORMOSAT-3 observations.</pre> <p> </p>

Solar activity and its impact on the mid-latitude trough during geomagnetic storms

<pre>Mid-latitude trough (MIT) is the distinct structure observed in Earth's ionosphere at high latitudes especially at the nighttimes. The phenomenon is observed at both hemispheres. As it resides at the topside ionosphere in sub-auroral region, its behaviour and properties are highly sensitive to the solar and geomagnetic activity. Generally as the geomagnetic activity is more pronounced the MIT is observed at lower latitudes, it also deepens and becomes much more distinct in comparison to the low magnetic activity periods. MIT responds as well to the rapid changes in geomagnetic conditions, as are the geomagnetic storms, mainly caused by the CMEs. Based on the observations gathered by DEMETER data between 2005 and 2010 years we present a set of geomagnetic storm cases and how the MIT properties has been changing as the storm evolves. We also discuss how it corresponds to the current solar activity as their evolutionary history described by a set of different parameters. </pre>