Wing-wing Interaction - When Exoplanets interact with each other

<p>Electromagnetic Star-Planet Interaction is a phenomenon that occurs when a planet is sufficiently close to its host star that Alfvén waves propagate to the star and can leave an imprint on the star. The resulting structure is called Alfvén wing. Stars also often have open field-line structures due to the influence of the stellar wind. In these open field line regions, two planets can share the same set of field lines at the same time. Therefore, it is possible that Alfvén wings interact with each other and cause a time-variability in the signal. We call this process wing-wing interaction. To understand wing-wing interaction further, we apply a three dimensional, fully time-dependent, magnetohydrodynamic model. There, we simulate two planets that generate star-planet interaction and eventually undergo wing-wing interaction. We present the temporal evolution of the Alfvén wings and of the Poynting flux. From these results, we can estimate how wing-wing interaction could appear in observations. </p>

Temporal variation of particle precipitation in Erath's polar cap from DMSP observations

<p>Previous observations and simulations have shown that the low-energy electron precipitation in the cusp plays an important role in ionosphere and thermosphere through particle impact ionization and heating. In this study, we investigate the precipitating particles in the Earth's polar cap region, which is also an open-field line region as the cusp. In many numerical simulations of the upper atmosphere, the polar cap region is described as a uniform area with no spatial and temporal variations of the particle energy and fluxes. We analyze years of the particle observations from DMSP satellites to show the temporal variations of particle characteristics in the region poleward of 80 degree magnetic latitudes in this study. The results show the solar cycle, annual and seasonal variations of particle (electrons, ions) energy, number flux and energy flux in the polar cap. The results will be useful to improve the polar-latitude precipitating particle description in upper atmosphere modeling.</p>

Earth’s polar outflow evolution from mid-Archean to present

<p>Habitable conditions on Earth developed in a tight connection to the evolution of terrestrial atmosphere which was strongly influenced by atmospheric escape. In this study, we investigated the evolution of the polar ion outflow from the Earth’s open field line bundle starting from mid-Archean (three gigayears ago) and to present. We performed Direct Simulation Monte Carlo (DSMC) simulations and estimated upper limits on escape rates from the Earth's polar areas assuming the present-day composition of the atmosphere. We performed two additional simulations with lower mixing ratios of oxygen of 1% and 15% to account for the composition changes after the Great Oxydation Event (GOE).</p> <p>According to our estimates, the maximum loss rates due to polar outflow was reached three gigayears ago equal to 3.3 x 10<sup>27 </sup>s<sup>-1</sup> and 2.4 x 10<sup>27 </sup>s<sup>-1</sup> for oxygen and nitrogen, respectively. We estimate the total maximum integrated mass loss equal to 39% and 10% of the modern atmosphere's mass, for oxygen and nitrogen, respectively. We also show that escape rates increase, if the oxygen mixing ratio is decreased (GOE simulations), which is due to reduced thermospheric cooling. According to these results, the main factors that governed the polar outflow in the considered time period are the evolution of the XUV radiation of the Sun and the atmosphere's composition. The evolution of the Earth's magnetic field plays a less important role. We conclude that although the atmosphere that has a present-day composition can survive the escape due to polar outflow from 3 gigayears ago and later, a higher level of CO<sub>2</sub> between 3.0 and 2.0 Ga is likely necessary to reduce the escape.</p>

DMSP/SSUSI observations of the high-latitude dayside aurora (HiLDA

<p>High-latitude dayside aurora (HiLDA) are large-scale discrete arcs or spot-like aurora poleward of the cusp, observed previously in the northern hemisphere by the Viking UV imager [Murphree et al., 1990] and by the IMAGE FUV [Frey et al., 2003]. The particular interest on HiLDA is to understand its formation related to the dayside reconnection and the resulted field-aligned currents (FACs) configuration in the polar cap (open field line region). In addition, the occurrence of HiLDA in the southern hemisphere is not well known.</p><p>In this study, we investigate the properties of HiLDA using DMSP/SSUSI images from the satellites F16, F17, F18, and F19. The combined data with auroral images from DMSP/SSUSI, ion drift velocity from SSIES, magnetic field perturbations from SSM, and energetic particle spectrum from SSJ make it possible to study the electrodynamics in the vicinity of the HiLDA and its connection the dayside cusp. HiLDA is formed due to monoenergetic electron precipitation (inverted-V structures) with the absence of ion precipitation. The field-aligned potential drop can be up to tens of keV. Applying the current-voltage relation, we suggest accelerated polar rain as the source of HiLDA, indirectly controlled by the solar wind/magnetosheath plasma population. The upward field-aligned current associated with the potential drop is a part of the cusp current system, produced by the dayside reconnection. Both lobe reconnection and reconnection on the duskside flanks play a role in the formation of HiLDA.</p><p>The occurrence of HiLDA is highly associated with the sunlit hemisphere and IMF By dominated conditions. Our results agree with previous observations, which show that HiLDA occurs during positive By dominated conditions in the northern summer hemisphere. We also confirmed that HiLDA occurs during negative By dominated conditions in the southern hemisphere. In addition, the fine structures of HiLDA are studied.</p><p>References</p><p><span>Murphree, J. S.</span>, <span>Elphinstone, R. D.</span>, <span>Hearn, D.</span>, and <span>Cogger, L. L.</span> ( <span>1990</span>), <span>Large‐scale high‐latitude dayside auroral emissions</span>, <em>J. Geophys. Res.</em>, <span>95</span>( <span>A3</span>), <span>2345</span>– <span>2354</span>, doi:.</p><p><span>Frey, H. U.</span>, <span>Immel, T. J.</span>, <span>Lu, G.</span>, <span>Bonnell, J.</span>, <span>Fuselier, S. A.</span>, <span>Mende, S. B.</span>, <span>Hubert, B.</span>, <span>Østgaard, N.</span>, and <span>Le, G.</span> ( <span>2003</span>), <span>Properties of localized, high latitude, dayside aurora</span>, <em>J. Geophys. Res.</em>, <span>108</span>, 8008, doi:, <span>A4</span>.</p>

Electromagnetic full- gyrokinetics in the tokamak edge with discontinuous Galerkin methods

We present an energy-conserving discontinuous Galerkin scheme for the full- $f$ electromagnetic gyrokinetic system in the long-wavelength limit. We use the symplectic formulation and solve directly for $\unicode[STIX]{x2202}A_{\Vert }/\unicode[STIX]{x2202}t$ , the inductive component of the parallel electric field, using a generalized Ohm’s law derived directly from the gyrokinetic equation. Linear benchmarks are performed to verify the implementation and show that the scheme avoids the Ampère cancellation problem. We perform a nonlinear electromagnetic simulation in a helical open-field-line system as a rough model of the tokamak scrape-off layer using parameters from the National Spherical Torus Experiment (NSTX). This is the first published nonlinear electromagnetic gyrokinetic simulation on open field lines. Comparisons are made to a corresponding electrostatic simulation.

Large polar caps for twisted magnetosphere of magnetars

The magnetic field of magnetars may be twisted compared with that of normal pulsars. Previous works mainly discussed magnetic energy release in the closed field line regions of magnetars. For a twisted magnetic field, the field lines will inflate in the radial direction. Similar to normal pulsars, the idea of light cylinder radius is introduced. More field lines will cross the light cylinder and become open for a twisted magnetic field. Therefore, magnetars may have a large polar cap, which may correspond to the hot spot during outburst. Particle flow in the open field line regions will result in the untwisting of the magnetic field. Magnetic energy release in the open field line regions can be calculated. The model calculations can catch the general trend of magnetar outburst: decreasing X-ray luminosity, shrinking hot spot etc. For magnetic energy release in the open field line regions, the geometry will be the same for different outburst in one magnetar.