Solar wind protons in the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko

<p>Against expectations, the Rosetta spacecraft was able to observe protons of solar wind origin in the diamagnetic cavity at comet 67P/Churyumov-Gerasimenko. This study investigates these unexpected observations and gives a working hypothesis on what could be the underlying cause.</p> <p>The cometary plasma environment of a comet is shaped by two distinct plasma populations: the solar wind, consisting of protons, alpha particles, electrons and a magnetic field, and the cometary plasma, consisting of heavy ions such as water ions or carbon dioxide ions and electrons. <br />As the comet follows its orbit through the solar system, the amount of cometary ions that is produced varies significantly. This means that the plasma environment of the comet and the boundaries that form there are also dependent on the comet's heliocentric distance. </p> <p>For example, at sufficiently high gas production rates (close to the Sun) the protons from the solar wind are prevented from entering the inner coma entirely. The region where no protons (and other solar wind origin ions) can be detected is referred to as the solar wind ion cavity. <br />A second example is the diamagnetic cavity, a region very close to the nucleus of the comet, where the interplanetary magnetic field, which is carried by the solar wind electrons, cannot penetrate the densest part of the cometary plasma. </p> <p>The Rosetta mission clearly showed that the solar wind ion cavity is larger than the diamagnetic cavity at a comet such as 67P/Churyumov-Gerasimenko. However, this new study finds that in isolated incidences this order can be reversed and ions of solar wind origin (mostly protons, but also helium) can be detected inside the diamagnetic cavity. We present the observations pertaining to these events and list and discard possible mechanisms that could lead to such a configuration. Only one mechanism cannot be discarded: that of a solar wind configuration where the solar wind velocity is aligned with the magnetic field. We show evidence that fits this hypothesis as well as solar wind models in support. </p>

POSSIBLE CONNECTION BETWEEN THE EARTHQUAKES TREMORS ONSET IN THE YELLOWSTONE SUPERVOLCANO’S SEISMIC ZONE AND INFLUENCE OF SOLAR FLARE PLASMA

The correlation between solar flares and coronal mass ejections generating solar wind plasma flows towards the Earth and the dynamics in time and power of earthquakes in the area of the Yellowstone supervolcano, that was not previously studied, is considered in four examples. The method of graphical correlation between the values of solar wind parameters, which bursts are directly related to the activation of solar processes, and subsequent increases in the values of earthquake magnitudes and their repeatability was used as a research tool. The author assumes that an additional energy input occurs to shallow earthquake foci and increases their power due to the action of breakthrough injections of plasma clumps into the Earth’s near-surface area detached into the magnetosphere geo-effective solar wind components. The problem under discussion is considered to be acute in connection with the work carried out here to predict a volcanic eruption. In the general scientific plan, it is proposed to include earthquakes study in programs of education as one of points for registration the influence of factors of solar-wind origin.

MMS Observations of the Charge State and Mass Dependent Energization of Heavy Ions During Injections in the Earth’s Magnetotail

<p>Particle injections transport particles from the Earth’s magnetotail to the inner magnetosphere. During this process, ions in the injections are substantially energized. The physical processes behind this energization are still under debate. Recent results from the Van Allen Probes mission at radial distances < 6 R<sub>E</sub> have shown that higher mass ions (helium and oxygen) with high charge states are often found at substantially higher energies than protons (up to MeV energies compared to a couple hundred keV) in the inner magnetosphere. Here we present results from the Magnetospheric Multiscale (MMS) mission over a broad range of radial distances (between 7-25 R<sub>E</sub>) where the energization of injected ions is charge state dependent. We demonstrate with these observations that injected ions exhibit behavior which is well ordered by energy per charge due to the gradient/curvature drift’s impact on particle trajectories as they drift in the direction of transient electric fields. The charge state dependent energization leads to the dominance of multiple charge state heavy ions, as opposed to H<sup>+</sup>, above ~250 keV throughout the Earth’s inner and middle magnetosphere. Additionally, there are also cases with hints of non-adiabatic energization observed in O<sup>+</sup> between ~100-250 keV, where O<sup>+</sup> potentially gets some extra-energization compared to H<sup>+</sup> due differences in their respective gyroradii. However, the highest energy ions (> 300 keV oxygen and helium) are still likely of solar wind origin and primarily accelerated due to their higher charge-state. In the process of these results we demonstrate the utility of a technique for deducing ion charge-states using instrumentation that does not directly discriminate by charge state.</p>

Unusually high magnetic fields in the coma of 67P/Churyumov-Gerasimenko during its high-activity phase

Aims. On July 3, 2015, an unprecedented increase in the magnetic field magnitude was measured by the Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko (67P). This increase was accompanied by large variations in magnetic field and ion and electron density and energy. To our knowledge, this unusual event marks the highest magnetic field ever measured in the plasma environment of a comet. Our goal here is to examine possible physical causes for this event, and to explain this reaction of the cometary plasma and magnetic field and its trigger. Methods. We used observations from the entire Rosetta Plasma Consortium as well as energetic particle measurements from the Standard Radiation Monitor on board Rosetta to characterize the event. To provide context for the solar wind at the comet, observations at Earth were compared with simulations of the solar wind. Results. We find that the unusual behavior of the plasma around 67P is of solar wind origin and is caused by the impact of an interplanetary coronal mass ejection, combined with a corotating interaction region. This causes the magnetic field to pile up and increase by a factor of six to about 300 nT compared to normal values of the enhanced magnetic field at a comet. This increase is only partially accompanied by an increase in plasma density and energy, indicating that the magnetic field is connected to different regions of the coma.

Solar-Wind Origin

The Sun continuously expels a fraction of its own mass in the form of a steadily accelerating outflow of ionized gas called the “solar wind.” The solar wind is the extension of the Sun’s hot (million-degree Kelvin) outer atmosphere that is visible during solar eclipses as the bright and wispy corona. In 1958, Eugene Parker theorized that a hot corona could not exist for very long without beginning to accelerate some of its gas into interplanetary space. After more than half a century, Parker’s idea of a gas-pressure-driven solar wind still is largely accepted, although many questions remain unanswered. Specifically, the physical processes that heat the corona have not yet been identified conclusively, and the importance of additional wind-acceleration mechanisms continue to be investigated. Variability in the solar wind also gives rise to a number of practical “space weather” effects on human life and technology, and there is still a need for more accurate forecasting. Fortunately, recent improvements in both observations (with telescopes and via direct sampling by space probes) and theory (with the help of ever more sophisticated computers) are leading to new generations of predictive and self-consistent simulations. Attempts to model the origin of the solar wind are also leading to new insights into long-standing mysteries about turbulent flows, magnetic reconnection, and kinetic wave-particle resonances.

Relative outflow enhancements during major geomagnetic storms – Cluster observations

The rate of ion outflow from the polar ionosphere is known to vary by orders of magnitude, depending on the geomagnetic activity. However, the upper limit of the outflow rate during the largest geomagnetic storms is not well constrained due to poor spatial coverage during storm events. In this paper, we analyse six major geomagnetic storms between 2001 and 2004 using Cluster data. The six major storms fulfil the criteria of Dst < −100 nT or Kp > 7+. Since the shape of the magnetospheric regions (plasma mantle, lobe and inner magnetosphere) are distorted during large magnetic storms, we use both plasma beta (β) and ion characteristics to define a spatial box where the upward O+ flux scaled to an ionospheric reference altitude for the extreme event is observed. The relative enhancement of the scaled outflow in the spatial boxes as compared to the data from the full year when the storm occurred is estimated. Only O+ data were used because H+ may have a solar wind origin. The storm time data for most cases showed up as a clearly distinguishable separate peak in the distribution toward the largest fluxes observed. The relative enhancement in the outflow region during storm time is 1 to 2 orders of magnitude higher compared to less disturbed time. The largest relative scaled outflow enhancement is 83 (7 November 2004) and the highest scaled O+ outflow observed is 2 × 1014 m−2 s−1 (29 October 2003).

On the local time dependence of the penetration of solar wind-induced electric fields to the magnetic equator

For a period of a few hours, the penetration of electric fields of solar wind origin is at its highest efficiency. In November 2003, five days of continuous vertical drift data were obtained at the Jicamarca Radio Observatory. Here we have isolated a range of frequencies centered at a few-hour period for a five-day period and have explored the local time dependence of the penetration, along with the time delay due to magnetospheric effects. We find that the latter ranges from 15 to 25 min. For the local time dependence, we find that the period of anti-correlation is roughly from 21:00 to 04:00 LT, with positive correlation at other local times.