M. A. Dayeh

The Heliotail Revealed by the Interstellar Boundary Explorer

Recent combined observations from the first three years of Interstellar Boundary Explorer (IBEX) data allow us to examine the heliospheres downwind region—the heliotail—for the first time. In contrast to a preliminary identification of a narrow offset heliotail structure, we find a broad slow solar wind plasma sheet crossing essentially the entire downwind side of the heliosphere at low to mid-latitudes, with fast wind tail regions to the north and south. The slow wind plasma sheet exhibits the steepest ENA spectra in the IBEX sky maps, appears as a two-lobed structure (lobes on the port and starboard sides), and is twisted in the sense of (but at a smaller angle than) the external magnetic field. The overall heliotail structure clearly demonstrates the intermediate nature of the heliospheres interstellar interaction, where both the external dynamic and magnetic pressures strongly affect the heliosphere.

PICK-UP ION DISTRIBUTIONS AND THEIR INFLUENCE ON ENERGETIC NEUTRAL ATOM SPECTRAL CURVATURE

This paper focuses on the analysis and significance of the spectral curvature of energetic neutral atoms (ENAs) detected by the Interstellar Boundary Explorer. The flux versus energy spectrum is analytically expressed in terms of the source proton distributions, namely: (1) the solar wind kappa distribution of protons and (2) the coexisting filled spherical shell distribution of pick-up ions (PUIs). The influence of PUIs on the spectral index and curvature is modeled and investigated in detail. It is analytically shown that (1) the PUI speed upper limit is restricted by the Earthward PUI velocity vector, (2) the PUI distribution causes a positive spectral curvature, and (3) the exact expressions of the spectral index and curvature can be used to extract information about the governing parameters of the parent proton distributions. The sky maps of the spectral curvature reveal a possible band-like configuration of positive spectral curvature that is missing in the original flux sky maps. This band can be roughly separated into the north/south polar regions and two ecliptic meridional “columns” located around the ecliptic longitudes ∼5 ◦ and ∼150 ◦ . The geometric locus between the two cones with noseward axis, and apertures ∼60 ◦ and ∼120 ◦ , configures the band-like region of (1) the positive curvature and (2) the maximum values of PUI distribution. Indeed, the observed curvature band is highly correlated with PUI distributions, and is possibly caused by the influence of PUIs on bending the spectrum from linear (log‐log scale) to concave upward, thus increasing its spectral curvature.

HEMISPHERIC ASYMMETRIES IN THE POLAR SOLAR WIND OBSERVED BY ULYSSES NEAR THE MINIMA OF SOLAR CYCLES 22 AND 23

We examined solar wind plasma and interplanetary magnetic field (IMF) observations from Ulysses first and third orbits to study hemispheric differences in the properties of the solar wind and IMF originating from the Suns large polar coronal holes (PCHs) during the declining and minimum phase of solar cyclesxa022 andxa023. We identified hemispheric asymmetries in several parameters, most notably ~15%-30% south-to-north differences in averages for the solar wind density, mass flux, dynamic pressure, and energy flux and the radial and total IMF magnitudes. These differences were driven by relatively larger, more variable solar wind density and radial IMF between ~36°S-60°S during the declining phase of solar cyclesxa022 andxa023. These observations indicate either a hemispheric asymmetry in the PCH output during the declining and minimum phase of solar cyclesxa022 andxa023 with the southern hemisphere being more active than its northern counterpart, or a solar cycle effect where the PCH output in both hemispheres is enhanced during periods of higher solar activity. We also report a strong linear correlation between these solar wind and IMF parameters, including the periods of enhanced PCH output, that highlight the connection between the solar wind mass and energy output and the Suns magnetic field. That these enhancements were not matched by similar sized variations in solar wind speed points to the mass and energy responsible for these increases being added to the solar wind while its flow was subsonic.

Interplanetary magnetic field dependence of the suprathermal energetic neutral atoms originated in subsolar magnetopause

Using energetic neutral atom (ENA) emission observations of the subsolar magnetopause measured by the Interstellar Boundary Explorer (IBEX), we study the correlation between the upstream interplanetary magnetic field (IMF) conditions and the spectral index of the source ion population. Our ENA data set includes hour-averaged ENA measurements at energies between ∼0.5 and ∼6u2009keV obtained by the IBEX High Energy ENA imager from January 2009 to May 2011. Under the condition of quiet geomagnetic activity (SYM-H index >−20u2009nT), we find that the shallower spectra in the suprathermal tail of the ion population of the subsolar magnetopause is weakly correlated (correlation coefficient of −0.30) with the shock angle of the Earths bow shock, but not correlated with parameters related to magnetic reconnection (i.e., elevation and clock angle of the interplanetary magnetic field orientation). The observed correlation suggests suprathermal ion energization from diffusive shock acceleration and thus that the suprathermal ions in the subsolar magnetopause are of shocked solar wind origin. We also argue that the roles of magnetospheric ion leakage or ion acceleration by magnetic reconnection are reduced in the magnetopause emissions compared to shock acceleration processes.

Shape of the terrestrial plasma sheet in the near‐Earth magnetospheric tail as imaged by the Interstellar Boundary Explorer

We present remote, continuous observations from the Interstellar Boundary Explorer of the terrestrial plasma sheet location back to -16 Earth radii (RE) in the magnetospheric tail using energetic neutral atom emissions. The time period studied includes two orbits near the winter and summer solstices, thus associated with large negative and positive dipole tilt, respectively. Continuous side-view images reveal a complex shape that is dominated mainly by large-scale warping due to the diurnal motion of the dipole axis. Superposed on the global warped geometry are short-time fluctuations in plasma sheet location that appear to be consistent with plasma sheet flapping and possibly twisting due to changes in the interplanetary conditions. We conclude that the plasma sheet warping due to the diurnal motion dominates the average shape of the plasma sheet. Over short times, the position of the plasma sheet can be dominated by twisting and flapping.

Spectral properties of large gradual solar energetic particle events - II -Systematic Q/M-dependence of heavy ion spectral breaks

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Spectral Evolution of Energetic Neutral Atom Emissions at the Heliospheric Poles as Measured by IBEX during its First Three Years

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Origin and Properties of Quiet-time 0.11-1.28 MeV Nucleon-1 Heavy-ion Population Near 1 au

0.1-500 MeV/nucleon H-Fe spectra in 46 large SEP events surveyed by Desai et al. (2016) with the double power-law Band function to obtain a normalization constant, low- and high-energy parameters

Origin of Quiet‐Time Suprathermal Tails Near 1 AU

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Origin of Quiet‐Time Suprathermal Heavy Ions Near 1 AU

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