Abstracted/indexed

Boundaries in the plasma around comet 67P separate regions with different properties. Many have been identified, including a new boundary called an infant bow shock. Here, we investigate how the plasma and fields behave at this boundary and where it can be found. The main result is that the infant bow shock occurs at intermediate activity and intermediate distances to the comet. Most plasma parameters behave as expected, however some inconsistencies indicate that the boundary is non-stationary.

Geomagnetic activity is known to exhibit semi-annual variation with larger occurrences during equinoxes. A similar seasonal feature was reported for relativistic (∼ MeV) electrons throughout the entire outer zone radiation belt. Present work, for the first time reveals that electron fluxes increase with an ∼ 6-month periodicity in a limited L-shell only with large dependence in solar activity cycle. In addition, flux enhancements are not essentially equinoctial.

We present findings of mass, velocity, and composition of 22 small-mass meteors detected optically in Arecibo, Puerto Rico. Spectral observations of these meteors showed evidence of various metals including Na, Mg, Ca, and Fe. Evidence was also found for differential ablation, the process by which more volatile elements ablate earlier in the meteor's path. These spectral observations of the smallest, faintest meteors greatly improve our understanding of the composition of this meteor population.

The paper discusses the excitation of monochromatic ELF/VLF electromagnetic waves produced by HF heating facilities currents in the nighttime ionosphere. The ground-based magnetic field is predominantly located under the source and wave has typical for whistler right hand polarization, but left hand polarization at large distances from the source. About half of the source energy propagates upward and approximately twenty percent propagates to the Earth-ionosphere waveguide.