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The linear stability of waves driven by ion beams produced during solar flare energy release are explored to assess their role in driving abundance enhancements in minority species such as 3He and in controlling, through pitch-angle scattering, proton/alpha confinement during energy release. The Arbitrary Linear Plasma Solver is used to solve the linear dispersion relation for a population of energetic, reconnection-accelerated protons streaming through a less energetic background plasma. We assume equal densities of the two populations, using an anisotropic (T∥/T⊥=10), one-sided kappa distribution for the energetic streaming population and a cold Maxwellian for the background. We find two unstable modes with parallel propagation: a right-handed wave with a frequency of the order of the proton cyclotron frequency (Ωcp) and a left-handed, lower frequency mode. We also find highly oblique modes with frequencies below Ωcp that are unstable for higher beam energies. Through resonant interactions, all three modes will contribute to the scattering of the high-energy protons, thereby limiting their transport out of the flare-acceleration region. The higher-frequency oblique mode, which can be characterized as a kinetic Alfvén wave, will preferentially heat 3He, making it a good candidate for the driver of the abundance enhancements commonly observed for this species in impulsive events. 

Abstract The waves generated by high-energy proton and alpha particles streaming from solar flares into regions of colder plasma are explored using particle-in-cell simulations. Initial distribution functions for the protons and alphas consist of two populations: an energetic, streaming population represented by an anisotropic (T_∥>T_⊥), one-sided kappa function and a cold, Maxwellian background population. The anisotropies and nonzero heat fluxes of these distributions destabilize oblique waves with a range of frequencies below the proton cyclotron frequency. These waves scatter particles out of the tails of the initial distributions along constant-energy surfaces in the wave frame. Overlap of the nonlinear resonance widths allows particles to scatter into near-isotropic distributions by the end of the simulations. The dynamics of³He are explored using test particles. Their temperatures can increase by a factor of nearly 20. Propagation of such waves into regions above and below the flare site can lead to heating and transport of³He into the flare acceleration region. The amount of heated³He that will be driven into the flare site is proportional to the wave energy. Using values from our simulations, we show that the abundance of³He driven into the acceleration region should approach that of⁴He in the corona. Therefore, waves driven by energetic ions produced in flares are a strong candidate to drive the enhancements of³He observed in impulsive flares. 

Icebergs calving into Greenlandic Fjords frequently experience strongly sheared flows over their draft, but the impact of this flow past the iceberg is not fully captured by existing parameterizations. We present a series of novel laboratory experiments to determine the dependence of submarine melting along iceberg sides on a background flow. We show, for the first time, that two distinct regimes of melting exist depending on the flow magnitude and consequent behavior of melt plumes (side-attached or side-detached), with correspondingly different meltwater spreading characteristics. When this velocity dependence is included in melt parameterizations, melt rates estimated for observed icebergs in the attached regime increase, consistent with observed iceberg submarine melt rates. We show that both attached and detached plume regimes are relevant to icebergs observed in a Greenland fjord. Further, depending on the regime, iceberg meltwater may either be confined to a surface layer or distributed over the iceberg draft.