Electron Power-Law Spectra in Solar and Space Plasmas

Particles are accelerated to very high, non-thermal energies in solar and space plasma environments. While energy spectra of accelerated electrons often exhibit a power law, it remains unclear how electrons are accelerated to high energies and what processes determine the power-law index $\delta$. Here, we review previous observations of the power-law index $\delta$ in a variety of different plasma environments with a particular focus on sub-relativistic electrons. It appears that in regions more closely related to magnetic reconnection (such as the `above-the-looptop' solar hard X-ray source and the plasma sheet in Earth's magnetotail), the spectra are typically soft ($\delta \gtrsim$ 4). This is in contrast to the typically hard spectra ($\delta \lesssim$ 4) that are observed in coincidence with shocks. The difference implies that shocks are more efficient in producing a larger non-thermal fraction of electron energies when compared to magnetic reconnection. A caveat is that during active times in Earth's magnetotail, $\delta$ values seem spatially uniform in the plasma sheet, while power-law distributions still exist even in quiet times. The role of magnetotail reconnection in the electron power-law formation could therefore be confounded with these background conditions. Because different regions have been studied with different instrumentations and methodologies, we point out a need for more systematic and coordinated studies of power-law distributions for a better understanding of possible scaling laws in particle acceleration as well as their universality.Comment: 67 pages, 15 figures; submitted to Space Science Reviews; comments welcom

Do magnetospheric shear Alfvén waves generate sufficient electron energy flux to power the aurora?

Using a self-consistent drift-kinetic simulation code, we investigate whether electron acceleration owing to shear Alfvén waves in the plasma sheet boundary layer is sufficient to cause auroral brightening in the ionosphere. The free parameters used in the simulation code are guided by in situ observations of wave and plasma parameters in the magnetosphere at distances >4 RE from the Earth. For the perpendicular wavelength used in the study, which maps to ∼4 km at 110 km altitude, there is a clear amplitude threshold which determines whether magnetospheric shear Alfvén waves above the classical auroral acceleration region can excite sufficient electrons to create the aurora. Previous studies reported wave amplitudes that easily exceed this threshold; hence, the results reported in this paper demonstrate that auroral acceleration owing to shear Alfvén waves can occur in the magnetosphere at distances >4 RE from the Earth

Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem

The impulsive phase of a solar flare marks the epoch of rapid conversion of energy stored in the pre-flare coronal magnetic field. Hard X-ray observations imply that a substantial fraction of flare energy released during the impulsive phase is converted to the kinetic energy of mildly relativistic electrons (10-100 keV). The liberation of the magnetic free energy can occur as the coronal magnetic field reconfigures and relaxes following reconnection. We investigate a scenario in which products of the reconfiguration - large-scale Alfven wave pulses - transport the energy and magnetic-field changes rapidly through the corona to the lower atmosphere. This offers two possibilities for electron acceleration. Firstly, in a coronal plasma with beta < m_e/m_p, the waves propagate as inertial Alfven waves. In the presence of strong spatial gradients, these generate field-aligned electric fields that can accelerate electrons to energies on the order of 10 keV and above, including by repeated interactions between electrons and wavefronts. Secondly, when they reflect and mode-convert in the chromosphere, a cascade to high wavenumbers may develop. This will also accelerate electrons by turbulence, in a medium with a locally high electron number density. This concept, which bridges MHD-based and particle-based views of a flare, provides an interpretation of the recently-observed rapid variations of the line-of-sight component of the photospheric magnetic field across the flare impulsive phase, and offers solutions to some perplexing flare problems, such as the flare "number problem" of finding and resupplying sufficient electrons to explain the impulsive-phase hard X-ray emission.Comment: 31 pages, 6 figure

Small-Scale Dynamic Aurora

Small-scale dynamic auroras have spatial scales of a few km or less, and temporal scales of a few seconds or less, which visualize the complex interplay among charged particles, Alfvén waves, and plasma instabilities working in the magnetosphere-ionosphere coupled regions. We summarize the observed properties of flickering auroras, vortex motions, and filamentary structures. We also summarize the development of fundamental theories, such as dispersive Alfvén waves (DAWs), plasma instabilities in the auroral acceleration region, ionospheric feedback instabilities (IFI), and the ionospheric Alfvén resonator (IAR)

CME -Associated Energetic Ions at 0.23 AU -- Consideration of the Auroral Pressure Cooker Mechanism Operating in the Low Corona as a Possible Energization Process

We draw a comparison between a solar energetic particle event associated with the release of a slow coronal mass ejection close to the sun, and the energetic particle population produced in high current density field-aligned current structures associated with auroral phenomena in planetary magnetospheres. We suggest that this process is common in CME development and lift-off in the corona, and may account for the electron populations that generate Type III radio bursts, as well as for the prompt energetic ion and electron populations typically observed in interplanetary space.Comment: Accepted for publication Ap

Hydrazone chelators for the treatment of iron overload disorders: iron coordination chemistry and biological activity

The potentially tridentate ligand 2-pyridinecarbaldehyde isonicotinoyl hydrazone (HPCIH) and its analogues are an emerging class of orally effective Fe chelators that show great promise for the treatment of Fe overload diseases. Herein, we present an extensive study of the Fe coordination chemistry of the HPCIH analogues including the first crystallographically characterised Fe-II complex of these chelators. Unlike most other clinically effective Fe chelators, the HPCIH analogues bind Fe-II and not F-III. In fact, these chelators form low-spin bis-ligand F-II complexes, although NMR suggests that the complexes are close to the high-spin/low-spin crossover. All the Fe complexes show a high potential Fe-III/(II) redox couple (> 500 mV vs. NHE) and cyclic voltammetry in aqueous or mixed aqueous/organic solvents is irreversible as a consequence of a rapid hydration reaction that occurs upon oxidation. A number of the HPCIH analogues show high activity at inducing Fe efflux from cells and also at preventing Fe uptake by cells from the serum Fe transport protein transferrin. As a class of ligands, these chelators are more effective at reducing Fe uptake from transferrin than inducing Fe mobilisation from cells. This may be related to their ability to intercept Fe-II after its release from transferrin within the cell. Our studies indicate that their Fe chelation efficacy is due, at least in part, to the fact that these ligands and their Fe-II complexes are neutral at physiological pH (7.4) and sufficiently lipophilic to permeate cell membranes

N-ftaloil-glicin-hidroksamska kiselina kao kelator željeza u serumu štakora

The aim of this study was to investigate the activity of N-phthaloyl-glycine-hydroxamic acid (Phth-Gly-HA) as a new iron chelator in vivo to be used in iron overload diseases. After intraperitoneal application of Phth-Gly-HA to male rats (1 mg kg1 body mass) once a day for seven days, iron serum level decreased by 21%, whereas the iron value dropped by 32% in female rats (1.5 mg kg1 body mass). The results indicate that the tested substance has the ability to bind serum iron by complexation. Besides transferrin iron release, mobilization of ferritin iron is also possibleU cilju pronalaženja novog efikasnog kelatora koji bi mogao poslužiti u liječenju bolesti izazvanih viškom željeza, u ovom je radu ispitano djelovanje N-ftaloil-glicin-hidroksamske kiseline (Phth-Gly-HA) in vivo. Istraživan je utjecaj kelatora na razinu željeza u serumu štakora nakon intraperitonealne primjene vodene otopine Phth-Gly-HA (0,1 mg mL1) jednom dnevno tijekom 7 dana. Kontrolne su životinje primale fiziološku otopinu. Kod mužjaka injektiranje test supstancije (1 mg kg1) uzrokovalo je pad serumskog željeza za 21%. Kod ženki je nakon tretmana (1,5 mg kg1) izmjereno sniženje razine željeza za 35%. Rezultati pokazuju da ispitivana supstanca ima sposobnost kompleksiranja serumskog željeza, pretežno transferinskog, ali da postoji mogućnost mobilizacije željeza i iz feritinskih zaliha

Mortality Burden of Heatwaves in Sydney, Australia Is Exacerbated by the Urban Heat Island and Climate Change: Can Tree Cover Help Mitigate the Health Impacts?

Heatwaves are associated with increased mortality and are exacerbated by the urban heat island (UHI) effect. Thus, to inform climate change mitigation and adaptation, we quantified the mortality burden of historical heatwave days in Sydney, Australia, assessed the contribution of the UHI effect and used climate change projection data to estimate future health impacts. We also assessed the potential for tree cover to mitigate against the UHI effect. Mortality (2006–2018) records were linked with census population data, weather observations (1997–2016) and climate change projections to 2100. Heatwave-attributable excess deaths were calculated based on risk estimates from a published heatwave study of Sydney. High resolution satellite observations of UHI air temperature excesses and green cover were used to determine associated effects on heat-related mortality. These data show that >90% of heatwave days would not breach heatwave thresholds in Sydney if there were no UHI effect and that numbers of heatwave days could increase fourfold under the most extreme climate change scenario. We found that tree canopy reduces urban heat, and that widespread tree planting could offset the increases in heat-attributable deaths as climate warming progresses.Timothy B. Chaston, Richard A. Broome, Nathan Cooper, Gerard Duck, Christy Geromboux, Yuming Guo, Fei Ji, Sarah Perkins-Kirkpatrick, Ying Zhang, Gnanadarsha S. Dissanayake, Geoffrey G. Morgan, and Ivan C. Haniga