We analyze multipoint measurements in magnetosheath plasmas, just upstream of the Earth's magnetopause, to investigate the morphology of the turbulent fields and coincident 3‐D ion distributions ...observed. Using interferometric and generalized wave polarization analyses, we show how the fields comprise a multiscale spectrum of Alfvénic structures composed of flow shears and vortices, and current sheets and filaments advected over the spacecraft with the magnetosheath flow. It is shown how these features are correlated with intervals of enhanced ion energy, temperature anisotropy, and impulsive variations in the agyrotropy of ion velocity space distributions. It is demonstrated that the observed variation in ion properties is inconsistent with an adiabatic response but is instead correlated with the spectral energy density of nonplanar structures at ion gyroradii scales. The capacity of these field structures to scatter ions is considered.
Plain Language Summary
The region of space just beyond the outer reaches of Earth's magnetic field is pervaded by electromagnetic structures on a variety of scales. In this letter we examine the toplogy of these structures on scales similar to that of the orbits of the positively charged particles (ions) in which they are immersed. Measurements of the distributions of these ions in concert with the field structure topology suggest that the structured fields drive ion scattering and energization. Because these particles are the source for much of the matter populating near‐Earth space, this research contributes to understanding of our local environment in the solar system and how it is in part defined by the exchange of energy between particles and electromagnetic fields.
Key Points
Broadband EM magnetosheath fluctuations have properties of a k‐spectrum of nonplanar Alfvénic structures on ion kinetic scales
Broadband EM magnetosheath fluctuations comprise a multiscale mixture of flow shears and vortices, current sheets, and filaments
Spectral energy densities in kinetic filamentary and vortical structures through the magnetosheath are correlated with ion energization
The evolution of structures associated with mirror modes during their flow in the Earth's magnetosheath is studied. The fact that the related magnetic fluctuations can take distinct shapes, from deep ...holes to high peaks, has been assessed in previous works on the observational, modeling and numerical points of view. In this paper we present an analytical model for the flow lines and velocity magnitude inside the magnetosheath. This model is used to interpret almost 10 years of Cluster observations of mirror structures: by back tracking each isolated observation to the shock, the "age", or flow time, of these structures is determined together with the geometry of the shock. Using this flow time the evolutionary path of the structures may be studied with respect to different quantities: the distance to mirror threshold, the amplitude of mirror fluctuations and the skewness of the magnetic amplitude distribution as a marker of the shape of the structures. These behaviours are confronted to numerical simulations which confirm the dynamical perspective gained from the association of the statistical analysis and the analytical model: magnetic peaks are mostly formed just behind the shock and are quickly overwhelmed by magnetic holes as the plasma conditions get more mirror stable. The amplitude of the fluctuations are found to saturate before the skewness vanishes, i.e. when both structures quantitatively balance each other, which typically occurs after a flow time of 100-200 s in the Earth's magnetosheath. Comparison with other astrophysical contexts is discussed.
The DEMETER Langmuir probe experiment, called “Instrument Sonde de Langmuir”
(ISL), has been designed for in situ measurements of the bulk parameters of the ionospheric thermal plasma. The ISL ...instrument is comprised of two sensors: (i) a classical cylindrical sensor and (ii) a spherical sensor with its surface divided in seven segments: six spherical caps electrically isolated and the rest of the sphere which is used as a guard electrode. The two main parameters measured by ISL are the electron density and temperature; they are obtained with a 1
s time-resolution. In addition, the ion density and its variation can be derived from the current-voltage characteristics of the probe, but it requires an a-priori knowledge of the ion composition and a more sophisticated processing than the one currently implemented. The novel design for the spherical sensor has been called the segmented Langmuir probe (SLP). The SLP current can be measured individually on each of the seven segments, thus providing angular sensitivity to the ram direction of the incoming ion flow. The SLP was flown for the first time onboard the DEMETER satellite for in-flight validation of this novel concept, but the main sensor used routinely during the mission is the cylindrical probe. The design of the instrument and the analysis technique for the cylindrical probe are described. A brief description of the SLP and of its capabilities is provided. An overview of the currently available ISL data products on the DEMETER Mission Science Data Centre is given. Selected examples of some “classical” ionospheric features as being observed by ISL are discussed.
The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design concept for a next-generation UHECR observatory, addressing the requirements for a large-area, low-cost detector suitable ...for measuring the properties of ultra-high energy cosmic rays (UHECRs), having energies exceeding 30 EeV, with an unprecedented aperture. We have developed a full-scale prototype consisting of four 200 mm diameter photo-multiplier tubes at the focus of a segmented mirror of 1.6 m in diameter. In October 2016, September 2017, and September 2018 we installed three such prototypes at the Black Rock Mesa site of the Telescope Array experiment in central Utah, USA. All three telescopes have been steadily taking data since installation. We report on the design and installation of these prototypes, and present some preliminary results, including measurements of artificial light sources, distant ultraviolet lasers, and UHECRs.
•Mercury's magnetic field contains magnetic cusps, areas of focused field lines containing trapped magnetospheric charged particles that will be funneled onto the Mercury surface at very high ...latitudes and direct energetic protons, ions and electrons directly onto ices in the polar regions.•Energy deposition onto the ices comes from magnetospheric charged particles, galactic cosmic rays (GCR), solar energetic particles (SEP) and Lyman-alpha and scattered UV photons.•This focused radiation will initiate chemistry that may create dark compounds that could be the dark low-albedo materials observed by MESSENGER instruments. Thick layers will be created by radiolysis and chemistry as well as gardening, overturn, sputtering and other physical processes occurring simultaneously.•Complex CHNOS molecules may be created by this process, such as aldehydes, amines, alcohols, cyanates, ketones, hydroxides, carbon oxides and suboxides, organic acids and others. Specific compounds are: H2CO, HCOOH, CH3OH, HCO, H2CO3, CH3C(O)CH3, C2O, CxO, C3O2, CxOy, CH3CHO, CH3OCH2CH2OCH3, C2H6, CxHy, NO2, HNO2, HNO3, NH2OH, Na2O, NaOH, HNO, N2H2, N3, HCN, CH3NH2, SO, SO2, SO3, OCS, H2S, CH3SH, even BxHy.•Magnetospheric energy sources dominate the energy flux onto the ices. The total energy fluxes of photons, GCRs and SEPs are each around two or more orders of magnitude less than magnetospheric fluxes. GCR and SEP have lower fluxes but will process deeper layers of the ices because of their greater depth of energy deposition.
Observations by the MESSENGER spacecraft during its flyby and orbital observations of Mercury in 2008–2015 indicated the presence of cold icy materials hiding in permanently-shadowed craters in Mercury's north polar region. These icy condensed volatiles are thought to be composed of water ice and frozen organics that can persist over long geologic timescales and evolve under the influence of the Mercury space environment. Polar ices never see solar photons because at such high latitudes, sunlight cannot reach over the crater rims. The craters maintain a permanently cold environment for the ices to persist. However, the magnetosphere will supply a beam of ions and electrons that can reach the frozen volatiles and induce ice chemistry. Mercury's magnetic field contains magnetic cusps, areas of focused field lines containing trapped magnetospheric charged particles that will be funneled onto the Mercury surface at very high latitudes. This magnetic highway will act to direct energetic protons, ions and electrons directly onto the polar ices. The radiation processing of the ices could convert them into higher-order organics and dark refractory materials whose spectral characteristics are consistent with low-albedo materials observed by MESSENGER Laser Altimeter (MLA) and RADAR instruments. Galactic cosmic rays (GCR), scattered UV light and solar energetic particles (SEP) also supply energy for ice processing. Cometary impacts will deposit H2O, CH4, CO2 and NH3 raw materials onto Mercury's surface which will migrate to the poles and be converted to more complex CHNOS-containing molecules such as aldehydes, amines, alcohols, cyanates, ketones, hydroxides, carbon oxides and suboxides, organic acids and others. Based on lab experiments in the literature, possible specific compounds produced may be: H2CO, HCOOH, CH3OH, HCO, H2CO3, CH3C(O)CH3, C2O, CxO, C3O2, CxOy, CH3CHO, CH3OCH2CH2OCH3, C2H6, CxHy, NO2, HNO2, HNO3, NH2OH, HNO, N2H2, N3, HCN, Na2O, NaOH, CH3NH2, SO, SO2, SO3, OCS, H2S, CH3SH, even BxHy. Three types of radiation processing mechanisms may be at work in the ices: (1) Impact/dissociation, (2) Ion implantation and (3) Nuclear recoil (hot atom chemistry). Magnetospheric energy sources dominate the radiation effects. Total energy fluxes of photons, SEPs and GCRs are all around two or more orders of magnitude less than the fluxes from magnetospheric energy sources (in the focused cusp particles). However, SEPs and GCRs cause chemical processing at greater depths than other particles leading to thicker organic layers. Processing of polar volatiles on Mercury would be somewhat different from that on the Moon because Mercury has a magnetic field while the Moon does not. The channeled flux of charged particles through these magnetospheric cusps is a chemical processing mechanism unique to Mercury as compared to other airless bodies.
We present a discussion of some numerical algorithms for the solution of the Vlasov–Maxwell system of equations in the magnetized, nonrelativistic case. We show that a splitting scheme combined with ...a Van Leer type of discretization provides an efficient and accurate scheme for integrating the motion of charged particles in their self-consistent electromagnetic field. The problem of open boundary conditions is also considered. We then discuss the parallelization strategy as used on large parallel computers. Finally, we present an example of the evolution of an electromagnetic beam plasma instability as a typical problem of interest in plasma physics research which can be studied with the Vlasov code.
BACKGROUND AND AIMS: Genome size and chromosome numbers are important cytological characters that significantly influence various organismal traits. However, geographical representation of these data ...is seriously unbalanced, with tropical and subtropical regions being largely neglected. In the present study, an investigation was made of chromosomal and genome size variation in the majority of Curcuma species from the Indian subcontinent, and an assessment was made of the value of these data for taxonomic purposes. METHODS: Genome size of 161 homogeneously cultivated plant samples classified into 51 taxonomic entities was determined by propidium iodide flow cytometry. Chromosome numbers were counted in actively growing root tips using conventional rapid squash techniques. KEY RESULTS: Six different chromosome counts (2n = 22, 42, 63, >70, 77 and 105) were found, the last two representing new generic records. The 2C-values varied from 1·66 pg in C. vamana to 4·76 pg in C. oligantha, representing a 2·87-fold range. Three groups of taxa with significantly different homoploid genome sizes (Cx-values) and distinct geographical distribution were identified. Five species exhibited intraspecific variation in nuclear DNA content, reaching up to 15·1 % in cultivated C. longa. Chromosome counts and genome sizes of three Curcuma-like species (Hitchenia caulina, Kaempferia scaposa and Paracautleya bhatii) corresponded well with typical hexaploid (2n = 6x = 42) Curcuma spp. CONCLUSIONS: The basic chromosome number in the majority of Indian taxa (belonging to subgenus Curcuma) is x = 7; published counts correspond to 6x, 9x, 11x, 12x and 15x ploidy levels. Only a few species-specific C-values were found, but karyological and/or flow cytometric data may support taxonomic decisions in some species alliances with morphological similarities. Close evolutionary relationships among some cytotypes are suggested based on the similarity in homoploid genome sizes and geographical grouping. A new species combination, Curcuma scaposa (Nimmo) Škorničk. & M. Sabu, comb. nov., is proposed.
With the aim to understand the origin of the pressure‐balanced magnetic structures in the form of holes and humps commonly observed in the solar wind and planetary magnetosheaths, high‐resolution ...hybrid numerical simulations of the Vlasov‐Maxwell (VM) equations using both Lagrangian (particle in cells) and Eulerian integration schemes are presented and compared with asymptotic and phenomenological models for the nonlinear mirror mode dynamics. It turns out that magnetic holes do not result from direct nonlinear saturation of the mirror instability that rather leads to magnetic humps. Nevertheless, both above and below threshold, there exist stable solutions of the VM equations in the form of large‐amplitude magnetic holes. Special attention is paid to the skewness of the magnetic fluctuations (that is negative for holes and positive for humps) and its dependency on the distance to threshold and the beta of the plasma. Furthermore, the long‐time evolution of magnetic humps resulting from the mirror instability in an extended domain far enough from threshold may, when the beta of the plasma is not too large, eventually lead to the formation of magnetic holes.
We show that ~1Hz magnetic compressional waves observed in Mercury's inner magnetosphere could be interpreted as ion-Bernstein waves in a moderate proton beta ~0.1 plasma. An observation of a proton ...distribution with a large planetary loss cone is presented, and we show that this type of distribution is highly unstable to the generation of ion-Bernstein waves with low magnetic compression. Ray tracing shows that as these waves propagate back and forth about the magnetic equator; they cycle between a state of low and high magnetic compression. The group velocity decreases during the high-compression state leading to a pileup of compressional wave energy, which could explain the observed dominance of the highly compressional waves. This bimodal nature is due to the complexity of the index of refraction surface in a warm plasma whose upper branch has high growth rate with low compression, and its lower branch has low growth/damping rate with strong compression. Two different cycles are found: one where the compression maximum occurs at the magnetic equator and one where the compression maximum straddles the magnetic equator. The later cycle could explain observations where the maximum in compression straddles the equator. Ray tracing shows that this mode is confined within plus or minus 12 degree magnetic latitude which can account for the bulk of the observations. We show that the Doppler shift can account for the difference between the observed and model wave frequency, if the wave vector direction is in opposition to the plasma flow direction. We note that the Wentzel-Kramers-Brillouin approximation breaks down during the pileup of compressional energy and that a study involving full wave solutions is required. Key Points * The ion-Bernstein (IB) mode is highly unstable to proton loss cones at Mercury * The IB mode can become highly compressional as it propagates * Ray tracing of the IB mode predicts compression peaking the off equator
PDF
