元素活动态提取条件和分析方法的应用研究

元素活动态分析作为深穿透地球化学的新方法,得到了广泛的应用。实验对水提取态、黏土吸附态、有机结合态和铁锰氧化物结合态四种元素活动态的提取条件进行了系统研究,分别考察了提取时间、液固比、离心转速、提取液放置时间对提取效果的影响,确定了元素活动态的最佳提取条件:提取时间为24h,液固比为10:1,离心转速4000rpm;提取液采用新型的高分辨率等离子体质谱法(HR-ICP-MS)测定,该仪器具有强大的动态线性范围(10^-12～10¹²)和高灵敏度,使可同时测定的元素拓展至50余种,可以大大提高工作效率。对HR-ICPMS的主要工作条件:辅助气流量、样品气流量和采样深度等利用响应面法进行了优化。本法将传统的过滤法改为离心法,避免了滤纸或穿滤引入的误差;将新型的高分辨率等离子体质谱法(HR-ICP-MS)应用到提取液的测定,提升了多元素同时分析能力,大大提高工作效率,同时也降低了该方法的检出限,改善了测定结果的精密度。依据实验结果,建立了HR-ICP-MS对四种元素活动态的分析方法,分别得到了四种活动态中各元素的方法检出限和方法精密度,水提取态、黏土...     

Topical Issues for Particle Acceleration Mechanisms in Astrophysical Shocks

Particle acceleration at plasma shocks appears to be ubiquitous in the universe, spanning systems in the heliosphere, supernova remnants, and relativistic jets in distant active galaxies and gamma-ray bursts. This review addresses some of the key issues for shock acceleration theory that require resolution in order to propel our understanding of particle energization in astrophysical environments. These include magnetic field amplification in shock ramps, the non-linear hydrodynamic interplay between thermal ions and their extremely energetic counterparts possessing ultrarelativistic energies, and the ability to inject and accelerate electrons in both non-relativistic and relativistic shocks. Recent observational developments that impact these issues are summarized. While these topics are currently being probed by astrophysicists using numerical simulations, they are also ripe for investigation in laboratory experiments, which potentially can provide valuable insights into the physics of cosmic shocks.     

Diagnostics of Near-Solar Plasma Turbulence Parameters Using the Radio Sounding Technique at Small Heliocentric Distances

We investigate the temporal correlation function and the mean intensity of monochromatic radio emission in the neighborhood of a regular caustic produced by radio sounding of near-solar plasma. Using asymptotic analysis and numerical simulation, we determine conditions under which the temporal correlation function is related to the temporal structure function by a relation similar to that used for the solar wind diagnostics (Coles and Harmon, Astrophys. J. 337, 1023, 1989) in the case of weak refraction of radio waves. Information on the correlation function and on the mean intensity in the caustic shadow region can be used to determine the parameters of the electron density fluctuation spectrum at small heliocentric distances.     

First observation of quasi-2-day oscillations in ionospheric plasma frequency at fixed heights

The existence and development of the quasi-2-day oscillations in the plasma frequency variations of the F region at northern middle latitudes are investigated. A new approach to study the quasi-2-day oscillations is presented, using a methodology that allows us to do such a study at fixed heights. The hourly values of plasma frequency at fixed heights, from 170 km to 220 km at 10 km step, obtained at the Observatori de lEbre station (40.8°N, 0.5°E) during 1995 are used for analysis. It is found that quasi-2-day oscillations exist and persisted in the ionospheric plasma frequency variations over the entire year 1995 for all altitudes investigated. The dominant period of oscillation ranges from 42 to 56 h. The amplitude of oscillation is from 0.1 MHz to 1 MHz. The activity of the quasi-2-day oscillation is better expressed during the summer half year when several enhancements, about 15–30 days in duration, were observed. The largest enhancements of the oscillation occurred during early June, July and early August; i. e., near and after the summer solstice when the 2-day wave in the middle neutral atmosphere typically displays its largest activity in the Northern Hemisphere. The results obtained may help us understand better the possible influencing mechanisms between the 2-day wave in the middle neutral atmosphere and the ionospheric quasi-2-day oscillations.     

Comet Hyakutake (C/1996 B2): Spectacular disconnection event and the latitudinal structure of the solar wind

Images of comet Hyakutake (C/1996 B2) are analyzed in conjunction with solar wind data from spacecraft to determine the relationship between solar wind conditions and plasma tail morphology. The disconnection event (DE) on March 25, 1996 is analyzed with the aid of data from the IMP-8 and WIND Earth-orbiting spacecraft and the DE is found to be correlated with a crossing of the heliospheric current sheet. The comet was within of Earth at the time of the DE and data from IMP-8 and WIND show no high-speed streams, significant density enhancements or shocks.The latitudinal variation in the appearance and orientation of the plasma tail are interpreted based on results from the Ulysses spacecraft. In the polar solar wind region, the comet has a relatively undisturbed appearance, no DEs were observed, and the orientation of the plasma tail was consistent with a higher solar wind speed. In the equatorial solar wind region, the comet's plasma tail had a disturbed appearance, a major DE was observed, and the orientation of the plasma tail was consistent with a lower solar wind speed. The boundary between the equatorial and polar regions crossed by comet Hyakutake in April 1996 was near 30°N (ecliptic) or 24°N (solar) latitude.     

SuperDARN: An example of a network approach to geospace science in the twenty-first century

The study of Earth's space environment, or geospace, has made considerable advances in the 50 years since the start of the Space Age, which was coincident with the 1957 International Geophysical Year. Space probes have visited most parts of that environment providing a wealth of in situ and remote-sensing measurements. Equally important in contributing to the advances made over the last 50 years have been the many instruments, which have been distributed on the surface of the Earth. In particular, the development of networks for the specific purpose of studying the dynamics of geospace, energy redistribution within geospace, and fundamental physical processes in plasmas has been hugely successful. Ground-based instruments remotely sense processes and phenomena in geospace and since this volume is large, networks of such instruments are the best way of measuring the global state of geospace and its dynamics. In this paper, I describe ways in which the Super Dual Auroral Radar Network (SuperDARN) has contributed to the success of ground-based networks, concentrating on science results, which have required the network approach so well demonstrated by SuperDARN. Such science includes the remote sensing of the reconnection electric field and its dynamics, the study of processes where asymmetries in the geospace system are induced by the external driving forces, and MHD waves, which play an important role in the transfer of energy and momentum within geospace. In addition, I discuss open science questions, which can be addressed by SuperDARN in the future, in particular in conjunction with current and future space missions as well as other ground-based networks.     

MESSENGER observations of the plasma environment near Mercury

The MESSENGER Fast Imaging Plasma Spectrometer (FIPS) measured the bulk plasma characteristics of Mercury's magnetosphere and solar wind environment during the spacecraft's first two flybys of the planet on 14 January 2008 (M1) and 6 October 2008 (M2), producing the first measurements of thermal ions in Mercury's magnetosphere. In this work, we identify major features of the Mercury magnetosphere in the FIPS proton data and describe the data analysis process used for recovery of proton density (n_p) and temperature (T_p) with a forward modeling technique, required because of limitations in measurement geometry. We focus on three regions where the magnetospheric flow speed is likely to be low and meets our criteria for the recovery process: the M1 plasma sheet and the M1 and M2 dayside and nightside boundary-layer regions. Interplanetary magnetic field (IMF) conditions were substantially different between the two flybys, with intense reconnection signatures observed by the Magnetometer during M2 versus a relatively quiet magnetosphere during M1. The recovered ion density and temperature values for the M1 quiet-time plasma sheet yielded n_p∼1–10 cm⁻³, T_p∼2×10⁶ K, and plasma β∼2. The nightside boundary-layer proton densities during M1 and M2 were similar, at n_p∼4–5 cm⁻³, but the temperature during M1 (T_p∼4–8×10⁶ K) was 50% less than during M2 (T_p∼8×10⁶ K), presumably due to reconnection in the tail. The dayside boundary layer observed during M1 had a density of ∼16 cm⁻³ and temperature of 2×10⁶ K, whereas during M2 this region was less dense and hotter (n_p∼8 cm⁻³ and T_p∼10×10⁶ K), again, most likely due to magnetopause reconnection. Overall, the southward interplanetary magnetic field during M2 clearly produced higher T_p in the dayside and nightside magnetosphere, as well as higher plasma β in the nightside boundary, ∼20 during M2 compared with ∼2 during M1. The proton plasma pressure accounts for only a fraction (24% for M1 and 64% for M2) of the drop in magnetic pressure upon entry into the dayside boundary layer. This result suggests that heavy ions of planetary origin, not considered in this analysis, may provide the “missing” pressure. If these planetary ions were hot due to “pickup” in the magnetosheath, the required density for pressure balance would be an ion density of ∼1 cm⁻³ for an ion temperature of ∼10⁸ K.     

ROY—A multiscale magnetospheric mission

The scientific rationale of the ROY multi-satellite mission addresses multiscale investigations of plasma processes in the key magnetospheric regions with strong plasma gradients, turbulence and magnetic field annihilation in the range from electron inertial length to MHD scales.The main scientific aims of ROY mission include explorations of:

(a)

turbulence on a non-uniform background as a keystone for transport processes;

(b)

structures and jets in plasma flows associated with anomalously large concentration of kinetic energy; their impact on the energy balance and boundary formation;

(c)

transport barriers: plasma separation and mixing, Alfvenic collapse of magnetic field lines and turbulent dissipation of kinetic energy;

(d)

self-organized versus forced reconnection of magnetic field lines;

(e)

collisionless shocks, plasma discontinuities and associated particle acceleration processes.

In the case of autonomous operation, 4 mobile spacecrafts of about 200 kg mass with 60 kg payload equipped with electro-reactive plasma engines will provide 3D measurements at the scales of 100-10000 km and simultaneous 1D measurements at the scales 10-1000 km. The latter smaller scales will be scanned with the use of radio-tomography (phase-shift density measurements within the cone composed of 1 emitting and 3 receiving spacecrafts).We also discuss different opportunities for extra measurement points inside the ROY mission for simultaneous measurements at up to 3 scales for the common international fleet.Combined influence of intermittent turbulence and reconnection on the geomagnetic tail and on the nonlinear dynamics of boundary layers will be explored in situ with fast techniques including particle devices under development, providing plasma moments down to 30 ms resolution.We propose different options for joint measurements in conjunction with the SCOPE and other missions:

•

simultaneous sampling of low- and high-latitudes magnetopause, bow shock and geomagnetic tail at the same local time;

•

tracing of magnetosheath streamlines from the bow shock to near-Earth geomagnetic tail;

•

passing “through” the SCOPE on the inbound orbit leg;

•

common measurements (with SCOPE and other equatorial spacecraft) at distances of ∼ few thousand km for durations of ∼several hours per orbit.

The orbit options and scientific payload of possible common interest are discussed in this work, including FREGAT cargo opportunities for extra payload launching and the “Swarm” campaigns with ejection of nano- and pico-satellites.     

Cassini observations of Saturn's inner plasmasphere: Saturn orbit insertion results

We present new and definitive results of Cassini plasma spectrometer (CAPS) data acquired during passage through Saturn's inner plasmasphere by the Cassini spacecraft during the approach phase of the Saturn orbit insertion period. This analysis extends the original analysis of Sittler et al. [2005. Preliminary results on Saturn's inner plasmasphere as observed by Cassini: comparison with Voyager. Geophys. Res. Lett. 32, L14S07, doi:10.1029/2005GL022653] to L∼10 along with also providing a more comprehensive study of the interrelationship of the various fluid parameters. Coincidence data are sub-divided into protons and water group ions. Our revised analysis uses an improved convergence algorithm which provides a more definitive and independent estimate of the spacecraft potential Φ_SC for which we enforce the protons and water group ions to co-move with each other. This has allowed us to include spacecraft charging corrections to our fluid parameter estimations and allow accurate estimations of fluctuations in the fluid parameters for future correlative studies. In the appendix we describe the ion moments algorithm, and minor corrections introduced by not weighting the moments with sinθ term in Sittler et al. [2005] (Correction offset by revisions to instruments geometric factor). Estimates of the spacecraft potential and revised proton densities are presented. Our total ion densities are in close agreement with the electron densities reported by Moncuquet et al. [2005. Quasi-thermal noise spectroscopy in the inner magnetosphere of Saturn with Cassini/RPWS: electron temperatures and density. Geophys. Res. Lett. 32, L20S02, doi:10.1029/2005GL022508] who used upper hybrid resonance (UHR) emission lines observed by the radio and plasma wave science (RPWS) instrument. We show a positive correlation between proton temperature and water group ion temperature. The proton and thermal electron temperatures track each with both having a positive radial gradient. These results are consistent with pickup ion energization via Saturn's rotational electric field. We see evidence for an anti-correlation between radial flow velocity V_R and azimuthal velocity V_φ, which is consistent with the magnetosphere tending to conserve angular momentum. Evidence for MHD waves is also present. We show clear evidence for outward transport of the plasma via flux tube interchange motions with the radial velocity of the flow showing positive radial gradient with functional dependence for 4<L<10 (i.e., if we assume to be diffusive transport then D_LL∼D₀L¹¹ for fixed stochastic time step δt). Previous models with centrifugal transport have used D_LL∼D₀L³ dependence. The radial transport seems to begin at Enceladus’ L shell, L∼4, where we also see a minimum in the W⁺ ion temperature . For the first time, we are measuring the actual flux tube interchange motions in the magnetosphere and how it varies with radial distance. These observations can be used as a constraint with regard to future transport models for Saturn's magnetosphere. Finally, we evaluate the thermodynamic properties of the plasma, which are all consistent with the pickup process being the dominant energy source for the plasma.     

Saturn's magnetospheric interaction with Titan as defined by Cassini encounters T9 and T18: New results

We present new results of Cassini's T9 flyby with complementary observations from T18. Based on Cassini plasma spectrometer (CAPS) and Cassini magnetometer (MAG), compositional evidence shows the upstream flow for both T9 and T18 appears composed of light ions (H⁺ and H₂⁺), with external pressures ∼30 times lower than that for the earlier TA flyby where heavy ions dominated the magnetospheric plasma. When describing the plasma heating and sputtering of Titan's atmosphere, T9 and T18 can be considered interactions of low magnetospheric energy input. On the other hand, T5, when heavy ion fluxes are observed to be higher than typical (i.e., TA), represents the limiting case of high magnetospheric energy input to Titan's upper atmosphere. Anisotropy estimates of the upstream flow are 1<T_⊥/T_‖<3 and the flow is perpendicular to B, indicative of local picked up ions from Titan's H and H₂ coronae extending to Titan's Hill sphere radius. Beyond this distance the corona forms a neutral torus that surrounds Saturn. The T9 flyby unexpectedly resulted in observation of two “wake” crossings referred to as Events 1 and 2. Event 2 was evidently caused by draped magnetosphere field lines, which are scavenging pickup ions from Titan's induced magnetopause boundary with outward flux ∼2×10⁶ ions/cm²/s. The composition of this out flow is dominated by H₂⁺ and H⁺ ions. Ionospheric flow away from Titan with ion flux ∼7×10⁶ ion/cm²/s is observed for Event 1. In between Events 1 and 2 are high energy field aligned flows of magnetosphere protons that may have been accelerated by the convective electric field across Titan's topside ionosphere. T18 observations are much closer to Titan than T9, allowing one to probe this type of interaction down to altitudes ∼950 km. Comparisons with previously reported hybrid simulations are made.