Searching the Sinus Amoris: Using profiles of geological units,impact and volcanic features to characterize a major terrane interface on the Moon

Geochemical profiles of surface units, impact, and volcanic features are studied in detail to determine the underlying structure in an area of extensive mare/highland interface, Sinus Amoris. This study region includes and surrounds the northeastern embayment of Mare Tranquillitatis. The concentrations of two major rock-forming elements (Mg and Al), which were derived from the Apollo 15 orbital geochemical measurements, were used in this study. Mapped units and deposits associated with craters in the northwestern part of the region tend to have correlated low Mg and Al concentrations, indicating the presence of KREEP-enriched basalt. Found along the northeastern rim of Tranquillitatis were areas with correlated high Mg and Al concentration, indicating the presence of troctolite. Distinctive west/east and north/south trends were observed in the concentrations of Mg and Al, and, by implication, in the distribution of major rock components on the surface. Evidence for a systematic geochemical transition in highland or basin-forming units may be observed here in the form of distinctive differences in chemistry in otherwise similar units in the western and eastern portions of the study region.     

Terrestrial analogs of the hellespontus dunes,Mars

Geomorphic features in the Hellespontus region, Mars, were compared with dunes of the crescentic ridge type in numerous terrestrial sand seas quantitatively by dimensional analysis of dune lengths, widths, and wavelengths. Mean values for the Hellespontus dunes are close to mean values derived from measurements of all sampled terrestrial sand seas. Terrestrial analogs of form and areal distribution of the Hellespontus dunes are shown by comparison of scale ratios derived from the measurements. Dunes of similar form occur in South West Africa, in Pakistan, in the southeastern Arabian peninsula, in the Sahara, in eastern USSR and northern China, and in western North America. Terrestrial analogs closest to form and areal distribution of the Hellespontus dunes are in the Kara Kum Desert, Turkmen SSR, and in the Ala Shan (Gobi) Desert, China.     

Bicentennial decrease of the solar constant leads to the Earth’s unbalanced heat budget and deep climate cooling

Long-wave energy emitted by the Earth-atmosphere into space is characterized by changes in power over time that always lag behind the changes in power of the absorbed solar radiation due to slow variation in enthalpy of the Earth-atmosphere system. Long-term variation of the solar energy radiation absorbed by the Earth remains uncompensated by the energy radiated into space over the interval of time that is determined by the thermal inertia. The basic state of the climate system is when the debit and credit sides in the Earth’s global annual mean energy budget (including the air and water envelopes) are almost always unbalanced. The annual mean balance of the heat budget of the Earth-atmosphere over a long time period will reliably define the behavior and magnitude of the energy excess accumulated by the Earth or energy deficit to allow us to determine adequately and to predict beforehand the trend and amplitude of the forthcoming climate change using the prognosis of variations in the total solar irradiance (solar constant). The decrease in solar constant has been observed since the early 1990s. The Earth as a planet will have a negative balance in the energy budget in the future as well, because the Sun is entering the decline phase of the bicentennial luminosity changes. This will lead to a drop in temperature in approximately 2014. The increase in albedo and decrease in greenhouse gas concentration in the atmosphere will result in the additional decrease in absorbed portion of the solar energy and reduced greenhouse effect. The additional drop in temperature exceeding the effect of decreased solar constant can occur as a result of successive feedback effects. A deep bicentennial minimum in solar constant is to be anticipated in 2042 ± 11 and the 19th Little Ice Age (for the last 7500 years) may occur in 2055 ± 11.     

Very Large Array and SOHO Observations of Type I Noise Storms,Large-Scale Loops and Magnetic Restructuring in the Corona

Very Large Array (VLA) observations at 91-cm wavelength are combined with data from the SOHO EIT, MDI and LASCO and used to study the evolving coronal magnetic environment in which Type I noise storms and large-scale coronal loops occur. On one day, we have shown the early evolution of a coronal mass ejection (CME) in projection in the disk by tracing its decimetric continuum emission. The passage of the CME and an associated EUV ejection event coincided with an increase in the 91-cm brightness temperature of an extended coronal loop located a significant distance away and with the displacement of the 91-cm source during the early stage of the CME. We suggest that the energy deposited into the corona by the CME may have caused a local increase in the thermal or nonthermal electron density or in the electron temperature in the middle corona resulting in a transient increase in the brightness of the 91-cm loop. On a second observing day, we have consolidated the known association between magnetic changes in the photosphere and low corona with noise storm enhancements in an overlying radio source well in advance of a flare event in the same region. We find anti-correlated changes in the brightness of a bipolar 91-cm Type I noise storm that appear to be associated with the cancellation and emergence of magnetic flux in the underlying photosphere. In this case, the evolving fields may have led to magnetic instabilities and reconnection in the corona and the acceleration of nonthermal particles that initiated and sustained the Type I noise storm.     

Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materials

Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, M?ssbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature M?ssbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. M?ssbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.     

天文学研究发展趋势分析--恒星与恒星系统

对在1981-2000年世界上所发表的和中国学者所发表的有关恒星与恒星系统的论文作统计发现：此期间世界上这一领域的发展较平稳，而我国的发展快速．这反映了改革开放后，我国基础学科研究大有进展．从各分支所占的比重和发展来看，我国在恒星与恒星系统的研究与世界同期有几乎相同的分布，因此总体上我国在这一领域的发展基本正常．当然有些分支发展较快，如有关超新星及其遗迹、星际介质和恒星形成区、化学丰度的研究等，这和一些较强的研究团组形成有关；在双星研究方面，我国则与世界发展一致，双星研究始终是恒星研究领域的重点；而在世界范围内较突出的关于银河系的研究，在我国却相对较弱．恒星和恒星系统这一研究领域20年的论文数统计显示，我国学者所发表的论文只占世界总论文数的1．3％，虽然在最后5年有大幅上升，但也只占2．0％，这与我国IAU会员数所占比例相比是偏少的．就世界整体而言，恒星领域的研究进展与整个天文学领域相比是较慢的，显然这与一批能做深空探测和高能波段观测的设备投入有关．因此，除了对恒星及恒星系统领域作统计分析外，对整个天文学领域各大分支作分析可能对制定今后我国天文学发展计划更有利。     

Analysis of All-China Sunshine Conditions of Site Selection for Large Solar Telescopes

The yearly and monthly data sets of sunshine duration and percent- age obtained at the 756 principal and primary standard meteorological stations all over China from 1971 to 2000, compiled by the Meteorological Reference Room of the National Center for Meteorological Information, are used to study the countrywide sunshine conditions and to analyze the factors which have an effect on the sunshine, in combination with the data of the key elements, such as the cloud cover and water vapor, recorded in China from 1951 to 2008. The obtained result shows that the distributions of the sunshine duration and sun- shine percentage in China are consistent with each other: small in southeastern China and large in northwestern China, increasing from southeast to northwest. In eastern China, the sunshine duration gradually increases from south to north and the sunshine condition in the western area is integrally better than that in the eastern area, tallying with the general rule. The sunshine condition in the Shiquanhe area in southwestern Tibet is the optimum, the sunshine conditions in the vicinity of the latitude zone of 40° N and in the area of southern Tibet take the second place, those in the south of the Yangtze River, in southern China, Sichuan Basin and in the eastern area of the Yunnan-Guizhou Plateau are rela- tively poor, and those in the other areas are placed in the middle. The sunshine duration is affected by the key elements like the cloud cover and water vapor, exhibiting a negative correlation with them.     

A comparative study of opaque phases in Qingzhen (EH3) and MacAlpine Hills 88136 (EL3): Representatives of EH and EL parent bodies

Abstract— Opaque minerals in the Qingzhen (EH3) and MacAlpine Hills (MAC) 88136 (EL3) enstatite chondrites were studied and compared with other EH and EL chondrites. All opaque minerals usually occur in multi‐sulfide‐metal clasts and nodules in the matrix between chondrules (El Goresy et al., 1988). The higher abundance of opaque minerals, the occurrence of niningerite and various alkali‐sulfides (e.g., caswellsilverite, phases A and B, djerfisherite) are diagnostic criteria for EH chondrites, while alabandite is characteristic for EL chondrites. In addition, EH chondrites are characterized by enrichments of Si in both kamacite and perryite, and alkali elements in sphalerite and chalcopyrite. The Mn contents of daubreelite and sphalerite are lower in EH than in EL chondrites. These are consistent with lower oxygen fugacity and higher H₂S fugacity of EH than EL chondrites. In contrast, the discovery of sphalerite and Zn‐rich daubreelite in MAC 88136 indicates that their absence in EL6 chondrites is probably related to thermal metamorphism in the parent body. Schreibersite microspherules are commonly enclosed in most sulfides in Qingzhen, but are absent in MAC 88136. They were once molten, and probably predated all sulfide host phases. The petrographic setting and chemical compositions of the sulfide hosts of the schreibersite microspherules in EH3 chondrites are consistent with formation by condensation. The earliest sulfide condensates oldhamite and niningerite occupy the interiors of the clasts and nodules, whereas the rims consist of troilite and djerfisherite. In addition, in Qingzhen, some other troilite, djerfisherite and sphalerite assemblages coexist with perryite. They were produced by sulfurization of metallic Fe‐Ni in the nebula. In MAC 88136, sulfurization of Si‐bearing Fe‐Ni metal is less pronounced, and it produced troilite, schreibersite and less abundant perryite. Two kinds of normal zoning and a reverse zoning trends of niningerite, and both normal and reverse zoning of sphalerite were found in clasts and nodules in Qingzhen. The coexistence of normal and reverse zoning profiles in niningerite grains in the same meteorite strongly suggests that they formed before accretion in the parent body, because an asteroidal metamorphic or an impact event in the parent body would have erased these contrasting profiles and destroyed the textural settings. In contrast, alabandite in MAC 88136 shows only normal zoning, with the FeS content decreasing to 9.3 mol% toward troilite, indicating very slow cooling at low temperature.     

Kinetic Alfven wave driven by density and magnetic field inhomogeneities in plasmas of finite β

On the basis of an analysis of the instability of drift caused by density and magnetic field inhomogeneities in plasmas with finite β, the effect of the instability on the excitation of kinetic Alfven wave (KAW) is probed. In the kinetic theory, which correctly treats the effect of the finite Larmor radius and the wave-particle resonant interaction, the motion of the ions is described with the Vlasov equation and the motion of electrons, with the kinetic drift equation. Comparing the effects by inhomogeneities in the density and in the magnetic field in plasmas with finite β, we found that the drift instability is more easily excited by the former, and in the instability so excited, the energy transfer is more intense. This energy transfer provides the physical basis for the excitation of KAW. As shown by numerical solutions, KAWs can be widely excited and produced in the magnetosphere, especially in the cusp of the magnetosphere, in the magnetopause and in the boundary layers of plasma sheets, where inhomogeneities are obvious. The results of the present work further illustrate that the KAW plays an important role in the energy transfer in magnetospheric regions.     

Petrology of magmatic silicate inclusions in the Allan Hills 77005 lherzolitic shergottite

Abstract— Magmatic inclusions occur in both chadacrystic olivine and oikocrystic pigeonite in ALH 77005 but are different from each other. Magmatic inclusions in olivine consist mainly of aluminous pyroxenes, intergrowths of plagioclase and silica, silica-predominant glass, and rhyodacitic glass, with minor amounts of chromite, spinel, pyrrhotite, and whitlockite. Those in pigeonite consist mainly of aluminous pyroxenes, nonaluminous ferroan pyroxenes, kaersutite, spinel, and K-rich trachytic glass, with minor amounts of pyrrhotite and whitlockite. The magmatic inclusions in chadacrystic olivine formed from trapped melts that were basaltic, apparently dry and crystallized additional olivine metastably. The basaltic magma, with entrained olivine, experienced magma mixing with K-rich and wet magmas, or assimilation of such crustal rocks, in the early to middle stages of the crystallization sequence of ALH 77005 during crystallization of chadacrystic olivine prior to precipitation of oikocrystic pigeonite. However the amount of mixed magmas or assimilated rocks was minor in comparison to the basaltic magma. Crystallization of pigeonite, augite, and plagioclase in the host lithologies took place in a shallow magma reservoir under an open-system condition, and the pigeonite trapped basaltic andesite to trachyandesitic melts, which resulted in magmatic inclusions in oikocrystic pigeonite. The magmatic inclusions in both olivine and pigeonite were formed under a rapid-cooling condition, resulting in a variety of inclusions. Kaersutite in magmatic inclusions in oikocrystic pigeonite crystallized under a closed-system wet condition during the late-stage crystallization of the inclusions.     

Interannual and seasonal variation of the Huanghe (Yellow River) water discharge over the past 50 years: Connections to impacts from ENSO events and dams

The Huanghe, the second largest river in China, is now under great pressure as a water resource. Using datasets of river water discharge, water consumption and regional precipitation for the past 50 years, we elucidate some connections between decreasing water discharges, global El Niño/Southern Oscillation (ENSO) events and anthropogenic impacts in the drainage basin. Global ENSO events, which directly affected the regional precipitation in the river basin, resulted in approximately 51% decrease in river water discharge to the sea. The degree of anthropogenic impacts on river water discharge is now as great as that of natural influences, accelerating the water losses in the hydrological cycle. The large dams and reservoirs regulated the water discharge and reduced the peak flows by storing the water in the flood season and releasing it in the dry season as needed for agricultural irrigation. Thus, as a result, large dams and reservoirs have shifted the seasonal distribution patterns of water discharge and water consumption and finally resulted in rapidly increasing water consumption. Meanwhile, the annual distribution pattern of water consumption also changed under the regulation of dams and reservoirs, indicating that the people living in the river basin consume the water more and more to suit actual agricultural schedule rather than depending upon natural pattern of annual precipitation. The combination of the increasing water consumption facilitated by the dams and reservoirs and the decreasing precipitation closely associated with the global ENSO events over the past half century has resulted in water scarcity in this world-famous river, as well as in a number of subsequent serious results for the river, delta and coastal ocean.     

Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience*

Abstract— The occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies. Its utility is due to its almost ubiquitous occurrence in terrestrial rocks, its overall stability and the fact that a variety of shock metamorphic effects, occurring over a range of shock pressures, have been well documented. These shock effects have been generally duplicated in shock recovery experiments and, thus, serve as shock pressure barometers. After reviewing the general character of shock effects in quartz, the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored. The short pulse lengths in experiments may account for the difficulty in synthesizing the high-pressure polymorphs, coesite and stishovite, compared to natural occurrences. In addition, post-shock thermal effects are possible in natural events, which can affect shock altered physical properties, such as refractive index, and cause annealing of shock damage and recrystallization. The orientations of planar microstructures, however, are unaffected by post-impact thermal events, except if quartz is recrystallized, and provide the best natural shock barometer in terms of utility and occurrence. The nature of planar microstructures, particularly planar deformation features (PDFs), is discussed in some detail and a scheme of variations in orientations with shock pressure is provided. The effect of post-impact events on PDFs is generally limited to annealing of the original glass lamellae to produce decorated PDFs, resulting from the exsolution of dissolved water during recrystallization. Basal (0001) PDFs differ from other PDF orientations in that they are multiple, mechanical Brazil twins, which are difficult to detect if not partially annealed and decorated. The occurrence and significance of shock metamorphosed quartz and its other phases (namely, coesite, stishovite, diaplectic glass and lechatelierite) are discussed for terrestrial impact structures in both crystalline (non-porous) and sedimentary (porous) targets. The bulk of past studies have dealt with crystalline targets, where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures. In sedimentary targets, the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature, which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets. This is discussed, along with examples of variations in the relative abundances of planar microstructures and their orientations, which are attributed to textural variations in sedimentary target rocks. Examples of the shock metamorphism of quartz in distal ejecta, such as at the K/T boundary, and from nuclear explosions are illustrated and are equivalent to that of known impact structures, except with respect to characteristics that are due to long-term, post-shock thermal effects. Finally, the differences between the deformation and phase transformation of quartz by shock and by endogenic, tectonic and volcanic processes are discussed. We confirm previous conclusions that they are completely dissimilar in character, due to the vastly different physical conditions and time scales typical for shock events, compared to tectonic and volcanic events. Well-characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment.     

The Mars water cycle

A model has been developed to test the hypothesis that the observed seasonal and latitudinal distribution of water on Mars is controlled by the sublimation and condensation of surface ice deposits in the arctic and antarctic, and the meridional transport of water vapor. Besides reproducing the observed water vapor distribution, the model correctly reproduces the presence of a large permanent ice cap in the arctic and not in the antarctic. No permanent ice reservoirs are predicted in the temperate or equatorial zones. Wintertime ice deposits in the arctic are shown to be the source of the large water vapor abundances observed in the arctic summertime, and the moderate water vapor abundances in the northern temperate region. Model calculations suggest that a year without dust storms results in very little change in the water vapor distribution. The current water distribution appears to be the equilibrium distribution for present atmospheric conditions.     

Galactic orbits of Hipparcos stars: Classification of stars

The Galactic orbits of 27 440 stars of all classes with accurate coordinates and parallaxes of more than 3 mas from the Hipparcos catalogue, proper motions from the Tycho-2 catalogue, and radial velocities from the Pulkovo Compilation of Radial Velocities (PCRV) are analyzed. The sample obtained is much more representative than the Geneva-Copenhagen survey and other studies of Galactic orbits in the solar neighborhood. An estimation of the influence of systematic errors in the velocities on orbital parameters shows that the errors of the proper motions due to the duplicity of stars are tangible only in the statistics of orbital parameters for very small samples, while the errors of the radial velocities are noticeable in the statistics of orbital parameters for halo stars. Therefore, previous studies of halo orbits may be erroneous. The distribution of stars in selection-free regions of the multidimensional space of orbital parameters, dereddened colors, and absolute magnitudes is considered. Owing to the large number of stars and the high accuracy of PCRV radial velocities, nonuniformities of this distribution (apart from the well-known dynamical streams) have been found. Stars with their peri- and apogalacticons in the disk, perigalacticons in the bulge and apogalacticons in the disk, perigalacticons in the bulge and apogalacticons in the halo, and perigalacticons in the disk and apogalacticons in the halo have been identified. Thus, the bulge and the halo are inhomogeneous structures, each consisting of at least two populations. The radius of the bulge has been determined: 2 kpc.     

Multifractality as a Measure of Complexity in Solar Flare Activity

In this paper we use the notion of multifractality to describe the complexity in Hα flare activity during the solar cycles 21, 22, and 23. Both northern and southern hemisphere flare indices are analyzed. Multifractal behavior of the flare activity is characterized by calculating the singularity spectrum of the daily flare index time series in terms of the Hölder exponent. The broadness of the singularity spectrum gives a measure of the degree of multifractality or complexity in the flare index data. The broader the spectrum, the richer and more complex is the structure with a higher degree of multifractality. Using this broadness measure, complexity in the flare index data is compared between the northern and southern hemispheres in each of the three cycles, and among the three cycles in each of the two hemispheres. Other parameters of the singularity spectrum can also provide information about the fractal properties of the flare index data. For instance, an asymmetry to the left or right in the singularity spectrum indicates a dominance of high or low fractal exponents, respectively, reflecting a relative abundance of large or small fluctuations in the total energy emitted by the flares. Our results reveal that in the even (22nd) cycle the singularity spectra are very similar for the northern and southern hemispheres, whereas in the odd cycles (21st and 23rd) they differ significantly. In particular, we find that in cycle 21, the northern hemisphere flare index data have higher complexity than its southern counterpart, with an opposite pattern prevailing in cycle 23. Furthermore, small-scale fluctuations in the flare index time series are predominant in the northern hemisphere in the 21st cycle and are predominant in the southern hemisphere in the 23rd cycle. Based on these findings one might suggest that, from cycle to cycle, there exists a smooth switching between the northern and southern hemispheres in the multifractality of the flaring process. This new observational result may bring an insight into the mechanisms of the solar dynamo operation and may also be useful for forecasting solar cycles.     

Microvariability and fast variability of stars. I. standard stars

This is a study of observations of the photometric quantities Vt and Bt, reported in the Hipparcos catalog, for 15 standard stars in order to search for microvariability and rapid variability in their emission. The microvariability is found to be characterized mainly by smooth fluctuations in the brightness. Changes in the magnitudes of the stars HD 28355 and HD 130109 with a period of ~150 min and an amplitude <0^m.02 appear to be caused by vertical shifts in their photospheres. Changes in the magnitudes with an amplitude of ~0^m.01 and a period of 11.4^d in the star e Eri were related to the rotation of spots. A similar microvariability period and amplitude in the star 51 Peg most likely originates in the influence of a planet.     

The potential importance of non-local,deep transport on the energetics,momentum, chemistry,and aerosol distributions in the atmospheres of Earth,Mars, and Titan

A review of non-local, deep transport mechanisms in the atmosphere of Earth provides a good foundation for examining whether similar mechanisms are operating in the atmospheres of Mars and Titan. On Earth, deep convective clouds in the tropics constitute the upward branch of the Hadley Cell and provide a conduit through which energy, moisture, momentum, aerosols, and chemical species are moved from the boundary layer to the upper troposphere and lower stratosphere. This transport produces mid-tropospheric minima in quantities such as water vapor and moist static energy and maxima where the clouds detrain. Analogs to this terrestrial transport are found in the strong and deep thermal circulations associated with topography on Mars and with Mars dust storms. Observations of elevated dust layers on Mars further support the notion that non-local deep transport is an important mechanism in the atmosphere of Mars. On Titan, the presence of deep convective clouds almost assures that non-local, deep transport is occurring and these clouds may play a role in global cycling of energy, momentum, and methane. Based on the potential importance of non-local deep transport in Earth's atmosphere and supported by evidence for such transport in the atmospheres of Mars and Titan, greater attention to this mechanism in extraterrestrial atmospheres is warranted.     

Organizing some very tenuous things: Resonant structures in Saturn's faint rings

Images of the dusty rings obtained by the Cassini spacecraft in late 2006 and early 2007 reveal unusual structures composed of alternating canted bright and dark streaks in the outer G ring (∼170,000 km from Saturn center), the inner Roche Division (∼138,000 km) and the middle D ring (70,000-73,000 km). The morphology, locations and pattern speeds of these features indicate that they are generated by Lindblad resonances. The structure in the G ring appears to be generated by the 8:7 Inner Lindblad Resonance with Mimas. Based in part on the morphology of the G ring structure, we develop a phenomenological model of Lindblad-resonance-induced structures in faint rings, where the observed variations in the rings' optical depth and brightness are due to alignments and trends in the particles' orbital parameters with semi-major axis. To reproduce the canted character of these structures, this model requires a term in the equations of motion that damps eccentricities. Using this model to interpret the structures in the D ring and Roche Division, we find that the D-ring patterns mimic those predicted at 2:1 Inner Lindblad Resonances and the Roche Division patterns look like those expected at 3:4 Outer Lindblad Resonances. As in the G ring, the effective eccentricity-damping timescale is of order 10-100 days, suggesting that free eccentricities are strongly damped by some mechanism that operates throughout all these regions. However, unlike in the G ring, perturbation forces with multiple periods are required to explain the observed patterns in the D ring and Roche Division. The strongest perturbation periods occur at 10.53, 10.56 and 10.74 hours (only detectable in the D ring) and 10.82 hours (detectable in both the D ring and Roche division). These periods are comparable to the rotation periods of Saturn's atmosphere and magnetosphere. The inferred strength of the perturbation forces required to produce these patterns (and the absence of evidence for other resonances driven by these periods in the main rings) suggests that non-gravitational forces are responsible for generating these features in the D ring and Roche Division. If this interpretation is correct, then some of these structures may have some connection with periodic signals observed in Saturn's magnetic field and radio-wave emissions, and accordingly could help clarify the nature and origin(s) of these magnetospheric asymmetries.     

Energies of Electrons Accelerated in Turbulent Reconnecting Current Sheets in Solar Flares

Yohkoh observations strongly suggest that electron acceleration in solar flares occurs in magnetic reconnection regions in the corona above the soft X-ray flare loops. Unfortunately, models for particle acceleration in reconnecting current sheets predict electron energy gains in terms of the reconnection electric field and the thickness of the sheet, both of which are extremely difficult to measure. It can be shown, however, that application of Ohm's law in a turbulent current sheet, combined with energy and Maxwell's equations, leads to a formula for the electron energy gain in terms of the flare power output, the magnetic field strength, the plasma density and temperature in the sheet, and its area. Typical flare parameters correspond to electron energies between a few tens of keV and a few MeV. The calculation supports the viewpoint that electrons that generate the continuum gamma-ray and hard X-ray emissions in impulsive solar flares are accelerated in a large-scale turbulent current sheet above the soft X-ray flare loops.     

Motion of charged particles in the magnetosphere

The adiabatic motion of charged particles in the magnetosphere has been investigated using Mead-Fairfield magnetospheric field model (Mead and Fairfield, 1975). Since the motion of charged particles in a dipolar field geometry is well understood, we bring out in this paper some important features in characteristic motion due to non-dipolar distortions in the field geometry. We look at the tilt averaged picture of the field configuration and estimate theoretically the parameters like bounce period, longitudinal invariant and the bounce averaged drift velocities of the charged particle in the Mead-Fairfield field geometry. These parameters are evaluated as a function of pitch angle and azimuthal position in the region of ring current (5 to 7 Earth radii from the centre of the Earth) for four ranges of magnetic activity. At different longitudes the non-dipolar contribution as a percentage of dipole value in bounce period and longitudinal invariant show maximum variation for particles close to 90° pitch angles. For any low pitch angle, these effects maximize at the midnight meridian. The radial component of the bounce averaged drift velocity is found to be greatest at the dawn-dusk meridians and the contribution vanishes at the day and midnight meridians for all pitch angles. In the absence of tilt-dependent terms in the model, the latitudinal component of the drift velocity vanishes. On the other hand, the relative non-dipolar contribution to bounce averaged azimuthal drift velocity is very high as compared to similar contribution in other characteristic parameters of particle motion. It is also shown that non-dipolar contribution in bounce period, longitudinal invariant and bounce averaged drift velocities increases in magnitude with increase in distance and magnetic activity.