Initial ISEE magnetometer results: magnetopause observations

The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes. During one of these passes the magnetosheath field was northward, during one it was slightly southward, and in two it was strongly southward. The velocity of the magnetopause is found to be highly irregular ranging from 4 to over 40 km s^-1 and varying in less time than it takes for a spacecraft to cross the boundary. Thicknesses ranged from 500 to over 1000 km.Clear evidence for reconnection is found in the data when the magnetosheath field is southward. However, this evidence is not in the form of classic rotational discontinuity signatures. Rather, it is in the form of flux transfer events, in which reconnection starts and stops in a matter of minutes or less, resulting in the ripping off of flux tubes from the magnetosphere. Evidence for flux transfer events can be found both in the magnetosheath and the outer magnetosphere due to their alteration of the boundary normal. In particular, their presence at the time of magnetopause crossings invalidates the usual 2-dimensional analysis of magnetopause structure. Not only are these flux transfer events probably the dominant means of reconnection on the magnetopause, but they may also serve as an important source of magnetopause oscillations, and hence of pulsations in the outer magnetosphere. On two days the flux transfer rate was estimated to be of the order of 2 × 10¹² Maxwells per second by the flux transfer events detected at ISEE. Events not detectable at ISEE and continued reconnection after passage of an FTE past ISEE could have resulted in an even greater reconnection rate at these times.     

Initial results from the ISEE-1 and -2 plasma wave investigation

In this paper we present an initial survey of results from the plasma wave experiments on the ISEE-1 and -2 spacecraft which are in nearly identical orbits passing through the Earth's magnetosphere at radial distances out to about 22.5R_e. Essentially every crossing of the Earth's bow shock can be associated with an intense burst of electrostatic and whistler-mode turbulence at the shock, with substantial wave intensities in both the upstream and downstream regions. Usually the electric and magnetic field spectrum at the shock are quite similar for both spacecraft, although small differences in the detailed structure are sometimes apparent upstream and downstream of the shock, probably due to changes in the motion of the shock or propagation effects. Upstream of the shock emissions are often observed at both the fundamental, f_-^p, and second harmonic, 2f_p^-, of the electron plasma frequency. In the magnetosphere high resolution spectrograms of the electric field show an extremely complex distribution of plasma and radio emissions, with numerous resonance and cutoff effects. Electron density profiles can be obtained from emissions near the local electron plasma frequency. Comparisons of high resolution spectrograms of whistler-mode emissions such as chorus detected by the two spacecraft usually show a good overall similarity but marked differences in detailed structure on time scales less than one minute. Other types of locally generated waves, such as the (n+1/2)f_-^gelectron cyclotron waves, show a better correspondence between the two spacecraft. High resolution spectrograms of kilometric radio emissions are also presented which show an extremely complex frequency-time structure with many closely spaced narrow-band emissions.     

The Dynamic Quasiperpendicular Shock: Cluster Discoveries

The physics of collisionless shocks is a very broad topic which has been studied for more than five decades. However, there are a number of important issues which remain unresolved. The energy repartition amongst particle populations in quasiperpendicular shocks is a multi-scale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. The most important processes take place in the close vicinity of the major magnetic transition or ramp region. The distribution of electromagnetic fields in this region determines the characteristics of ion reflection and thus defines the conditions for ion heating and energy dissipation for supercritical shocks and also the region where an important part of electron heating takes place. In other words, the ramp region determines the main characteristics of energy repartition. All these processes are crucially dependent upon the characteristic spatial scales of the ramp and foot region provided that the shock is stationary. The process of shock formation consists of the steepening of a large amplitude nonlinear wave. At some point in its evolution the steepening is arrested by processes occurring within the shock transition. From the earliest studies of collisionless shocks these processes were identified as nonlinearity, dissipation, and dispersion. Their relative role determines the scales of electric and magnetic fields, and so control the characteristics of processes such as ion reflection, electron heating and particle acceleration. The determination of the scales of the electric and magnetic field is one of the key issues in the physics of collisionless shocks. Moreover, it is well known that under certain conditions shocks manifest a nonstationary dynamic behaviour called reformation. It was suggested that the transition from stationary to nonstationary quasiperiodic dynamics is related to gradients, e.g. scales of the ramp region and its associated whistler waves that form a precursor wave train. This implies that the ramp region should be considered as the source of these waves. All these questions have been studied making use observations from the Cluster satellites. The Cluster project continues to provide a unique viewpoint from which to study the scales of shocks. During its lifetime the inter-satellite distance between the Cluster satellites has varied from 100 km to 10000 km allowing scientists to use the data best adapted for the given scientific objective. The purpose of this review is to address a subset of unresolved problems in collisionless shock physics from experimental point of view making use multi-point observations onboard Cluster satellites. The problems we address are determination of scales of fields and of a scale of electron heating, identification of energy source of precursor wave train, an estimate of the role of anomalous resistivity in energy dissipation process by means of measuring short scale wave fields, and direct observation of reformation process during one single shock front crossing.     

Small-Angle Scattering and Diffusion: Application to Relativistic Shock Acceleration

We investigate ways of accurately simulating the propagation of energetic charged particles over small times where the standard Monte Carlo approximation to diffusive transport breaks down. We find that a small-angle scattering procedure with appropriately chosen step-lengths and scattering angles gives accurate results, and we apply this to the simulation of propagation upstream in relativistic shock acceleration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lunar photography: Techniques and results

Conclusion The lunar photography missions have included flyby, impacter, lander, and orbiter spacecrafts. These missions have provided photographs of the far side of the moon and a ten-fold increase in frontside resolution plus higher resolution of selected frontside areas. The resolutions which have been achieved vary from 1 m for the Lunar Orbiter to 1/2 m for the impacting Ranger to millimeters for Luna-IX and the Surveyors. The return from these missions have resolved much of the mystery surrounding the moon.The prime objective of the U.S. photographic missions has been the support of the Apollo-manned lunar landing program. The Ranger program, the Surveyor program, and the Lunar Orbiter program provided a logical progression in the utilization of a developing space exploration technology. These programs have provided the required information and have confirmed that the Apollo landing vehicle design is compatible with the conditions to be experienced on selected areas of the lunar surface.The future manned landing missions can be expected to provide additional lunar photography. Since the astronauts can be more selective in their photography, even more outstanding and informative results should be achieved. The addition of movies and even live television coverage will permit earth-based man to share more directly in the manned exploration of the moon.The unmanned photographic exploration of the moon has provided much of the technology required for similar missions to the planets. The U.S. Mariner-IV was the first successful mission to obtain close-up photographs of the planet Mars. It can be expected that both the U.S.A. and Russia will try for further photographic successes in the exploration of our solar system.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration.     

Attitude determination with GPS: experimental results

An approach to global positioning system (GPS) attitude determination and the results of an experimental evaluation are presented. The most outstanding features of the method are the fundamental observable used for attitude calculation, the triple difference, and the introduction of a new parameter, the differential dilution of precision (DDOP), which relates the GPS satellite geometry to the GPS accuracy when measuring angular magnitudes. The experiment used two commercial off-the-shelf GPS C/A code receivers delivering integrated Doppler measurements. The algorithm is robust with respect to phase cycle slips and does not require solving the usual integer ambiguity of the measurements. The preliminary results show that absolute attitude determination requires a calibration of the baseline and that the relative attitude accuracy is on the order of 0.1° or 2 mrads for the case of a 2-m-long baseline     

The Origin of Solar Energetic Particle Events: Coronal Acceleration versus Shock Wave Acceleration

We review evidence that led to the view that acceleration at shock waves driven by coronal mass ejections (CMEs) is responsible for large particle events detected at 1 AU. It appears that even if the CME bow shock acceleration is a possible model for the origin of rather low energy ions, it faces difficulties on account of the production of ions far above 1 MeV: (i) although shock waves have been demonstrated to accelerate ions to energies of some MeV nucl^–1 in the interplanetary medium, their ability to achieve relativistic energies in the solar environment is unproven; (ii) SEP events producing particle enhancements at energies 100 MeV are also accompanied by flares; those accompanied only by fast CMEs have no proton signatures above 50 MeV. We emphasize detailed studies of individual high energy particle events which provide strong evidence that time-extended particle acceleration which occurs in the corona after the impulsive flare contributes to particle fluxes in space. It appears thus that the CME bow shock scenario has been overvalued and that long lasting coronal energy release processes have to be taken into account when searching for the origin of high energy SEP events.     

Dynamics of the earth's ring current: Theory and observation

The development of currents within an arbitrary distribution of particles trapped in the geomagnetic field is described. These currents combine to form the earth's ring current and thus are responsible for the worldwide depressions of surface magnetic field strength during periods of magnetic activity known as magnetic storms. Following a brief review of trapped particle motion in magnetic fields, ring current development is described and presented in terms of basic field and particle distribution parameters. Experimental observations then are presented and discussed within the theoretical framework developed earlier. New results are presented which, in the area of composition and charge state observations, hold high promise in solving many long standing ring current problems. Finally, available experimental results will be used to assess our present understanding as to ring current sources, generation, and dissipation.     

SSRT: First results of millisecond spike observations

We present the results of the first observations of spike-like phenomena with the Siberian Solar Radio Telescope (SSRT) in the one-dimensional mode at the frequency of 5.7 GHz with high spatial and temporal resolutions.     

A simple smoother: closed-form solution and analytical results

A closed-form solid-state solution for a simple one-dimensional smoother is presented. The target position-velocity dynamics are modeled as a linear discrete Gauss-Markov process: the discrete position measurements are assumed to be independent and identically normally distributed. Analytical results derived from estimating optimum steady-state position and velocity are given as well as the improvement provided by smoothing relative to pure filtering estimates. Analytical results, including appropriate limiting cases, show that the ratios of the RMS smoothing to the RMS filtering error are from 1/2 to 1 in position and from 1/2 to 1/√2 in velocity. As a numerical example a highly maneuvering target characterized by an acceleration width of 30 m/s² is considered     

3C 273: A review of recent results

3C 273 is the most extensively studied quasar both from the ground and from space. Recent satellite observations have given important information on the overall electromagnetic spectrum of 3C 273 in the -ray, X-ray, and UV ranges. The most salient results are: (i) the energy per decade of frequency emitted by 3C 273 is nearly constant between 6000 Å and 500 MeV and is 20 × 10⁴⁶ erg s^-1 for H = 50 km s^-1 Mpc^-1; (ii) there is no absorption in the soft X-ray range in contrast to the X-ray spectrum of Seyfert nuclei; (iii) the optical and UV spectra cannot be fitted by power-law spectra only, and the energy distribution in this range suggests that a substantial fraction of the energy in the UV is emitted as back-body radiation at 20 000 K. If the peculiar shape of the UV spectrum is indeed caused by black-body radiation, then an estimate of the energy emitted under this form is 2.5 × 10⁴⁶erg s^-1, corresponding to an optically thick disk of 10¹⁶ cm in diameter.The UV spectrum of 3C 273 shows absorption lines at zero redshift caused by interstellar matter in the disk and halo of our Galaxy. The strength of C iv 1550 in absorption indicates the presence of a hot outer region in the halo. Extragalactic objects with mostly continuous UV spectra, such as 3C 273, are very promising UV sources which allow us to observe the absorbing material over the entire line of sight throughout the galactic halo.     

Cosmic Rays From Supernova Remnants: a Brief Description of the Shock Acceleration of gas and Dust

Space Science Reviews - We summarize our model of galactic cosmic-ray (GCR) origin and acceleration, wherein a mixture of interstellar and/or circumstellar gas and dust is accelerated by a...     

Spectral analyses of Wolf-Rayet stars: Theory,results, conclusions

Stratified Non-LTE models for expanding atmospheres became available in the recent years. They are based on the idealizing assumptions of spherical symmetry, stationarity and radiative equilibrium. From a critical discussion we conclude that this standard model is basically adequate for describing real Wolf-Rayet atmospheres and hence can be applied for quantitative spectral analyses of their spectra.By means of these models, the fundamental parameters have been determined meanwhile for the majority of the known Galactic WR stars. Most of them populate a vertical strip in the Herzsprung-Russell diagram at effective temperatures of 35 kK, the luminosities ranging from 10^4.5 to 10^5.9 L . Only early-type WN stars with strong lines and WC stars are hotter. The chemical composition of WR atmospheres corresponds to nuclear-processed material (WN: hydrogen burning in the CNO cycle; WC: helium burning). Hydrogen is depleted but still detectable in the cooler part of the WN subclass.Different scenarios for the evolutionary formation of the Wolf-Rayet stars are discussed in the light of the empirical data provided from the spectral analyses. Post-red-supergiant evolution can principally explain the basic observational properties, except the rather low luminosities of a considerable fraction of WN stars. Among the alternative scenarios, close-binary evolution can theoretically produce the least-luminous WN stars. However, final conclusions about the evolutionary formation of the WR stars are not yet possible.     

MR2251-178: Preliminary results of an X-ray monitoring programme

We present the initial results from an X-ray monitoring programme of the bright QSO MR2251-178.     

High energy cosmic ray nuclei results on Ulysses: 1. Mission overview

The cosmic ray flux observed with the Kiel Electron Telescope on board the ULYSSES spaceprobe varies with solar activity as well as with heliospheric position. Determination of the latitudinal gradients requires a careful analysis of the influences of the current sheet tilt angle, the number of major solar flares, interplanetary shocks and interaction regions evolving in the expanding solar wind. In this paper we concentrate on nuclei with rigidity above 1 GV. We discuss the effects of the variable solar activity in the declining phase of the present solar cycle and the variation with radial distance as a basis for separating latitudinal effects. We show that during this phase of the solar cycle modulation of GV nuclei is ordered by temporal evolution, radial distance and negligible latitudinal effects even at latitudes between 30° and 50° South.     

The ELDORA/ASTRAIA airborne Doppler weather radar: results fromrecent field tests

The ELDORA/ASTRAIA airborne Doppler weather radar was recently placed in service by US and French atmospheric sciences research laboratories. The ELDORA/ASTRAIA radar is designed to provide high resolution measurements of the air motion and rainfall characteristics of atmospheric storms which are too large, remote or fast-moving to be adequately observed by ground-based radars. This paper discusses the measurement requirements and the design goals of the radar and presents sample measurements from a recent weather research field program     

Effectiveness of MMW aerosols in defeating a battlefieldsurveillance radar: field demonstration preliminary results

The US Army ERDEC is developing advanced aerosol systems to combat threat surveillance, fire control, and seeker systems operating in the visible, infrared, and millimeter wave portions of the electromagnetic spectrum. One such system is the M56 multispectral smoke generator, which presently operates in the visible and infrared portions of the spectrum; a millimeter wave (MMW) Module is in development to extend the M56 spectral range. This paper documents preliminary results of a field demonstration test of the M56 MMW Module. An MMW instrumentation radar was modified to simulate the scan pattern and radar parameters of a tactical battlefield surveillance radar system. A test grid was populated with both stationary and moving tactical targets, and the radar scanned the grid to simulate a surveillance radar in operation. Once a realistic tactical engagement scenario was developed, MMW aerosols were deployed to demonstrate the impact such aerosols could have on radar detection and classification performance