A far ultraviolet imager for the International Solar-Terrestrial Physics Mission

The aurorae are the result of collisions with the atmosphere of energetic particles that have their origin in the solar wind, and reach the atmosphere after having undergone varying degrees of acceleration and redistribution within the Earth's magnetosphere. The global scale phenomenon represented by the aurorae therefore contains considerable information concerning the solar-terrestrial connection. For example, by correctly measuring specific auroral emissions, and with the aid of comprehensive models of the region, we can infer the total energy flux entering the atmosphere and the average energy of the particles causing these emissions. Furthermore, from these auroral emissions we can determine the ionospheric conductances that are part of the closing of the magnetospheric currents through the ionosphere, and from these we can in turn obtain the electric potentials and convective patterns that are an essential element to our understanding of the global magnetosphere-ionosphere-thermosphere-mesosphere. Simultaneously acquired images of the auroral oval and polar cap not only yield the temporal and spatial morphology from which we can infer activity indices, but in conjunction with simultaneous measurements made on spacecraft at other locations within the magnetosphere, allow us to map the various parts of the oval back to their source regions in the magnetosphere. This paper describes the Ultraviolet Imager for the Global Geospace Sciences portion of the International Solar-Terrestrial Physics program. The instrument operates in the far ultraviolet (FUV) and is capable of imaging the auroral oval regardless of whether it is sunlit or in darkness. The instrument has an 8° circular field of view and is located on a despun platform which permits simultaneous imaging of the entire oval for at least 9 hours of every 18 hour orbit. The three mirror, unobscured aperture, optical system (f/2.9) provides excellent imaging over this full field of view, yielding a per pixel angular resolution of 0.6 milliradians. Its FUV filters have been designed to allow accurate spectral separation of the features of interest, thus allowing quantitative interpretation of the images to provide the parameters mentioned above. The system has been designed to provide ten orders of magnitude blocking against longer wavelength (primarily visible) scattered sunlight, thus allowing the first imaging of key, spectrally resolved, FUV diagnostic features in the fully sunlit midday aurorae. The intensified-CCD detector has a nominal frame rate of 37 s, and the fast optical system has a noise equivalent signal within one frame of 10R. The instantaneous dynamic range is >1000 and can be positioned within an overall gain range of 10⁴, allowing measurement of both the very weak polar cap emissions and the very bright aurora. The optical surfaces have been designed to be sufficiently smooth to permit this dynamic range to be utilized without the scattering of light from bright features into the weaker features. Finally, the data product can only be as good as the degree to which the instrument performance is characterized and calibrated. In the VUV, calibration of an an imager intended for quantitative studies is a task requiring some pioneering methods, but it is now possible to calibrate such an instrument over its focal plane to an accuracy of ±10%. In summary, very recent advances in optical, filter and detector technology have been exploited to produce an auroral imager to meet the ISTP objectives.     

Concerning the interpretation of the ultraviolet radiation from B stars

Measurements of the shape of the ultraviolet spectrum from B stars are compared with the theoretical spectra predicted from a homogeneous series of eight model atmospheres which are known to be close to a state of radiative equilibrium and to give a good representation of the ordinarily observed spectral region. The broad-band photometer measurements of Byram, Chubb, and Friedman in the region 1314 indicate that the stars become brighter in the ultraviolet as their temperature increases. The theoretical spectra reproduce this trend. However, the theoretical spectra are about three times as bright at 1314 relative to their brightness at 5560 as is observed.The spectral observations at 50Å resolution of Stecher and Milligan of six absorption-line stars are compared in detail with theoretical spectra. The observed shape of the spectrum is reproduced well by the models from 2600 to longer wavelengths. At wavelengths shorter than 2600 Å, the observed fluxes from B stars are less than the predicted fluxes. At 2000 the deficiency is between a factor two and a factor four. The spectrum of Canis Majoris is observed to have a different shape from that found for four other early-type stars. In the case of Canis Majoris the deficiency at 2000 is about a factor 13.The proper manner in which to compare theory and observation is discussed and some astrophysical terminology is explained. Theoretical fluxes, , are given in Table 1 for eight early B type model atmospheres at wavelengths between the Lyman limit and 6251. These fluxes have been computed without consideration of the opacity due to line blanketing. It is shown that line blanketing can probably account for the differences noted between predicted and observed ultra-violet spectra of B stars. It is not necessary at present to invoke unusual sources of opacity in the stellar atmosphere or in the space between the star and the earth in order to explain the observations. Spectra of B stars in the 2000 region at sufficient resolution to show the line spectrum would clarify the problem.     

Far ultraviolet imaging from the IMAGE spacecraft. 2. Wideband FUV imaging

The Far Ultraviolet Wideband Imaging Camera (WIC) complements the magnetospheric images taken by the IMAGE satellite instruments with simultaneous global maps of the terrestrial aurora. Thus, a primary requirement of WIC is to image the total intensity of the aurora in wavelength regions most representative of the auroral source and least contaminated by dayglow, have sufficient field of view to cover the entire polar region from spacecraft apogee and have resolution that is sufficient to resolve auroras on a scale of 1 to 2 latitude degrees. The instrument is sensitive in the spectral region from 140–190 nm. The WIC is mounted on the rotating IMAGE spacecraft viewing radially outward and has a field of view of 17° in the direction parallel to the spacecraft spin axis. Its field of view is 30° in the direction perpendicular to the spin axis, although only a 17°×17° image of the Earth is recorded. The optics was an all-reflective, inverted Cassegrain Burch camera using concentric optics with a small convex primary and a large concave secondary mirror. The mirrors were coated by a special multi-layer coating, which has low reflectivity in the visible and near UV region. The detector consists of a MCP-intensified CCD. The MCP is curved to accommodate the focal surface of the concentric optics. The phosphor of the image intensifier is deposited on a concave fiberoptic window, which is then coupled to the CCD with a fiberoptic taper. The camera head operates in a fast frame transfer mode with the CCD being read approximately 30 full frames (512×256 pixel) per second with an exposure time of 0.033 s. The image motion due to the satellite spin is minimal during such a short exposure. Each image is electronically distortion corrected using the look up table scheme. An offset is added to each memory address that is proportional to the image shift due to satellite rotation, and the charge signal is digitally summed in memory. On orbit, approximately 300 frames will be added to produce one WIC image in memory. The advantage of the electronic motion compensation and distortion correction is that it is extremely flexible, permitting several kinds of corrections including motions parallel and perpendicular to the predicted axis of rotation. The instrument was calibrated by applying ultraviolet light through a vacuum monochromator and measuring the absolute responsivity of the instrument. To obtain the data for the distortion look up table, the camera was turned through various angles and the input angles corresponding to a pixel matrix were recorded. It was found that the spectral response peaked at 150 nm and fell off in either direction. The equivalent aperture of the camera, including mirror reflectivities and effective photocathode quantum efficiency, is about 0.04 cm². Thus, a 100 Rayleigh aurora is expected to produce 23 equivalent counts per pixel per 10 s exposure at the peak of instrument response.     

Preoperational testing of data link-based air traffic managementsystems in Magadan, far East Russia

The Global Positioning System (GPS) has been used in many ways which were unimagined by its original planners and implementers. This paper discusses one such application; the surveillance of commercial aircraft in a developing airspace environment. GPS provides system users with the ability to determine their own position with an accuracy, reliability and cost that is unprecedented. Voice procedures augmented by radar have been the primary tools for air traffic surveillance since the end of World War II. But for some countries the equipage of aircraft with GPS and a data link capable of carrying position reports to the ATC authorities is providing a viable alternative to long-range secondary radar systems. In the summer and fail of 1995, ARINC installed and demonstrated equipment in Magadan, Russia which permits air traffic controllers of MagadanAeroControl to monitor GPS position reports generated by aircraft as far away as Canada and the South Pacific. The position reports were displayed against maps and flight tracks. This equipment has clearly demonstrated an alternative technology for the upgrading of the ATC system in Siberia and other remote areas     

Impacts of solar and auroral storms on power line systems

A sensitive search for pulsars inside a sample of gamma-ray source error boxes has been carried out using the Arecibo and Parkes radiotelescopes. The paper describes the motivation of this search and the characteristics of the experiments used. As a preliminary result, new pulsars have been discovered and some of them are possibly candidates to be the counterparts of the gamma-ray sources.     

风力机远尾流的计算研究

基于工程上广泛使用的Park模型构造了一种新的远场尾流计算模型,同时又提出了一种CFD与制动盘理论相结合的方法对单个风力机远尾迹区的流动状况进行了数值模拟.新的尾流计算模型是由一维Park模型进行三角函数修正得到的,CFD方法是结合制动盘理论使用FLUENT提供的Fan边界数值求解整个尾流流场.给出了单台风力机尾流中风轮中心的轴向速度分布以及风力机下游不同位置处的径向速度分布,并与风洞实验结果以及Park模型的计算结果进行分析对比,表明本文的两种计算方法都能够较好地捕捉尾流的流场特性.由于新的远场尾流计算模型较之原Park模型能够更准确地反映径向尾流分布,且计算量非常小,因此可作为工程开发的有效工具.制动盘理论结合CFD的方法也能够在计算量相对较小的情况下,准确的反映远尾流的流场信息,这两种方法都可为风场微观选址和风力机排布提供参考依据.     

Role of ionospheric effects and plasma sheet dynamics in the formation of auroral arcs

At the ionospheric level, the substorm onset (expansion phase) is marked by the initial brightening and subsequent breakup of a pre-existing auroral arc. According to the field line resonance (FLR) wave model, the substorm-related auroral arc is caused by the field-aligned current carried by FLRs. The FLRs are standing shear Alfvén wave structures that are excited along the dipole/quasi-dipole lines of the geomagnetic field. The FLRs (that can cause auroral arc) thread from the Earthward edge of the plasma sheet and link the auroral arc to the plasma sheet region of 6–15 R _E. The region is associated with magnetic fluctuations that result from the nonlinear wave-wave interactions of the cross-field current-instability. The instability (excited at the substorm onset) disrupts the cross-tail current which is built up during the growth phase of the substorms and results in magnetic fluctuations. The diversion of the current to polar regions can lead to auroral arc intensification. The current FLR model is based on the amplitude equations that describe the nonlinear space-time evolution of FLRs in the presence of ponderomotive forces exerted by large amplitude FLRs (excited during substorms). The present work will modify the FLR wave model to include the effects arising from magnetic fluctuations that result from current disruption near the plasma sheet (6–15 R _E). The nonlinear evolution of FLRs is coupled with the dynamics of plasma sheet through a momentum exchange term (resulting from magnetic fluctuations due to current disruption) in the generalized Ohm's law. The resulting amplitude equations including the effects arising from magnetic fluctuations can be used to study the structure of the auroral arcs formed during substorms. We have also studied the role of feedback mechanism (in a dipole geometry of the geomagnetic field) in the formation of the discrete auroral arc observed on the nightside magnetosphere. The present nonlinear dispersive model (NDM) is extended to include effects arising from the low energy electrons originating from the plasma sheet boundary layer. These electrons increase the ionospheric conductivity in a localized patch and enhance the field-aligned current through a feedback mechanism. The feedback effects were studied numerically in a dipole geometry using the the NDM. The numerical studies yield the magnitude of the field-aligned current that is large enough to form a discrete auroral arc. Our studies provide theoretical support to the observational work of Newell et al. that the feedback instability plays a major role in the formation of the discrete auroral arcs observed on the nightside magnetosphere.     

Optics of the far infra-red and submillimetre space telescope

Some of the considerations in the design of the telescope for FIRST are discussed. It is pointed out that instruments that operate at submillimetre wavelengths need to be analyzed with techniques derived from both the Radio and Optical/IR traditions. The issue of emissivity of reflector surfaces is also discussed.     

Validation of techniques for space based remote sensing of auroral precipitation and its ionospheric effects

Knowledge of the spatial distribution of auroral precipitation and its associated ionospheric effects is important both to scientific studies of the Earth's environment and successful operation of defense and communication systems. Observations with the best spatial and temporal coverage are obtained through remote sensing from space-based platforms. Various techniques have been used, including the detection of visible, ultraviolet and X-ray emissions produced by the precipitating particles. Interpretation of the measurements is enabled through theoretical modeling of the interaction of precipitating particles with atmospheric constituents. A great variety of auroral precipitation exists, with each kind differing in the type and energy distribution of the particles, as well as in its spatial and temporal behavior. Viable remote sensing techniques must be able to distinguish at least the species of particle, the total energy flux, and the average energy. Methods based on visible, ultraviolet and X-ray emissions meet these requirements to varying degrees. These techniques and the associated space instrumentation have evolved in parallel over the last two decades. Each of the methods has been tested using simultaneous measurements made by space-based imaging systems and ground-based measurements made by radars and optical instruments. These experiments have been extremely helpful in evaluating the performance and practicality of the instruments and the results have been crucial in improving instrument design for future remote sensing platforms. The next decade will see continued development and test of remote sensing instruments and the measurements, in addition to providing important operational data, will be increasingly more critical in addressing a number of scientific problems in auroral and atmospheric physics.     

Global imaging of O+ from IMAGE/HENA

The magnetospheric O⁺ population in the 52–180 keV range during storms is investigated through the analysis of energetic neutral atom (ENA) images. The images are obtained from the high energy neutral atom (HENA) imager onboard the IMAGE satellite. At each substorm onset following the commencement of a geomagnetic storm the oxygen ENA display ～30 min intense bursts. Only very weak corresponding features in the 60–119 keV hydrogen ENA can be occasionally seen. The dominating fraction of the oxygen ENA emissions are produced when O⁺ ions mirror/precipitate at low altitudes, where the number density of the neutral atmosphere is high. During the storm we observed several bursts of oxygen ENA, but it is still not clear how much the O⁺ content of the ring current increases during the storm main phase. Our observations suggest that the responsible injection mechanism is mass-dependent and scatters the pitch angles. This leads us to favor a non-adiabatic mechanism proposed by (Delcourt, 2002).     

The interpretations of ultraviolet observations of comets

Summary Ultraviolet observations of comets from above the Earth's atmosphere have provided excellent new results and improved older ground based observations (OH) by an order of magnitude. Satellites are especially suitable because long integration times and observations during extended time intervals are possible.The existing cometary L observations have confirmed the relatively high overall gas production rates on the order of 10³⁰ molecule s^–1. The results strongly support the concept of an icy conglomerate solid cometary nucleus. Additional observations of hydroxyl and oxygen favor water to be one of the most abundant molecules in comets. The observations are in agreement with the predominent role of water in the evaporation process of the nuclear ices but are not proof in themselves.Water did not outnumber other consitutents by orders of magnitude in comets Bennett and Kohoutek. At least in these comets, carbon-containing molecules were possibly as numerous as water. Determination of the carbon scale length is necessary for a more quantitative statement.A hydrogen velocity of 7–9 km s^–1 was observed in comet Bennett as well as in comet Kohoutek for a variety of heliocentric distances and varying production rates. Determinations of the outflow velocity from L isophotes agree with line profile observations of L and H. Hydroxyl may constitute the main source for the hydrogen atoms with v _H - 8 km s^–1. The decay process, however, leading to this particular velocity is not yet known. Possibly a large portion of the OH radicals do not decay into hydrogen atoms or at least not into slow ones. If the high velocity component of 20 km s^–1 or more comprises a larger amount (up to 50%), most of the quoted hydrogen production rates must be revised upward.The intrinsic cometary brightness is only a very crude indicator of a comet's actual gas production rate as shown by comparison of comets Bennett and TSK. Comets can be successfully used as (extra ecliptic) space probes to measure interplanetary quantities, e.g., the curvature of the extended hydrogen clouds can be used for the absolute determination of the solar emission independent of instrumental calibration. Generally time dependent hydrogen density models must be used for the interpretation. The strength of the ultraviolet L emission favors its measurement as a standard procedure for the observation of comets (possibly together with OH (3090 Å)). These observations provide the most accurate results on the total cometary gas production rate and its variation with heliocentric distance.Dedicated to Professor L. Biermann in recognition of his inspiring guidance.On leave of absence from Max-Planck-Institut für Physik und Astrophysik, Munich.     

An optical and ultraviolet survey of Algols

We present a-table of results from our survey of Algols, conducted with the Lick Observatory ITS scanners and the IUE spectrometer.We have determined the continuous flux distributions for a number of the Algol systems. Optical scans were made with the ITS scanners of Lick Observatory, while for the ultraviolet flux distributions, we used the IUE satellite spectrometer in the low-dispersion mode. The following table summarizes the results: {ie340-01}     

The extreme ultraviolet spectrum of the sun

The present state of knowledge of the spectrum of the sun from 3000 Å to 170 Å is critically reviewed. The characteristics of the different photographic and photoelectric spectroscopic instruments and the results are summarized and compared. Topics covered are line identifications, intensities, the continuum and its origin, the sun's surface in Lyman alpha, the profiles of H and K of Mg II, Lyman alpha and beta, and monitoring work conducted from rockets and satellites, including OSO-I.     

无人驾驶飞机综述

阐述了无人驾驶飞机的发展状况和特点 ,分析了 2 1世纪无人驾驶飞机的发展趋势     

Global Imaging of Proton and Electron Aurorae in the far Ultraviolet

The IMAGE spacecraft carries three FUV photon imagers, the Wideband Imaging Camera (WIC) and two channels, SI-12 and SI-13, of the Spectrographic Imager. These provide simultaneous global images, which can be interpreted in terms of the precipitating particle types (protons and electrons) and their energies. IMAGE FUV is the first space-borne global imager that can provide instantaneous global images of the proton precipitation. At times a bright auroral spot, rich in proton precipitation, is observed on the dayside, several degrees poleward of the auroral zone. The spot was identified as the footprint of the merging region of the cusp that is located on lobe field lines when IMF B_z was northward. This identification was based on compelling statistical evidence showing that the appearance and location of the spot is consistent with the IMF B_z and B_y directions. The intensity of the spot is well correlated with the solar wind dynamic pressure and it was found that the direct entry of solar wind particles could account for the intensity of the observed spot without the need for any additional acceleration. Another discovery was the observation of dayside sub-auroral proton arcs. These arcs were observed in the midday to afternoon MLT sector. Conjugate satellite observations showed that these arcs were generated by pure proton precipitation. Nightside auroras and their relationship to substorm phases were studied through single case studies and in a superimposed epoch analysis. It was found that generally there is substantial proton precipitation prior to substorms and the proton intensity only doubles at substorm onset while the electron auroral brightness increases on average by a factor of 5 and sometimes by as much as a factor of 10. Substorm onset occurs in the central region of the pre-existing proton precipitation. Assuming that nightside protons are precipitating from a quasi-stable ring current at its outer regions where the field lines are distorted by neutral sheet currents we can associate the onset location with this region of closed but distorted field lines relatively close to the earth. Our results also show that protons are present in the initial poleward substorm expansion however later they are over taken by the electrons. We also find that the intensity of the substorms as quantified by the intensity of the post onset electron precipitation is correlated with the intensity of the proton precipitation prior to the substorms, highlighting the role of the pre-existing near earth plasma in the production of the next substorm.     

The interpretation of the XUV solar spectrum

This paper reviews (a) the earth's ionosphere, and (b) the solar atmosphere, in relation to the recent observations of solar XUV. The expected ionospheric characteristics are derived as directly as possible from the XUV observations and then compared with the well-known D-, E-, and F-layer formations. The comparison leads to (1) a high ionospheric recombination coefficient decreasing rapidly with height, (2) contributions to the E-layer from both UV and X-rays, and (3) very little difference in the solar cycle variations from the D-, E-, and F-layers although intensity variations are greater from high than low ions. The flux measurements of the identified XUV solar emission lines give information on the numbers of ions in the solar atmosphere. This makes it possible to derive (1) the amount of solar material in each temperature range, (2) the chemical abundances, and (3) the physical differences between quiet solar atmosphere, centres of activity, and flares. When the new dielectronic recombination coefficients are well investigated it should be possible to redetermine the distribution of solar material with temperature. The fitting of such results to chromospheric and coronal models provides many problems.     

可变几何燃烧室技术发展

对航空发动机可变几何燃烧室的研究状况进行了总结,燃烧室中可变几何结构包括气流分配器、旋流器、掺混孔、火焰稳定器等。可变几何的概念提供了一种灵活控制燃烧室内部气流分配的可能性,为减少发动机尾气排放、提高燃烧效率、保持燃烧室工作的稳定性和可靠性提供了新的突破点。