行星际磁场与磁尾磁通量绳形成的关系

收集了Cluster卫星在2001-2005年间观测到的磁尾磁通量绳事件,并对磁通量绳(magnetic flux rope)形成及其内部磁场结构与行星际磁场(IMF)的关系作了统计研究.考虑磁通量绳被观测到时行星际磁场的条件,在所有73个磁通量绳事件中,行星际磁场By分量占有主导地位的事件有80%,且78%的事件具有与行星际磁场By分量相同方向的核心场.行星际磁场通过在磁层顶与地球磁场相互作用改变南北等离子体片内磁场相对方向,形成有利于磁通量绳形成的磁场位形,并且行星际磁场By分量的方向对磁通量绳内部核心场的方向具有决定性影响.从统计结果来看,磁通量绳的形成并不会依赖于行星际磁场Bz分量的方向.     

Langley method applied in study of aerosol optical depth in the Brazilian semiarid region using 500, 670 and 870 nm bands for sun photometer calibration

Due to the high costs of commercial monitoring instruments, a portable sun photometer was developed at INPE/CRN laboratories, operating in four bands, with two bands in the visible spectrum and two in near infrared. The instrument calibration process is performed by applying the classical Langley method. Application of the Langley’s methodology requires a site with high optical stability during the measurements, which is usually found in high altitudes. However, far from being an ideal site, Harrison et al. (1994) report success with applying the Langley method to some data for a site in Boulder, Colorado. Recently, Liu et al. (2011) show that low elevation sites, far away from urban and industrial centers can provide a stable optical depth, similar to high altitudes. In this study we investigated the feasibility of applying the methodology in the semiarid region of northeastern Brazil, far away from pollution areas with low altitudes, for sun photometer calibration. We investigated optical depth stability using two periods of measurements in the year during dry season in austral summer. The first one was in December when the native vegetation naturally dries, losing all its leaves and the second one was in September in the middle of the dry season when the vegetation is still with leaves. The data were distributed during four days in December 2012 and four days in September 2013 totaling eleven half days of collections between mornings and afternoons and by means of fitted line to the data V₀ values were found. Despite the high correlation between the collected data and the fitted line, the study showed a variation between the values of V₀ greater than allowed for sun photometer calibration. The lowest V₀ variation reached in this experiment with values lower than 3% for the bands 500, 670 and 870 nm are displayed in tables. The results indicate that the site needs to be better characterized with studies in more favorable periods, soon after the rainy season.     

Dust emission phenomena of cometary analogues

Experiments with cometary analogues are reported, which were performed at DLR - Köln in a small vacuum chamber and in the Space Simulator. The results apply to the emission processes of ice-dust grains from the surface of mineral-ice mixtures during insolation. The emission phenomena were observed with CCD-video-cameras. The camera used at the small chamber was equipped with a magnifying (10x) macro-lens. The magnified pictures show that the ice-dust agglomerates carry tiny ice particles on their surfaces. These may play the role of interlinking bonds between one grain and its neighbors. In the enlarged view it can be seen that the ice-dust grains do not erupt with high velocity out of the surface. The upstreaming gas jet originating from the sublimation of the volatile components first erodes the interlinking bonds between the particles. When the drag force exerted on the particles exceeds the force of gravity, the particles lift off. In most of the observed cases this initial lift off velocity is very small e.g. a few cm/s.

During a comet-simulation experiment in the Space-Simulator in November 1989 the trajectories of emitted dust particles were recorded for the first time with a high speed shutter video system 60 cm from the model comet. The video tapes were evaluated with a computerized image processing system. Unique insights in the gas-dust-interaction immediately at and above the insolated icy body were obtained. The trajectories differ markedly in all cases from the the ballistic parabolas calculated from the measured starting conditions: elevation angle and speed. The trajectory is mainly dominated by the momentum transfer from the gas jet to the dust particles. Many of the particles have millimeter sizes. The observed velocities at the end of the visible trajectory are in the order of a few meters per second.     

Synchrotron nebulae

The most frequent manifestation of synchrotron nebulae is the radio emission emanating from radio galaxies and supernova remnants. In general the synchrotron spectra of these objects do not extend into optical and x-ray domains presumably because the high energy electrons needed to sustain such emission are too short-lived. In fact, we knew of only one class of objects in which synchrotron nebulae are observed at frequencies above the radio, namely Crab-like supernova remnants (SNR). In these instances, a central pulsar is presumed to continually accelerate electrons up to the requisite energies, thus balancing the high synchrotron loss rate. The first part of this talk will discuss the available x-ray observations of these sources as well as some of the difficulties in their interpretation. The last part of the talk will be concerned with a new class of synchrotron nebulae associated with binary star systems.     

Is there an instrumental drift in the counting rate of some high latitude neutron monitors?

For the last six decades the neutron monitors have provided a continuous string of very reliable data to the heliophysics community. Although neutron monitors are not the primary source of data for the galactic cosmic rays, these data serve as a baseline reference for the data collected by the detectors on board the satellites and deep space probes, far away from earth orbit. The pressure corrected hourly data are available from the World Data Centers. These data have been used to derive deep insights pertaining to the electromagnetic states of the heliosphere and the modes of transport of energetic charged particles in the tangled interplanetary magnetic fields. We present evidence that some of the high latitude neutron monitors are undergoing long-term drifts in their baselines. In particular, we argue that there is no physical basis to justify the observed long-term downward trend in the baseline of the South Pole neutron monitor. The real reason may have to do with its maintenance at a distant location with challenging logistics and an improper normalization of its data after the 26 months break in the 1970s.     

The Galaxy Cluster Mass Scale and Its Impact on Cosmological Constraints from the Cluster Population

Space Science Reviews - The QB50 mission is a satellite constellation designed to carry out measurements at between 200–380 km altitude in the ionosphere. The multi-needle Langmuir probe...     

Statistical evaluation of GLONASS amplitude scintillation over low latitudes in the Brazilian territory

The ionospheric scintillation, generated by the ionospheric plasma irregularities, affects the radio signals that pass through it. Their effects are widely studied in the literature with two different approaches. The first one deals with the use of radio signals to study and understand the morphology of this phenomenon, while the second one seeks to understand and model how much this phenomenon interferes in the radio signals and consequently in the services to which these systems work. The interest of several areas, particularly to those that are life critical, has increased using the concept of satellite multi-constellation, which consists of receiving, processing and using data from different navigation and positioning systems. Although there is a vast literature analyzing the effects of ionospheric scintillation on satellite navigation systems, the number of studies using signals received from the Russian satellite positioning system (named GLONASS) is still very rare. This work presents for the first time in the Brazilian low-latitude sector a statistical analysis of ionospheric scintillation data for all levels of magnetic activities obtained by a set of scintillation monitors that receive signals from the GLONASS system. In this study, data collected from four stations were used in the analysis; Fortaleza, Presidente Prudente, São José dos Campos and Porto Alegre. The GLONASS L-band signals were analyzed for the period from December 21, 2012 to June 20, 2016, which includes the peak of the solar cycle 24 that occurred in 2014. The main characteristics of scintillation presented in this study include: (1) the statistical evaluation of seasonal and solar activity, showing the chances that an user on similar geophysical conditions may be susceptible to the effects of ionospheric scintillation; (2) a temporal analysis based on the local time distribution of scintillation at different seasons and intensity levels; and (3) the evaluation of number of simultaneously affected channels and its effects on the dilution of precision (DOP) for GNSS users are also presented in order to alert the timetables in which navigation will be most susceptible to such effects, as well as statistics on simultaneously affected channels. Relevant results about these statistical characteristics of scintillation are presented and analyzed providing relevant information about availability of a navigation system.     

The USSR and satellite communications : Competition and cooperation

This article examines the USSR's satellite communications provision in the international arena. The author first outlines the Intercosmos programme, collaboration between the USSR and France and India, and maritime satellite communications. He then discusses in detail the INTERSPUTNIK system, and Soviet international coverage and competitiveness in television. In conclusion, the complex interaction and overlap between cooperation and competition in space is explained.     

The role of HZE particles in space flight: results from spaceflight and ground-based experiments.

Selected results from experiments investigating the potentially specific radiobiological importance of the cosmic HZE (= high Z, energetic) particles are discussed. Results from the Biostack space flight experiments, which were designed to meet the experimental requirements imposed by the microdosimetric nature of this radiation field, clearly indicate the existence of radiation mechanisms which become effective only at higher values of LET (linear energy transfer). Accelerator irradiation studies are reviewed which conform with this conjecture. The recently discovered production of "micro-lesions" in mammalian tissues by single HZE particles is possibly the most direct evidence. Open questions concerning the establishment of radiation standards for manned spaceflight, such as late effects, interaction with flight dynamic parameters, and weightlessness, are indicated.     

Simulation of launch and re-entry acceleration profiles for testing of shuttle and unmanned microgravity research payloads

Microgravity experiments designed for execution in Get-Away Special canisters, Hitchhiker modules, and Reusable Re-entry Satellites will be subjected to launch and re-entry accelerations. Crew-dependent provisions for preventing acceleration damage to equipment or products will not be available for these payloads during flight; therefore, the effects of launch and re-entry accelerations on all aspects of such payloads must be evaluated prior to flight. A procedure was developed for conveniently simulating the launch and re-entry acceleration profiles of the Space Shuttle (3.3 and 1.7 × g maximum, respectively) and of two versions of NASA's proposed materials research Re-usable Re-entry Satellite (8 × g maximum in one case and 4 × g in the other). By using the 7 m centrifuge of the Gravitational Plant Physiology Laboratory in Philadelphia it was found possible to simulate the time dependence of these 5 different acceleration episodes for payload masses up to 59 kg. A commercial low-cost payload device, the “Materials Dispersion Apparatus” of Instrumentation Technology Associates was tested for (1) integrity of mechanical function, (2) retention of fluid in its compartments, and (3) integrity of products under simulated re-entry g-loads. In particular, the sharp rise from 1 g to maximum g-loading that occurs during re-entry in various unmanned vehicles was successfully simulated, conditions were established for reliable functioning of the MDA, and crystals of 5 proteins suspended in compartments filled with mother liquor were subjected to this acceleration load.