Life-time of ionospheric scintillations from multi-satellite radio transmission recordings

Amplitude recordings from five U.S. Navy Navigational Satellites (NNSS), at a frequency of 150 MHz, were used to estimate the life-time of scintillation producing ionization patches in the F-region. The median life-time of scintillations, which was found to be 5 hr, differs to a considerable degree from the life-time of ionospheric reflections reported elsewhere. It is suggested that various spatial resolutions of ionospheric sounding techniques may account for the difference in the computed life-times.     

Generation of ionospheric irregularities by thermal-source: A new mechanism

A new mechanism for the generation of ionospheric irregularities of scale sizes of the order of 100 m or more, has been developed on the basis of thermal energy source due to collisional current dissipation. The important role is played by the diffusion of particles along and across the magnetic field. The threshold condition for the instability has been obtained and it is shown that these irregularities can be generated in the F-region height of auroral ionosphere when the electric field is enhanced to about 10 mV m^?1.     

The interpretation of 6300 Å airglow observations of ionospheric irregularities

The variations in intensity of 6300 Å airglow throughout the ionosphere above an observor are represented by a three dimensional Fourier series. Filtering effects caused by the field of view of an observing instrument are then calculated assuming that all Fourier components move with the same velocity. The results suggest that the observations of Mullaney et al. (1972) can be interpreted as the power spectrum of horizontal structures in the airglow.     

Nighttime fluctuations (scintillations) in Faraday rotation angle of VHF signals from geostationary satellites

Faraday rotation angle records of VHP (137.35 MHz) signals from ATS-3 received at São José dos Campos (Magnetic dip-23.7°) exhibit nighttime fluctuations during equinoctial and summer months. These fluctuations have periodicities ranging from several seconds to about an hour. We investigate the relationship between these fluctuations and the F-layer irregularities.     

Optical measurements of the Moon as a tool to study its surface

This survey is a general overview of modern optical studies of the Moon and their diagnostic meaning. It includes three united parts: phase photometry, spectrophotometry, and polarimetry. The first one is devoted to the progress in the photometry of the Moon, which includes absolute albedo determination to refine the albedo scale (e.g., to connect lunar observations and the data of lunar sample measurements) and mapping the parameters of a lunar photometric function (e.g., the phase-angle ratios method) with the aim of making qualitative estimates of regolith structure variations. This part also includes observations of the lunar opposition effect as well as photogrammetry and photoclinometry techniques. In particular, available data show that because of the low albedo of the lunar surface, the coherent backscattering enhancement hardly influences the lunar opposition spike, with the exception of the brightest lunar areas measured in the NIR. The second part is devoted to chemical/mineral mapping of the Moon's surface using spectrophotometric measurements. This section also includes analyses related to the detection of water ice or hydroxyl, prognoses of maturity, and helium-3 abundance mapping. In particular, we examine the relationship between superficial OH/H₂O compounds spectrally detected recently and bulk “water ice” found earlier by the Lunar Prospector GRS and LRO LEND, assuming that the compounds are delivered to cold traps (permanently shadowed regions) with electrostatically levitated dust saturated by solar wind hydrogen. Significant problems arise with the determination of TiO₂ content, as the correlation between this parameter and the color ratio C(750/415 nm) is very non-linear and not universal for different composition types of the lunar surface; a promising way to resolve this problem is to use color ratios in the UV spectral range. The third part is devoted to mapping of polarization parameters of the lunar surface, which enable estimates of the average size of regolith particles and their optical inhomogeneity. This includes considerations of the Umov effect and results of spectropolarimetry, negative polarization imagery, and measurements of other polarimetric parameters, including the third Stokes parameter. Although these three research divisions have not been developed equally and the numbers of proper references are very different, we try to keep a balance between them, depicting a uniform picture. It should be emphasized that many results presented in this review can be applied to other atmosphereless celestial bodies as well.     

Electron beam emission from the EXOS-B (JIKIKEN) satellite as a powerful diagnostic tool in the magnetosphere

In an electron beam emission experiment on board the EXOS-B (JIKIKEN) satellite (200 V, 1 mA-maximum), several types of waves are strongly excited by the beam such as plasma frequency, upper hybrid frequency, electron cyclotron frequency, their harmonics and nonlinear coupling of these waves. Measurements of these waves give information on local plasma density and magnetic field strength and it is revealed that the electron beam emission from the spacecraft is a powerful diagnostic tool in the magnetosphere. A long term observation in this electron beam experiment has provided us with the average plasma density profile in the magnetosphere. It is also useful for the detection of the plasmapause. Plasma density measurements down to the order of 10 cm^–3 are possible. The instrument itself is very simple and compact, so that it will be a powerful plasma diagnostic tool in future magnetospheric and planetary explorations.     

The heliometer as a tool for the measure of the Moon

The heliometer has been the only instrument for the measurement of the lunar physical libration for more than a century. Bessel (1839), who introduced the use of the heliometer for the systematic measurement of the relative positions of craters on the lunar disc, has also developed the necessary formulation for the calculation of the lunar physical libration from the heliometric measurements. That methodology is presented, and results obtained by Bessel's students and other investigators who followed Bessel's method, are discussed.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).     

Helioseismology as a diagnostic of the solar interior

Helioseismology has given us a unique window into the solar interior. Helioseismic data have enabled us to study the internal structure and dynamics with unprecedented detail. This has also allowed us to use the Sun as a laboratory to study the basic properties of stellar matter. We describe how helioseismology is used to determine solar structure and what we have learned about the Sun so far. We also describe how knowledge of the solar structure can be used to constrain the physics inputs.     

Analytical signal as a tool for studying solar p-modes

A technique for analyzing periodic processes based on the introduction of an analytical signal is described. This technique allows the instantaneous frequency, amplitude, and phase of oscillations to be obtained. The data on solar brightness fluctuations collected with the DIFOS multichannel photometer onboard the CORONAS-F satellite are processed. The p-mode spectral lines are broadened mainly by amplitude fluctuations, while the frequency stability appears to be high (～10^?4). A method for separating signals with close frequencies is developed. The p-mode with l = 0 and n = 21 is used as an example to show that the separation of signals with close frequencies is possible when the conventional spectral methods are inefficient. Analysis of the phase shifts between the oscillations observed in various optical channels of the DIFOS photometer has revealed that the five-minute oscillations travel from the upper and deep photospheric layers toward the middle photospheric layers. This effect directly proves that the evanescent p-modes in the photosphere are nonadiabatic.     

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

During the previous years spacecraft observations of so-called Energetic Neutral Atoms (ENAs) have become an important remote-sensing technique in planetary science for analyzing the solar wind plasma flow around the upper atmospheric environments of Solar System bodies. ENAs are produced whenever solar- or stellar wind protons interact via charge exchange with a neutral particle from a planetary atmosphere so that their signals constrain both, ion distributions and neutral gas densities. The observation of ENAs which have been generated due to charge exchange with stellar wind plasma have been used for the indirect mass loss and stellar wind property estimation of Sun-like stars by observing the interaction regions carved out by the collisions between stellar winds and the interstellar medium. In this work we review ENA-observations and data interpretations at Solar System planets and recent hydrogen-cloud observations in UV Lyman-α absorption around hydrogen-rich extra-solar gas giants. We discuss the production of stellar wind related hydrogen ENA-clouds around close-in exoplanets and show how a detailed analysis of attenuation spectra obtained for transiting hydrogen-rich close-in gas giants can be used for the study of the upper atmosphere structure, the planet’s magnetosphere and to obtain information on stellar wind properties. Finally, we discuss how future hydrogen cloud observations around exoplanets by space observatories like the Russia-led World Space Observatory-UV (WSO-UV) together with ESAs planned PLATO mission can be used for the reconstruction of the solar wind history or the test of magnetosphere evolution hypotheses.     

Abundance Gradients as a tool for understanding the Formation of the Milky Way

According to the two-infall model for the chemical evolution of the Galaxy the halo and bulge formed on a relatively short timescale (0.8–1.0 Gyr) out of the first infall episode, whereas the disk accumulated much more slowly and ‘inside-out’ during a second independent infall episode. We explored the effects of a threshold in the star formation process, during both the halo and disk phases. In the comparison between model predictions and available data, we have focused our attention on abundance gradients as well as gas, stellar and star formation rate distributions along the disk. We suggest that the mechanism for the formation of the halo leaves detectable imprints on the chemical properties of the outer regions of the disk, whereas the evolution of the halo and the inner disk are almost completely disentangled. This is due to the fact that the halo and disk densities are comparable at large Galactocentric distances and therefore the gas lost from the halo can substantially contribute to building up the outer disk. We predict that the abundance gradients along the Galactic disk have increased in time during the first billion years of the disk evolution and remained almost constant in the last ~5Gyrs. This revised version was published online in September 2006 with corrections to the Cover Date.     

A numerical study of polar ionospheric currents

Numerical calculations for the electric current in the polar ionosphere have been made by assuming some realistic distributions of the electric field and conductivity. Two dynamo actions are taken into account; one of which is induced by ionospheric winds and the other by the solar wind. For the solar wind dynamo action, it is found that the secondary polarization field caused by non-uniform distribution of ionospheric conductivity is much larger than the primary field induced by the solar wind, suggesting its important effect on charged particles in the magnetosphere, and that the irrotational current having a source and sink is of the same order of magnitude as the solenoidal current closing its circuit in the ionosphere. It is also found that the solar wind is, in general, more effective than the ionospheric winds in producing polar current systems such as DP 1 and 2, but in some cases the ionospheric winds have a significant effect on the current distribution.     

一个甚高频频率合成器的设计

介绍一个专用甚高频频率合成器的设计方案和实施中的一些关键技术．该合成器输出频率范围为９９．３ＭＨｚ～１００．７ＭＨｚ；步距分粗（２０ｋＨｚ）细（１００Ｈｚ）两档；输出短期频率的稳定度为３×１０（－９）／２５ｍｓ和１×１０（－１０）／ｓ．     

Zatrikean pre-geometry as a tool for modelling in theoretical astrophysics

In this paper, we present an axiomatic foundation on zatrikean (i.e., chess-like) pre-geometry. Furthermore, we find that rotation can induce such a pre-geometry; and this rotationally induced zatrikean pre-geometry can, in turn, decisively affect all the interrelated physical phenomena, which in their majority are significant for theoretical astrophysics and cosmology.     

Analysis of the non-Gaussian spectra of interplanetary scintillations

The non-Gaussian intensity fluctuation spectra observed by Cohenet al. (1967) are analysed. Computations of the length scales derived from the phase autocorrelation functions using Buckley's method (1971, I) indicate that for a rms phase deviation of 4 radians or more the diffracting medium behaves as one with its phase structure having ‘inner’ and ‘outer’ scales of turbulent blobs or eddies which are present in a turbulent medium.