Short-term intrinsic-intensity variations of pulsars

Pulsars show intensity variations over timescales ranging from a few microseconds to a few years. Short-term intensity variations,i.e. those having timescales of a few minutes to a few hours had been difficult to study as their timescales are similar to those due to interstellar scintillations. We present here a method to separate the autocorrelation function of the short-term broadband intensity variations from that of the interstellar scintillations and thus overcome the above difficulty. The method assumes that the intrinsic variations are correlated over a bandwidth much larger than the decorrelation bandwidth for scintillations. Hence the ratio of the power in the variations due to the two causes depends on the bandwidth used. By applying the method to the intensity variations of 24 pulsars, we show that the presence of short-term intrinsic variations is very common in the radiation of pulsars. Quasi-periodicities were detected in the intensity variations of many pulsars, but their origin is not clear.     

Short-period interplanetary and polar magnetic field variations

It is shown that the dependence of the variations of vertical component of the polar cap magnetic field on the sector structure (actually, the azimuthal or Y component) of the interplanetary magnetic field as first discovered by Svalgaard (1968) and Mansurov (1969) extends to variations as brief as 1 hr or even less. The relation between sector structure dependent variations and substorm fields as indicated by the southward-directed component of the interplanetary magnetic field is investigated by comparing brief variations over selected intervals of time. The independence of the variations of the polar cap vertical and horizontal components suggests that there are at least two different current systems which produce brief variations in the polar cap. One of the current systems is related to the substonn field; the other is strongly seasonally dependent and is confined to the dayside sector of the Earth.     

The temperature variations in the troposphere,stratosphere, and mesosphere of the Northern Hemisphere, 1965–1981

We have used temperature data obtained from radiosondes and rocketsondes for the time interval 1965–1981 to estimate the interconnection of mean-annual temperature fluctuations at the various layers from the surface to the lower mesosphere of the Northern Hemisphere. Profiles of coefficients of correlation of the mean-annual temperature at each layer with mean-annual temperature at higher layers are shown for locations in the low, middle, and high latitudes. It is suggested that the mean-annual temperature variations at high latitudes of the troposphere are related with mean-annual temperature variations of the high latitudes of the lower stratosphere. Also, the mean-annual temperature variations at the high latitudes of the lower stratosphere are connected with mean-annual temperature variations at the high latitudes of the upper stratosphere. Furthermore, the mean-annual temperature variations of the upper stratosphere have an impressive correlation with mean-annual temperature variations of the lower mesosphere for whole northern hemisphere.     

Photospheric limb-darkening signatures of global structure variations

Observations of short-term irradiance variations and consideration of mechanisms of the solar activity cycle suggest the possibility of long-term variation of the solar flux. Since the limb darkening is sensitive to effective temperature and convective efficiency, observations of the solar limb darkening may provide a useful means to detect and study long-term global variations. The limb-darkening responses to impulsive variation (in depth) of the source function, to effective temperature variation, and to convection variations are presented. For the variations considered, the limb-darkening variation is approximately linearly proportional to the associated parameters. The minimum detectable amplitude of those parametric variations is derived as a function of observational noise. Given our demonstrated errors of observation, single-parameter sensitivies are 3 K for effective temperature variation and 0.007 for local mixing-length variation for year to year changes at 99% confidence.     

双向定时近周日误差成分初步分析

该文介绍了利用地球同步卫星定位系统进行双向定时的基本原理,采用北京和乌鲁木齐两站的试验数据进行了计算分析,发现双向定时结果明显存在周期性变化,并且两地结果随地方时的变化趋势基本一致。谱分析表明:两站的主要周期谱基本一致,都比较明显地存在近周日和近半日变化。这种周期性变化可能主要由电离层延迟随地方时的变化引起。     

Long period variations of the motion of a satellite due to non-resonant tesseral harmonics of a gravity potential

The main effects of tesseral harmonics of a gravity potential expansion on the motion of a satellite, are short period variations as well as long period variations due to resonances. However, other smaller long period and secular variations can arise from interactions between tesseral terms of the same order. The analytical integration of these effects is developed, using numerical evaluation of Kaula eccentricity and inclination functions. Examples for some Earth's geodetic satellites show that secular effects can reach a few decameters per year. The secular variations can even reach several hundred of meters per year for the Mars natural satellite Phobos.     

The response of ozone to solar activity variations: A review

Observational evidence and theoretical predictions of the response of ozone to solar variations are reviewed. Short-term solar proton effects, possible effects of galactic cosmic rays modulated by the Sun, and the effects of 27-day solar rotation and 11-year solar cycle variations are discussed. Solar proton effects on HO _x chemistry in the mesosphere and NO _x chemistry in the stratosphere with resulting catalytic destruction of O₃ help validate present day photochemical models. If there is an 11-year solar cycle variation in global ozone, the large dynamical effects at individual locations and the lack of good global coverage of ground based and in situ measurements can disguise it. Recently, with the global coverage of satellites, it has become possible to accurately determine global mean ozone. It has been found that variations in global mean ozone filtered for seasonal variations are highly correlated with variations of the 10.7 cm solar activity index and that global mean ozone responds rapidly to solar activity index variations. Photochemical models indicate that the observed 3% variations in global mean ozone over the solar cycle can be accounted for by solar UV variations which are not inconsistent with recent solar measurements.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The ionospheric current at the Nigerian equator as determined from the geomagnetic daily variations

A critical analysis of the theoretical methods for obtaining the ionospheric and induced currents from the geomagnetic variations is performed, and the ionospheric currents in the electrojet are analyzed, through the geomagnetic variations in the proximity of the dip equator in Nigeria. For this purpose, a method, previously introduced by the authors, is applied, which makes it possible to discuss the contribution of the currents induced in the Earth by those variations. The result is compared with that obtained from the variations in the South American area. It is found that the amplifications could be very different in the two areas.     

On the short term variations of solar activity during solar cycle 21

Short-term variations of the last solar activity cycle were studied by the flare and coronal indices using Gleissberg method. Systematic short-term variations are found from their course during the 21st solar activity cycle. Comparison of their autocorrelograms constructed by the new set of data obtained from the magnitude of the fluctuations showed us the existence of the phase shift between the temporal variations of the two indices.     

Variability of radiation from the Crab Nebula

We consider variations of the radiation from the Crab Nebula in two energy ranges: X-rays (2–10 keV) and very-high-energy (>1 TeV) gamma rays. We demonstrate the presence of sine-shaped quasi-periodic variations in the X-ray range, with the period P = 862 d. A positive correlation was detected between variations of X-rays and gamma rays (the HEGRA data) with time.     

A beam ratio technique for microwave observation of S-component sources

The fluctuations in the tropospheric attenuation constitute a major problem when S-component source variations are studied. On records made by means of ‘single beam’ antenna systems, separating solar variations from spurious effects can be very difficult. The twin-beam, beam ratio technique circumvents this problem by deriving a ratio with respect to a reference beam which is identically affected by the tropospheric attenuation and by receiver gain variations.     

Confirmation of the oblique pulsator model for the rapidly oscillating Ap star HR 3831

We have detected pulsational radial velocity variations in the rapidly oscillating Ap star HR 3831 which are amplitude- and phase-modulated in the same manner as the photometric variations. In particular, the radial velocities show the same 180° phase reversal at magnetic quadrature as the photometric variations. This confirms the oblique pulsator model, and rules out the spotted pulsator model for these stars.     

致密射电源的快速偏振变化和星际闪烁模型

以类星体０９１７＋６２４中１９８９年５月观测到的ＩＤＶ事件为实例,尝试提出一个４成分模型（１个稳定成分和 ３个闪烁成分）以充分解释在 ６ ｃｍ波长上观测到的偏振变化,包括流量和偏振流量的相关性和反相关性以及它们之间的快速转化．对于 ２０ ｃｍ波长上观测到的偏振变化,３成分模型（１个稳定成分和３个闪烁成分）已足以解释全部现象．文中提出的闪烁模型在解释ＩＤＶ事件的偏振变化方面改进了以前的模型拟合．     

Long-term optical and X-ray variability of the Seyfert galaxy Markarian 79

We present the results of concurrent X-ray and optical monitoring of the Seyfert 1 galaxy Mrk 79 over a period of more than 5 yr. We find that on short to medium time-scales (days to a few tens of days) the 2–10 keV X-ray and optical u - and V -band fluxes are significantly correlated, with a delay between the bands consistent with 0 d. We show that most of these variations may be well reproduced by a model where the short-term optical variations originate from reprocessing of X-rays by an optically thick accretion disc. The optical light curves, however, also display long time-scale variations over thousands of days, which are not present in the X-ray light curve. These optical variations must originate from an independent variability mechanism and we show that they can be produced by variations in the (geometrically) thin disc accretion rate as well as by varying reprocessed fractions through changes in the location of the X-ray corona.     

Atmospheric angular momentum variations of Earth, Mars and Venus at seasonal time scales

Atmospheric angular momentum variations of a planet are associated with the global atmospheric mass redistribution and the wind variability. The exchange of angular momentum between the fluid layers and the solid planet is the main cause for the variations of the planetary rotation at seasonal time scales. In the present study, we investigate the angular momentum variations of the Earth, Mars and Venus, using geodetic observations, output of state-of-the-art global circulation models as well as assimilated data. We discuss the similarities and differences in angular momentum variations, planetary rotation and angular momentum exchange for the three terrestrial planets. We show that the atmospheric angular momentum variations for Mars and Earth are mainly annual and semi-annual whereas they are expected to be “diurnal” on Venus. The wind terms have the largest contributions to the LOD changes of the Earth and Venus whereas the matter term is dominant on Mars due to the CO₂ sublimation/condensation. The corresponding LOD variations (ΔLOD) have similar amplitudes on Mars and Earth but are much larger on Venus, though more difficult to observe.     

Spatial variations of fundamental constants

We show how observational limits on possible time variations of fundamental constants of nature are influenced by spatial variations in the density and gravitational potential. Bekenstein's generalization of Maxwell's equations, incorporating variations of the fine structure 'constant', is used as a simple example. These features are expected to be present in a wide class of theories with varying 'constants' and will affect attempts to coordinate cosmological and geophysical bounds on allowed time variations.     

Latitudinal variations in Titan’s methane and haze from Cassini VIMS observations

We analyze observations taken with Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), to determine the current methane and haze latitudinal distribution between 60°S and 40°N. The methane variation was measured primarily from its absorption band at 0.61 μm, which is optically thin enough to be sensitive to the methane abundance at 20-50 km altitude. Haze characteristics were determined from Titan’s 0.4-1.6 μm spectra, which sample Titan’s atmosphere from the surface to 200 km altitude. Radiative transfer models based on the haze properties and methane absorption profiles at the Huygens site reproduced the observed VIMS spectra and allowed us to retrieve latitude variations in the methane abundance and haze. We find the haze variations can be reproduced by varying only the density and single scattering albedo above 80 km altitude. There is an ambiguity between methane abundance and haze optical depth, because higher haze optical depth causes shallower methane bands; thus a family of solutions is allowed by the data. We find that haze variations alone, with a constant methane abundance, can reproduce the spatial variation in the methane bands if the haze density increases by 60% between 20°S and 10°S (roughly the sub-solar latitude) and single scattering absorption increases by 20% between 60°S and 40°N. On the other hand, a higher abundance of methane between 20 and 50 km in the summer hemisphere, as much as two times that of the winter hemisphere, is also possible, if the haze variations are minimized. The range of possible methane variations between 27°S and 19°N is consistent with condensation as a result of temperature variations of 0-1.5 K at 20-30 km. Our analysis indicates that the latitudinal variations in Titan’s visible to near-IR albedo, the north/south asymmetry (NSA), result primarily from variations in the thickness of the darker haze layer, detected by Huygens DISR, above 80 km altitude. If we assume little to no latitudinal methane variations we can reproduce the NSA wavelength signatures with the derived haze characteristics. We calculate the solar heating rate as a function of latitude and derive variations of ∼10-15% near the sub-solar latitude resulting from the NSA. Most of the latitudinal variations in the heating rate stem from changes in solar zenith angle rather than compositional variations.     

引力常数随时间变化对双星轨道演变的长期效应(椭圆轨道情形)

给出了以偏近点角为自变量的变引力常数的摄动方程组的解.解包括轨道半长轴的长期和周期变化项,其他轨道根数在一阶解中无长期项,只有周期项.近星点经度和平经度在二阶解中显示长期项变化.给出了由于引力常数变化对双星轨道演变情况的数值估计,对结果做了讨论并给出结论.     

Spatial and temporal variations in the solar brightness

We have investigated long-term variations of solar brightness as a function of both time and solar latitude using eight years of ground-based photometric data in conjunction with space-based irradiance data. In particular, we have examined whether the combination of sunspot brightness deficits and facular brightness excesses is sufficient to explain the solar cycle irradiance variations. After correcting for the contribution from sunspots, we find that the irradiance data can be adequately explained by a model in which the remaining brightness variations are due entirely to facular contributions confined to the magnetically active latitudes. Thus we find no support for the hypothesis that there are convectively driven hot bands in the active latitudes, and our data show brightness variations that are well described by a facular contrast function.