Giant Equatorial Radio Telescope

A giant radio telescope for observing galactic and extragalactic radio sources at metre wavelengths is proposed. By locating a parabolic cylindrical antenna at a site close to the Equator such that its axis lies parallel to earth's axis, it is possible to construct a large collecting area economically. The proposed instrument will be very powerful for studying compact and diffuse features of radio sources, monitoring their variability, recombination and deuterium line work, studies of interplanetary medium and pulsar search.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Equatorial coronal arches and geomagnetic disturbance

Central-meridian passage of coronal equatorial arches is followed, statistically, after about 7 days by geomagnetic disturbance. Sector-boundary crossings at Earth are most likely to occur 5 days after arch CMP, while metric noise sources cluster at the location of the arches. This agrees with the location of the noise sources relative to sector boundaries described by Sakurai and Stone (1971), rather than with that found by Martres et al. (1970) for 1964 and 1966, and may indicate evolution of the relation between coronal and interplanetary structure. We looked for, but did not find, clustering of coronal arches at a particular phase of the Olsen rotation scheme.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Pulsar investigation using interstellar scintillation

We discuss the resolution of pulsar magnetospheres using interstellar scintillation. The two-dimensional spatial structure of pulsar emission zones can be obtained from analysis of diffractive scintillations at low frequencies. Based on refractive and diffractive scintillation of pulsars we can also reconstruct the distribution of turbulent plasma along the line of sight, and using this analysis a new approach to pulsar distance estimation can be made. This revised version was published online in July 2006 with corrections to the Cover Date.     

Symmetric motions in the Equatorial Magnetic-Binary Problem

Classical numerical techniques are applied to find families of symmetric periodic orbits in the Equatorial Magnetic-Binary Problem. Stability for each orbit is also studied by means of variational methods. Finally an example in a concrete system is given to verify the procedure proposed.     

Using eclipse observations to test scintillation models

Near second and third contact during a solar eclipse the spatial spectrum of the solar illumination changes as the relative power at high spatial frequencies increases strongly. Since groundlevel atmospheric scintillation depends on a weighted integral of the image power spectrum, we can expect to see a measureable time dependence to solar scintillation during an eclipse. This effect was observed during an annular solar eclipse and quantitatively compared with a scintillation model.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

Equatorial orbits in superposed dipole and uniform magnetic fields

In the present work we study the equatorial motions of charged par ticles that are performed within a field consisting of the superposition of a dipole field—that could represent the magnetic field of a planet — and of a uniform magnetic field normal to the dipole's equator. We use a non-dimensional coordinate system in which the velocity of the charged particle is unit. The model depends on two parameters: the constant of the generalized momentum and the parameter of the interplanetary magnetic field. It is proved that the motion is always bounded. The regions of the motion and the corresponding orbits are studied with respect to the constant of the generalized momentum. We also, investigate numerically conditional periodic and asymptotic orbits.     

Equatorial magnetic helicity flux in simulations with different gauges

We use direct numerical simulations of forced MHD turbulence with a forcing function that produces two different signs of kinetic helicity in the upper and lower parts of the domain. We show that the mean flux of magnetic helicity from the small‐scale field between the two parts of the domain can be described by a Fickian diffusion law with a diffusion coefficient that is approximately independent of the magnetic Reynolds number and about one third of the estimated turbulent magnetic diffusivity. The data suggest that the turbulent diffusive magnetic helicity flux can only be expected to alleviate catastrophic quenching at Reynolds numbers of more than several thousands. We further calculate the magnetic helicity density and its flux in the domain for three different gauges. We consider the Weyl gauge, in which the electrostatic potential vanishes, the pseudo‐Lorenz gauge, where the speed of light is replaced by the sound speed, and the ‘resistive gauge’ in which the Laplacian of the magnetic vector potential acts as a resistive term. We find that, in the statistically steady state, the time‐averaged magnetic helicity density and the magnetic helicity flux are the same in all three gauges (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Equatorial ionospheric plasma density bubbles observed by ESRO-4

It is shown that the ESRO-4 satellite, in a polar orbit, was able to observe equatorial plasma bubbles using the fixed-bias total ion current probe. Experimental conditions were suitable for observations during a period at the vernal equinox 1973, when 21 plasma density depletion events were identified, extending across the equator. Statistical analysis suggests that the bubble cross-sections, transformed on to the zero-dip surface, were elongated, with an axial ratio of the order of 7:1, and were tilted upwards by about 10° to the east. The observations were made selectively near the F-layer peak; no movement of bubbles was measured.     

Flare-associated shock waves observed by interplanetary scintillation

Daily observations of a grid of scintillating sources during the period January–August 1971 indicate that enhancements in scintillation index which cannot be related to corotating structure, are related to interplanetary shock waves associated with solar flares. Only 3 enhancements in scintillation index associated with shock waves were observed during the eight months period of observations.     

Interstellar scintillation of compact extragalactic radio sources

The recent discovery of radio variability of a quasar on short time-scales (hours) prompts us to examine what is expected in respect of the interstellar scintillation of very compact, extragalactic radio sources. We find that large-amplitude, rapid, variability is predicted at commonly observed radio frequencies (1–20 GHz) over the vast majority of the extragalactic sky. As a guide to assist observers in understanding their data, we demonstrate simple techniques for predicting the effects of interstellar scintillation on any extragalactic source.     

Equatorial depletions in the 630.0 nm airglow at Vanimo

Using ground based airglow photometry, depletions in the 630.0 nm airglow were observed at Vanimo near the southern limb of the intertropical airglow arc. The results were compared with the more common properties of equatorial plasma bubbles such as depletion magnitude, cross-sectional size and East-West drift, with good agreement. In particular, airglow depletion depths ranged from 18 to 64% with a maximum loss in emission rate of 700 R (55%) on a night when the maximum recorded airglow was almost 1700 R. This corresponds to an electron density depletion of about 1.5 × 10¹² el m ^?3 observed near solar maximum. It is somewhat higher than values reported near solar minimum. The airglow depletions move eastward with velocities ranging from 90 to 140 ms ^?1. There is qualitative evidence of vertical motion and strong correlation with range type spread F.     

Interstellar scintillation measurements of pulsars at 326.5 MHz

We have measured the decorrelation frequency (f _v ) and decorrelation time (t _v ) for 15 pulsars. We show by combining our data with those of others thatfv∫ DM^-1.79±0.14 andt _v ∫ DM^-0.80±0.15 up to a dispersion measure (DM) of about 60 cm³ pc. The combined data set does not form a complete sample, but the relations obtained from our measurements on 14 pulsars, which form almost a complete sample up to 41 cm³ pc, are consistent with the above relations, suggesting that these relations are not seriously affected by selection effects. The relations are broadly in agreement with those expected from a homogeneous interstellar medium and are in disagreement with earlier conclusions by others that these relations steepen even for low-DM pulsars. The agreement suggests that the local interstellar medium is homogeneous at least up to a distance of about 2 kpc.     

赤道式天文望远镜极轴调整分析及观测结果

天文望远镜的指向精度和跟踪精度是评判一架天文望远镜的重要指标。赤道式天文望远镜的指向精度和跟踪精度受到极轴位置准确性的影响。正确地安装好极轴位置显得非常重要。极轴校正是一项很重要的工作。介绍了用观测恒星的方法来校正极轴位置,分析了合理地选择目标恒星,得出结论:在调整极轴东西方向时选择子午圈上的恒星作为观测目标恒星,在调整极轴俯仰方向时选择90°时角圈上的恒星作为观测目标恒星。经过多次调整极轴东西方向和极轴俯仰方向并对两个方向交替进行调整,望远镜的极轴将处于相当准确的位置。     

An Overview of Saturn's Equatorial Storms: 1990 - 1997

We present an overview of the studies we have performed of the unusual storm activity that is occurring in the Equatorial Zone (EZ) of Saturn since 1990 based on a long-term CCD imaging (261-953 nm). This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of Polar and Equatorial Magnetic Fields Near Sunspot Minimum

We investigate the polar magnetic fields near sunspot minimum using high-resolution videomagnetograph data from Big Bear Solar Observatory. To avoid the problem of center-to-limb variation of the projected longitudinal field, we compare polar with equatorial field strengths for the same limb distance. Polar fields are stronger than the quiet equatorial field, but no greater than equatorial limb data containing unipolar regions. The difference is entirely in the stronger field elements. The polar background fields are of mixed polarity but show a net weak field opposite in sign to that of the stronger polar elements. We believe this to be the first evidence of widespread background field. No dependence of the measured signal on the B-angle was found, so the high-latitude fields do not change strength near the pole. Further, there was no significant change in the polar fields in the 15-month period studied. We tried to derive a high-latitude rotation rate; our data show motion of high-latitude magnetic elements, but the diurnal trajectory is not much bigger than random motions and field changes, so the result is inconclusive. We suggest that the polar fields represent the accumulation of sunspot remnants, the elements of which last for years in the absence of other fields.     

Short-Term Variations in the Equatorial Rotation Rate of Sunspot Groups

We have detected several periodicities in the solar equatorial rotation rate of sunspot groups in the catalog Greenwich Photoheliographic Results (GPR) during the period 1931?–?1976, the Solar Optical Observing Network (SOON) during the period 1977?–?2014, and the Debrecen Photoheliographic Data (DPD) during the period 1974?–?2014. We have compared the results from the fast Fourier transform (FFT), the maximum entropy method (MEM), and the Morlet wavelet power-spectra of the equatorial rotation rates determined from SOON and DPD sunspot-group data during the period 1986?–?2007 with those of the Mount Wilson Doppler-velocity data during the same period determined by Javaraiah et al. (Solar Phys. 257, 61, 2009). We have also compared the power-spectra computed from the DPD and the combined GPR and SOON sunspot-group data during the period 1974?–?2014 to those from the GPR sunspot-group data during the period 1931?–?1973. Our results suggest a ～?250-day period in the equatorial rotation rate determined from both the Mt. Wilson Doppler-velocity data and the sunspot-group data during 1986?–?2007. However, a wavelet analysis reveals that this periodicity appears mostly around 1991 in the velocity data, while it is present in most of the solar cycles covered by the sunspot-group data, mainly near the minimum epochs of the solar cycles. We also found the signature of a period of ～?1.4 years in the velocity data during 1990?–?1995, and in the equatorial rotation rate of sunspot groups mostly around the year 1956. The equatorial rotation rate of sunspot groups reveals a strong ～?1.6-year periodicity around 1933 and 1955, a weaker one around 1976, and a strong ～?1.8-year periodicity around 1943. Our analysis also suggests periodicities of ～?5 years, ～?7 years, and ～?17 years, as well as some other short-term periodicities. However, short-term periodicities are mostly present at the time of solar minima. Hence, short-term periodicities cannot be confirmed because of the larger uncertainty in the data.     

Solar scintillation and the monitoring of solar seeing

A non-telescopic method of determining the quality of atmospheric seeing is discussed for large angular diameter objects, such as the Sun. In this method the concept of thermodynamic fluctuations is used to relate the observed intensity fluctuations to the r.m.s. angular diameter of the atmospheric seeing cells and telescopic angle of arrival fluctuations. Comparison between the measured r.m.s. cell size and telescopic angle of arrival fluctuations are presented for various degrees of seeing. Cross-correlation coefficients of 0.95 have been measured during such comparisons.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation. Partial support for NSO is provided by USAF under a Memorandum of Understanding with the NSF.     

The hubble diagram of quasars showing interplanetary scintillation

A further investigation is made on the redshift -magnitude diagram of quasars showing Interplanetary scintillation. The conclusion is that such objects, when limited further to the subset of small light variation amplitudes, probably have about the same luminosities. Using these, the best value of the deceleration parameter q_o is estimated to be +1.9.     

Measurements of stellar scintillation using photon counting statistics

The properties of the stellar scintillation were investigated using high speed photometry. The zenithal dependence of the total scintillation power turned out to be weaker than predicted by scintillation theory. The dependence of the total scintillation power on wavelength and the distribution of the intensity fluctuations according to a log-normal distribution agree with the theoretical predictions. The temporal behaviour of the stellar scintillation shows correlation time scales of less than 10 ms and some ten second which indicate the presence of the inner and outer scale of the atmospheric turbulence. The influence of other processes which cause intensity variations on the measurement of the total scintillation power was analyzed.