Changes in the ionospheric F2-layer at a place near the Sq-current focus during geomagnetic storms

In this paper hourly data of maximum electron density and total electron content in a unit column up to the level of peak electron density of the F2-layer at Puerto Rico (magnetic dip 52.5°N) in the American sector are studied to find their DS and D_st variations and to compare them with those of the horizontal component of the Earth's magnetic field for 93SC type geomagnetic storms which occurred during the period September 1957–March 1962. These variations are obtained separately for positive and negative F2-storms and then averaged for all the types. It is found that the positive F2-storms are in a way connected with the equatorial type of DS variation of the H-field and the negative F2-storms with the high-latitude type DS variation of the H-field. The D_st variation of the H-field is practically of the same character for both positive and negative F2-storms. These findings combined with those of others indicate that it is the DS current in the ionosphere that cause the observed changes in the F2-layer through electromagnetic movements; diffusion along the field lines and changes in the loss-rates of electrons may also contribute to the nett effects. A statistical survey shows that while there are equal chances for positive F2-storms in Summer and Winter at Puerto Rico, there is a much larger number of negative F2-storms in Summer than in Winter. At a southern conjugate place, there is a much larger number of positive F2-storms in Winter, but equal number of negative F2-storms in Summer and Winter. More than half the total number of the F2-storms are found to be similar types (33 per cent positive, 23 per cent negative) from the consideration of the F2-changes during individual magnetic storms at the conjugate places. These are discussed in the concluding section of the paper.     

Electron excitation and auroral emission parameters

Auroral luminosities of the main emission lines in the aurora have been calculated for excitation by an isotopic primary electron flux with spectra of the form J(E) = AE exp (−E/E₁) + B(E₂)E exp (−E/E₁). The variation of emissions from O and N₂⁺ with height are shown, as are the variations of column integrated intensities and pertinent intensity ratios with the characteristic energy E₂, this leading to a method of estimating the electron spectrum from ground observation.     

The angular momentum of a Kerr black hole

It is pointed out that, when calculating the angular momentum of a Kerr black hole, we should allow for the effect of accretion of scattered electrons in the retrograde direction. By using the radius of smallest circular orbit of the particle as a measure for the capture cross-section by the hole, the calculation is greatly simplified. Thorne's result, a/M = 0.9982, when retrograde photons are considered, is easily obtained. If we allow for retrograde electrons, we get a/M = 0.9986, if we allow for both retrograde electrons and photons, we get a/M = 0.9968; and if we further allow for pair annihilation, we get a/M = 0.9961.     

Observations from space of the solar corona/inner zodical light

Observations, from the Apollo 16 Spacecraft, in lunar orbit, of the total radiance of the K + F corona, from 3 R to 55 R are presented and discussed.

The logarithmic slope of the K + F coronal radiance, in the region r > 20 R, is found to be n = 1.93, slightly less steep than previous determinations. The photometric axis of the radiance is found to be displaced 3 ± 1° north of the ecliptic, for the region r > 20 R, and this displacement is interpreted as an annual variation due to non-coincidence of the ecliptic and the symmetry axis of the zodiacal cloud.     

The infrared variability of QSO 3C 273

The near-infrared data of the quasar 3C273 are collected from available literature and are used to analyze its variability properties. The largest amplitudes of variations are ΔJ = 1.0, ΔH = 0.9, and ΔK = 0.86. The color indices are J − H = 0.82, J − K = 1.96, and H − K = 1.13. Analysis with the discrete correlation function (DCF) method indicates that the variability between any two infrared bands is correlated without any time lag. The relation between the color index and brightness is also investigated and the result indicates that the spectrum steepens when the source first dims, while it flattens after the source has dimmed to a some extent, suggesting that the emission of 3C 273 at near-IR consists of at least two components. Some discussions are presented.     

Mg II h and k lines Stark parameters

Stark widths (W) and shifts (d) of the astrophysically very important singly ionized magnesium (Mg II) resonance h and k (279.5528 and 280.2705 nm) spectral lines in the 3s–3p transition have been measured at a 26,000 K electron temperature and 1.1 × 10²³ m⁻³ electron density in helium–oxygen plasma created in an optically thin linear, low-pressure, pulsed arc discharge. The magnesium atoms, as impurities in the driving gas, have been introduced by erosion from the pure magnesium bands fixed on the discharge electrodes providing conditions free of the self-absorption in the resonance h and k lines. Besides, the W and d values of the 279.0777 nm and 279.7998 nm Mg II lines in the 3p–3d transition have also been measured. Our W and d have been compared to the existing experimental and theoretical data. Good agreement was found with the results calculated by the semiclassical perturbation formalism, especially in the case of the Stark widths.     

Whistler wave instabilities in collisionless current sheet

Instability of whistler wave in collisionless current sheet is studied with numerical solution of the general dispersion relation obtained in Ref.[4] for the physical model A. As revealed by the results, the whistler wave can be directly absorbed by collisionless current sheets. On the neutral sheet (z/d_i = 0) oblique whistler waves over a rather wide range of wave numbers can propagate, while they are basically stable. In the ionic inertial region (z/d_i < 1), the obliquely propagating whistler wave is unstable. On the edge of the ionic inertial region (z/d_i = 1), the whistler wave is still unstable, with an increase in the growth rate, and in the frequency of the unstable wave. The growth rate is larger for the whistler wave propagating towards the neutral sheet (k_zd_i < 0) than away from the neutral sheet (k_zd_i > 0).     

Modification of the mean field theory of super-dense matter

We further discussed the Modified Mean Field Theory proposed in [1,2]. We found that this model has a new solution ml = 2; adding -meson, we calculated the symmetric energy of nuclear matter a₄; with the new parameters we calculated the equations of state with and without the addition of -meson; we compared the two; we also compared with the results for ml = 4.3; we made a preliminary theoretical investigation of the form of the vector meson mean field using the two-body correlation function; lastly, using the structural equation of neutron star we calculated the maximum mass for the various equations of state. The results are:

MMFT-2 (ml = 2): M_max = 2.22M (without -meson) M_max = 2.27M (with -meson)

MMFT-1 (ml = 4.3): M_max = 1.69M (without -meson) M_max = 1.89M (with -meson)

     

Kp index correlations with solar-wind parameters during the first and second stages of a recurrent geomagnetic storm

The dependence of geomagnetic activity during a recurrent magnetic storm on the solar-wind magnetic field and plasma parameters has been studied. According to variations of solar-wind magnetic field strength B, a recurrent magnetic storm is divided into two stages: the first proceeding during the peak of B, and the second proceeding after the return of B to quiet level. The K_p index vs solar-wind parameters scattering diagrams for stages I and II differ significantly. In particular, the random scattering for stage I is much larger than for stage II. It was found that for stage I the K_p index correlates with B, with the sign and value of northsouth field component B_z and with the magnitude ΔB of field fluctuations, the situation being similar to that during sporadic magnetic storms, though the scale of the event is smaller. For stage II, the K_p index does not correlate with B, but strongly correlates with ΔB and weaker—with B_z. So geomagnetic activity at stage II is supported mainly by solar-wind magnetic field fluctuations. The dependence of the K_p index on plasma parameters (concentration of protons n, bulk velocity v and temperature T) is weak for both stages.     

Relationship between pulse width and energy in GRB 060124: from X-ray to γ-ray bands

GRB 060124 is the first event that both prompt and afterglow emission were observed simultaneously by the three Swift instruments. Its main peak also triggered Konus-Wind and HETE-II. Therefore, investigation on both the temporal and spectral properties of the prompt emission can be extended to X-ray bands. We perform a detailed analysis on the two well identified pulses of this burst, and find that the pulses are narrower at higher energies, and both X-rays and γ-rays follow the same w–E relation for an individual pulse. However, there is no a universal power-law index of the w–E relation among pulses. We find also that the rise-to-decay ratio r/d seems not to evolve with E and the r/d values are well consistent with that observed in typical GRBs. The broadband spectral energy distribution also suggests that the X-rays are consistent with the spectral behavior of the γ-rays. These results indicate that the X-ray emission tracks the γ-ray emission and the emissions in the two energy bands are likely to be originated from the same physical mechanism.     

Improved absorption cross-sections of oxygen in the wavelength region 205–240 nm of the Herzberg continuum

The laboratory values of the Herzberg continuum absorption cross-section of oxygen at room temperature from Cheung et al. (1986, Planet. Space Sci. 34, 1007), Jenouvrier et al. (1986a, Planet. Space Sci. 34, 253) and Jenouvrier et al. (1986, J. quant. Spectrosc. radiat. Transfer 36, 349) have been compared and re-analyzed. There is no discrepancy between the absolute values of these two sets of independent measurements. These values have been combined together in a linear least-squares fit to obtain improved values of the Herzberg continuum cross-section of oxygen at room temperature throughout the wavelength region 205–240 nm. Agreement with in situ and other laboratory measurements is discussed.     

A survey of flux transfer events recorded by the UKS spacecraft magnetometer

The UKS spacecraft operated from August 1984 through to January 1985. During that time, it made multiple crossings of the magnetopause in local time sectors extending from mid-afternoon to just behind the dawn meridian. We have surveyed the magnetometer records from these magnetopause encounters and have compiled a catalogue of flux transfer events (FTEs using criteria identical to those employed by Rijnbeek et al. (1984, J. Geophys. Res. 89, 786) in their survey of ISEE spacecraft magnetometer data. Using the catalogue, we find that FTE occurrence determined from the UKS data set is substantially less than that detected using data from the early ISEE 1/2 spacecraft orbits. The UKS data set shows a correlation between FTE occurrence and southward external magnetic field, but there are several instances of passes in which no FTEs are detected but for which the external field was unam- biguousluy southward. The passes with the largest number of events are those for which the field outside the magnetopause has a large B_M component. We conclude that the lower latitude of the UKS encounters is responsible for the discrepancy with the ISEE occurrence. The most likely source region appears to be near the subsolar region.     

Average high latitude magnetic field: Variation with interplanetary sector and with season—II : Comparison of disturbance levels and discussion of ionospheric currents

Average high latitude magnetic field data from northern observatories are examined for three ranges of magnetic disturbance level, Kp = 1− to 1+,2− to 3+ and ≥ 4−. Except for 0–8^h MLT, 55–78° invariant latitude, during away interplanetary magnetic field sectors, the variations between season and sector have the same characteristics at all Kp ranges. Because the amplitude of sector differences is much larger at sunlit local times than in the midnight sector, it is concluded that the current system of Svalgaard (1973) is not adequate to describe the sector variations in magnetic disturbance. Other current systems are discussed briefly. The disturbance morphology and seasonal variation at all Kp levels confirms the results of previous studies which indicate that latitudinally broad current systems, like S_q^p and nonionospheric sources are present in addition to latitudinally narrow electrojet currents. Comparison of data between Kp levels indicates that the Harang discontinuity shifts toward earlier MLT with increasing Kp level.     

Full-wave VLF modes in a cylindrically symmetric enhancement of plasma density

VLF waves in the magnetosphere may be guided by ducts, i.e. enhancements of plasma density aligned with the geomagnetic field. It is required to account for the good transmission properties of these ducts as some leakage of energy is expected, with consequent attenuation. We consider a cylindrical duct, whose axis is parallel to a uniform magnetic field. The electron density of a cold plasma is a function only of radial distance r from the axis, taking constant values in inner and outer regions r < a and r > b, and varying smoothly in the duct wall a < r < b. We compute full-wave ‘trapped’ VLF modes. Results are presented for a range of values of the parameters of the model. In general we find that attenuation of leading modes is very low, agreeing with observation. Specific features are that leakage (arising from mode conversion in the duct wall) increases as the wall is made thinner, that leakage for the leading modes is less for weaker ducts, that many modes may propagate, and that, because of interference effects, some higher order modes also suffer little attenuation.     

Some aspects of Sporadic-E at mid-latitudes

Evidence is presented to suggest that the ƒ₀E_s value tends to be high at positions in the E_s-layer where trough slope-lines and crest slope-lines of F2-layer irregularities meet the E_s-layer. These slope-lines are drawn through the troughs and crests, respectively, of the characteristic kinks in the F2-layer ionization contours, which are associated with F2-layer irregularities.

A rotating-loop direction-finding system has allowed an estimation of the distribution of ionization, which gives rise to Sporadic-E echoes. Analysis of Sporadic-E occurrence, on two occasions, suggests that the reflecting surfaces are frontal in nature, the fronts having a separation from each other of some tens of kilometres, and probably existing as closed curves, with diameters of the order of several hundreds of kilometres. A possible association between these structures and the occurrence of the green line of the airglow, is discussed.

A distribution of ionization, which will give contours showing “clouds” of ionization at some frequencies and a ripple structure at other frequencies, is proposed, in an endeavour to explain the apparent dual nature of Sporadic-E occurrence.

The evidence seems to indicate that the mechanism operating at the E_s-layer level, producing the phenomenon of Sporadic-E, is the same as that which produces the F2-layer irregularities which are responsible for “Spread-F”.     

The distribution of stably trapped magnetospheric plasma as determined from Pi2 micropulsations and the auroral electrojet index, AE

The distribution of stably trapped plasma is determined as a function of equatorial geocentric distance, R. Observed Pi2 micropulsation periods and the magnitudes of their associated magnetic bays, measured by the auroral electrojet index, AE, are used in determining this distribution. Plasma density is found to vary inversely as approximately the sixth power of R. When Pi2 period-AE relations are studied for varying time lags, the pulsation periods are found to define prolonged intervals of abnormal AE levels. Thus the periods may be potentially useful in forecasting geomagnetic disturbances or abnormally quiet intervals. A qualitative physical model is proposed to explain the observational relations.     

Mangeto-optical effects in sunspots and their vector magnetic field

The system of transfer equations of the four Stokes parameters I, Q, U, V under the action of the magneto-optical effect (i.e. the Unno-Beckers equations) are numerically solved in this paper for the magneto-sensitive lines FeI λλ 6302.499 and 5324.191 using an appropriate sunspot model. The errors in the expressions for the coefficients _r and _W in Beckers' paper [2] have been corrected for. From the results of calculations, features of the profiles of the Stokes parameters dependent on the magnetic vector have been isolated. Our computations also show that the magneto-optical effect should be taken into consideration in the measurement of the vector magnetic fields.

In the fourth section of this paper we have established a simple and convenient method for obtaining-information on the magnetic vector (including the field strength B, its inclination to the line of sight γ and its azimuth χ) from the profiles of the Stokes parameters. It consists of three steps: (1) The value of B is determined from the distance of the highest point in the V-profile from the central line. (2) γ is then found from V_max, i.e maximum value of V. (3) Lastly, the angle χ is found from Q₀, i.e. the value of Q at line centre.     

A further study of the method of identifying absorption line systems in QSO spectra

The method of identifying absorption line systems in QSO spectra (Cui et al. 1983; Chen et al. 1983) is further developed here. Certain limitations of the method and their improvements are discussed. Certain other problems requiring further study are pointed out. The improved method is applied to PKS 0528-250, and gives two new absorption line systems Z_a = 0.065 and 0.0345 in addition to the four systems Z_a = 2.8110, 2.8130, 2.5275, 2.1410, consistent with the systems A₁A₂, B, C of Norton et al. (1980). However, the systems D₁, D₂, E, F and G of Chen and Norton (1984) are not recovered. The reason for this discrepancy is discussed.     

Determination of the regional deformation rates of Shanghai and Kashima VLBI stations based on ITRF97

The vertical deformation rates (VDRs) and horizontal deformation rates (HDRs) of Shanghai VLBI station in China and Kashima and Kashima34 VLBI stations in Japan were re-analysed using the baseline length change rates from Shanghai to 13 global VLBI stations, and from Kashima to 27 stations and from Kashima34 to 12 stations, based on the NASA VLBI global solution glb1123 (Ma, 1999). The velocity vectors of the global VLBI stations were referred to the ITRF97 reference frame, and the Eulerian vectors of different models of plate motion were used for comparative solutions. The VDR of Shanghai station is estimated to be −1.91±0.56 mm/yr, and those of Kashima and Kashima34 stations, −3.72±0.74mm/yr and −8.81±0.84mm/yr, respectively. The difference between the last two was verified by further analysis. Similar estimates were also made for the Kokee, Kauai and MK_VLBA VLBI stations in mid-Pacific.     

Objective prism survey of QSO candidates in field centered at 0000 + 00°00'' II. The southeastern quarter

We give the coordinates, B_j^* magnitudes and identification of charts for 121 QSO candidates of reliability Q 4 found in the southeastern quarter of the UK Schmidt Sky Region 823 centered at 00^h00^m + 00°00'. For the Q 5 objects, spectral lines were identified and their redshifts given.