Correlations between ground observations of Pi 2 geomagnetic pulsations and satellite plasma density observations

Ground observations of Pi 2 geomagnetic pulsations are correlated with satellite measurements of plasma density for three time intervals. The pulsations were recorded using the IGS network of magnetometer stations and the plasma density measurements were made on board GEOS-1 and ISEE-1. Using the technique of complex demodulation, the amplitude, phase and polarisation characteristics of the Pi 2 pulsations are observed along two meridional profiles; one from Eidar, Iceland (L = 6.7) to Cambridge, U.K. (L = 2.5) and the other from Tromso, Norway (tL = 6.2) to Nurmijarvi, Finland (L = 3.3). The observed characteristics of the Pi 2 pulsations are then compared with the plasma density measurements. Close relationships between the plasmapause position and the position of an ellipticity reversal and a variation in H component phase are observed. A small, secondary amplitude maximum is observed on the U.K./Iceland meridian well inside the position of the projection of the equatorial plasmapause. The primary maxima on the two meridians, in general occur close to the estimated position of the equatorward edge of a westward electrojet. Using the plasma density measurements, the periods of surface waves at the plasmapause for two intervals are estimated and found to be in good agreement with the dominant spectral peaks observed at the ground stations near the plasmapause latitude and within the plasmasphere. The polarisation reversal, together with phase characteristics, spectral evidence and the agreement between the theoretical and observed periods leads to the suggestion that on occasions a surface wave is excited on the plasmapause as an intermediate stage in the propagation of Pi 2 pulsations from the auroral zone to lower latitudes.     

Observations of Pg pulsations in the Northern Auroral zone and at lower latitude conjugate regions

An analysis is made of giant pulsation (Pg) data recorded at ground stations in the Northern Auroral Zone in Scandanavia (mainly at Tromsø, L = 6.4 and Kiruna, L = 5.5) during the period September 1976 to December 1977. They are shown to have a meridional variation of amplitude and polarization consistent with a field line resonance structure and their vertical component behaviour suggests that they also have a rapid azimuthal phase variation. Limited data from conjugate stations at L = 4.4 are used to show that Pg's are odd mode oscillations of the field line. Pg's are equated to the observation of a unique compressional wave in space at synchronous orbit and it is suggested that they result from the drift wave instability of the compressional Alfven wave at the outer edge of the quiet time ring current.     

On the diurnal period variation of midlatitude ULF pulsations

Magnetometer studies of the periods of mid-latitude ULF pulsations have produced conflicting results on the variation of the pulsation periods with both latitude and local time. Since the mid-latitude geomagnetic field is not expected to be significantly distorted by the solar wind, the observed diurnal period variations should be determined by changes in the ambient plasma density. We have applied a physically realistic plasmasphere model to the determination of pulsation eigenperiods over a 24-h interval at L=2.3 (appropriate to Wellington, New Zealand). The resulting model pulsation eigenperiods are largest during the day, with minimum and maximum values at 05.00 and 18.00 L.T. respectively. The model predicts a general increase in the eigenperiods during the replenishment of the protonosphere after a period of geomagnetic activity.     

Pi2 pulsations in the magnetosphere

Several substorms were observed at Explorer 45 in November and December 1971, and January and February 1972, while the satellite was in the evening quadrant near L = 5. These same substorms were identified in ground level magnetograms from auroral zone and low latitude stations. The satellite vector magnetic field records and rapid run ground magnetograms were examined for evidence of simultaneous occurrence of Pi2 magnetic pulsations. Pulsations which began abruptly were observed at the satellite during 7 of the 13 substorms studied and the pulsations occurred near the estimated time of substorm onset. These 7 pulsation events were also observed on the ground and 6 were identified in station comments as Pi2. All of the events observed were principally compressional waves, that is, pulsations in field magnitude. There were also transverse components elliptically polarized counter-clockwise looking along the field line. Periods observed ranged from 40 to 200 sec with 80 sec often the dominant period.     

Ionospheric Joule dissipation as a damping mechanism for high latitude ULF pulsations: Observational evidence

On 9 January 1979 an SI-excited pulsation event was observed by the Scandinavian Magnetometer Array. The pulsation period shows a clear variation with latitude which suggests decoupled oscillations of individual magnetic field shells. The pulsation amplitudes exhibit an e-fold decay with the damping rate γ varying both in longitudinal and latitudinal directions. Assuming Joule heating in the ionosphere as the dominant damping mechanism (and thus γ ～ Σ^?1_p) approximate height-integrated Pedersen conductivity profiles were calculated which fit well with previously observed Σ_p distributions. This is interpreted as observational evidence for ionosopheric Joule dissipation as the major damping mechanism for high-latitude ULF-pulsations.     

Radial pulsation of less-massive yellow supergiants

Linear and nonlinear pulsation computations for the modelsM=0.8M _⊙,L=10000 and 20000L _⊙ were carried out in order to understand FG Sge's pulsation. The results may be summarized as follows:

1. In the modelsL=10000L _⊙, the fundamental blue edge is nearT _e =5700 K. The models show that instability of the third overtone extends to 7400 K and still has large positive growth rates. A nonlinear model of 7000 K shows a small amplitude ΔV=10 km s^?1, ΔM _bol=0.03 with a period of around 18 days, nearly equal to that of the third overtone.
2. In the linear models ofL=20000L _⊙, the fundamental blue edge is shifted to 7000 K but the damping of this mode is so small that it is marginally stable to 7700 K. The third overtone has large positive growth rates of this region. The nonlinear model at 7700 K, however, shows no indication of third overtone pulsation.

We also examine the possibility, suggested by Whitney (1978), that the mass of FG Sge is 0.4M _⊙.     

G298 – A New Candidate γ Doradus Star in the Direction of the Globular Cluster M4

G298 = L3216 (V = 12.68, B?V = 0.59) is a field star in the direction of the globular cluster M4. It was used as one of our comparison stars in the past, now it is shown that G298 is a new γ Dor variable star with a period of 1.03099 day and peak to peak amplitude of about 0.02 mag in V. Its spectral type is F2 (IV ?).     

The effect of the Earth’s oblateness on the Moon’s physical libration in latitude

The Moon’s physical libration in latitude generated by gravitational forces caused by the Earth’s oblateness has been examined by a vector analytical method. Libration oscillations are described by a close set of five linear inhomogeneous differential equations, the dispersion equation has five roots, one of which is zero. A complete solution is obtained. It is revealed that the Earth’s oblateness: a) has little effect on the instantaneous axis of Moon’s rotation, but causes an oscillatory rotation of the body of the Moon with an amplitude of 0.072″ and pulsation period of 16.88 Julian years; b) causes small nutations of poles of the orbit and of the ecliptic along tight spirals, which occupy a disk with a cut in a center and with radius of 0.072″. Perturbations caused by the spherical Earth generate: a) physical librations in latitude with an amplitude of 34.275″; b) nutational motion for centers of small spiral nutations of orbit (ecliptic) pole over ellipses with semi-major axes of 113.850″ (85.158″) and the first pole rotates round the second one along a circle with radius of 28.691″; c) nutation of the Moon’s celestial pole over an ellipse with a semi-major axis of 45.04″ and with an axes ratio of about 0.004 with a period of T = 27.212 days. The principal ellipse’s axis is directed tangentially with respect to the precession circumference, along which the celestial pole moves nonuniformly nearly in one dimension. In contrast to the accepted concept, the latitude does not change while the Moon’s poles of rotation move. The dynamical reason for the inclination of the Moon’s mean equator with respect to the ecliptic is oblateness of the body of the Moon.     

Time of flight calculations for high latitude geomagnetic pulsations

High latitude geomagnetic field lines differ significantly from a dipole geometry. Time of flight calculations using the Mead-Fairfield (1975) model of the geomagnetic field are presented for different tilt angles and K_p conditions. Typical standing wave periods of geomagnetic pulsations are estimated for three different magnetospheric cold plasma regions, corresponding to waves guided in (i) the plasmatrough, (ii) the extended plasmasphere and (iii) regions of enhanced proton density (detached plasma) within the plasmatrough.Pc4/5 pulsation studies at high latitudes are briefly reviewed and some new results from Tromso are given. Many of the observations reveal hydromagnetic waves whose location and period are consistent with ducting in a region of enhanced plasma density within the plasmatrough.     

The effect of damping on geomagnetic pulsation amplitude and phase at ground observatories

We present some results from a model of forced oscillations of the magnetosphere. The purpose of this work is to examine the effects and consequences of damping on geomagnetic pulsations as observed on the ground. The aim of the current work is to quantify the amount of damping applicable to geomagnetic pulsation waveforms. Ionospheric conductivities vary with latitude and time of day and this variation will effect the damping of geomagnetic pulsations. The variations in ionospheric conductivities are taken into account to predict the changes in amplitude and phase of geomagnetic pulsations over an extended latitudinal array of ground observatories. Three situations are modelled where the damping factor γ/ω_n, which is related to the amplitude loss per cycle, is different: (i) γ/ω_n approximately equal to 0.01, this corresponds to the ionospheric Joule damping of Newton et al. (1978); (ii) λ/ω_n equal to 0.1, this value is consistent with the empirically determined day-time damping factors from the observed latitude-dependent transient decays of the pulsation single effect events discussed by Siebert (1964). The value of 0.1 as the damping factor is taken as typical of day-time conditions and its effect on amplitude and phase for continuous pulsations is considered; and (iii) λ/ω_n is latitude-dependent; three different levels of damping are used appropriate for the night-time conditions associated with the auroral electrojet, plasmatrough and plasmasphere.The results from the model suggest that observationally determined damping factors are greater than those computed from ionospheric Joule damping alone. The model also illustrates the broadening of the latitudinal resonance width with increasing damping and the reducing of the phase change across resonance to less than 180°. The model also successfully reproduces features of pulsation single effect events and Pi2 pulsations.     

A γ Doradus candidate in eclipsing binary BD And?

The BVR photometric light curves of the eclipsing binary BD And were obtained in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the photometric solutions were derived. The results show that BD And is a detached binary system, whose components have a little temperature difference of about 40 K. By analyzing photometric available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.011 days and a period of 9.6 years. The results indicate that the periodic oscillation could be caused by a third component physically attached to the eclipsing binary. After removing the light variations due to the eclipses and proximity effects, the light-curve distortions are further explained by the pulsation of the primary component with a dominant period of ∼1 day. In accordance with the position of the primary component on the Hertzsprung–Russell diagram and its pulsation period, the primary component of BD And could be an excellent γ Doradus candidate. It is rarely phenomenon that a component of the eclipsing binary system is a γ Doradus variable.     

A Model of the Mira–Type Star T UMi

Stellar evolution calculations were carried out from the main sequence to the final stage of the asymptotic giant branch for stars with initial masses 1 M_⊙ ≤ M_ZAMS ≤ 2 M_⊙ and metallicity Z = 0.01. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of radiation hydrodynamics and time–dependent convection describing radial stellar pulsations. The study was aimed to construct the hydrodynamic models of Mira–type stars that show the secular decrease in the pulsation period Π commenced in 1970th at Π = 315 day. We show that such a condition for the period change is satisfied with evolutionary sequences 1 M_⊙ ≤ M_ZAMS ≤ 1.2 M_⊙ and the best agreement with observations is obtained for M_ZAMS = 1.2 M_⊙. The pulsation period reduction is due to both the stellar radius decrease during the thermal pulse of the helium burning shell and mode switch from the fundamental mode to the first overtone. Theoretical estimates of the fundament parameters of the star at the onset of pulsation period reduction are as follows: the mass is M = 0.93 M_⊙, the luminosity is L = 4080 L_⊙, and the radius is R = 220 R_⊙. The mode switch occurs 35 years after the onset of period reduction.     

Statistical studies of geomagnetic pulsations with periods between 10 and 70 sec and their relationship to the plasmapause region

Geomagnetic pulsations, in the period range 10–150 sec, have been analysed from five stations; Eskdalemuir (L = 3.1), Lerwick (L = 4.0), St. Anthony (L = 4.9), Sodankyla (L = 5.3) and Tromsø (L = 6.6). The results of 12 observatory years' worth of data are presented in the form of contour maps showing the frequency of occurrence of the pulsations as a function of K_p index and of local time. The maps show that a ground based observatory is more likely to record shorter period oscillations (pc 3) when the geomagnetic field line linking the station with the southern hemisphere passes through the plasmatrough than when the observatory field line links the plasmasphere. The peak occurrence of pc 3 for the observatories considered is at 08:45 hr ± 1 hr LT and is related to the observatory L value and the average night-time K_p index by the equation, L = 8.1 ? 1.2K_p. At Eskdalemuir, the spectrum is broader band than the other stations and tends to divide into two peaks; the pc 3 (20 sec) peak tends to occur when the plasmapause has moved in close to the observatory; while the pc 4 (60 sec) peak occurs when the K_p values have been lower and the plasmapause is further away at higher latitudes.     

Analysis of condensates formed at the viking 2 lander site: The first winter

A thin light-colored ground covering appeared on the surface of Mars near the Viking 2 lander from L_s = 230° to L_s = 16°, a total of 249 Mars days, during the lander's first winter on the surface. This paper presents a reduction of applicable lander imagery during the period. Imaging sequences, relative surface albedo, spectral reflectance estimates, and limited photometric data are presented and compared with previous laboratory measurements. Photometric data are best fit by an average Minnaert k = 1.1 (blue), k = 1.0 (green), and k = 0.95 (red). Appearance and disappearance rates, spectral reflectance, and photometric data all tend to confirm an earlier proposal that the covering was a combination of H₂O and CO₂, which fell already condensed onto dust particles brought northward by the season's first major dust storm. Under this assumption, the covering thickness is estimated to be between 0.5 and a few millimeters.     

Pc5 pulsations associated with ring current proton drifts: Stare radar observations

Detailed properties of a Pc5 pulsation with large azimuthal wavenumber observed using the STARE radar have recently been reported. A further four examples of this type of pulsation are presented, and it is shown that their properties are generally similar to those of the first example. However, there are some differences, the most important being that the variation of azimuthal phase velocity with latitude is significantly different for different time intervals during individual events, so that a mean phase velocity for a given latitude cannot be defined.When mapped to the equatorial plane in a dipole geomagnetic field, the variation of azimuthal phase velocity with L resembles the gradient-curvature drift of energetic protons in only a few time intervals within the events. The results are interpreted in terms of current theories of drift and bounce resonance of energetic particles with hydromagnetic waves. It is found that no single theory explains all aspects of the observations.     

The horizontal propagation of Pc1 pulsations in the ionosphere

The propagation properties of the various elements of the plane-wave angular spectrum of a Pc1 pulsation signal in the ionosphere are determined by a full-wave numerical analysis. A spectral component is characterized by the wave-vector azimuthal direction, and the Snell constant S. The isotropic R-mode transmission coefficient to ground is fairly flat for S ? 400, but thereafter (S > 500) drops rapidly with increasing S. Coupling of energy from the field-guided L-mode to the R-mode occurs along the entire length of the L-mode trajectory within the ionospheric duct in which the R-mode can propagate. Within the duct, the R-mode attenuation is determined largely by R to L-mode coupling, which is larger for E-W than for N-S azimuths, especially for steep angles of incidence (S < 100). This should lead to enhanced injection of energy into E-W high altitude, high velocity paths, but to higher E-W attenuation at oblique angles. For oblique propagation (S ? 200) horizontal group velocities are slightly higher than the Alfvén phase velocity at the F-layer peak, but about twice as high for steep angles (S ≈ 100).     

Investigations of Pi2 micropulsations—I. Frequency spectra and polarisation

Pi2 micropulsations are recorded at four sites with approximately the same geo-magnetic longitude but spanning 36° in latitude. Frequency analyses on these signals show that they normally contain more than one spectral component and that these components, all of which commence simultaneously, are not normally harmonically related. In addition, the spectral content is found not to vary significantly with latitude.No significant correlations are found between K_p and the maximum period, the minimum period, or the number of frequency components, in a Pi2. However the ‘average’ Pi2 frequency is found to vary linearly with both K_p and the magnitude of the accompanying auroral bay. In addition, the signals measured at the ‘low’ and at the ‘high’ latitude sites are found to exhibit an overwhelming preference for the left-hand sense of polarisation, while those at the ‘middle’ latitude sites show no preference for either sense.     

VLF goniometer observations at halley bay,Antarctica—II. Magnetospheric structure deduced from whistler observations

On 26 July 1967, a magnetically quiet day (ΣK_p = 12?) with high whistler activity at Halley Bay, it was found possible, by measurement of whistler nose-frequency and dispersion and the bearings of the whistler exit points, to make a detailed study of the magnetospheric structure associated with the whistler ducts.During the period 0509–2305 UT most of the exit points of whistlers inside the plasmasphere were situated along a strip about 100km wide passing through Halley Bay in an azimuthal direction 30°E of N between 57° and 62° invariant latitude. A mechanism which can give rise to such a well-defined locus which co-rotates with the Earth is not clear. Nevertheless, it does appear that the locus coincides with the contour of solar zenith angle 102° at 1800 UT 25 July. This was also the time of occurrence of a sub-storm and it is suggested that the magnetospheric structure was initiated by proton precipitation along the solar zenith angle 102° contour.At mid-day knee-whistlers observed outside the plasmapause had exit points which were closely aligned along an L-shell at an invariant latitude of 62.5°. They exhibited a marked variation (~ 3:1) in electron tube content over about 12° of invariant longitude and a drift of about 8 msec^?1 to lower L-shells.Throughout the period of observation the plasmapause lay about 2° polewards of the mean position found by Carpenter (1968) for moderately disturbed days.     

For infrared spectrophotometry of Jupiter and Saturn

Infrared spectral observations of Mars, Jupiter, and Saturn were made from 100 to 470 cm^?1 using NASA's G. P. Kuiper Airborne Observatory. Taking Mars as a calibration source, we determined brightness temperatures of Jupiter and Saturn with approximately 5 cm^?1 resolution. The data are used to determine the internal luminosities of the giant planets, for which more than 75% of the thermally emitted power is estimated to be in the measured bandpass: for Jupiter L_J = (8.0 ± 2.0) × 10^?10L_⊙ and for Saturn L_S = (3.6 ± 0.9) × 10^?10. The ratio R of thermally emitted power to solar power absorbed was estimated to be R_J = 1.6 ± 0.2, and R_S = 2.7 ± 0.8 from the observations when both planets were near perihelion. The Jupiter spectrum clearly shows the presence of the rotational ammonia transitions which strongly influence the opacity at frequencies ?250 cm^?1. Comparison of the data with spectra predicted from current models of Jupiter and Saturn permits inferences regarding the structure of the planetary atmospheres below the temperature inversion. In particular, an opacity source in addition to gaseous hydrogen and ammonia, such as ammonia ice crystals as suggested by Orton, may be necessary to explain the observed Jupiter spectrum in the vicinity of 250 cm^?1.     

Meridional characteristics of a Pc 4 micropulsation event in the plasmasphere

An analysis was made of a complex large amplitude Pc 4 micropulsation, of four hours duration around local noon, observed at five ground stations in the United Kingdom (2.4? L ?3.8). The final pulsation waveform was shown to be the results of the superposition of wave packets of different periods. The meridional variation of the amplitude of the different period wavepackets was consistent with their being fundamental “toroidal” field line resonances within the plasmasphere, rotated through 90° in their transmission through the ionosphere in accordance with recent theoretical predictions. Other predicted ionospheric effects, such as the loss of the sense-of-polarization reversal across the amplitude maximum, were apparent in the meridional variation of the polarization characteristics.