Whistler wave amplitude oscillation and frequency modulation in the magnetospheric cavity

A magnetospheric cavity model is presented to explain self-pulsing and frequency modulation of ducted whistler waves associated with triggered emissions. Partial reflection of these waves at the ends of the duct suggests such a magnetospheric cavity analogous to a laser cavity.     

Whistler observations of magnetospheric electric field in the night side plasma-sphere at low latitude

Whistlers recorded at low latitude ground stations of Gulmarg, Nainital and Varanasi were used to infer the east-west component of electric field on the nightside plasmasphere atL=1.2, 1.12, and 1.07 during magnetic storm periods. The method of measuring electric field from the observed cross-L motions of whistler ducts within the plasma-sphere, indicated by changes in nose frequency of whistlers has been outlined. The nose frequencies of the non-nose whistlers under consideration have been deduced from Dowden-Allocock linear Q-technique. The results show eastward electric fields of 0.7 mVm^–1 in the equatorial plane of Gulmarg and 0.3 mVm^–1 in the equatorial plane of Nainital in the premidnight local time sector. Near midnight, there is a sharp transition from eastward field to a westward electric field of 0.2–0.7 mV m^–1 for Gulmarg, 0.3–0.5 mV m^–1 for Nainital and 0.1–0.3 mVm^–1 for Varanasi.     

Whistler wave cascades in solar wind plasma

Non-linear, three-dimensional, time-dependent fluid simulations of whistler wave turbulence are performed to investigate role of whistler waves in solar wind plasma turbulence in which characteristic turbulent fluctuations are characterized typically by the frequency and length-scales that are, respectively, bigger than ion gyrofrequency and smaller than ion gyroradius. The electron inertial length is an intrinsic length-scale in whistler wave turbulence that distinguishably divides the high-frequency solar wind turbulent spectra into scales smaller and bigger than the electron inertial length. Our simulations find that the dispersive whistler modes evolve entirely differently in the two regimes. While the dispersive whistler wave effects are stronger in the large-scale regime, they do not influence the spectral cascades which are describable by a Kolmogorov-like   k ^−7/3  spectrum. By contrast, the small-scale turbulent fluctuations exhibit a Navier–Stokes-like evolution where characteristic turbulent eddies exhibit a typical   k ^−5/3  hydrodynamic turbulent spectrum. By virtue of equipartition between the wave velocity and magnetic fields, we quantify the role of whistler waves in the solar wind plasma fluctuations.     

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).     

Coupled mode propagation in PP micropulsation ducts

The ducted propagation of PP micropulsations along field-aligned columns of enhanced ionization is considered, the ‘dotting’ of PP spectrograms being regarded as a consequence of simultaneous propagation along a group of such ducts. Theory introduced in a previous paper is modified so as to remove an inconsistency, and as a result of this modification there is coupling between the two types of circular polarization (L and R) which occur. Dispersion of a PP wave packet is, however, still characteristic of L mode propagation, and interpretation of PP spectrograms is largely unaffected.     

Occurrence of abnormal Sq (H) phase in the equatorial electrojet region

From an analysis of published geomagnetic data of stations in the Indian equatorial region, it is shown that on days with an abnormal S_q (H) phase limited to the electrojet belt, conditions characteristic of complete or partial counter-electrojet prevail around the usual time interval of the diurnal maximum of the H-field.     

Dynamo region and the equatorial electrojet in the Jovian atmosphere

The existence of the dynamo region is identified in the atmosphere of Jupiter. It is found that the dynamo region extends from an altitude of 130 km (0.153 mbar) to 330 km (0.027 μbar) reckoned from zero altitude corresponding to 43.8 mbar pressure level. Physical features of the equatorial electrojet in the ionosphere of Jupiter are modelled in detail. The Jovian equatorial electrojet has a maximum eastward current density of about 1.5 Akm^?2 at an altitude of 270km (0.33 μbar) with a latitudinal half width of about ±11°. The thickness of the equatorial half width is 100 km in altitude range. The type I instability in the electrojet can exist only if the electron streaming velocity exceeds the value of about 250 m s^?1.     

Rotation of the large-scale solar magnetic fields in the equatorial region

A study is made of the rotation of large-scale magnetic fields using the synoptic maps from the Kitt Peak National Observatory for the time interval 1976–1985. The auto-correlation method and the mass-centers method of magnetic structures was applied to infer mean differential rotation profiles and rotation profiles separately for each magnetic field polarity. It has been found that in both hemispheres the leading polarity rotates faster than the following polarity at all latitudes by about 0.04° day^–1. The maximum rotation rate of the leading polarity is reached at about 6° latitude. In the mean profile for both polarities, this brings about two angular velocity maxima at 6° latitudes in both hemispheres. Such a profile appears as to have a dimple on the equator.     

Periodicities and asymmetry of the jovian activity in the equatorial region

The atmospheric activity in the equatorial region of Jupiter, approximately in the zone between the zenocentric latitude ±12° has been studied during the period 1963-1967 by computing the photometric coefficient of activity.A north-south asymmetry has been found. Different periodicities of the activity for zones of different latitudes are found.     

A wave driven model of the Jovian equatorial jet

We explore the consequences of assuming that the equatorial jet, which is the most prominent feature of the atmospheric motions on Jupiter, is driven by vertically propagating Kelvin and mixed Rossby-gravity waves that are absorbed during their passage through the stratosphere to produce a mean zonal flow. Since even the basic atmospheric parameters on Jupiter are still largely a matter of conjecture, we are not able to produce a unique model but one that can span a whole range of possible conditions and which can be refined (or rejected) as more information becomes available.     

Do we need a surface wave approach to the magnetospheric resonances?

In this paper we study a possible existence of surface wave (SW) global modes of the outer magnetosphere. The SW modes are supported by two plasma discontinuities: the plasmapause and the boundary between the open and closed field lines of the magnetosphere. Conditions under which the SW global modes can propagate azimuthally and along the magnetic field lines are examined. The ionosphere at the ends of the field lines is considered as reflecting boundaries of these SW modes. As a result SW standing wave structures along the magnetic field fluxes can be formed. Two branches of SW modes are derived. The low frequency branch, f_s,1 falls in the Pc5 range, while the high frequency branch, f_s,2—in the Pc4 range, where f_s,1(2) is the fundamental SW global mode frequency. Their frequencies possess quantized properties in the following way: f≡(1,2,3, …)f_s,1(2). The high frequency SW branch, f_s,2 exists only for relatively great azimuthal wavenumbers k_⊥. It is pointed out that most of the SW global mode characteristics are similar to those of the FLR. These results are applied to 1.8 mHz global mode observations on 11 January 1997. Spectral, phase and polarization properties of this Pc5 pulsation event under northward IMF conditions are examined as we see them from ground-based (L’Aquila and TNB observatories) and satellite (POLAR and INTERBALL) observations.     

Electromagnetic wave propagation and instabilities in the magnetosphere

Growth rates for both the RH- and LH-modes of an EM wave propagating along a magnetic field through an isotropic loss-cone plasma have been obtained. It is found that growing modes can exist, and are found to depend critically on the mirror ratioR, and the specific details of the distribution function of the energetic component. To study the energetic-particle distribution observed at low energies by satellites within the magnetosphere, an isotropic double-humped loss-cone velocity distribution is then studied with a view to determining whether the secondary hump can introduce an instability not present for monotonic distribution. It is found that such a distribution can be unstable in a mirror geometry if the energetic component is sufficiently monoenergetic. Within the magnetosphere, nearly monoenergetic fluxes are observed, peaking in the energy range 1–10 keV, depending on the McIlwain parameterL. It is possible that the initial injection of monoenergetic particles may have been much more sharply peaked than the one presently observed, and, as a result of wave-particle interactions, subsequently relaxed to the presently observed distribution. It is seen here that the EM waves within the magnetosphere can contribute to the relaxation of such an initial injection.     

Shock wave propagation in non-ideal fluids

Expressions for the variation of shock strength and its propagation in non-ideal fluids are presented by using the method developed by Whitham. The effects of the presence of rotation, rotation and magnetic field on the strength and propagation velocity of shock waves have been discussed separately. Finally, the effects of the presence of gravitation on the shock strength and on propagation velocity have been studied.     

A study of blanketing sporadic E in the equatorial region

Ionosonde data, obtained on blanketing sporadic E at some equatorial stations during the I.G.Y. have been analysed to yield temporal and latitude variations. The results are compared with corresponding ones for the middle latitudes and they are also discussed in the light of the wind-shear mechanism. The main features of the occurrence frequency are (i) the absence of a morning peak in the daily variation, (ii) an equinoctial maximum and a June-solstitial minimum, (iii) and a stronger dependence on the dip angle (or geomagnetic latitude) than on geographic latitude. The latitude variation obtained also suggests that blanketing sporadic E would occur over both the dip and geomagnetic equators.     

Spherical shock wave propagation in self-gravitating stars

The problem of shock wave propagation in a heat-conducting and self-gravitating medium has been studied. The shock is strong enough so that the ambient gas pressure can be neglected. The variation of velocity, density, temperature, and mass distributions behind the shock have been obtained from a numerical solution of similarity equations involved.     

Geology of the Venus equatorial region from Pioneer Venus radar imaging

Pioneer Venus radar data has provided images (resolution 20- to 40-km) of approximately 50% of the total surface of Venus in a band between 45 ° N to 15 ° S. These data are used to map the broad radar characteristics of the equatorial region on the basis of radar brightness and texture. Seven radar units are defined and are used to assess the geologic character of the equatorial region. These units fall into two distinct classes, those that are radar-bright (35% of the equatorial region) which correspond to highlands and zones of intense tectonic deformation, and radar-dark units, corresponding primarily to plains (65% of the equatorial region). The correspondence between features in the 15 ° region of overlap between the Pioneer Venus and Venera 15/16 images is examined and used to extend units mapped in the northern high latitudes into the equatorial region. On the basis of the distribution of the radar units, properties of RMS slope, reflectivity, the scattering behavior of the surface, and topographic signature, seven physiographic units are mapped in the equatorial region and are identified by increasing complexity as plains (undivided), dark halo plains, upland rises, upland plateaus, interhighland tectonic zones, tectonically segmented linear highlands, and tectonic junctions. The physiographic units are distributed in a nearly continuous interconnecting zone of volcanic rises and tectonic features that extends for nearly 360 ° around the equator of the planet. The distribution of large circular structures interpreted as coronae is also examined and it is concluded that the abundances of the largest structures, diameters greater than 500 km, is less than in the northern high latitudes with a notable absence of smaller coronae. The absence of small coronae may be due to the resolution limit of the Pioneer Venus data since analyses of higher resolution Arecibo and Goldstone imagery suggests that a number of corona-like features not identified in the PV data are present.'Geology and Tectonics of Venus', special issue edited by Alexander T. Basilevsky (USSR Acad. of Sci. Moscow), James W. Head (Brown University, Providence), Gordon H. Pettengill (MIT, Cambridge, Massachusetts) and R. S. Saunders (J.P.L., Pasadena).     

Daily variation of the geomagnetic field in equatorial region and sector boundary passage

The mean daily range in horizontal intensity at low latitudes shows a significant departure on the day of a sector boundary passage in relation to its magnitude on adjacent days with a measure of dependence on phase of the solar activity. It is shown that this arises because of a substantial difference, in the nature of the response to sector boundary passage, between the instantaneous maximum field and minimum field. From the fact that the responses at three stations spanning the latitudes near dip equator to that near the focus of Sq currents are almost identical, it is suggested that the cause of the observed feature is primarily disturbance and is essentially non-ionospheric. Differences in the nature of responses between pre-1957 and post-1957 periods reported earlier in the planetary indices or low latitude disturbance indices are shown to be true for the daily range, maximum and minimum fields at low latitudes.     

Energy dissipation in wave propagation in general-relativistic plasma

Based on a recent communication by the present authors the question of energy dissipation in magnetohydrodynamical waves in an inflating background in general relativity is examined. It is found that the expanding background introduces a sort of dragging force on the propagating wave such that, unlike the Newtonian case, energy gets dissipated as it progresses. This loss in energy having no special-relativistic analogue is, however, not mechanical in nature as in case of an elastic wave. It is also found that the energy loss is model dependent and also depends on the number of dimensions.