Particle and field observations from Explorer 45 during the December 1971 magnetic storm period

A discussion is presented of a Pc 5 magnetic pulsation event observed at L • 5.5 at the equator in the magnetosphere and at four ground stations in the vicinity of the foot of the field line through the satellite. A large degree of similarity is observed in the field variations in the azimuthal (E-W) component at all locations. The wave in the transverse plane at the satellite is right-handed polarized, whereas St the ground stations it is observed to be left-handed polarized at all latitudes. All of the observations are consistent with a model of a wave source with a narrow localization between L • 4.5 and L • 5.0 in the latitudinal direction and a long azimuthal wavelength. Hot plasma particle measurements made on the satellite during the time of the event suggest that the excitation of the drift mirror instability may produce the hydromagnetic waves. Magnetic pulsations in the Pc 5 frequency range (1.6-6.6 mHz), being generally of appreciable amplitude in and near the auroral zone, have been extensively studied over the years, and their morphological characteristics as observed on the ground have been summarized from rapid run and normal run magnetograms on a global statistical basis [e.g., Hirasawa, 1970; Saito, 1969; Jacobs, 1970; Barfield and McPherron, 1972a; Gupta, 1973]. Recently, latitudinal chains of observing stations have been used to study, more intensively, individual Pc 5 pulsation events [e.g., Obertz and Raspopov, 1968; Bji•rnsson et at., 1971; Samson and Rostoker, 1972; Samson, 1972], particularly with the view toward examining (1) the frequency dependence, with latitude, of individual events and (2) the reversals of polarization of the Pc 5 waves around some high-latitude 'demarcation line.' The statistical probability of occurrence of Pc 5 [Saito, .1969; Jacobs, 1970; Gupta, 1973] and Pi 3 [Morgan and Lanzerotti, 1973] frequency band magnetic pulsations as observed on the ground tends to indicate that one time interval of maximum occurrence probability lies in the hours around 1800 LT. Other than the survey of Heppner et at. [1970], which found a maximum of probability of occurrence of Pc 4 and Pc 5 compressional waves on the day side, no statistical study has been made of Pc 5 waves in the magnetosphere. The Pc 5 magnetic pulsations that have been studied within the magnetosphere have generally been confined to storm time observations [Brown et al., 1968; Lanzerotti et al., 1969; Son•nerup et al., 1969; Barfield and Coleman, 1970; Barfield et al., 1972; Barfield and McPherron, 1972a, b]. Few studies of simultaneous satellite-ground magnetic pulsation observations have been reported [Patel and Cahill, 1964; Patel, 1965; Lanzerotti and Tartaglia, 1972]. Indeed, with respect to Pc 5 events, Barfield et al. [1972] concluded th•tt Pc 5 frequency waves were not observed on the ground at the same time as their satellite wave observations within the magnetosphere. However, a later discussion [Barfield and McPherron, 1972b] made the painful but unfortunately true observation that the normal procedure...

Section: Would Suggest That Either This Is the Location Of The Disturmentioning

confidence: 94%

Storm time Pc 5 magnetic pulsation at the equator in the magnetosphere and its latitude dependence as measured on the ground

Lanzerotti¹,

Fukunishi²,

Lin³

et al. 1974

“…It was shown by Mauk et al [1996] This situation is very similar to the situation at Earth. Earth magnetospheric injections occur in regions where the plasma beta can be high and in the region of transition between dipolar and neutral sheet geometries [Hoffman, 1973;Williams, 1983;DeForest and Mcllwain, 1971;Kaufmann, 1987]. It is believed that the hot plasma injections are driven by energy that is stored in the form of magnetic fields and associated electric currents.…”

Section: Implications Of the Radial Distribution Of Injectionsmentioning

confidence: 99%

Storm‐like dynamics of Jupiter's inner and middle magnetosphere

Mauk¹,

Williams²,

McEntire³

et al. 1999

111

168

Abstract. The discovery of energy-time dispersed, charged particle signatures of dynamic, longitudinally confined charged particle injections within Jupiter's inner magnetosphere has been reported previously as measured in >20-keV particle intensities by the Galileo energetic particles detector (EPD). While these events have similarities to so-called substorm injections observed within the Earth's magnetosphere, it is unknown whether the driving mechanisms are similar. Over 100 Jovian injection events have now been documented between radial distances of -9 Rj (the inner boundary of most of the observations) and 27 Rj. Injections occur at all System III longitudes and local time positions. Similar to Earth magnetospheric injections, the Jovian injections occur throughout the broad radial region of transition between the quasidipolar and neutral sheet magnetic field configurations, and where the charged particle energy densities are competitive with the magnetic energy densities. The Jovian injections can be clustered in time, analogous to what often happens during well-known magnetic storms that occur in the Earth's magnetosphere. During one particular periapsis of Galileo's orbital trajectory, the magnetosphere was observed by EPD to become suddenly very disturbed with multiple injections following a prolonged period (>24 Earth hours) of relative quiescence. Because of the prestorm coincidence of a signature of an apparent Earth-like global magnetospheric disturbance, we hypothesize that this Jovian storm occurred when the inner and middle magnetosphere were triggered out of marginal stability by the passage of a magnetohydrodynamic fast mode wave launched at the magnetopause by a pressure variation in the interplanetary (solar wind) environment.

“…A convenient way to quantitatively illustrate the magnetic field distortions due to external current sources like the ring current is by means of the quantity AB, defined by Sugiura et al [1971] as the observed magnetic field magnitude minus the magnitude of a geomagnetic reference field. The eastward ring current lessens the effects of the westward current near the Earth so that the greatest magnetic field depression, i.e., the most negative AB values, occurs at radial equatorial distances of approximately 3 RE [Sugiura, 1972;Su and Konradi, 1975] even during magnetically active times [e.g., Hoffman, 1973]. Also, although ring current growth occurs predominately at afternoon and evening magnetic local times [e.g., Siscoe and Crooker, 1974, and references therein], the final particle and magnetic field distributions are fairly symmetric about the Earth [e.g., Smith and Hoffman, 1973] and are usually intensified relative to the initial quiet state.…”

Section: Jxb=vpmentioning

confidence: 99%

A magnetospheric magnetic field model with flexible current systems driven by independent physical parameters

Hilmer

Voigt

1995

A tilt-dependent magnetic field model of the Earth's magnetosphere with variable magnetopause standoff distance is presented. Flexible analytic representations for the ring and cross-tail currents, each composed of elements derived from the Tsyganenko and Usmanov (1982) model, are combined with the fully shielded vacuum dipole configurations of Voigt (1981). The ring current, consisting of axially symmetric eastward and westward currents fixed about the dipole axis, resembles that inferred from magnetic field observations yet permits easy control of inner magnetospheric inflation. The cross-tail current contains a series of linked current sheet segments which allow for the tilt-dependent flexing of the current sheet in the x-z plane and arbitrary variations in current sheet position and intensity along the length of the magnetotail. Although the current sheet does not warp in the y-z plane, changes in the shape and position of the neutral sheet with dipole tilt are consistent with both MHD equilibrium theory and observations. In addition, there is good agreement with observed AB profiles and the average equatorial contours of magnetic field magnitude. While the dipole field is rigorously shielded within the defined magnetopause, the ring and cross-tail currents are not similarly confined, consequently, the moders region of validity is limited to the inner magnetosphere. The model depends on four independent external parameters, namely, (1) the dipole tilt angle, (2) the magnetopause standoff distance, (3) the midnight equatorward boundary of the diffuse aurora, and (4) the geomagnetic index Dst. In addition, we present a simple but limited method of simulating several substorm related magnetic field changes associated with the disruption of the near-Earth cross-tail current sheet and collapse of the midnight magnetotail field region. These include the classic dipolarization of the near-Earth field and the reduction of the far-tail equatorial field accompanying current sheet thinning. This feature further facilitates the generation of magnetic field configuration time sequences useful in plasma convection simulations of real magnetospheric events. IntroductionA wide variety of currents are required to support the magnetospheric magnetic field structure in the presence of flowing solar wind plasma and the interplanetary magnetic field. In addition to the magnetic field generated in the Earth's interior, the major contributors to this structure include magnetopause currents, the ring and cross-tail currents, and a variety of field-aligned currents. The intensities of these currents fluctuate constantly as they feed into each other to form the global circuit. For this reason, a model of magnetic fields and currents must represent a diverse array of magnetospheric configurations as well as the "average" configurations. It must rely on physical magnetospheric and solar wind parameters and reproduce appropriate configuration changes. These changes include the distortion of magnetic field and its mapping characteristics ...