摘要:

The time evolution of the ring current population during the recovery phase of a typical moderate magnetic storm is studied, using a newly developed kinetic model for H+, He+and O+ions which includes nonequatorially mirroring particles. The bounce‐averaged distribution function is defined for variables that are accessible to direct measurement, and some useful formulas for calculating the total energy and number density of the ring current are derived. The bounce‐averaged kinetic equation is solved, including losses due to charge exchange with neutral hydrogen and Coulomb collisions with thermal plasma along ion drift paths. Time‐dependent magnetospheric electric fields and anisotropic initial pitch angle distributions are considered. The generation of ion precipitating fluxes is addressed, a process that is still not completely understood. It is shown that both the decrease of the distribution function due to charge exchange losses and the buildup of a low‐energy population caused by Coulomb collisions proceed faster for particles with smaller pitch angles. The maximum of the equatorial precipitating fluxes occurs on the nightside during the early recovery phase and is found to be of the order of 104–105cm−2sr−1s−1keV−1. The mechanisms considered in this paper indicate that magnetospheric convection plays the predominant role in causing ion precipitation; Coulomb scattering contributes significantly to the low‐energy ion precipitation insi

ISSN:0148-0227    

DOI:10.1029/95JA02000

年代:1996

数据来源: WILEY

摘要:

The phase and spectral characteristics of long‐period geomagnetic pulsation wave trains consisting of two overlapping responses to independent excitations are investigated. The major purposes of the work are to expand diagnostic processes in pulsation analysis and to use these techniques to determine the phase and spectral characteristics of these wave trains. It is shown that the inherent phase and amplitude modulation in such wave trains can significantly alter the power spectrum and can introduce either a phase jump or a phase skip. When the two individual responses have the same underlying (carrier) frequency, the spectral peak or peaks of the composite wave train can be offset from the carrier frequency, and these offsets are associated with a phase jump or skip. These phase and spectral characteristics are dependent on the difference in phase between the two responses and on the extent of their overlap. Analytic signal representation of our modeled wave trains yields more accurate estimates of the underlying pulsation frequency than do the power spectra. When the frequencies of the two responses differ, the phase and spectral characteristics become more complex. Finally, the analytic approach is applied to a real pulsation even

ISSN:0148-0227    

DOI:10.1029/95JA03193

年代:1996

数据来源: WILEY

摘要:

Knowledge of the average size and shape of the near‐Earth magnetotail is an essential element for our understanding of the magnetospheric response to the influence of the solar wind. An empirical model of the near‐Earth magnetotail has been developed, which depends upon distance downtail (xGSM), the solar wind momentum flux (ρv2sw), and the zGSMcomponent of the interplanetary magnetic field (IMFBz). This model has been created by using the pressure balance relation to calculate a set of flare angles for the nightside magnetopause in the region −22RE≤xGSM≤ −10RE. Observations of the magnetic field in the lobe by ISEE 2 and simultaneous observations of the magnetic field and plasma properties of the solar wind by IMP 8 were used to determine the internal and external pressure components, respectively. Examination of calculated flare angle values reveal a dependence upon downtail distance and ρv2sw. Normalized to the median downtail distance and dynamic pressure, the angle of flare of the magnetopause is found to increase linearly with decreasingBzwhen the IMF is southward, but there is little variation when the IMF is northward. The empirical function derived for the flaring angle of the magnetotail is used to determine a relation for the radius of the tail. Comparisons with previous empirical models and results are also performed. In addition, values of magnetic flux within the magnetotail are calculated for times of sudden i

ISSN:0148-0227    

DOI:10.1029/95JA02834

年代:1996

数据来源: WILEY

摘要:

From 2000 UT on March 17 to 0400 UT on March 18, 1993, when Geotail was in the distant tail, it underwent a series of mantle crossings. These mantle crossings are manifested in the magnetic field and plasma data as smooth excursions between magnetosheath values and lobe values. We test the one‐dimensional self‐similar MHD slow mode expansion fan model of the mantle by comparing the modeled predictions with the data, including, for the first time, magnetic field data. We use the measured speed, density, magnetic field strength, ion and two different electron temperatures to initialize the mantle flow. Using this range of upstream parameters, we show that the model reasonably well brackets the observed variations of both magnetic field and plasma parameters through the mantle. The total pressure through the modeled fan remains constant as the thermal pressure at the outer edge converts into magnetic field pressure at the inner edge. Using the modeled fit, we estimate the mantle to be 10–12 RE

ISSN:0148-0227    

DOI:10.1029/95JA02724

年代:1996

数据来源: WILEY

摘要:

An extended analysis of the kinetic stability theory of a current sheet in a curved and sheared magnetic field reversal with respect to a tearing mode perturbation is presented. The coupling between quasi‐parallel and quasi‐perpendicular mode components is newly taken into account. We obtain that an unstable branch of tearing mode instability with a growth rate less than the electron bounce frequency can be excited. The dependencies of the growth rate of this instability on the shear (Bs) and normal (Bn) field components as far as on the wave length of the mode are illustrated. The resulting tearing mode destabilization takes place favorably for an inclination of the magnetic field near the quasi‐neutral plane at about 45° with respect to the neutral plane. Our theory reveals that for proper geometry of magnetic field lines in field reversal region a collisionless ion tearing mode can be triggered and magnetic flux ropes are formed. The growth of the unstable tearing mode can be accompanied by the generation of magnetic field aligned electric fields and ion accele

ISSN:0148-0227    

DOI:10.1029/95JA02450

年代:1996

数据来源: WILEY

摘要:

The energy principle for magnetotail tearing is reexamined using conservation of electron particle number along a flux surface as a means of calculating the volume‐integrated perturbed number density 〈n1〉, wheren1is the perturbed electron number density and the angle brackets denote integration along a field line. It is shown that if the electron response is magnetohydrodynamic, then 〈n1〉 can be calculated as a function of the perturbation vector potential componentA1y(assuming magnetotail coordinates) independent of the potential componentsA1xandA1zand independent of the scalar potential ϕ. This result holds as long as the equilibrium and the tearing perturbations are two‐dimensional, independent of theycoordinate. In the case of a parabolic field model, the resulting 〈n1〉 exactly matches the results obtained previously byLembége and Pellat[1982], who used the kinetic drift equation to calculate the electron response. Thus the compressional stabilization of the tearing mode is a direct consequence of, and can be completely calculated from, the conservation of electron particle number along the field line. Further, it is shown that 〈n1〉 is independent ofBy, the guide component of the magnetic field, so the inclusion of a guide field does not alter the tearing st

ISSN:0148-0227    

DOI:10.1029/95JA02986

年代:1996

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/95JA03200

年代:1996

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/95JA03382

年代:1996

数据来源: WILEY

摘要:

A Fabry‐Perot spectrometer is used at Sondre Stromfjord, Greenland, during periods of quiet auroral conditions to isolate the resonant fluorescent component of the geocoronal atomic hydrogen Balmer alpha emission. The data demonstrate that we can detect a weak, 8‐rayleigh emission with signal‐to‐noise ratio of 6 using 25‐min of integration. Moreover, these observations have sufficient spectral resolution to determine effective exospheric temperatures with statistical uncertainties of about 35%. Energetic neutral hydrogen, due presumably to neutralized proton precipitation, appears in the line profile background, and, as such, is distinct from the quiescent, less energetic, geocoronal component excited by resonant fluorescence of solar Lyman bet

ISSN:0148-0227    

DOI:10.1029/95JA01818

年代:1996

数据来源: WILEY

摘要:

Airglow enhancement observations have been considered as supporting evidence of electron acceleration in ionosphere heating experiments by high‐power HF waves. Here we analyze some of the 6300‐Å airglow data from the Platteville, Colorado, heating experiments of 1970, employing new electron impact excitation rates for the O(1D) state and empirical, but in accord with experimental and theoretical constraints, plasma heating rates and show that these airglow enhancements should be attributed to excitation by thermal electrons. An important aspect of the present analysis is the excellent agreement of the observed and the calculated airglow enhancements over several complete transmitter on/off cycles of several minutes duration and an increasing airglow trend of 1 hour duration. The fact that the OI red line may be thermally excited and the scarcity of observations of simultaneous OI red and green line enhancements imply that electron acceleration, even to a few eV, may require very special experimental and ionospheric conditions that are not very often real

ISSN:0148-0227    

DOI:10.1029/95JA02760

年代:1996

数据来源: WILEY