摘要:

Observations with the SAS 2 high‐energy γ ray telescope have been used in a study of the earth albedo γ radiation above 35 MeV in the equatorial region. The γ ray intensity has a peak toward the horizon which is about a factor of 10 more intense than the radiation coming up from the nadir. The horizon is about 2 orders of magnitude more intense than the cosmic γ radiation from most parts of the sky. The radiation from the western horizon is about 4 times as intense as the radiation from the eastern horizon and about 3 times as intense as that from the northern or southern directions. This azimuthal variation results from geomagnetic effects on the incident cosmic rays which interact in the atmosphere to produce the albedo γ rays. The upcoming high‐energy γ ray intensity seen with SAS 2 has a variation with vertical cutoff rigidity consistent with the empirical relationship ofR−1.13 obtained by Gur'yan et al. (1979). The integral photon number spectrum from the horizon has an energy dependence ofE−(1.0±0.1), which is flatter than the spectrum seen from the nadir,E

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01265

年代:1981

数据来源: WILEY

摘要:

From presently available observations one can infer that the Alfvénic turbulence measured in the solar wind, predominantly on trailing edges of high‐speed streams, is a mixture of modes with two different polarizations, namely, Alfvénic modes and modes which are the incompressible limit of slow magnetosonic waves. Using Helios 2 magnetic data and a variance analysis, we have separated parallel (to the mean field) and perpendicular components of the fluctuations and studied the possible correlation between such components which would be predicted as a consequence of the incompressible character of the turbulence. Correlations between eigenvalues of the variance matrix are also investigated and discus

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01271

年代:1981

数据来源: WILEY

摘要:

Electrostatic ion waves with frequencies 0.5–6 kHz are often detected in the solar wind upstream of the bow shock. The ion waves are correlated with the low‐frequency magnetic field fluctuations that are driven by upstreaming protons of energies 4–7 keV. In terms of the frequency of occurrence, the ion waves occur primarily in the region connected to the bow shock by the solar wind magnetic field. The ion waves therefore appear to be driven by a beam‐plasma interaction involving the 4‐ to 7‐ keV protons streaming into the solar wind along magnetic field lines connected to the bow shock. A statistical study of the characteristic ion wave spectrum suggests that it may contain waves similar to Buneman waves with rest frame frequenciesf∼3.5fpi, wherefpiis the ion plasma frequency and wavelengths λ ∼ km. We suggest that the ion waves are driven by a Landau resonant wave‐particle interaction with the 4‐ to 7‐keV protons, after initial excitation by upstreaming suprathermal electrons. The study suggests that previously detected ion acoustic waves are not the only waves associated with upstreaming protons. Bragg scattering off ion waves with wavelengths of 1–2 km is suggested to explain distant (>0Re) source locations for terrestrial kilometric radiation. The ion waves are also suggested as a possible upstream agent for stochastically accelerating the>30‐keV protons that are correlated with the upstreaming 4‐ to 7‐keV protons. Electron plasma oscillations, associated with upstreaming electrons, often appear to be anticorrelated with the ion waves, implying some interaction that damp

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01279

年代:1981

数据来源: WILEY

摘要:

An attempt is made to interpret solar wind variations observed at the earth's distance, namely the solar cycle variations, the semi‐annual variations, and the 27‐day variations, as well as the polarity changes of the interplanetary magnetic field, mainly in terms of two effects, a positive latitudinal gradient of the solar wind speed and a wobbling solar dipole, combined with the annual (heliospheric) latitudinal excursion of the earth. It is shown that a significant part of the solar wind variations observed at the earth's distance and the changes of polarity pattern of the interplanetary magnetic field can be reasonably well reproduced by the two effe

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01290

年代:1981

数据来源: WILEY

摘要:

Strong evidence is presented for escape of magnetospheric particles along reconnected field lines into the magnetosheath, using observations of ∼30‐ to ∼120‐keV/charge protons and alpha particles made by the Max‐Planck‐Institut/University of Maryland instrument on Isee 1. During three magnetopause crossings, which have been identified from tangential stress balance analysis as reconnection events, the magnetospheric particle distribution extends well into the magnetosheath, and the particles in the magnetosheath show a strong anisotropy along the magnetic field. The proton to alpha particle ratio in this layer as well as in distinct bursts within the magnetosheath is the same as this ratio within the magnetosphere (at equal energy per charge). We conclude that the most likely explanation for these observations is that magnetospheric particles are escaping along reconnected field lines into the magnetosheath. It is argued that magnetospheric particles are seen in the magnetosheath up to the reconnection separatrix, and the magnetosheath bursts are interpreted as multiple encounters of this magnetosheath layer by the satellite due to bound

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01299

年代:1981

数据来源: WILEY

摘要:

This paper examines the possible occurrence of tearing modes in the dayside magnetopause. First, the expected magnetic signature of tearing, as obtained from existing theory, is reviewed. Magnetometer data from one terrestrial magnetopause crossing and one crossing of Jupiter's magnetopause are then examined in detail. Magnetic field oscillations are found in three subsegments of the terrestrial crossing at a frequency of 0.1–0.2 Hz and with peak amplitudes of 5‐10 nanotesla (nT), and in one segment of the Jovian crossing, at 0.05–0.1 Hz and with 2‐nT amplitude. The frequency range, as well as the orientation of the magnetic field perturbation vectors, agrees with a model in which tearing‐produced magnetic islands are convected past the satellite with the plasma flow in the current layer. In both cases the magnetopause structure was of the rotational discontinuity type with a nonvanishing normal magnetic field component. Hence, if the tearing structures were active, i.e., growing, at the observation site, ion tearing (or perhaps resistive tearing, with the resistivity provided by microturbulence) must be invoked. But it is also possible that the structures were passive, consisting of ‘debris’ from active tearing elsewhere on the magnetopause surface, this debris being convected along the magnetopause past the obs

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01305

年代:1981

数据来源: WILEY

摘要:

High‐resolution NO (X²Π, Δυ=1) emission data, obtained in an aurora between 100 and 125 km by the rocket‐borne HIRIS cryogenic interferometer spectrometer, have been analyzed by a spectral simulation/least squares technique. The vibrational state population distributions determined by this method exhibit significant population of up to six vibrational states of NO and a multimodal behavior with vibrational quantum number that is not predicted by present models. This result is interpreted in terms of direct auroral formation of NO(υ) by the chemiluminescent reaction of N(²D) with O2, coupled with excitation of NO(υ=1) by collisions between thermal atomic oxygen and aurorally enhanced NO(υ=0). The distribution shapes and their apparent invariance between 100 and 125 km suggest that collisional relaxation of NO(υ), probably by atomic oxygen, prevails over radiative cascade at these altitudes; this result is not in keeping with the present understanding of the kinetics and component densities in this region. The apparent auroral photoefficiency for NO(Δυ = 1) radiation deduced from these measurements is 1.1±0.4% over the range 100–125 km, with a calibration uncertainty of a factor of 2.5; approximately 70–90% of the observed radiation is directly excited via

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01313

年代:1981

数据来源: WILEY

摘要:

A statistical study of 215 magnetic pulsation events identified on the basis of waveform and period as Pc 4 (45‐ to 150‐s period) observed at synchronous orbit by ATS 6 is reported. The study was designed to be similar to that done with Pc 3 (10‐ to 45‐s period) by Arthur et al. (1977). These Pc 4 are found to occur most often near 1800 local time but are observed at all local times. The dominant period is ∼100 s, but a secondary peak in the distribution occurred at ∼53 s. They tend to be nearly linearly polarized, principally transverse to the ambient magnetic field. The Pc 4 are found to divide naturally into two classes (radial and azimuthal) on the basis of the azimuth of the major axis of polarization. These classes divide further into low‐frequency (≤0.015 Hz) and high‐frequency (≥0.015 Hz) classes. These four classes organize the remaining wave characteristics quite well. Division of the Pc 4 events into these classes does not lead to identification of a single source mechanism as it did with Pc 3. However, some correspondence between the classes and various proposed me

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01325

年代:1981

数据来源: WILEY

摘要:

Twenty‐two days of data from the Lochkeed ion mass spectrometer aboard the Scatha satellite were used to perform a statistical study of short‐lived H+and O+bursts observed in the equatorial magnetosphere. The results of the study indicate that the ion bursts were transient phenomena occurring primarily in the nighttime sector during periods of enhanced geomagnetic activity. The average energy of the bursts, 〈W〉, was 1 keV, although the bursts were found to occur over any portion of the instrument's 100‐eV to 32‐keV energy range. Over one third of the observed bursts were associated with field‐aligned electrons flowing from the same hemisphere as the bursts. The energy width (ΔW/〈W〉 ≃1) and the pitch angle width (as great as 30°) of the bursts suggest that the ions had undergone substantial velocity space diffusion close to th

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01335

年代:1981

数据来源: WILEY

摘要:

Using magnetic data from the high‐latitude North American IMS network, Pi 3 pulsations having periods 6–25 min are analyzed. The latitude and magnetic local time distributions of the sense of polarization and the position of maximum intensity for Pi 3 pulsations are studied. These characteristics are compared with those of other pulsations such as Pc 5 and Pi 2. The following characteristics are found: (1) In the Xm‐Ymplane in dipole coordinates, regions of right‐handed (R) and left‐handed (L) polarizations are clearly separated during daytime; in the morning the R region is at higher latitudes than the L region, and in the afternoon the relative positions are reversed. The dividing line of the two regions is approximately at 70° dipole latitude at dawn and dusk and is about 75° latitude near noon. Between 2100 and 0500 MLT there are small R or L regions and a large mixed region. (2) For the polarization in the Xm‐Z plane the distribution is rather simple; namely it shows predominantly L polarization on the dayside and R polarization on the nightside, where the sense of polarization is defined by viewing the Xm‐Z plane from its west side. (3) The gross daytime distributions of the Pi 3 pulsations are similar to those for Pc 5, while the nightside distributions resemble those for Pi 2. (4) The maximum amplitude of Pi 3 occurs near the auroral electrojet region around midnight, while it is at much higher latitudes during late morning hours. For each of the three components, Xm, Ym, and Z, the locus of maximum amplitude forms an oval shape, but the oval does not coincide with Feldstein's auroral oval. On the basis of the morphological characteristics of Pi 3 pulsations found by the present analysis, we believe that dayside Pi 3 pulsations have a different generation mechanism from that for nightside Pi 3 events. The Kelvin‐Helmholtz instability on the magnetopause is likely to be the primary excitation source for the daytime Pi 3 events. For the cause of the nightside Pi 3 pulsations, oscillations of a magnetospheric‐ionospheric current system appear to be a m

ISSN:0148-0227    

DOI:10.1029/JA086iA03p01345

年代:1981

数据来源: WILEY