摘要:

Using the standard quasi‐linear Fokker‐Planck approach and an expansion of the cosmic ray distribution function in Legendre polynomials, we derive a complete set of Fokker‐Planck coefficients and expressions for the complete cosmic ray diffusion tensor due to linearly polarized planar Alfvén waves propagating at an angle to the average magnetic field. We find that although an off‐diagonal term formally appears in the diffusion tensor, it is identically zero. In addition, the cross‐field diffusion coefficient is identically the same as that found for wave propagation exactly parallel to the average magn

ISSN:0148-0227    

DOI:10.1029/JA080i019p02701

年代:1975

数据来源: WILEY

摘要:

An updated analysis and interpretation are presented of the magnetic field observations obtained during the Mariner 10 encounter with the planet Mercury on March 29, 1974. The combination of data relating to position of the detached bow shock wave and magnetopause and the geometry and magnitude of the magnetic field within the magnetospherelike region surrounding Mercury lead to the conclusion that an internal planetary field exists with dipole moment approximately 5.1 × 1022G cm³. The limited data set precludes quantitative determination of an intrinsic field more complex than a centered dipole. The dipole axis has a polarity sense similar to that of earth and is tilted 7° from the normal to Mercury's orbital plane. The magnetic field observations reveal a significant distortion of the modest Hermean field (350 γ at the equator) by the solar wind flow and the formation of a magnetic tail and neutral sheet which begins close to the planet on the night side. Presently, an active dynamo mechanism in the planetary interior appears to be favored in the interpretation of the field origin, although fossil remanent magnetization cannot be excluded. The composite data set is not consistent with a complex induction process driven by the solar wind f

ISSN:0148-0227    

DOI:10.1029/JA080i019p02708

年代:1975

数据来源: WILEY

摘要:

An objective method of inferring the polarity of the interplanetary magnetic field using theHcomponent at Godhavn is presented. The objectively inferred polarities are compared with a subjective index inferred earlier (Svalgaard, 1972b). It is concluded that no significant difference exists between the two methods. The inferred polarities derived from GodhavnHare biased by theSqpsignature in the sense that during summer, prolonged intervals of geomagnetic calm will result in inferred away polarity regardless of the actual sector polarity. This bias does not significantly alter the large‐scale structure of the inferred sector structur

ISSN:0148-0227    

DOI:10.1029/JA080i019p02717

年代:1975

数据来源: WILEY

摘要:

Comprehensive plasma observations carried out on board the Heos 2 satellite have provided the first systematic description of plasmas in the distant polar magnetosphere. These observations have revealed the presence of a persistent layer of tailward‐flowing magnetosheathlike plasma inside of and adjacent to the magnetopause. This region has been termed the ‘plasma mantle.’ The mantle has been found to extend over the entire surface of the magnetosphere tailward of the polar cusp and northward of the plasma sheet. Vela observations of a ‘magnetotail boundary layer’ obtained in the vicinity of the plasma sheet by Hones and coworkers refer to the same phenomenon. The salient features of the plasma mantle as provided by Heos measurements from February to December 1972 can be summarized as follows: (1) The mantle was found to be present in over 70% of the passes through the polar magnetosphere in the region described above. (2) Its thickness varies greatly, ranging up to ≳ 4RE, and does not appear to depend significantly on position or the state of the magnetosphere as measured byKp. (3) A tailward‐directed bulk flow parallel to the local terrestrial magnetic field was nearly always distinctly measurable. It was found to lie usually between 100 and 200 km s−1and was always less than the concurrent flow speed in the nearby magneto sheath. (4) The flow speed in the mantle is positively correlated with the flow speeds in the magnetosheath and solar wind but depends only very weakly, if at all, on distance from the polar cusp, i.e., onXGSM. (5) A narrow region of low density and/or low flow speed plasma, i.e., a ‘gap,’ 0.1–0.2REthick, is frequently observed between the plasma mantle and the magnetopause. (6) The mantle protons are normally significantly cooler alongBthan perpendicular, i.e.,T∥

ISSN:0148-0227    

DOI:10.1029/JA080i019p02723

年代:1975

数据来源: WILEY

摘要:

Near dawn on October 9, 1972, UT, a barium plasma injection experiment was carried out from Poker Flat, Alaska, during quiet magnetic conditions (Kp= 1+). The visible plasma flux tube produced was more diffuse than the flux tubes in previous experiments, but it could be tracked for 30 min out to an altitude of 2.5RE. The flux tube remained integral for about 20 min, when a single striation separated from the main streak. Comparisons of the observed flux tube orientation with theoretical field models show no significant deviations ascribable to field‐aligned currents. Cross‐field drift rates of the foot of the flux tube indicate anEfield of approximately 7 mV/m at 200‐km altitude. Although an attempt was made via a jet aircraft flight, barium ions were not detected in the southern conjugate region. No energetic particle precipitation phenomena were observed which could be ascribed to the barium plasma inje

ISSN:0148-0227    

DOI:10.1029/JA080i019p02738

年代:1975

数据来源: WILEY

摘要:

During the solar particle event of April 12–14, 1973, a flux depression of solar protons in the dawn side pseudotrapping region relative to the flux in the dusk side pseudotrapping region was frequently observed with the low‐altitude polar‐orbiting satellite Esro 4. This flux decrease is interpreted as being due to weak pitch angle scattering of the solar protons during their drift from dusk to dawn. Treating the pitch angle diffusion as a simple initial value problem, we derive quantitative values of the equatorial bounce‐averaged pitch angle diffusion coefficients at small pitch angles for different energies. These values represent lower limits for magnetospheric conditions at the time of the Esro 4 observations. Through the assumption that the pitch angle diffusion is a gyroresonant interaction process of the particles with either Alfvén or ion cyclotron waves, the necessary power of the waves at the resonant interaction frequency is ca

ISSN:0148-0227    

DOI:10.1029/JA080i019p02745

年代:1975

数据来源: WILEY

摘要:

In addition to the intense and highly variable auroral kilometric radiation the earth also radiates a weak nonthermal continuum from energetic electrons in the outer radiation zone. The intensity of this continuum radiation decreases with increasing frequency and is usually below the cosmic noise level at frequencies above 100 kHz. In this paper we show that the frequency spectrum of the continuum radiation consists of two components, a trapped component, which is permanently trapped within the magnetosphere at frequencies below the solar wind plasma frequency, and an escaping component, which propagates freely away from the earth at frequencies above the solar wind plasma frequency. The low‐frequency cutoff of the continuum radiation spectrum is at the local electron plasma frequency, which can be as low as 500 Hz in the low‐density regions of the distant magnetotail. Direction‐finding measurements and measurements of the spatial distribution of intensity for both the trapped and the freely escaping components are used to determine the region in which the continuum radiation is generated. These measurements all indicate that the continuum radiation is generated in a broad region which extends through the morning and early afternoon from about 4.0 to 14.0 hours local time immediately beyond the plasmapause boundary. In contrast to the auroral kilometric radiation, which is generated in the high‐latitude auroral zone regions, the continuum radiation appears to be generated over a broad range of latitudes, including the magnetic equator. In some cases the continuum radiation appears to be closely associated with intense bands of electrostatic noise which are observed near the electron plasma frequency at the plasmapause. Possible mechanisms by which this radiation could be generated, including gryosynchrotron radiation from energetic electrons in the outer radiation zone, are di

ISSN:0148-0227    

DOI:10.1029/JA080i019p02751

年代:1975

数据来源: WILEY

摘要:

Direction‐finding measurements with plasma wave experiments on the Hawkeye 1 and Imp 8 satellites are used to locate the source region of auroral kilometric radiation. This radiation has peak intensities between about 100 and 300 kHz and is emitted in intense sporadic bursts lasting for from half an hour to several hours. At peak intensity the total power emitted in this frequency range exceeds 109W. The occurrence of this radiation is known to be closely associated with bright auroral arcs which occur in the local evening auroral regions. Hawkeye 1 provides direction‐finding measurements of kilometric radiation from observations at high latitudes (5–20RE) over the northern polar regions, and Imp 8 provides similar observations at large radial distances (23–46RE) near the equatorial plane. Results from both satellites place the source of the intense auroral kilometric radiation in the late local evening at about 22.0 hours LT and at a distance of about 0.75REfrom the polar axis of the earth. These direction‐finding measurements, together with earlier results from the Imp 6 satellite, strongly indicate that the intense auroral kilometric radiation is generated by energetic auroral electrons at low altitudes in the evening auroral zone. The observed source location is in good quantitative agreement with the source position expected from simple propagation and ray path consi

ISSN:0148-0227    

DOI:10.1029/JA080i019p02764

年代:1975

数据来源: WILEY

摘要:

Observations of magnetospheric radio noise by the Goddard Space Flight Center radio experiment on the Imp 6 spacecraft have revealed a quasi‐continuous component at frequencies between 30 and 110 kHz. When the spacecraft is in the interplanetary medium or the magnetosheath, a low‐frequency cutoff often characterizes the otherwise power law (f−α) spectrum of this noise. A positive correlation is observed between this cutoff frequencyfcoand the solar wind plasma frequencyfsw, deduced from the Los Alamos plasma experiment on the same spacecraft; on the average,fco≈ 1.3fsw. If one pictures the magnetosheath as a homogeneous layer of plasma lying between the radio noise source (atL∼ 4‐7) and the spacecraft in the interplanetary medium and having an electron density 2–3 times that of the solar wind, then one will expectfco≳ 21/2fsw−31/2fsw. Within the limits of experimental error this simple model correctly accounts for the observations. A rough calculation shows that radio wave scattering by electron density fluctuations in the magnetosheath plasma is likely to be important for frequencies below 200 kHz. However, the effects of such scattering cannot be detected in the Imp 6 observations considered here because neither concurrent measurements nor sufficiently accurate models of the necessary magnetosheath plasma parameters are p

ISSN:0148-0227    

DOI:10.1029/JA080i019p02771

年代:1975

数据来源: WILEY

摘要:

The effect of different plasma parameters on the stability of the half‐harmonic electron gyrofrequency waves is investigated. By making some simplifying assumptions about the cold plasma and using a ring distribution for the warm component the role of the different parameters is demonstrated. A maximum value of the ratio of the cold to hot plasma density above which we cannot get instability is derived, and this ratio increases with the temperature anisotropy. Calculations of the growth rates show that there is a sharp peak when θ = tan−1k⊥/k∥

ISSN:0148-0227    

DOI:10.1029/JA080i019p02775

年代:1975

数据来源: WILEY