摘要:

Molecular nitrogen density measurements obtained from the neutral atmospheric composition experiment on board the Ogo 6 satellite are used to study the morphology of the polar energy deposition during periods of magnetic disturbances. The data presented were obtained for eight families of polar perigee passes during 1969 and 1970. The data show a strong magnetic local time and invariant latitude dependence, the majority of the energy deposition being in the night sectors, extending down from the pole well into the mid‐invariant latitude region

ISSN:0148-0227    

DOI:10.1029/JA082i004p00455

年代:1977

数据来源: WILEY

摘要:

Atomic nitrogen number densities in the upper thermosphere measured by the open source neutral mass spectrometer (OSS) on Atmosphere Explorer‐C during 1974 and part of 1975 have been used to construct a global empirical model at an altitude of 375 km based on a spherical harmonic expansion. The most evident features of the model are large diurnal and seasonal variations of atomic nitrogen and only a moderate and latitude‐dependent density increase during periods of geomagnetic activity. The model also suggests the presence of a substantial semiannual variation and of nighttime minima at mid‐latitudes. Maximum and minimum N number densities at 375 km for periods of low solar activity are 3.6 × 106cm−3at 1500 LST (local solar time) and low latitude in the summer hemisphere and 1.5 × 105cm−3at 0200 LST at mid‐latitudes in the winter hemisphere. The amplitude of the diurnal variation at equatorial latitudes is about

ISSN:0148-0227    

DOI:10.1029/JA082i004p00461

年代:1977

数据来源: WILEY

摘要:

An atmospheric emission line centered at 22,235 MHz has been detected repeatedly over the period of March–August 1975 with a radio telescope located at Westford, Massachusetts (42.5°N, 71.5°W). The line has also been detected in absorption against the sun's microwave continuum. From its exact coincidence in frequency with the well‐known 1.3‐cm line of the water molecule the line is identified with atmospheric water vapor. A mixing ratio distribution between altitudes of 50 and 80 km is derived from the measured line amplitude and shape. Mixing ratios as large as 15 ppm by volume, about 2 times larger than the maximum predicted by photochemical equilibrium calculations, are found at these mesospheric al

ISSN:0148-0227    

DOI:10.1029/JA082i004p00472

年代:1977

数据来源: WILEY

摘要:

Two mechanisms have been proposed for solar wind particle injection at the dayside magnetospheric cusps: magnetic merging and cross‐field diffusion. These two mechanisms are experimentally distinguishable in that they produce different latitudinal distributions of particles penetrating to the low‐altitude cusp. An examination of proton and electron measurements obtained by the AE‐C satellite in the low‐altitude dayside cusp reveals evidence of both types of injection processes. A majority of the injection events, especially the more intense fluxes, are best explained by a merging injection model in which cusp particles are confined to the poleward side of the last closed field line and have a characteristic energy that decreases with increasing latitudinal distance from the last closed field line. Less frequent and less intense injection events are better explained in terms of a diffusive injection of cusp particles onto closed dayside field lines with a characteristic energy that increases with increasing latitudinal distance from the last closed field line. Although diffusion appears to be quantitatively less important than merging in terms of the instantaneous particle injection rate, cross‐field diffusion nevertheless appears to proceed at an unexpectedly fast rate, possibly exceeding the Bohm diffus

ISSN:0148-0227    

DOI:10.1029/JA082i004p00479

年代:1977

数据来源: WILEY

摘要:

Data from two intervals when pulsation activity was simultaneously observed on both ATS 1 and Ogo 5 satellites are presented. The first example, a Pc 4, indicates that this pulsation is caused by a field line near L = 7 resonating in its second‐harmonic mode. This is inferred from both plasma density measurements and polarization characteristics. The wave was not observed at three ground stations in the vicinity of the satellite conjugate points. This indicates that Pc 4 waves are very localized in latitude and that a close array (<100 km) is needed to perform effective correlation with satellites. The second event, which is also in the Pc 4 band, can again be inferred to be a field line resonance from the polarization characteristic

ISSN:0148-0227    

DOI:10.1029/JA082i004p00492

年代:1977

数据来源: WILEY

摘要:

Data obtained by the Chatanika, Alaska, incoherent scatter radar have been used to study ionospheric electric fields, conductivities, and currents associated with three sudden commencements (sc) of geomagnetic activity which occurred on August 4, 1972. Each sc appears to have had a different ionospheric response. The first sc, which began at 0119 UT (1519 Alaskan Standard Time (AST)), showed a small rise in the electric field several minutes after sc onset. No change in the local ionospheric conductivity was noted. The second sc at 0220 UT (1620 AST) was linked to a large increase in the electric field and a small increase in particle precipitation. Both effects appear to have resulted from an equatorward shift of the auroral oval in response to the initiation of a sc‐triggered auroral substorm. The third sc at 2054 UT (1054 AST) came with an abrupt burst of 30‐ to 40‐keV electrons which increased the ionospheric Hall conductivity by a factor of 2. This sc was accompanied by a Pc 5 pulsation event. TheHcomponent variations of this event are well reproduced by the local ionospheric currents. TheDcomponent pulsations, however, show substantial disagreement. A large equatorward displacement of the midday auroral oval took place following this sc with intense particle impact ionization to altitudes as low as 60 km. Throughout the third sc, substantial ionization was present in theDregion arising from solar proton precipitation. No changes in theDregion electron densities were seen at sc onset, implying that the solar proton flux was not appreciably affected by the magnetospheric distur

ISSN:0148-0227    

DOI:10.1029/JA082i004p00499

年代:1977

数据来源: WILEY

摘要:

Low fluxes of stagnant or irregularly flowing plasma along the inside of the magnetopause, labeled as the entry layer by Haerendel and Paschmann, are observed on Explorer 33 orbits which cross the dayside magnetopause and on one orbit which skims the dawn flank. The data indicate that the entry layer is a permanent magnetospheric feature which extends across the dayside and along the flanks to large distances down the tail on dipolelike field lines between extensions of the northern and southern polar cusps. Pressure anisotropies are present in the entry layer but are often weaker and less frequent than those in the adjacent magnetosheath. These anisotropies give clues about the process of entry layer formation. The sense of anisotropy when it is present on both sides of the magnetopause is the same for magnetosheath fields with a southward component and opposite for fields with a northward component. These correlations are consistent with entry layer filling by bulk flow along field lines opened by magnetic merging in the one case and by diffusion onto closed field lines in the other.

ISSN:0148-0227    

DOI:10.1029/JA082i004p00515

年代:1977

数据来源: WILEY

摘要:

The amplitude behavior of several hundred VLF whistler mode pulse signals and of their associated artificially stimulated emissions (ASE's) has been analyzed with digital signal processing techniques. A survey of the results indicates that the pulse signals characteristically show exponential growth with time that is highly repeatable over short periods. However, the growth rate varies widely from time to time, covering a range of 25–250 dB/s. During the exponential growth phase of the pulse there is no observable change in frequency. Emissions may begin when growth stops or when the input pulse terminates, whichever occurs first. Low growth rates and falling emissions characterize the beginning and ending of extended periods of emission activity. Rising emissions are prominent at the height of activity. ASE's triggered by station NAA (14.7 kHz, 1 MW radiated) begin when the transmitted Morse dash terminates (dash length, 150 ms). Some ASE's triggered by pulses from Siple Station, Antarctica (1.6–7 kHz, ≤ 1 kW), and Omega, New York (10.2 kHz, 100 W), show similar behavior; others, however, begin prior to the termination of the triggering pulse when the pulse length exceeds 200 ms. Growth and frequency change of the ASE tend to be independent of one another. For transmitted pulses of sufficient duration the amplitude saturates prior to termination. Signal amplitudes may reach 30 dB or more above the initial level. During growth the measured bandwidth of the signal remains near the minimum possible (∼27 Hz) with the given analysis resolution (∼30 ms, ∼50 Hz). By comparison with mathematical models it is shown that the observed signals have the maximum possible coherence for the measured values of growth rate and duration. These observations are in qualitative agreement with a model that attributes signal growth and ASE's to an interaction between coherent waves and counterstreaming gyroresonan

ISSN:0148-0227    

DOI:10.1029/JA082i004p00523

年代:1977

数据来源: WILEY

摘要:

Simultaneous observations of substorm‐associated electron flux variations made on the satellites Explorer 45 and ATS 5 are used to infer the value of the dawn‐dusk electric field present during a substorm. The observations were made during a substorm which occurred on December 17, 1971, while the two satellites were in the evening local time sector, within the plasma sheet, and separated by ≃1.5REin radial distance. A comparison of the variations at the two satellites shows that the substorm onset was observed at ATS 5 ≃11 min before the onset at Explorer 45. We infer that a dawn‐dusk electric field of ≃11 kV/RE(≃2 mV/m) was present during the substorm. We demonstrate that the observations made at the two satellites are compatible with the model of a uniform enhanced dawn‐dusk electric field acting upon a particle source which is spatially uniform in the region from which particles are convected to sy

ISSN:0148-0227    

DOI:10.1029/JA082i004p00531

年代:1977

数据来源: WILEY

摘要:

The population of protons having energy 5 ≤Ep≤ 50 MeV at the inner boundary of the radiation belt was investigated in near‐equatorial latitudes by a particle telescope having large gathering power and, consequently, high statistical accuracy. The measurements were performed from March 10 until May 10, 1970, on board the second German research satellite Dial. A nearly complete coverage was obtained for the region 1.15 ≤L≤ 1.40 and 1 ≤B/Bo≤ 1.7. Particle fluxes are ordered as a function ofB/Bo,Lbeing fixed. ForB/Bovalues corresponding to mirror point heights above 300 ± 50 km the fluxes follow a (B/Bo)−n/2law which can be converted to equatorial pitch angle distributionsJ⊥sinnθ via Liouville's theorem. For 1.15 ≤L≤ 1.25 the exponentnincreases steeply with decreasingLand the shape of the energy spectrumJ⊥remains essentially constant. At this lower edge of the radiation belt the proton population in the above energy range is determined from an equilibrium between the cosmic ray albedo neutron decay source and atmospheric loss processes. For largerL, radial diffusion sets in and leads to a distortion of the spectrum, with a shift of the intensity maximum toward lower energies with increasingL. The observed spectra are in satisfactory agreement with solutions of the transport equation (Claflin and White, 1974) based on one‐ and two

ISSN:0148-0227    

DOI:10.1029/JA082i004p00537

年代:1977

数据来源: WILEY