摘要:

Present radiometric and polarimetric measurements of the sizes and albedos of asteroids 1 Ceres and 4 Vesta, although uncertain in absolute calibration, determine the ratio of diameters with sufficient precision (Ceres/Vesta = 1.87 ± 0.03) to permit meaningful discussion of their relative densities. These measurements combined with the known masses yield a ratio of densities Vesta/Ceres = 1.33 ± 0.17, thus demonstrating that: (1) the bulk compositions are likely different, and (2) the difference is consistent with indications from remotely‐determined surface composition that Vesta is differentiated while Ceres may be of undifferentiated carbonaceous chondritic composit

ISSN:0094-8276    

DOI:10.1029/GL003i012p00701

年代:1976

数据来源: WILEY

摘要:

Experiment results are presented which show that electrostatic cyclotron harmonic (Bernstein) waves generated by supra‐thermal electrons can decay parametrically into whistler mode waves with very high efficiency. The spectral intensity of the whistler mode waves so produced has a maximum at twice the lower hybrid frequency. It is proposed that this is the dominant process responsible for the generation of VLF hiss and the so‐called VLF sauc

ISSN:0094-8276    

DOI:10.1029/GL003i012p00705

年代:1976

数据来源: WILEY

摘要:

It has recently been suggested that Io is an important source of ions for the plasma detected by Pioneer 10 in the inner magnetosphere of Jupiter. Assuming this to be true, we show that near the orbit of Io the central collector of the Pioneer‐10 plasma instrument could detect only inwardly diffusing ions created at a radial distance greater than that of the spacecraft. The rapid decrease in ion density observed beyond Io's orbit is attributed, at least partially, to this effect and thus may not represent a real plasma boundary such as a "plasmapause." Instead, the drop in observed ion density could correspond to a decrease in the density of Io‐associated neutral particles orbiting Jupi

ISSN:0094-8276    

DOI:10.1029/GL003i012p00708

年代:1976

数据来源: WILEY

摘要:

This paper presents initial results from the first comprehensively instrumented rocket flown through a Farley‐unstable polar cap E‐region. Groundbased ionosondes and magnetometers at two locations and HF radar backscatter at the launch site were used to determine the presence of a geographically widespread ionospheric plasma instability. The observed wave direction, electric field, and current density fit the predictions of the linear theory of the Farley instability, whereas the gradient‐drift instability seems to be excluded by the geometry of the observa

ISSN:0094-8276    

DOI:10.1029/GL003i012p00711

年代:1976

数据来源: WILEY

摘要:

Measurements of the geocoronal absorption at the center of the solar Lyman‐α line, performed by the University of Paris instrument on board OSO‐5 are compared to aspherical models. The deduced values of the minimum hydrogen density were analysed over periods of one year, between 1969 and 1972. They indicate a systematic departure up to 40% from exospheric models. This feature corresponds to a dayside sub‐solar hydrogen bulge characterized by a 25% decrease of the hydrogen density at 50° away (northward or southward) from the solar direction. This bulge could be due to solar direction related anisotropies of the hydrogen production, diffusion, transport and loss mechanisms which are neglected in the exospheric t

ISSN:0094-8276    

DOI:10.1029/GL003i012p00715

年代:1976

数据来源: WILEY

摘要:

The neutral composition and the temperature data obtained from the AEROS‐B Neutral Atmosphere Temperature Experiment (NATE) and the Neutral and Ion Mass Spectrometer (NIMS) are compared, and the general validity of inferring gas temperatures from N2and Ar density profiles is examined by comparing them with the in situ measured values of the neutral kinetic temperature (NATE). At times serious discrepancies are noted between the inferred and the measured temperature. This is particularly evident during periods of increased magnetic activity when the normally observed latitudinal variations are apparently modulated by waves propagating from the polar region to low latitudes. Under these conditions the N2and Ar densities and temperature oscillations are usually out of phase, and the temperatures inferred from N2and Ar at a given point become meaningles

ISSN:0094-8276    

DOI:10.1029/GL003i012p00718

年代:1976

数据来源: WILEY

摘要:

Two Doppler radars at the National Severe Storms Laboratory were used to measure a tornadic storm wind field. The derived wind fields suggest dynamical contributions to storm organization and development. Location of the vortex with respect to the parent circulation is consonant with the veering of the damage path to the right of storm motion. Wind fields derived from the radar observations indicate vorticity production processes important to tornado maintenance.

ISSN:0094-8276    

DOI:10.1029/GL003i012p00721

年代:1976

数据来源: WILEY

摘要:

A program of measurements in and outside the plume of Etna volcano has shown that radon daughters (as well as gaseous radon) are directly emitted from the magma. Enrichment factors have been observed : 4 for bismuth vs lead and 6 for polonium vs lead. The210Pb total output measured for the Etna plume is an insignificant source for this nuclide.

ISSN:0094-8276    

DOI:10.1029/GL003i012p00724

年代:1976

数据来源: WILEY

摘要:

Classical linearized gravity wave theory is employed to derive relationships between amplitude ratios and phase angles of atmospheric constituents undergoing acoustic‐gravity wave oscillations. These results are compared with recently reported Atmospheric Explorer‐C satellite data. Calculated amplitude and phase characteristics, for a large class of pure internal gravity wave oscillations, are in accord with the AE‐C satellite measure

ISSN:0094-8276    

DOI:10.1029/GL003i012p00727

年代:1976

数据来源: WILEY

摘要:

The vibrational energy distributions of hydroxyl molecules in the lower atmosphere were calculated; as expected, the distributions are found to be highly nonequilibrated. Attention is drawn to the role that vibrationally‐excited molecules may play in modifying the chemistry of the lower atmosphere. The most likely role for OH‡in the stratosphere is via reactions that may not otherwise be energetically via

ISSN:0094-8276    

DOI:10.1029/GL003i012p00731

年代:1976

数据来源: WILEY