摘要:

The interaction between the solar wind and the outflowing plasmas from a comet has been studied by using a two‐dimensional time‐dependent magnetohydrodynamic (MHD) simulation. The model reproduced several features of the comet‐solar wind interaction predicted by earlier theories and observed on the recent cometary probes. These include the formation of the contact surface and the cometary magnetotail. For a constant interplanetary magnetic field (IMF) the cometary plasma captures field lines which drape over the comet to form an antiparallel magnetic field configuration in the tail and a thin plasma sheet. Eventually, tail magnetic reconnection begins to occur at several points. When the IMF orientation is reversed dayside magnetic reconnection occurs at the subsolar point and a large disturbance propagates down the

ISSN:0094-8276    

DOI:10.1029/GL013i009p00929

年代:1986

数据来源: WILEY

摘要:

The rate constant for the combination reaction of CFCl2O2and NO2was measured as a function of pressure and temperature under stratospheric conditions. The results show that the reaction is fast and that significant amounts of the peroxynitrate CFCl2O2NO2can be formed. The data were introduced into a 2D photochemical model in order to evaluate an upper limit for the amount of chlorine stored in the form of the peroxynitrate. The calculation shows that this reservoir effect cannot exceed a few percent of the total chlorine contained in the stratosphere.

ISSN:0094-8276    

DOI:10.1029/GL013i009p00933

年代:1986

数据来源: WILEY

摘要:

Visible limb radiances measured by the Solar Mesophere Explorer (SME) are used to obtain volume scattering ratios for aerosol loading in the 30‐55 km altitude range of the stratosphere. Global maps of these ratios are presented for the period January, 1982 to August, 1984. Significant aerosol scattering from the "mystery cloud" and El Chichon aerosol layers are found above 30 km. A timescale of approximately 2 months between the appearance of the aerosol at 30.5 km and at 37.5 km is consistent with vertical transport of aerosol or vapor by eddy diffusion above 30 km. An anticorrelation exists between aerosol scattering and stratospheric temperatures. Periods of lower stratospheric temperatures may account for the formation of aerosol between 40 and 55 km altitud

ISSN:0094-8276    

DOI:10.1029/GL013i009p00937

年代:1986

数据来源: WILEY

摘要:

Current densities of 2.5*10−4amp/m² can be generated by constant groundwater migration in artesian aquifers. These DC currents are sufficient to generate magnetic anomalies exceeding 200 nT in both the Menindee Trough (Australia) and the Karoo Basin (South Africa). Telluric currents associated with ionospheric activity can be detected by variations in magnetic induction but constant offsets associated with streaming potentials and geochemical activity (SP anomalies) are obscured by noise. Consequently some regional magnetic anomalies may be wrongly attributed to variations in magnetic susceptiblity with residuals explained by remanen

ISSN:0094-8276    

DOI:10.1029/GL013i009p00941

年代:1986

数据来源: WILEY

摘要:

Meteorological satellite imagery has been used to map the changes of surface brightness and texture associated with the seasonal progression of snow melt on the arctic pack ice in 1977 and 1979, and, using an image processor, surface albedo has been estimated. This is the first basin‐wide information on the temporal and spatial change of the ice surface and its albedo. In both years studied, melt progressed poleward from the Barents and Kara Seas and from the southern Beaufort and Chukchi Seas. Average surface albedo of the Arctic Basin fell to 0.40, and in the central Arctic to about 0.50, in late July of each year, but the melt occurred approximately 3 weeks later in 1979 than in 1977. Results suggest a significant year‐to‐year variability in the arctic energy and mass bal

ISSN:0094-8276    

DOI:10.1029/GL013i009p00945

年代:1986

数据来源: WILEY

摘要:

Theoretical studies indicate that interactions between the Earth's mantle and fluid core could produce a near 460‐day, retrograde circular component of the nutation, often called the free‐core nutation (FCN). Until now this phenomenon has never been observed. We use the 5.5 years of VLBI observations primarily collected under project IRIS to search for evidence of the FCN. The observations are consistent with an irregular excitation process, and a model which assumes a step excitation in the FCN amplitude to about 2.0 milliseconds of arc in late 1985 fits the data well. Theoretical analysis appears to rule out the strong Mexican earthquake of September 19, 1985, as a cause of the excitat

ISSN:0094-8276    

DOI:10.1029/GL013i009p00949

年代:1986

数据来源: WILEY

摘要:

A short 12‐fold CDP seismic‐reflection survey was performed along the road to Doublespring Pass across the fault scarp formed by the October 28, 1983, magnitude‐7.3, Idaho earthquake. This high‐resolution reflection survey was conducted to determine the feasibility of using reflection seismology to delineate shallow structures in a fault zone. Field‐recording parameters were designed to optimize seismic reflections in the 30‐150 msec range corresponding to 10‐100 m in depth. A modified 30‐06 hunting rifle was used as the energy source. Single 100‐Hz geophones at 1.5‐m group intervals in conjunction with 220‐Hz low‐cut recording filters (24 dB/octave) provided dominant frequencies above 150 Hz on field records. As would be expected from geologic considerations, the processed data suggest the existence of faulting in the subsurface. Strong events between 30 and 80 msec on the upthrown side of the scarp are of distinctly different character and frequency than those on the downdropped side at similar times. This indicates different geologic units are present at approximately the same reflection time on opposite sides of the fault zone. The northeastern edge of the scarp may not represent the true subsurface boundary of the upthrown block. Projection to the surface of the northeasternmost edge of the seismically determined subsurface graben is 10‐15 m farther northeast than expected from surface faulting. High‐frequency energy present within the subsurface expression of the graben is primarily noise and is related to the deformed and incoherent nature of

ISSN:0094-8276    

DOI:10.1029/GL013i009p00953

年代:1986

数据来源: WILEY

摘要:

Anomalously high ambient acoustic noise was observed within the caldera of Axial Seamount, located on the Juan de Fuca Ridge at 46°N. Noise spectra from 2 to 30 Hz were calculated from hydrophone signals from four separate seismic recording systems. Noise levels varied up to 25 dB over 6 km. This observation suggests the noise source is at or near the sea floor. By assuming spherical spreading, we estimate the source of the noise to be within 400 m of one of the instruments. A low temperature hydrothermal vent field, located within 600 m of this instrument, has been previously mapped with submersibles and is likely the source of the anomalous noise. A high temperature, black smoker, vent field, also located within the caldera, shows no evidence of anomalous acoustic noise

ISSN:0094-8276    

DOI:10.1029/GL013i009p00957

年代:1986

数据来源: WILEY

摘要:

MAGSAT anomaly maps over the Indian region are prepared after removal of core and external current contributions. To examine the physical reality of the map, we calculate the geomagnetic scalar field at MAGSAT height in spherical co‐ordinates, using the equivalent point source distribution of magnetic dipoles. The calculation assumes: (i) the source field of the anomaly to lie within the crust; (ii) only induced magnetisation exists; (iii) the susceptibility is constant over the whole region. Crustal thickness is deduced from Bouguer gravity anomaly maps. Evaluation of the anomaly is done numerically using the Gauss‐Legendre quadrature integration method. The computed values agree reasonably well with the observed anomalies. This suggests that the crustal component is quite accurately discernible in the MAGSAT data. Further, anomalies over India seem to be accountable with induced magnetisation alone and the Curie isotherm appears to coincide with the crustal de

ISSN:0094-8276    

DOI:10.1029/GL013i009p00961

年代:1986

数据来源: WILEY

摘要:

A depleted‐mantle nodule from Kilbourne Hole, New Mexico, has been analyzed in detail to test a recent model for the formation of alkali basalts by two‐component mixing of depleted mantle and enriched (kimberlite) mantle. The bulkrock chemistry of the nodule can be reconstructed from its constituent phases, except for calcium, sodium and several incompatible elements. It is found that acid‐leachates derived from the surfaces of the minerals contain the "missing" complement of these elements. Furthermore, major element compositions indicate that each leachate may be a mixture of nodule mineral plus kimberlite. It is suggested that the host alkali basalt lava could have formed by the same mixing process, as the lava and enclosed nodule are in approximate Nd isotopic equilibrium, and calculated mineral/melt partition coefficients for the rare earth elements (REE) between nodule minerals and host lava match those determined experimen

ISSN:0094-8276    

DOI:10.1029/GL013i009p00965

年代:1986

数据来源: WILEY