摘要:

We have determined the directions of arrival of auroral kilometric radiation during three separate intervals using data from the DE 1 plasma wave instrument. In the case of the dominant extraordinary mode component, these directions were consistent with generation at the local electron cyclotron frequency on nightside auroral field lines. The ordinary mode component appeared to have a similar source in one case, but in other cases came from different directions. These other cases were consistent with reflection at the plasmapause and the wall of the auroral plasma cavity.

ISSN:0094-8276    

DOI:10.1029/GL012i008p00479

年代:1985

数据来源: WILEY

摘要:

The theory of the generation of broadband electrostatic noise in the magnetotail is extended through numerical solution of the dispersion relation under conditions that exist in the plasma sheet boundary layer. It is found that the low‐frequency portion of the spectrum has a broad angular spectrum but a fairly sharp peak near 75° with respect to the magnetic field, while the high‐frequency portion has a narrower angular spectrum that is strongly concentrated along the magnetic field line. These results are in excellent agreement with observations of the broadband wave spectrum and a recent measurement of the propagation direction. The effect of a second cold component of electrons is analyzed, and it is found that it can increase the upper cutoff frequency of BEN to the observed value at about the plasma frequ

ISSN:0094-8276    

DOI:10.1029/GL012i008p00483

年代:1985

数据来源: WILEY

摘要:

Interferometric observations of the 630.0 nm nightglow brightness at the equatorial station of Arequipa, Peru [16.2°S, 71.4°W geographic, 3.2°S dip latitude] have revealed widespread areas of airglow depletion, with reductions in intensity as large as factors of 3 or 4. These depletions correlated closely with large increases of the equatorward (northward) wind and the 630.0 nm kinetic temperature. On occasion, the usually small meridional wind reached a velocity of 100 m/s near 22hLT lasting for 1 to 2 hours. The temperature increases of 100 K or more existed only in the poleward (southward) direction. Comparisons with modelling calculations suggest that this effect results from an upward movement of the ionosphere along the inclined magnetic field lines, driven by the equatorward neutral wind. The airglow column integrated emission rate is consequently decreased by the slower rate of formation and subsequent dissociative recombination of molecular oxygen ions within the higher F‐layer. We conclude that the transient period of equatorward wind is a result of the passage of the midnight pressure b

ISSN:0094-8276    

DOI:10.1029/GL012i008p00487

年代:1985

数据来源: WILEY

摘要:

A minimum is observed at midnight in the time variation of averaged zonal winds measured in‐situ near the equator at an average altitude of about 350 km, and we inquire whether observations of the equatorial midnight pressure bulge are consistent with this feature. The observed zonal wind maintains an eastward direction all night. It increases steadily in the early evening reaching a maximum of about 160 m/s at 2100 hrs local time (LT), dropping to a minimum of about 70 m/s around 2400 LT, then up to about 120 m/s around 0300 LT, decreasing thereafter and turning westward in the morning around 0500 LT. The nighttime eastward ion drift at Jicamarca, averaged over periods of similar solar activity (1970‐71), shows the same signature, but generally with amplitude between 70 and 90% of the zonal wind amplitude. The 1978‐81 Jicamarca ion drifts are similar except from 2400 to 0300 LT when they are about 30% larger than the in‐situ zonal wind averages. The ion‐drift is used together with the measured zonal winds to estimate the ion‐drag effect in the momentum equation. The pressure term of this equation is estimated using in‐situ measurements of the neutral temperature and density. The pressure term is found to be large before 2100 LT (∼0.05 m/s²), consistent with the steady increase in zonal wind before 2100LT, drops rapidly to near zero (roughly 0.005 m/s) before 2200 LT, and then increases slowly beginning at 2300 to about 0.015 m/s² just before 0300 LT when it is observed to reverse. The small pressure term observed from 2100 to 2400 LT is associated with the midnight pressure bulge and accounts for the decay of the wind from 160 m/s at 2100LT to 70 m/s at midnight. The larger value at 0300LT is consistent with the second maximum in the wind. It is found that the existing data sets are consistent in terms of zonal momentum balance. The striking similarity between the zonal wind and the eastward ion‐drift is responsible for the small ion‐drag term before midnight which is required to maintain the large

ISSN:0094-8276    

DOI:10.1029/GL012i008p00491

年代:1985

数据来源: WILEY

摘要:

A rocket‐launched parachute‐deployed chemiluminescence sensor measured the vertical profile of nitric oxide from Poker Flat, Alaska, latitude 65.13 degress North, in August 1984 and in January and February 1985. All data refer to daylight periods shortly after local noon and cover altitudes from a lower limit of 27‐30 km up to 48‐53 km. Between 35 and 45 km the results indicate a large seasonal variation, with wintertime mixing ratios being roughly a factor of two above summer values. The winter profiles contained sharp positive vertical gradients that persisted through the highest altitudes observed, and near 50 km the mixing ratio from the Feburary flight exceeded that seen in summer by a factor of four. Above the stratopause the mixing ratio observed in February increased dramatically and between 52 and 53 km reached 148.9 ppbv, an order of magnitude greater than typical mid‐latitude values measured with this instrument. Such behavior is consistent with the absence of photodissociation in winter and a downward flux of odd nitrogen arising from a source located significantly higher than the stratopause, almost surely in the lower thermosphere. These results clearly support the existence of a vertical coupling between diverse regions of the atmosphere in the high latitu

ISSN:0094-8276    

DOI:10.1029/GL012i008p00495

年代:1985

数据来源: WILEY

摘要:

Upper Triassic‐Lower Jurassic rocks at Quesnel Lake form part of the Quesnel terrane, which was emplaced against the Omineca Belt, part of the North American (paleo‐)continental margin, in the late Early Jurassic. Hard magnetizations, which may or may not be primary, were identified in volcanic wackes, but they are poorly grouped. However, removed magnetizations of intermediate unblocking temperatures (200‐500°C) and coercivities (30‐50 mT) are systematically directed northeast and downward (D=35°, I=57°, a95=9° 5 sites, 22 specimens; paleopole 62°N, 15°W, dm=13°, dp=10°) with respect to present horizontal. We interpret this to be an overprint, acquired after Middle to Late Jurassic folding, as a result of mid‐Cretaceous plutonism during the Cretaceous Normal Superchron. The paleopole is compatible with Early to mid‐Cretaceous paleopoles from other terranes in the southern Canadian Cordillera, but does not agree with observations from post‐Jurassic cratonic rocks. This disagreement indicates that in the mid‐Cretaceous these terranes, along with at least part of the Omineca Belt to which they were attached, formed a quasi‐rigid super‐terrane which was situated about 2000 km farther south than its present posi

ISSN:0094-8276    

DOI:10.1029/GL012i008p00498

年代:1985

数据来源: WILEY

摘要:

During the summer of 1984, Brown University measured magnetic variations at a series of 9 sites along an 80 km profile which began in the Willamette Valley in West‐Central Oregon, extended westward across the Coast Range, and terminated at the coast of the Pacific Ocean. Our primary objective was to investigate the "coast effect" with a density of coverage and at shorter periods (10‐100 sec) than had previously been attempted in this region. The data collected show a significant coast effect at sites closest to the ocean. While it is tempting to assume that, to first‐order, all such effects are due to induced electric currents flowing in the ocean, our studies for the Oregon coast show that the contribution of electric currents flowing in the lithosphere, especially the contribution of induced currents in a thick accretionary wedge of marine sediments offshore, is actually more significant than the contribution from the ocean itself. In addition, we have detected a conductive feature beneath the Coast Range which appears to be another zone of structurally coherent sediments along our profile. The pattern of short‐wavelength induction anomalies inland suggests that at these periods a very close spacing of sites (5 km or less) is called for in future

ISSN:0094-8276    

DOI:10.1029/GL012i008p00502

年代:1985

数据来源: WILEY

摘要:

Particulate Fe and Cu concentrations are used in conjunction with dissolved Mn values to identify hydrothermal venting at several sites along the Mid‐Atlantic Ridge (MAR). In dispersed hydrothermal plumes, as defined by dissolved Mn anomalies, suspended matter Fe and Cu values were as high as 15.8% and 1100µg/g respectively, relative to Al at 1.7%. Suspended matter Fe and Cu values correlate well with dissolved Mn concentrations, tracing the intensity of dispersed plumes. In contrast with Fe and Cu, particulate Mn values in vent plumes were low at 700‐1200µg/g. Calculated (Al + Fe + Mn)/Al ratios for MAR particles increase with increasing dissolved Mn concentrations. This ratio is used to estimate the percent hydrothermal component of the suspended matter. These sensitive tracers identify a 2‐20% hydrothermal contribution to the 10 ± 2µg of total suspended matter/1 found along the ri

ISSN:0094-8276    

DOI:10.1029/GL012i008p00506

年代:1985

数据来源: WILEY

摘要:

Since March 1977 we have measured Cl−concentration in the groundwater almost every day at Shiota mineral spring near the Yamasaki fault, which is situated in the northern Kinki and Chugoku Districts, Southwest Japan, to see if the Cl−concentration shows any variations which may be related to seismic activity near Shiota mineral spring. From March 1977 through December 1984 there occurred 6 earthquakes of M3.5 or greater near Shiota mineral spring and two of M6.0 or greater in the northern Kinki and Chugoku Districts. The Cl−concentration anomalously changed four times before these earthquakes though the pattern of preseismic changes of the Cl−concentration was not uniform. We conclude that measurement of Cl−concentration at a carefully chosen mineral spring near an active fault should give information useful for earthquake p

ISSN:0094-8276    

DOI:10.1029/GL012i008p00510

年代:1985

数据来源: WILEY

摘要:

The space‐time history of the rupture process of a large earthquake can be determined from directivity analysis of source time functions deconvolved from long‐periodPwaves. However, such analysis requires a good azimuthal distribution of stations, which is often difficult to obtain. We have developed a method for deconvolution of long‐periodPPwaves which is useful for a distance range of 70° ‐ 123° and 145° ‐ 165°, thus increasing both the available data and the ray parameter aperture. ThePPwaveform is Hilbert transformed to remove the effect of thePPcaustic and then deconvolved in the time domain. We have tested the method on the 2 July 1974 Kermadec event (Ms=7.2) and obtained nearly identical source time functions fr

ISSN:0094-8276    

DOI:10.1029/GL012i008p00514

年代:1985

数据来源: WILEY