摘要:

The University of Iowa Lepedea on board ISEE 1 is used to investigate the characteristics of the central plasma sheet under all levels of geomagnetic activity. Positive ion responses from 1 eV to 45 keV are used in this study. All the periods during 1978 when the central plasma sheet is encountered are included. Our study excludes all boundary layer samples. The results of this study show that the central plasma sheet consists of plasma with high thermal energy (several keV) but low bulk speeds. This remains true even during high geomagnetic activity. The main effect of increasing activity is heating of the plasma sheet, preferentially at the high‐latitude boundarie

ISSN:0094-8276    

DOI:10.1029/GL013i007p00652

年代:1986

数据来源: WILEY

摘要:

A precipitation index is described which quantifies the intensity and spatial extent of high‐latitude particle precipitation based on observations made along individual satellite passes. By sorting plasma convection data according to this index, average patterns of the ionospheric convection electric field have been derived from a data set consisting of five years' observations by the Millstone Hill radar. Reference to the instantaneous precipitation index, and the average patterns keyed to it, provides a means of characterizing the global precipitation and convection patterns throughout an even

ISSN:0094-8276    

DOI:10.1029/GL013i007p00656

年代:1986

数据来源: WILEY

摘要:

Cross sections for photodissociation of O2(a¹Δg) are presented as functions of wavelength from 1900 to 3000 Å Contrary to an earlier suggestion, it is shown that the process is unimportant as a source of stratospheric odd oxyg

ISSN:0094-8276    

DOI:10.1029/GL013i007p00660

年代:1986

数据来源: WILEY

摘要:

On taking account of the symmetry numbers involved it is found that the rate coefficient of the ter‐molecular association process giving heavy ozone is greater than that of the corresponding process giving regular ozone. It is suggested that this is the explanation of the50O3enhancement observed in the stratospher

ISSN:0094-8276    

DOI:10.1029/GL013i007p00664

年代:1986

数据来源: WILEY

摘要:

Following the solar proton event (SPE) of July 13, 1982, an increase in the strength of nitric oxide T bands was observed in spectral scans of the atmospheric albedo made by the solar backscattered ultraviolet instrument on Nimbus 7. Analysis of the (10), (01), and (02) T band strengths allows us to estimate the cumulative amount of nitric oxide above an altitude of 50 km. We observe an increase in nitric oxide in southern hemisphere high latitudes following the SPE amounting to about 5×1014molecules per cm² above an altitude of approximately 50 km. The observed increase persists until the middle of September. A similar increase is not observed in the northern hemisphere, indicating that under summer conditions the mesospheric/thermospheric NO distribution returns to normal within a few days after the end of an SP

ISSN:0094-8276    

DOI:10.1029/GL013i007p00667

年代:1986

数据来源: WILEY

摘要:

The absorption cross‐section of ozone at 253.7 nm is frequently used as a standard for the entire UV wavelength range. The presently accepted value is 1.147 × 10−17cm², known with an uncertainty of about 2%. The cross‐section has been recently measured by simultaneously monitoring the ozone pressure, the impurities in the ozone gas, the gas temperature and the UV beam intensity. The cross‐section at room temperature was found to be 1.137 × 10−17cm², having an uncertainty of ±.7%. The improved accuracy will aid a number of ozone experiments including the in situ photometers and Solar Backscatter Ultraviol

ISSN:0094-8276    

DOI:10.1029/GL013i007p00671

年代:1986

数据来源: WILEY

摘要:

Multiple‐event relocation of earthquakes associated with the Gorda ridge and Gorda basin indicates that activity tends to cluster spatially with some suggestion of linear trends in the epicenters of events near the central segment of the ridge, sub‐parallel to the ridge axis. Events in the interior of the basin may be related to relic faults formed at the ridge crest that remain zones of weakness in the plate and are subject to periodic reactivation as well as the proposed Gorda fault which crosses the plate in a NW‐SE dire

ISSN:0094-8276    

DOI:10.1029/GL013i007p00674

年代:1986

数据来源: WILEY

摘要:

Maximum heat flow measurements at three locations in the sediment‐filled Escanaba Trough of the Gorda ridge exceed 1200 mW/m². At other ridge crests with thick sediment cover, heat flow values of this magnitude are accompanied by high temperature hydrothermal vent activity and massive sulfide deposition. A dredge haul from the southernmost high heat flow location recovered pyrrhotite, thereby confirming the presence of recent high temperature venti

ISSN:0094-8276    

DOI:10.1029/GL013i007p00678

年代:1986

数据来源: WILEY

摘要:

We have formulated a new class of plate‐bending equations which simulates the flexure of the lithosphere at mid‐ocean ridges. The stress‐accumulation effect in a growing (moving and thickening) lithosphere significantly changes the flexural behavior. It is shown that the growing plate flexes more easily than the conventional static plate due to the fact that the bending stress vanishes on the base of the plate. We apply this new plate model to the East Pacific Rise. Compared with Madsen et al. (1984), the fits to the gravity and topography observations are improved. Assuming the thickness varies in proportion to the square‐root of distance from the ridge crest, the best fitting thickening rate for the growing plate model is 0.7 (km1/2), or 5.5 km/(m.y.)1/2, which further implies that the 600 or 700°C isotherm marks the bottom boundary of the effective elastic thickness of the lit

ISSN:0094-8276    

DOI:10.1029/GL013i007p00681

年代:1986

数据来源: WILEY

摘要:

The North American Central Plains electrical conductivity (NACP) anomaly has been known for almost two decades, and its influence on palaeotectonic models of the North American continent has been significant. Magnetometer array studies have located the structure in a gross sense, but there has not been, until now, a comprehensive magnetotelluric (MT) survey of it. In this letter we report on the preliminary interpretation of data from thirty‐five MT sites recorded along a 400 km East‐West profile just north of the US‐Canadian border. We show that the anomaly at this latitude is 75 km farther east of the location previously mapped by the array studies. Modelling indicates that the conductive body has its top surface at about 10 km depth and appears to be anticlinal in shape. The profile also extends sufficiently east that it traverses another previously known electrical structure, referred to herein as the TOBE anomaly. We consider briefly other geophysical and geological data for the region, and tentatively infer that the NACP structure is terminated to the east by the interpreted southern extension of the Tabbernor fault/fold system, and that the TOBE anomaly is an expression of the known southern extension of the Thompson nickel belt, both beneath Phanerozoic sediments of the Williston

ISSN:0094-8276    

DOI:10.1029/GL013i007p00685

年代:1986

数据来源: WILEY