摘要:

The calculated value of the energy consumption rate UTwithin the near‐Earth and middle magnetosphere depends significantly on the assumed loss time τ of the ring current, which is known not to be a constant. In much previous work, τ was taken to be a function of a combination of solar wind quantities (the ε parameter) assumed to represent the solar wind energy input into the magnetosphere. This may lead to problems of circular reasoning and artificial interdependence of quantities when the statistical relation between UTand ε is investigated. To avoid these problems, I propose that τ be taken as a function not of ε but of UTitself. Values of UTindependent of ε or any other similar solar wind quantity can then be obtained at a cost of only a modest increase of computationa

ISSN:0094-8276    

DOI:10.1029/GL014i012p01183

年代:1987

数据来源: WILEY

摘要:

The first attempts to use the EISCAT VHF radar to make incoherent scatter measurements of the mesosphere took place in February 1987 and some of the results are presented. Measurements of the electron concentration were made together with tentative calculations of the ratio of negative ions to free electrons. The vertical motion of the neutral atmosphere was also deduced and both chaotic and well‐defined wave structures were observed. One particularly well‐defined wave is examined and possible mechanisms are discussed, including generation by the solar termina

ISSN:0094-8276    

DOI:10.1029/GL014i012p01187

年代:1987

数据来源: WILEY

摘要:

Using numerical model calculations, we investigate the transient heating effect from magnetospheric charged particle precipitation as proposed by Baker et al. (1987). Under extreme circumstances, the transient temperature increase may reach 1 K if the heating duration lasts more than one minute and the energy influx reaches 104ergs/cm²/s. Otherwise, the expected temperature rise should be substantially smaller (ΔT<0.05 K). From this point of view, optical observations capable of differentiating various degrees of particle irradiation effect (i.e., modification of optical properties of surface dust layer and/or regolith structure) might be more appropriate to pinpoint signature of Mercury's auroral zone

ISSN:0094-8276    

DOI:10.1029/GL014i012p01191

年代:1987

数据来源: WILEY

摘要:

Electron temperature was measured by means of planar probes on Japan's ninth scientific satellite OHZORA. The measurement, which was carried out simultaneously both along and vertical to the geomagnetic line of force, showed anisotropy of electron temperature. The temperature of the electrons along the geomagnetic field, T∥, is very often higher than the temperature of electrons collected by the electrode whose normal is perpendicular to the geomagnetic field, T⟂. Anisotropy increases as we move to higher geomagnetic latitudes. Anisotropy occurs more often in the early morning than at any other time of day. There is also a tendency for anisotropy to occur more often at lower altitudes.It is suggested that the existence of anisotropy of electron temperature can explain some puzzling phenomena that have previously not been explai

ISSN:0094-8276    

DOI:10.1029/GL014i012p01195

年代:1987

数据来源: WILEY

摘要:

Spherules collected form Antarctic ice have been studied by using instrumental neutron activation analysis, energy dispersive X‐ray spectrometry and X‐ray diffration photography. Peculiar spherules, Ca‐Ti‐rich (perovskite) type (CTS) and Fe‐Cr‐Ni‐rich type (FCN), were found in the Mizuho ice core at depths of 32 to 33.5 m. Both types have rare earth element (REE) abundances; i.e., significant relative enrichment of light REE over heavy REE, which is commonly seen for terrestrial perovskite, however, with anomalous enrichment of Nd and Sm. In the Allan Hills bare ice, only a "chondritic" type without depletion of Au and S (CAS) was recognized. Size distributions and influx rates of spherules for these ices and the Mizuho surface snow indicate that Antarctic spherules are composed of steady‐falling and occasional populations. All the results combine to suggest that CTS and FCN may be droplets strewn by the impact of a huge meteorite, and CAS must be debris from one of the chondrites that fell on the source region of the Allan Hills bare ice and survive terrestr

ISSN:0094-8276    

DOI:10.1029/GL014i012p01199

年代:1987

数据来源: WILEY

摘要:

A study designed to examine the basic theory of thermoremanent magnetization acquisition parallel to the earth's ambient magnetic field upon cooling and to evaluate intra‐flow variations of very young basalt flows has yielded some startling initial results. Two extensively sampled flows, the 1950 flow of Mauna Loa and the 1972 flow from Mauna Ulu, Kilauea, have been found to have paleomagnetic directions statistically different from the present geomagnetic field direction (PFD) in Hawaii. The 1950 flow shows very consistent, but shallow directions throughout the flow, with a mean inclination 6° shallower than the PFD. Directions from the 1972 flow vary from site to site both along the length of the unit and within vertical sections. Relative between site consistency is low, with all sites but one having paleomagnetic directions distinct from the PFD, however, the mean inclination for this flow, 33.4°, is only about 3° shallower than expected. The source of such anomalous behavior in the recording of ambient field directions is yet unknown, although several possible causes are exam

ISSN:0094-8276    

DOI:10.1029/GL014i012p01203

年代:1987

数据来源: WILEY

摘要:

In addition to classical body domain patterns, a profusion of complex maze like domain structures have been observed using the Bitter technique on titanomagnetites. Controversy persists over how important a role such complicated domain patterns play in remanent magnetization. We have compared the magnetic properties of single particles, which exhibit complex patterns with those that exhibit simple ones. IRM acquisition and DC and AF demagnetization of IRMs of single particles were measured. We found that both types of grains exhibit similar bulk magnetic properties. The simple patterns reorganize with changing magnetization state while complicated patterns apparently remain constant. We suggest that the remanent magnetization of grains with complicated patterns is carried by the bulk of the particle within which a more simple domain structure controls magnetic behavior.

ISSN:0094-8276    

DOI:10.1029/GL014i012p01207

年代:1987

数据来源: WILEY

摘要:

Four late Pleistocene tephra deposits from the East Eifel volcanic field have been dated by40Ar/39Ar single grain laser fusion of K‐feldspar and phlogopite crystals. This is a high‐speed and high precision technique which, because it is grain‐specific, can directly detect the presence of older contaminating material. Our results indicate that the Hüttenberg tephra from Wehr volcano erupted 213±4 ka BP, and that the Rieden volcanic complex erupted at least over the period 410 to 470 ka BP. Essential Rieden phonolite lapilli contain abundant sanidine with apparent ages older than the erupt

ISSN:0094-8276    

DOI:10.1029/GL014i012p01211

年代:1987

数据来源: WILEY

摘要:

A component with ∼6% mantle helium (³He/4He=5‐9×10−7) has been identified in borewaters from the Great Artesian Basin, Australia that is isotopically distinct from previously identified in situ production (³He/4He = 1.6×10−8) and a crustal degassing flux (³He/4He = 6.75×10−8). The occurrence of this component is limited to three identified localities (∼20.5°S 144°E; ∼25.5°S 146°E; ∼27°S 144.5°E) all within the region of high reduced heat flow in eastern Australia. No evidence for a mantle component was apparent in central Australia. This component is most probably the result of continued intrusive volcanism (<1 m.y.) associated with the Cainozoic lava flow fields in the region. Although the volcanic activity has no present‐day surface manifestation, its mantle helium was probably carried to the near‐surface by large‐scale fluid

ISSN:0094-8276    

DOI:10.1029/GL014i012p01215

年代:1987

数据来源: WILEY

摘要:

We have analyzed fundamental spheroidal mode spectra obtained from very long period Geoscope records, in terms of global distribution of eigenfrequencies and attenuation. With a new data set and a different data processing approach, involving time variable filtering and the removal of higher order effects in the spectra, we confirm the strong upper mantle degree two signature in the eigenfrequency data. The higher frequency content of the Geoscope spectra allows us to put better constraints on the depth range at which this pattern originates, which appears to be somewhat shallower than was proposed before. While some effect may persist down to the bottom of the transition zone, the frequency signature of the strongest degree two pattern requires an S velocity heterogeneity concentrated in the depth range 300‐500 km and this signature is also apparent in the distribution of Q, which is indicative of a probable thermal origin. The data also resolve a shallow degree 2 pattern, well explained by heterogeneity spanning from the surface to depths of about 300 km, and associated with the distribution of tectonic provinces. It is shifted by about 45° with respect to the deep degree 2 pattern, and its expression in the Q data is not cle

ISSN:0094-8276    

DOI:10.1029/GL014i012p01219

年代:1987

数据来源: WILEY