摘要:

Low‐latitude ionospheric disturbances, which were characterized by severe scintillations in the C‐band range accompanied by complex dynamical behavior of the low‐latitude ionosphere, were examined, taking into consideration previous results. From the analyses of foF2 and h′F data, these disturbance events are found to be characterized by a two‐stage process. During the first stage, which starts during the magnetospheric energy storage process before the onset of substorms, h′F begins to increase simultaneously at all observing stations due to eastward electric fields penetrating from the magnetosphere. At subequatorial stations, increases of foF2 follow as a signature of enhancements of the equatorial anomaly. During the second stage, values of h′F increase again, indicating a motion from north to south, with no increase of foF2. In this stage, dynamical effects including neutral winds become important, as well as electric fields. In addition, it is shown from the analysis of one year's data for 1978 that the occurrence of disturbance events as presented in this paper is a general feature in the evening section under the condition of ring current

ISSN:0094-8276    

DOI:10.1029/GL013i013p01399

年代:1986

数据来源: WILEY

摘要:

Data from the Solar Mesosphere Explorer satellite of polar mesospheric clouds have been used in determining the variation of cloud height from 1981 to 1985. Applying various corrections to the apparent tangent heights measured at the atmospheric limb, we find no significant variation of height within an individual cloud season (−10 days to + 50 days relative to summer solstice) either with latitude or local time. Furthermore, no significant year‐to‐year variation is found over the 4‐year time span. We find significantly higher (2 km) PMC cloud heights in the north than in the south. The average value of 85.0 ± 1.5 km for the northern PMC is in good agreement with measurements from the OGO‐6 satellite, rocket‐borne photometers and ground‐based triangulation of noct

ISSN:0094-8276    

DOI:10.1029/GL013i013p01403

年代:1986

数据来源: WILEY

摘要:

Measurements on stratospheric aerosols at Syowa Station (69°00′S, 39°35′E) in 1983, 1984 and 1985 are described. The year‐to‐year changes in aerosol content were influenced by volcanic eruption of Mt. El Chichon (spring 1982, Mexico) and variations of stratospheric temperature. The aerosol load in winter of 1983 was about five times larger than the load of 1985. The particle content of spring 1985 was larger than that of spring 1983 even though the effect of the volcanic eruption was more severe in 1983. This may be a result of the decrease in average stratospheric temperature in spring. If heterogeneous reactions including the particles are indeed important for Antarctic ozone depletion, the rate of ozone depletion from heterogeneous reactions in the Antarctic spring must have increased from 198

ISSN:0094-8276    

DOI:10.1029/GL013i013p01407

年代:1986

数据来源: WILEY

摘要:

Preliminary results from a study characterizing S(IV) compounds in wintertime precipitation samples indicate that bisulfite ion is not the primary form of S(IV), as previously believed. By employing a differencing technique that permits estimation of both SO2· aq and non‐SO2· aq compound concentrations, it was found that, on an average, more than 60% of the total S(IV) is present in a form other than dissolved SO2. Formaldehyde analyses on selected samples suggest that the most likely form of the S(IV) is hydroxymethanesulfonate, although other aldehyde‐S(IV) adducts may also be present. The non‐SO2‐compounds represented a significant portion of the total sulfur concentrations present in the samples analyzed, with contributions ranging from 1.2 to 27%. Because of the stability and oxidation resistance of these S(IV) compounds, sulfur deposition estimates that are based solely on sulfate measurements are undoubtedly low, especially for wintertime events. The study underscores the importance of S(IV) compounds in atmospheric scavenging

ISSN:0094-8276    

DOI:10.1029/GL013i013p01411

年代:1986

数据来源: WILEY

摘要:

Pioneer Venus radar data on surface properties have been used to compare the Vega spacecraft landing sites with the northern 1/4 of Venus mapped by the orbiters Venera 15 and 16. The regions surrounding both landing sites possess surface reflectivity and small‐scale roughness properties most similar to those of mapped volcanoes and volcanic plains regions and different surface properties than those of mapped tectonic units. Regions analogous to the Vega 1 site are relatively rare, covering 2.8% of the mapped surface. Vega 2 analogs are much more common and cover 22.6% of the surface. Neither landing site is representative of the nearby highlands of Aphrodite, but the Vega 2 landing site is similar to much of the northern plains of Venu

ISSN:0094-8276    

DOI:10.1029/GL013i013p01415

年代:1986

数据来源: WILEY

摘要:

The widths of terrace structures in complex craters on the moon are compared to existing theoretical models of their origin. Terrace widths in an individual crater increase monotonically outward toward the crater rim. Similarly, the width W of the terraces lying closest to the rim of a crater of diameter D increases monotonically, obeying a least squares power law relation W(km) = 0.09D0.87(km). A simple model of slumping that ignores inertial forces and assumes a constant bedrock yield strength is in good agreement with the observations.

ISSN:0094-8276    

DOI:10.1029/GL013i013p01419

年代:1986

数据来源: WILEY

摘要:

Rayleigh waves from underground nuclear explosions which are accompanied by high levels of tectonic strain release are observed to be reversed and time delayed relative to Rayleigh waves from “normal” underground explosions. The “time delays” can be explained as an interference effect between the explosion and tectonic source time functions which magnifies the true phase difference between the source functions. The phase of the explosion source time function is advanced relative to the phase of the tectonic source function, and the magnitude of the time advance is directly related to the amount of overshoot in the explosion source time function. The phase distortion is more complex than a simple time delay, and may appear as a constant phase shift with no linear trend. Apparent time advances are also possible; however because of small differences between the excitation functions of the explosion and tectonic sources at shallow depths, the phase shift will appear more frequently as an apparent time delay. Observations of Rayleigh wave phase shifts from underground explosions at the Soviet East Kazakh test site recorded at SRO stations are in very good agreement with simulated phase shifts derived from synthetic calcu

ISSN:0094-8276    

DOI:10.1029/GL013i013p01423

年代:1986

数据来源: WILEY

摘要:

Source characteristics of the May 7, 1986 Andreanof Islands earthquake (51.412°N, 174.830°W, NEIC) are investigated from WWSSN, GDSN and IDA records. First motions from over 60 stations determine one steeply dipping nodal plane. We constrained this nodal plane and inverted long‐period surface waves at a period of T=256 sec and determined the second nodal plane to be dip 18°, rake 116°, and strike 257°. This shallowly dipping thrust mechanism is consistent with plate motions in this region. Seismic moment from surface‐wave inversion is 1.3×1028dyne‐cm corresponding to Mw=8.0. Amplitudes of body and surface waves from short‐period instruments yield magnitudes of and Ms=7.7. The teleseismic average P‐wave moment rate spectrum from 17 short‐ and intermediate‐period instruments is slightly lower than that of an average Mw=8.0 subduction‐zone event. We constrained the fault plane as determined above to deconvolve the first 90 secs of the long‐period body wave at 11 teleseismic stations to determine the source time function and the spatial distribution of moment release. The source time function consists of 4 moment‐releasing episodes which have a total moment release of 9.4×1027dyne‐cm. The fault ruptured bilaterally with the largest moment releasing subevent occurring between 30‐45 sec. This subevent nucleates approximately 75‐90 km west of the determined epicenter. This region corresponds to the epicentral area of the 1957 Great Aleutian earthquake which is one of the largest

ISSN:0094-8276    

DOI:10.1029/GL013i013p01426

年代:1986

数据来源: WILEY

摘要:

Cores from two natural joints were studied to estimate the degree of correlation between the surfaces and the distribution of apertures. Matched pairs of profiles were taken from both surfaces of each joint. These profiles were then placed together to produce a linear trace of the apertures. Power spectra of the individual surfaces were compared to that of the apertures. Correlation between the surfaces is evidenced by the lack of long wavelength power in the aperture traces relative to the individual surfaces. The correlation lengths for the two joints studied are between 0.5‐5 mm. It is clear that the correlation between the surfaces must be considered, when studying the mechanical and transport properties of rock joint

ISSN:0094-8276    

DOI:10.1029/GL013i013p01430

年代:1986

数据来源: WILEY

摘要:

A Brunhes‐age viscous remanent magnetization (VRM) carried by magnetite and hematite in the El Paso and Montoya dolomite formations has unblocking temperatures significantly higher than those predicted by single‐domain theory. The samples appear to contain a substantial fraction of pseudo‐single domain magnetite, suggesting transdomain processes may be responsible for the stable VRM. A strong inverse correlation between the occurrence of high unblocking temperatures and high isothermal remanence fractions acquired above 0.3 Tesla suggests that the hematite grain size may also be important in determining the range of observed temperatures. Larger grains are inferred to have lower coercivities but higher unblocking temperatures. An older, reverse‐polarity component is also observed, and appears to be a record of late Cretaceous‐Tertiary tectonic

ISSN:0094-8276    

DOI:10.1029/GL013i013p01434

年代:1986

数据来源: WILEY