摘要:

In the critical region, the complex amplitude of the interfering system of a head wave and its associated reflected wave can be described by a single formula for all eight types of interference waves. The formula consists of transmission, reflection and head wave coefficients, geometrical parameters of the layers and an appropriate Weber function. The real and imaginary parts of the Weber function can be shown to be the solutions of a system of first order differential equations. The system may be solved numerically with the help of existing subroutines in the computer software libraries. Upon determining the Weber function, one may construct amplitude‐distance curves for the interference reflected‐head waves of any desired type. Some properties of the amplitude‐distance characteristics can be directly inferred from the Weber function. The very good matching between this method and asymptotic ray theory outside the critical region suggests that a combination of the two would provide an efficient technique for ray amplitude calcul

ISSN:0094-8276    

DOI:10.1029/GL004i007p00255

年代:1977

数据来源: WILEY

摘要:

A series of aerial photographs were obtained of a nuée ardente produced by the February 8, 1976 eruption of the St. Augustine volcano, Alaska. The nuée ardente reached a maximum velocity of 50 m s−1while descending the steeper (∼1∶3) slope of the volcano. It later slowed to a velocity of 6 m s−1as it traversed the gentler slope (∼1∶25) at the base of the volcano, where it formed a deposit. The nuée ardente appeared to originate with the collapse or penetration of a newly formed dome, rather than the collapse of a vertical eruption column. Fluidization by fine particles in the nuée ardente probably contributed

ISSN:0094-8276    

DOI:10.1029/GL004i007p00259

年代:1977

数据来源: WILEY

摘要:

Dynamic compression studies using high velocity impact are usually considered to involve a catastrophic process of indeterminate loading rate by which a material is brought to a shock compressed state. Although this is frequently the case, methods are also available to control the rate of strain during the shock compression process. One of the most accurate of these methods makes use of the anomalous nonlinear elastic property of glass to transform an initial shock or step wave input into a ramp wave of known amplitude and duration. Fused silica is the most carefully calibrated material for this purpose and, when placed between the test specimen and the impact projectile, can provide loading strain rates in the range of 104/s to 106/s for final stress states of approximately 3.9 GPa or less.Ramp wave compression experiments have been conducted on dolomite at strain rates of 3 × 104/s. Both initial yielding and subsequent deformation at this strain rate agrees well with previous shock wave studies (⋵ ∼ 106/s) and differs substantially from quasi‐static measurements (⋵ ∼ 10−4/s). The ramp wave studies have also uncovered a pressure‐induced phase transition in dolomite initiat

ISSN:0094-8276    

DOI:10.1029/GL004i007p00263

年代:1977

数据来源: WILEY

摘要:

Climatic changes, geomagnetic intensity fluctuations, and variations of the eccentricity of the earth's orbit during the past 0.8 m. y. are compared. In general, warm climate stages are aligned with low magnetic field intensities and high orbital eccentricity. We tentatively conclude that the eccentricity of the earth's orbit may partially modulate both the earth's magnetic field and climate.

ISSN:0094-8276    

DOI:10.1029/GL004i007p00267

年代:1977

数据来源: WILEY

摘要:

The first measurement of the hemispheric distribution of N2O concentrations in the lower stratosphere of the Northern Hemisphere is reported for July 1975. This distribution is similar to those of CCl3F and SF6, although N2O is more stable in the stratosphere than either of the other trace gases. The inventory of N2O in the stratosphere of the Northern Hemisphere in July 1975 against which future observations can be compared is 136 Tg.

ISSN:0094-8276    

DOI:10.1029/GL004i007p00271

年代:1977

数据来源: WILEY

摘要:

Very‐low‐frequency (VLF) chorus activity detected by the Ogo 3 satellite has the highest probability of occurrence in regions threaded by geomagnetic field lines that intersect industrialized areas. Interpretation of these results is based on radiated power line harmonics that leak into the magnetosphere and stimulate the recorded emissions through cyclotron interaction with trapped energetic electrons. These results emphasize the need for a careful evaluation of the effects of man‐made VLF noise on the ionosphere and magnetos

ISSN:0094-8276    

DOI:10.1029/GL004i007p00275

年代:1977

数据来源: WILEY

摘要:

A remote sensing laser Raman backscattering technique has made the first field measurements, from a boat, of subsurface temperature in natural ocean waters. These results and the measurement systems rapidly developing from them open wide areas of exploitation. The technique utilizes the observation of the 3400 cm−1O‐H stretching Raman band of liquid water. The spectral data were analyzed to obtain the subsurface water temperature in accordance with previous laboratory studies. The importance of such a measurement by the Raman scattering technique is that it now enables depth resolved profiles of ocean water temperature to be obtained by remote sensing from airborne platforms that can be adapted for application to many problem areas of physical oceanography, meteorology, climatology, ocean technology, and thermal discharge management. An accuracy of ± 2°C has been obtained in the initial field experiments. A more refined system has been designed which will permit accuracies of better than ± 1°C in the first one or two optical attenuation lengths o

ISSN:0094-8276    

DOI:10.1029/GL004i007p00279

年代:1977

数据来源: WILEY

摘要:

Two recently published reports propose different causes for the Chandler wobble excitation. One study suggests that earthquakes are important, while another investigation by us favors meteorological sources. Upon re‐examination of the earthquake data, we find that the magnitude of the estimated earthquake contribution could explain about 25% of the Chandler wobble variance, but that there is no supporting evidence of correlation with observed polar motion. We conclude that there is presently no reason to believe the earthquake portion of the Chandler wobble excitation is any larger than 25%. On the other hand, the contribution of meteorological variation appears to be not less than 25%, and may easily be much mor

ISSN:0094-8276    

DOI:10.1029/GL004i007p00283

年代:1977

数据来源: WILEY

摘要:

A positive gravity anomaly is associated with the Mississippi embayment. When correction for low density sedimentary rocks is made the anomaly is seen to be continuous along the embayment, with an amplitude of 15 to 45 mgals increasing southward. The axis of the embayment anomaly follows the course of the Mississippi river. The seismic refraction profile critical to Ervin and McGinnis' interpretation of a fossil rift cushion underlying the embayment was located on the margin of the embayment anomaly where the structure is most complex. The continuity of the gravity anomaly indicates that a reversed refraction line along this axis, and a reflection line across it, might yield definitive results.

ISSN:0094-8276    

DOI:10.1029/GL004i007p00285

年代:1977

数据来源: WILEY

摘要:

Stimulated Brillouin scattering can cause asymmetries of ± 25% and ± 1% in the double humped spectra of incoherent backscatter measured at Jicamarca and at Arecibo, respectively. Errors of 10‐15 m/sec in the measured velocity could have been caused by ignoring the effects of these asymmetries at Arecibo but the typical errors were probably much smal

ISSN:0094-8276    

DOI:10.1029/GL004i007p00289

年代:1977

数据来源: WILEY