摘要:

Observations at Fort Yukon, Alaska, in August 1962 showed that most of the 10‐ to 110‐sec‐period infrasonic pressure waves during that period originated in auroral disturbances. Associated magnetic and cosmic noise absorption effects, together with determinations of the arrival direction of the pressure fluctuations, indicated an ionospheric source. We also studied a unique event, not of the auroral type, which appeared to give evidence that a large, primarily tropospheric pressure front could produce a disturbance in the ionosphere. Mechanisms for the two types of observations can be found in well‐accepted, auroral‐zone ionospheric

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05909

年代:1963

数据来源: WILEY

摘要:

The minor surface magnetic activity during the flight of Explorer 10 consisted mainly of worldwide simultaneous events. In space Explorer 10 found periods of plasma alternating with plasma‐free periods. A comparison of the surface data and the data from Explorer 10 suggests that the plasma‐free periods represent times when Explorer 10 was inside the broad tail of the magnetosphere. This tail could have had a generally cylindrical sh

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05917

年代:1963

数据来源: WILEY

摘要:

It has been shown that some types of VLF emissions (hooks, risers, and falling tones) may be the result of cyclotron emission by energetic electrons trapped in the earth's magnetic field. Observational evidence suggests that a relatively intense electromagnetic whistler‐mode wave may be necessary to trigger each such emission. An interaction mechanism is proposed by which certain electrons may couple with a wave already propagating along the same line of force. A gyroresonance is established which organizes the electrons so that cyclotron radiation can be coherent. A change in phase relationship occurs for those electrons that have a longitudinal velocity component such that the Doppler‐shifted frequency of the whistler wave seen by the electron is equal or nearly equal to the electron gyrofrequency. This condition is met by electrons moving in a direction opposite to the whistler wave and is satisfied only over a certain fraction of the line of force. Observations also show instances of a sudden change in slope of the rising tail of a hook or other VLF emission at the crossing of the spectrums of the emission and a whistler. This change is interpreted as the effect of the encounter of a whistler with the electron stream that changes both energy and pitch angle of the emitting electr

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05925

年代:1963

数据来源: WILEY

摘要:

Nighttime geomagnetic micropulsations were observed in the 1.5‐cps frequency band down to a limiting sensitivity of 0.05 mγ. These results were compared with all‐sky and localized radar meteor rates obtained at the same site to investigate the magnetic effects produced by meteors. The variation of meteor rates for each hour, plotted through a succession of nights, is not significantly related to the corresponding micropulsation activity. Individual meteor occurrence has been examined by recording on the same chart as the micropulsation activity. Most individual meteors do not have any associated micropulsation activity, but the number of coincidences is greater than random, and it remains possible that some of the larger meteors do produce magnetic eff

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05937

年代:1963

数据来源: WILEY

摘要:

The transport equations that describe irreversible processes in the very dilute, reacting, ionized gas mixture which comprises the upper atmosphere are derived. These equations have application in the description of the properties of the ambient atmosphere and in the determination of the effects of the passage of a traversing vehicle through the atmosphere. In particular, the intensity and frequency of the radiation emitted as night glow from the upper atmosphere will be affected by the phenomena described.

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05947

年代:1963

数据来源: WILEY

摘要:

In the area around King Baudouin Station (70°S, 24°E), it is shown that a reference horizon, easy to identify, was formed by the stratospheric fallout of radioactive debris from thermonuclear bomb tests. Gross β activity and Sreo have been measured in snow and firn samples from 1935 to 1960. The samples were dated by stratigraphy and by oxygen isotope‐ratio measurements. The contribution of natural radionuclides is negligible, and the gross β activity can be taken as a measure of the fission products concentration. The following average values were found: from 1955 to 1960, 14 dpm/kg of snow; beginning of 1955, 22 dpm/kg (Sr90= 4.5); 1953 and 1954, 2 dpm/kg; and from 1935 to 1952: 0.5 dpm/kg (Sr90<0.1). The sharp tenfold increase in the β activity at the beginning of 1955 is attributed to the sudden release in the antarctic troposphere of fission products from the Castle thermonuclear tests series (March 1954). The previous and first thermonuclear test (Ivy, November 1952) is less marked. The β activity before 1952 is essentially due to Pb210and K40. There are indications that this radio‐active horizon has been formed at the same time over the whole ice cap, but direct checks are needed on more, well‐dated fi

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05965

年代:1963

数据来源: WILEY

摘要:

The results of seismic measurements made during the Antarctic Peninsula over‐snow traverse of 1961–1962 are presented and discussed. Maps of snow surface and bedrock elevation are presented. The Antarctic Peninsula is shown to be an island separated from the Sentinel Range by a channel 1000 m below sea level and from the Eights Coast of Ellsworth Land by a channel 500 m deep. A reflection horizon 450 m above the base of the ice near Eights Station was observed. Wide‐angle reflections showed the existence of a low‐velocity layer below this reflecting horizon which is interpreted as the result of moraine within the ice. An 18‐km refraction profile showed a velocity of 3.87 km/sec in the top 0.9 km of ice, a velocity of 4.39 krn/sec in the next 0.2 km, a velocity of 5.29 krn/sec in the next 3.5 km, and a possible velocity of 6.0 km/sec in the r

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05973

年代:1963

数据来源: WILEY

摘要:

The first deep‐water, in situ measurements of sound velocity in sea‐floor sediments (other than seismic) have been made from the bathyscaphTrieste. These measurements were made at three stations off San Diego during August–October 1962 at depths of 338 to 1235 meters. Specially designed probes measured sound travel time over a 1‐m path, 46 cm below the water‐sediment interface at frequencies of 25 kc/s; probe accuracy was about ±0.5 m/sec. Laboratory measurements of sound speed in sediment can be corrected to in situ conditions in the sea floor by applying full corrections for temperature and pressure, using tables for sound speed in sea water. A significant portion of the vertical sound velocity gradient within the sea floor must be due to thermal gradients. At the Mohole (Guadalupe) site, for example, the thermal gradient (plus a small increment due to pressure) accounts for an increase in sound velocity of 53 m/sec in the upper 100 meters of the sediment. In situ sound speeds of less than 1 per cent error can be predicted for fine‐grained, high‐porosity sediments off San Diego by means of present sound‐speed versus porosity curves; these curves need re

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05991

年代:1963

数据来源: WILEY

摘要:

A map of earthquake epicenters is presented for the South Pacific Ocean for the period 1957 to 1963. For much of this region the accuracy in locating epicenters has been improved by nearly an order of magnitude in comparison with that of previous studies. In several areas of the South Pacific the seismic activity is confined to narrow zones that are less than 50 km wide. Near 55°S and between 122° and 135°W the pattern of epicenters is offset approximately 1000 km. Seismic and bathymétrie data indicate that a fracture zone intersects the Easter Island ridge in this region. Epicentral data suggest that several other fracture zones may be present in the South Pacific and eastern Indian oceans. Regions of relatively high seisrnicity on the oceanic ridges may be related to the presence of fracture zones that intersect the crest of the ridge. Seismic activity along these fracture zones is restricted almost exclusively to the region between the displaced crests of the oceanic ridge. A number of topo‐graphic profiles across the oceanic ridges in the South Pacific and eastern Indian oceans are compared with the epicentral determina

ISSN:0148-0227    

DOI:10.1029/JZ068i021p05999

年代:1963

数据来源: WILEY

摘要:

It is well known that in laboratory studies of wave phenomena in flumes and models the flow is laminar. From field observations, however, it is known that turbulence exists for most or all cases of finite wave motion. An experimental investigation of the range of validity of the theory of mass transport by waves proposed by Longuet‐Higgins for a viscous boundary layer at the bottom led to the discovery of the value of the critical Reynolds number at which turbulence occurs on a smooth horizontal bed. This experimental value is compared with theoretical and experimental observations of other authors. The value of the critical Reynolds number was found to be given byVoδ/v= (π/vT)1/2H/sinh kd

ISSN:0148-0227    

DOI:10.1029/JZ068i021p06007

年代:1963

数据来源: WILEY