摘要:

The rate of decrease in the magnitude of the maximum tangential velocity of laboratory Karman vortexes is found to be essentially as predicted by means of a two‐dimensional theory for the diffusion of vorticity. The implication is clear that surface friction effects are not overriding. Certain features of atmospheric Karman vortexes suggest that they are in some important respects dynamically similar to the laboratory vortexes, and thus these vortexes may also experience rather small energy losses from surface frictio

ISSN:0148-0227    

DOI:10.1029/JC075i006p01033

年代:1970

数据来源: WILEY

摘要:

At least two mechanisms operate over water to produce atmospheric space charge. Although both processes produce positive charge over the ocean, on Lake Superior it was found that breaking waves produced negative space charge, whereas the classical electrode effect with its accompanying positive space charge was observed when the lake's surface was calm. Laboratory bubbling of a lake‐water sample also produced a net negative atmospheric charg

ISSN:0148-0227    

DOI:10.1029/JC075i006p01041

年代:1970

数据来源: WILEY

摘要:

Peak spectral intensities emitted by seven types of lightning phenomena, viz., first and subsequent return strokes, stepped and dart leaders, cloud‐to‐air flashes, intracloud pulses, and M components of return strokes, are reported in five narrow regions of the visible and near‐visible spectrum. At 3914 A the peak continuum radiation varies from 300 to 107watts ster−1A−1, averaged over a 23‐A bandwidth and integrated over the whole source. For the average lightning stroke, the spectral intensities at the other regions studied, relative to that near 3914 A, are: 0.95 at 4140 A (continuum), 2.1 at 6563 A (Hα plus continuum), 4.8 at 8220 A (NI[2] plus continuum), and 0.7 at 8900 A (continuum).Return strokes are usually the most intense lightning phenomena but can vary in intensity by a factor of 1000 from storm to storm and by a factor of 50 within one flash. The most intense return strokes appear to have the highest radiating temperature. Stepped and dart leaders are a factor of 20 to 100 less intense than their return strokes, but the leaders and return strokes have similar spectra. Pulses originating within clouds vary in intensity from the weakest pulses observed to ∼105watts ster−1A−1near 3914 A and are substantially stronger in the near‐infrared channels, relative to the 3914‐A channel, than the average stroke. M‐component brightenings of return‐stroke channels are of lower excitation than typical return strokes but are otherwise similar to them. There is no indication in any of these strokes of the strong N2+1N (3914 A) radiation present in some slit spec

ISSN:0148-0227    

DOI:10.1029/JC075i006p01049

年代:1970

数据来源: WILEY

摘要:

Expressions are derived relating the stepped leader radiation field to the leader current and current propagation velocity. These expressions are also applicable to the return stroke. The waveforms of the stepped leader radiation field measured by Pierce, Appleton, and Chapman can be reproduced by the sum of the effects of two current waves: (1) a slow current wave with a current width at half‐maximum of about 14 μsec and a propagation time of about 12 μsec, which produces the wings of the radiation field curve, and (2) a fast current wave with a current width at half‐maximum of 4 to 5 μsec and a propagation time of about 1 μsec, which produces the positive and negative peaks of the radiation field. The fast current is associated with the luminous leader step; the slow current is most reasonably associated either with the leader step or with the leader channel above the step. The peak current for the typical stepped leader waveform described by Pierce is calculated to be between about 800 amps and 5 ka; the maximum rate of change of current between about 0.25 and 1.5 ka/μsec. Alternatively, the maximum rate of change of leader current is derived from Hodges's data on the ratio of peak leader radiation field to peak return stroke radiation field. For a modal type α stepped leader the maximum rate of change of current is found to be about 2 ka/μsec; for a modal type β leader, about 10 ka/μsec. The currents calculated to flow in the stepped leader provide a charge transfer of between about 2×10−3and 10−2coul per leader step, an insufficient amount of charge to account for the 10−3coul/m found on a typical fully developed stepped leader. Relatively steady currents must therefore flow in the leader channel to account for the charge transfer. Since the significant light output from a stepped leader has considerably shorter time duration than the significant current, it is probable that the photographed luminosity of the leader is due to the electrical breakdown at the propagating current fronts, rather than to the larger currents tha

ISSN:0148-0227    

DOI:10.1029/JC075i006p01058

年代:1970

数据来源: WILEY

摘要:

The feasibility of deducing the spectrum of the permittivity fluctuations of the turbulent atmosphere from different types of laser experiments is discussed in a theoretical framework. At optical wavelengths the permittivity spectrum is proportional to the temperature spectrum. It is shown that measurements of the amplitude covariance function over short paths of the order of 10 to 30 meters will reveal information about the inner scale of turbulence and the spectral shape in the viscous dissipation range. Amplitude covariance measurements over longer paths, of the order of 100 to 2000 meters, are sensitive to the spectral shape in the inertial subrange, although they are still influenced somewhat by the inner scale. Phase measurements are quite insensitive to the spectral shape, but do give information about the outer scale of turbulence. These measurements may be performed over any reasonable path length. Angle‐of‐arrival measurements are extremely sensitive to the spectral shape in the inertial subrange, but the experiment would require extremely sophisticated equipm

ISSN:0148-0227    

DOI:10.1029/JC075i006p01067

年代:1970

数据来源: WILEY

摘要:

A propagation experiment was performed with a coherent beam of optical‐frequency radiation transmitted over a 10‐meter path. The combination of short path length and short wavelength makes the experiment sensitive to the fine‐scale structure of the turbulent atmosphere. From the propagation measurements, we are able to infer both the characteristic size of the small‐scale eddies known as the microscalel0and the functional form of the spectrum of permittivity fluctuations at wave numbers in the region of dissipation (i.e., wave numbers of the order of the micr

ISSN:0148-0227    

DOI:10.1029/JC075i006p01077

年代:1970

数据来源: WILEY

摘要:

By the analysis of water and sediment cores, the total inventory of strontium 90 in Crater Lake, Oregon, was determined to be 4.2 curies. In terms of surface fallout, this is equivalent to about 70 mc/km2. The comparable fallout on the surrounding land area, determined from analyses of soil sections was 58 mc/km2, and a value predicted by extrapolation from other Oregon stations was 73 mc/km2. Hence, no substantial difference in the efficiency of fallout collection could be attributed to the mere presence of the large water surface.

ISSN:0148-0227    

DOI:10.1029/JC075i006p01084

年代:1970

数据来源: WILEY

摘要:

Measurements of Sr90in Lake Michigan water and sediments indicate that fallout is no greater over the lake than over nearby land. Excess “oceanic” fallout over land fallout is in controversy. The Lake Michigan result favors no enhancem

ISSN:0148-0227    

DOI:10.1029/JC075i006p01092

年代:1970

数据来源: WILEY

摘要:

In the central North Pacific, the transition between subarctic and subtropical water masses takes place between 42° and 32°N. The width of the zone and the sharpness of its boundaries are largely determined by the wind stress distribution at the sea surface. The northern boundary is characterized by numerous temperature inversions, the disappearance of the subarctic halocline, gravitational instabilities, and a complicated sound velocity structure. The southern boundary is marked by sharp thermohaline gradients and instabilities in the upper‐most layer. The vertical distribution of properties in the transition zone is characterized by a deep salinity minimum of about 33.95‰ at 500 meters, by a sound velocity minimum of slightly less than 1480 m sec−1at 800 meters, and by an almost linear temperature gradient in the upper 600 meters. Both the salinity and sound velocity minimum rise northward and lose their identity at the northern boundary. The baroclinic and barotropic modes of motion in the transition zone are very slow with speeds rarely exceeding 5 cm sec−1. A strong westward setting current with surface speeds in excess of 100 cm sec−1was found 22 km north of Kahuku Point, Oahu, Hawaii. The width of the high‐speed core was about 6 km, and the relative vorticity due to horizontal current shear reached values in excess o

ISSN:0148-0227    

DOI:10.1029/JC075i006p01097

年代:1970

数据来源: WILEY

摘要:

A detailed thermal structure in the eastern Bering Sea is described, based on data obtained by the training shipOshoro Maruduring the summers of 1964, 1965, and 1966. The description is based on the movement of extremely cold water over the continental shelf in the eastern Bering Sea and on the intrusions of warm water mainly across the Amukta and Amchitka passes. Some of the tendency of decrease and increase of temperature is also presented in a vertical section. The typical feature of vertical temperature distribution is mostly represented by five stratified thermal layers.

ISSN:0148-0227    

DOI:10.1029/JC075i006p01110

年代:1970

数据来源: WILEY