摘要:

From an examination of about 1000 electric field wave forms produced by lightning return strokes in 16 storms at distances between 20 and 100 km from an observation site at the Kennedy Space Center, Florida, a typical return stroke current wave form is derived. For this current wave form, the electric field intensity at distances between 0.5 and 100 km is computed for three values of return stroke velocity. The resultant curves for close lightning are compared with measured field wave forms. The transmission line return stroke model is used in all calculations since, as discussed, the Bruce‐Golde model cannot account for the observed electric field characteristic

ISSN:0148-0227    

DOI:10.1029/JC078i018p03523

年代:1973

数据来源: WILEY

摘要:

The transmission line return stroke model is used to derive individual current versus time wave forms from measured electric fields. A total of 98 strokes in 21 flashes at distances less than or equal to 10 km and 63 strokes in 18 flashes at distances between 10 and 32 km are analyzed for current wave shape and magnitude. For the closer strokes, return stroke velocity is also determined from the electric field wave forms. Values are in the range 0.8–2.4 × 108m/sec. Eighteen detailed current and field wave forms and a statistical distribution of peak currents are presented. The maximum value of peak current is near 100 ka; the maximum value of rate of change of current averaged from 0 to peak is near 200 ka/μsec. Return stroke channel currents are found to exhibit a sharp initial peak which currents measured in tall structures at the base of the lightning channel apparently do not exhibit. A complete discussion of errors is gi

ISSN:0148-0227    

DOI:10.1029/JC078i018p03530

年代:1973

数据来源: WILEY

摘要:

Analysis is presented for predicting the local radiative flux and the volumetric rate of absorption of solar radiation in water on spectral and total bases. The model considers absorption, multiple scattering, internal reflection of radiation at the air‐water interface, and reflection at the bottom. Numerical results are reported for pure water with isotropic, Rayleigh, forward, and experimental scattering distribution functions and illustrate the effects of multiple scattering and other physical parameters on radiant energy transfer in waters. It is shown that models which ignore scattered energy can lead to serious errors in the predictions of the radiative flux and the volumetric rate of solar energy absorption. Results indicate that it is unrealistic to choose a priori a mean value of the absorption or attenuation coefficient for predicting radiative transfer in water

ISSN:0148-0227    

DOI:10.1029/JC078i018p03538

年代:1973

数据来源: WILEY

摘要:

A mechanism of steady state creep is proposed to describe the attenuation rate of long‐period ocean waves in fields of sea ice. It is shown that this mechanism fits the existing wave observations ofRobin[1963] andWadhams[1973] provided a Glen‐type flow law is employed with an exponentn= 3 and a flow law parameter 〈B〉 similar to the value for polycrystalline ice near the meltin

ISSN:0148-0227    

DOI:10.1029/JC078i018p03552

年代:1973

数据来源: WILEY

摘要:

A combination of remote sensing from an aircraft and simultaneous surface measurements have confirmed the feasibility of identifying old and new sea ice according to its emission of thermal radiation at wavelengths between 0.3 and 3 cm. Emissivity of first‐year thick ice with a surface temperature of about 260°K is 0.95 or greater for wavelengths between 0.81 and 11 cm; the emissivity of multiyear ice is 0.8 at 0.81 cm and 0.95 at 11 cm, increasing monotonically in this wavelength interval. The ease with which multiyear ice can be distinguished from first‐year ice using a passive microwave radiometer is demonstrated by comparing mosaics prepared both from photographs and images of 1.55‐cm rad

ISSN:0148-0227    

DOI:10.1029/JC078i018p03564

年代:1973

数据来源: WILEY

摘要:

A sonic anemometer, lyman alpha humidiometer, and thermistor thermometer were operated on ice at 75°N, 15°W in March‐April 1972 as part of the Aidjex pilot study. Spectra of temperature and humidity fluctuations and cospectra for the sensible and latent heat fluxes were similar to those published for neutral conditions over sea and land. Bulk transfer coefficients wereCT= 1.2 × 10−3andCQ= 0.55 × 10−3, respectively. The Bowen ratio of sensible to latent heat fluxes ranged from 1 to 15 and can be obtained from values of the temperature and humidity spectra at low frequencies except when the latent heat flux is very small. These data were recorded at the spring equinox, and the dominant feature of the heat fluxes is their diurnal variation. Evaporation continued for several hours after the sensible heat flux changed to the downward direction. Over Robeson Channel in July 1972 the heat transfer coefficient wasCT= 1.0 × 10−3for stabl

ISSN:0148-0227    

DOI:10.1029/JC078i018p03573

年代:1973

数据来源: WILEY

摘要:

Data from a recording current meter operated for 104 days in Lake Ontario were augmented with 3 hours of temperature‐compensated hot‐film anemometer data to develop the kinetic energy spectra for a frequency range of 6.0–1.0 × 10−7Hz. The measurements were taken approximately 1 km offshore in 9 meters of water, the instruments being located 5.3 meters from the surface. Three hours of hot‐film anemometer readings were also collected well offshore in the epilimnion at a depth of 5.8 meters below the surface in 22 meters of water during similar wind climates and sea states. All data were processed by a fast Fourier transform by using ensemble averaging. It was found that the spectrum in the nearshore region was different from that in the offshore region. The nearshore spectrum approximated a slope of −3.0, the energy‐containing wave number being 5.3 × 10−3cm−1and the integral scale being 2.4 meters, whereas the offshore spectrum approximated a slope of −1.6, the energy‐containing wave number being 1.0 − 10−4cm−1and the integral scale being 4.3 meters. The viscous dissipation in the nearshore region was 0.11 cm2/sec3, the energy‐containing wave number being 1.0 × 10−4cm−1. Viscous dissipation in the offshore experiment was 0.09 cm2/sec3, the energy‐containing wave number being 3.9 × 10−3cm−1. Little or no kinetic energy ex

ISSN:0148-0227    

DOI:10.1029/JC078i018p03585

年代:1973

数据来源: WILEY

摘要:

A large‐diameter (14 cm) long piston corer (20–40 meters) has been used successfully to obtain relatively undisturbed sediment samples in water depths from 80 to 5500 meters with recovery ratios ranging between 0.76 and 0.87. The first recovered core (KN‐10‐1) was taken in the Stellwagen basin, western Gulf of Maine, at 81‐meter water depth using a pipe length of 33.5 meters and total core weight of 3500 kg. The 21.74 meters of recovered sediment is black, gray to olive green silty illitic clay. Visual observations and results of consolidation studies indicate that structural disturbance to the sediments was not severe, that it is normally consolidated, and that no postdepositional compaction occurred. Another core (KN‐27‐1) was taken about 3 km east of the first core location, and 19.65 meters of sediment were recovered. An anomalous zone in core KN‐10‐1 reveals high water content (96%) and high shear strength (260 g/cm2). A marked abundance of diatoms may explain the high water content, and the highly flocculated nature of the abundant clay minerals observed with a scanning electron microscope accounts for the high shear strength. A similar anomalous zone in core KN‐27‐1 occurs where the water content is 53% and shear strength is about 250 g/cm2. Preliminary correlations with the 3.5 kHz subbottom profiles suggest that changes in both texture and water content may produc

ISSN:0148-0227    

DOI:10.1029/JC078i018p03597

年代:1973

数据来源: WILEY

摘要:

A wave guide mode computer model is used to calculate ELF radio fields in the earth‐ionosphere wave guide. Results are compared with those calculated by Galejs and by Johler and Lewis for both homogeneous and diffuse inhomogeneous ionospheres as well as with measurements of Sanguine test transmissions. Good agreement is found in all comparisons except for those with the Johler and Lewis calculations for an inhomogeneous ionospher

ISSN:0148-0227    

DOI:10.1029/JC078i018p03617

年代:1973

数据来源: WILEY

摘要:

The increase in terminal velocity of large water drops in the presence of vertical electric fields has been measured in a wind tunnel and found to be negligible (0.1 m sec−1change per 1 kv cm−1field increment). Preliminary work indicates decreases of similar magnitude in oblique electric fie

ISSN:0148-0227    

DOI:10.1029/JC078i018p03619

年代:1973

数据来源: WILEY