摘要:

Radar altimeter signals transmitted from the low‐orbiting satellite Geos 3 were analyzed for two selected orbits over high seas associated with hurricane ‘Caroline’ in the Gulf of Mexico and a North Atlantic storm. The measured values of significant wave height are in reasonable agreement with surface measurements, provided that the altimeter data are properly edited. The internal consistency of estimated wave heights for the North Atlantic storm, a standard deviation of 0.6 m or less, and the good agreement with surface truth lend credence to the method. A statistical analysis of the pulse slope variation gives estimated values of significant wave height within ±1 m of the true values 75% of the time for spatial averaging over

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05011

年代:1978

数据来源: WILEY

摘要:

A lightning detector, consisting of 12 silicon photodiodes, each with a field of view of 700 × 700 km on the earth, has been flown on a Defense Meteorological Satellite Program satellite. Peak amplitude of the lightning flash was digitized within a range of 16 discrete levels, and the largest amplitude observed within a 1‐s sample interval was recorded. Approximately 10,000 lightning flashes were analyzed. The frequency of occurrence of peak lightning power within the range 108–1010W has been obtained. The median power level was 1 × 109W, and about 2% of the lightning flashes had peak power greater than 1010W. These data are compared to similar results from a ground‐based experiment. Lightning flash rate per unit area of cloud cover in a storm complex was 4 × 10−5s−1km−2. The long‐term flash rate per unit surface area on the earth was 6 × 10−8s−1km−2, but this value may be biased toward high rates by the method of

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05019

年代:1978

数据来源: WILEY

摘要:

An axisymmetric, time‐dependent, numerical cloud model has been applied to study how an isolated convective cloud can be electrified when rain and cloud particles are allowed to be charged by two particle charging mechanisms: ion attachment and polarization. Charge transports by electrical conduction, air convection, turbulent mixing, and the particle terminal velocities are all simulated. The close tie‐in of the electrical development with the evolutions of the cloud growth is one of the distinctive features of the study. The full dynamical‐microphysical‐electrical interactions are allowed in the simulation. The results of numerical experiments make it appear likely that the polarization charging mechanism is an important one for the electrification of warm clouds. The results also show that with the inclusion of the polarization charging mechanism and depending on the growth stage of the cloud the cloud can be electrified into various charge center structures, which have been observed and reported in the literature for many years. The numerical results show that the cloud cannot be rapidly electrified until rainwater forms and the polarization charging mechanism operates. Initially, the cloud is charged into a ‘positive dipole’ structure with a positive charge center in the upper part of the cloud and a negative one below. As the cloud grows further, another positive charge center forms below the main negative one. This weaker positive center is closely associated with the positively charged rain formed in that region. As the rain falls out of the cloud, this positive center extends below the cloud base. When the cloud top reaches its maximum level, the cloud base starts to rise and the cloud grows weaker thereafter. In the later stage of the development the charge distribution patterns of the rain field dominate the whole electrical structure of the model. The electrical pattern thereafter is greatly affected by the downward movement of the rain. With the fallout of the rain the cloud charge centers exhibit successfully a positive dipole structure and then a ‘negative dipole’ structure consisting of a negative charge center in the upper part of the cloud and a positive one below. The electrical force effects on the terminal velocities of the rain and cloud particles are also included in the study. The results show that the rain particle terminal velocities start to decrease by a few meters per second in a region where the electric field strength grows beyond 2 × 105or 3 × 105V/m. The cloud particle terminal velocities reach only several centimeters per second, even in the thunderstorm electrical state. As a result of the levitation effect on rain, the simulated cloud in the present study develops double maxima in the cloud water content, giving it a more irregular appearance than the weakly electrified or non

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05025

年代:1978

数据来源: WILEY

摘要:

During the winter of 1976, along with the continuing studies of ice crystals in the cap cloud on Elk Mountain, measurements were made of ice crystal charges and the atmospheric electric field strength. The electric field was, in general, found to be of the same sign as the fair weather field. The net particle charges were predominantly positive with mean values of the order of ±10−14C with fairly symmetrical distributions of positive and negative charges. The ‘mirror image’ effect was seldom observed perhaps because of the small extent and short lifetime of the cap cloud. The absence of large negative charges suggests that the particles and particle charges do not originate from blowing snow. A mechanism of charging which may explain the symmetrical charge distributions is inductive charge transfer between particles which contact and then separate in random directions relative to the electric

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05050

年代:1978

数据来源: WILEY

摘要:

A new objective method of comparing cloud amount frequency and distribution is described. The analysis, which uses the beta distribution to model cloud frequency curves, depends upon the numerical values of two defining parameters (η and γ). Comparison of cloud amount frequency derived from ground‐based data for six different climatological regions is made, and conclusions about the effect of the underlying surface type are drawn. The analysis seems to indicate that cloud amount frequency over land areas at different latitudes have pronounced similarities. This objective method will also be of use for climatological analysis of satellite observations of cloud co

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05057

年代:1978

数据来源: WILEY

摘要:

Examination of the density field suggests that the large‐scale anticyclonic gyre generally supposed to obtain within the upper waters of the North Atlantic Ocean is considerably altered at middepths. Not only is there a strong return flow westward just south and east of the Gulf Stream‐North Atlantic Current, but this return flow also turns southward near 30°N and continues eastward all across the Atlantic. The warm and saline waters of the outflow from the Mediterranean Sea join the westward return flow south of the Gulf Stream‐North Atlantic Current and are carried westward as they spread and mix, providing the great wedge of warm, saline waters found from 600 to 2500 m in the North At

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05063

年代:1978

数据来源: WILEY

摘要:

Radon 222 and STD profiles were obtained as part of the Geosecs program in the Vema Channel in the southwest Atlantic Ocean and in the Samoan, Clarion, and Wake Island passages in the Pacific Ocean. The standing crop of excess radon 222 is higher in the passages than at other nearby locations, The most likely explanation for this is that there is a high flux of radon 222 from the floor of the passages. Since much of the floor is covered with manganese nodules and encrustations, the high flux of radon 222 may be attributable to the high concentrations of radium 226 in the outer few millimeters of such deposits. Laboratory measurements of radon 222 emissivity from manganese encrustations obtained in the Vema Channel support this hypothesis. The excess radon 222 in the Vema Channel and Wake Island Passage is found in substantial quantities at heights above bottom greatly exceeding the heights at which excess radon 222 is found in nonpassage areas. The horizontal diffusion of radon emanating from the walls of the passages is unlikely to be the cause of the observed concentrations because the ratio of wall surface area to water volume is very low. The profiles must therefore be a result of exceptionally high apparent vertical mixing in the passages. Further work is needed to determine the nature of this apparent vertical mixing. The excess radon 222 and STD data in all four passages have been fit with an empirical model in which it is assumed that the buoyancy flux is constant with distance above bottom. The fits are very good and yield apparent buoyancy fluxes that are between 1 and 3 orders of magnitude greater than those obtained at nearby stations outside the passages for three of the four passages.

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05068

年代:1978

数据来源: WILEY

摘要:

Current observations over three isobaths (50, 100, and 200 m) on the Oregon continental shelf are available for winter and spring 1975 and summer 1973. In each season there are low‐frequency current fluctuations with periods of several days, predominantly alongshore, that are correlated with the along‐shore wind stress and sea level at Newport. The amplitude of the current fluctuations is greatest in winter and least in summer, but the ratio between current and wind stress fluctuations does not change appreciably. In each season the alongshore fluctuations have the same sign throughout the water column, and they are nearly in phase across the shelf. The vertical and offshore structure of the fluctuations was examined by means of empirical orthogonal functions. In winter the amplitude decreases with depth at each location; in summer it is nearly constant at all locations. The near‐bottom shear is consistent with Ekman veering. Away from the bottom the shear is in approximate geostrophic balance. The fluctuations have a significant baroclinic component in winter but not in summer. In each season the amplitude of the fluctuations decreases with distance from shore, but the offshore length scale is about twice as great in winter as it is in s

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05077

年代:1978

数据来源: WILEY

摘要:

Current, salinity, and temperature data obtained from lower Cook Inlet during May‐September 1973 have been analyzed. These data define a regional mean circulation whose main features are (1) a concentrated southward flow along the western shore of lower Cook Inlet of water from upper Cook Inlet which has been diluted by river input, (2) an intense westerly flow across the lower inlet which originates from Kennedy Entrance, exits via Shelikof Strait, and is bathymetrically steered in a cyclonic sense during its transit across the inlet, and (3) a slow northward drift in eastern lower Cook Inlet. The southward flow is an estuarine mode due to freshwater input to upper Cook Inlet. The westerly flow is driven by the westward flowing Alaska Current. The weak northward drift replaces water which has been entrained into the south flowing current. Large tidal and wind‐induced currents are superposed on this mean flow and contribute to complex temperature and salinity distributions. The circulation scheme as redefined here allows for vertical motions and has important consequences in relation to high regional biological productivity and fates of contamina

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05090

年代:1978

数据来源: WILEY

摘要:

Temperature profiles at two locations in the tropical North Pacific Ocean (8°27′N, 150°47′W and 11°43′N, 138°23′W) are analyzed and compared with similar data from the central gyres of the Atlantic and Pacific oceans. The vertical fine structure spectra in the thermocline (300–600 m) divide into two wave number bands, each of which has a distinct slope. For 0.003

ISSN:0148-0227    

DOI:10.1029/JC083iC10p05099

年代:1978

数据来源: WILEY