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A method is presented for the retrieval of classification parameters of clouds observed by satellite-borne imaging systems. It is based on a two-dimensional fast Fourier transform of cloud images and an analysis of their power spectra. The parameters retrieved provide quantitative information on mean brightness, size, shape and directional properties of clouds. The efficacy of the subdivision of the original cloud image into smaller regions and the determination of individual parameters is demonstrated by applying this procedure to some NOAA and INSAT cloud images. 相似文献
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David A. Flemer Donald R. Heinle Carolyn W. Keefe D. Heyward Hamilton 《Estuaries and Coasts》1978,1(3):157-163
A comparative study of the standing crop of marsh vegetation was made of the Patuxent River and Parker Creek, two tributaries of Chesapeake Bay. The biomass of marsh vegetation in the tidal freshwater and brackish regions of the Patuxent was relatively uniform with regard to salinity, seasonally high concentrations of dissolved nitrogen, and phosphorus and nutrient gradient. Maximum values of biomass occurred in the tidal freshwater and slightly brackish water region of Parker Creek, a system whose nutrient concentrations approximated 20% of those of Patuxent River. Biomass values for the Patuxent River and Parker Creek averaged about 1417 and 895 g m?2 dry weight, respectively. Estimates of total annual marsh production based on the maximum standing crop was 27×103 and 519 metric tons, respectively, for the Patuxent River and Parker Creek. 相似文献
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Profiles of variable emission lines in the spectra of Wolf-Rayet stars are calculated using a stochastic cloud model for the inhomogeneous atmospheres of early-type stars. The model assumes that most of the line flux is formed in cold, dense condensations (clouds) that move through a rarified inter-cloud medium whose density monotonically decreases outwards. The formation of clouds is taken to be stochastic. Wavelet analysis is used to estimate the parameters of cloud ensembles. The model can reproduce the general pattern of line-profile variability observed in the spectra of Wolf-Rayet stars. 相似文献
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The possible existence of clusters of microscopic gas-dust particles forming gigantic clouds is demonstrated in the framework of the photogravitational three-body problem. These clouds are pulsating formations representing heterogeneous ensembles of particles of various sizes, densities, and susceptibilities to the radiation pressure, with each of the particles moving along its own trajectory. The conditions for the existence of co-linear and triangular libration points are derived by analyzing the dynamical equations describing the motion of a test particle in the gravitational-repulsive field of two gravitating and radiating bodies moving in an elliptical orbit about their common center of mass. The stability of these libration points is studied for various eccentricities e, mass parameters µ, and reduction coefficients characterizing the action of the stellar radiation on particles, and the results generalized in diagrams. We demonstrate the formation of clouds of particles located at multiple stable libration points. The extent of these clouds and their distances from the binary components are estimated. Scenarios for the subdivision of the clouds based on variations of e and µ are presented. The results of computations for a binary star with characteristics similar to those for α Cen are presented. 相似文献
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Identifying the spatial extent of volcanic ash clouds in the atmosphere and forecasting their direction and speed of movement has important implications for the safety of the aviation industry, community preparedness and disaster response at ground level. Nine regional Volcanic Ash Advisory Centres were established worldwide to detect, track and forecast the movement of volcanic ash clouds and provide advice to en route aircraft and other aviation assets potentially exposed to the hazards of volcanic ash. In the absence of timely ground observations, an ability to promptly detect the presence and distribution of volcanic ash generated by an eruption and predict the spatial and temporal dispersion of the resulting volcanic cloud is critical. This process relies greatly on the heavily manual task of monitoring remotely sensed satellite imagery and estimating the eruption source parameters (e.g. mass loading and plume height) needed to run dispersion models. An approach for automating the quick and efficient processing of next generation satellite imagery (big data) as it is generated, for the presence of volcanic clouds, without any constraint on the meteorological conditions, (i.e. obscuration by meteorological cloud) would be an asset to efforts in this space. An automated statistics and physics-based algorithm, the Automated Probabilistic Eruption Surveillance algorithm is presented here for auto-detecting volcanic clouds in satellite imagery and distinguishing them from meteorological cloud in near real time. Coupled with a gravity current model of early cloud growth, which uses the area of the volcanic cloud as the basis for mass measurements, the mass flux of particles into the volcanic cloud is estimated as a function of time, thus quantitatively characterising the evolution of the eruption, and allowing for rapid estimation of source parameters used in volcanic ash transport and dispersion models.
相似文献8.
A one-dimensional method for reconstructing the structure of prestellar and protostellar clouds is presented. The method is
based on radiative-transfer computations and a comparison of theoretical and observed intensity distributions at both millimeter
and infrared wavelengths. The radiative transfer of dust emission is modeled for specified parameters of the density distribution,
central star, and external background, and the theoretical distribution of the dust temperature inside the cloud is determined.
The intensity distributions at millimeter and IR wavelengths are computed and quantitatively compared with observational data.
The best-fit model parameters are determined using a genetic minimization algorithm, which makes it possible to reveal the
ranges of parameter degeneracy as well. The method is illustrated by modeling the structure of two infrared dark clouds IRDC-320.27+029
(P2) and IRDC-321.73+005 (P2). The derived density and temperature distributions can be used to model the chemical structure
and spectral maps in molecular lines. 相似文献
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The effects of meridional circulation on the solar dynamo wave are investigated in the Parker approximation using WKB techniques. The meridional circulation can substantially prolong the activity cycle; however, in the framework of the approximation considered, it cannot reverse the direction of propagation of the dynamo wave. If the circulation speed is too high, the solution is concentrated near the pole and can no longer be described in the Parker approximation. 相似文献
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卡斯巴-钠长律(简称卡-钠律)是一种复合双晶律,又名罗克·图尔奈律(Roc Tournélaw),双晶结合面CP=(010),双晶轴TA=⊥[001]/(010),常见于中基性斜长石中,特别是在中性和中基性的火山岩中的斜长石斑晶里更为常见。笔者在旋转台鉴定工作中发现,当被测的An30-70斜长石具有卡-钠律双晶时,联合运用欧拉角Ⅱ(Euler angleⅡ)中的Ⅰ角,即Nm∧[001],与卡-钠双晶寇勒角(Khler angle)中的Nm1∧Nm2来鉴定其成分和结构状态,效果甚好,优于传统的双晶法。 相似文献
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Andrew Tupper Christiane Textor Michael Herzog Hans-F. Graf Michael S. Richards 《Natural Hazards》2009,51(2):375-401
A critical factor in successfully monitoring and forecasting volcanic ash dispersion for aviation safety is the height reached by eruption clouds, which is affected by environmental factors, such as wind shear and atmospheric instability. Following earlier work using the Active Tracer High Resolution Atmospheric Model for strong Plinian eruptions, this study considered a range of eruption strengths in different atmospheres. The results suggest that relatively weak volcanic eruptions in the moist tropics can trigger deep convection that transports volcanic material to 15–20 km. For the same volcanic strength there can be ~9 km difference between eruption heights in moist tropical and dry subpolar environments (a larger height difference than previously suggested), which appears consistent with observations. These results suggest that eruption intensity should not be estimated from eruption height alone for tropospheric eruptions and also that the average height of volcanic eruptions may increase if the tropical atmospheric belt widens in a changing climate. Ash aggregation is promoted by hydrometeors (particularly liquid water), so the smaller modelled eruptions in moist atmospheres, which have a relatively small ash content for their height and water content, result in a relatively small proportion of fine ash in the dispersing cloud when compared to a dry atmosphere. This in turn makes the ash clouds much more difficult to detect using remote sensing than those in dry atmospheres. Overall, a weak eruption in the tropics is more likely to produce a plume above cruising levels for civil aviation, harder to detect and track, but with a lower concentration of fine ash than a mid-latitude or polar equivalent. There is currently no defined ‘acceptable’ concentration of ash for aircraft, but as these results suggest low-grade encounters in the tropics from undetected clouds are likely, it would be desirable to explore that issue. 相似文献
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V. Sasi Kumar S. Sampath P. V. S. S. K. Vinayak R. Harikumar 《Journal of Earth System Science》2007,116(5):451-463
Rainfall intensities measured at a few stations in Kerala during 2001–2005 using a disdrometer were found to be in reasonable
agreement with the total rainfall measured using a manual rain gauge. The temporal distributions of rainfall intensity at
different places and during different months show that rainfall is of low intensity (< 10 mm/hr), 65% to 90% of the time.
This could be an indication of the relative prevalence of stratiform and cumuliform clouds. Rainfall was of intensity < 5
mm/hr for more than 95% of the time in Kochi in July 2002, which was a month seriously deficient in rainfall, indicating that
the deficiency was probably due to the relative absence of cumuliform clouds. Cumulative distribution graphs are also plotted
and fitted with the Weibull distribution. The fit parameters do not appear to have any consistent pattern. The higher intensities
also contributed significantly to total rainfall most of the time, except in Munnar (a hill station). In this analysis also,
the rainfall in Kochi in July 2002 was found to have less presence of high intensities. This supports the hypothesis that
the rainfall deficiency was probably caused by the absence of conditions that favoured the formation of cumuliform clouds. 相似文献
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《Sedimentology》1994,41(2):379-380
Book Review in This Article
From Shoreline to Abyss: Contributions in Marine Geology in Honor of Francis Parker Shepard, ed. by R. H. Osborne 相似文献
From Shoreline to Abyss: Contributions in Marine Geology in Honor of Francis Parker Shepard, ed. by R. H. Osborne 相似文献
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Smelt (Osmerus mordax) from six rivers along the coast of Massachusetts were examined for the microsporidianGlugea hertwigi and piscine erythrocytic necrosis (PEN), a viral blood disease. Of the 485 smelt sampled, 13.4% were affected byGlugea. Incidence ranged from 18.0% in the Town River to 0% in the Parker River. PEN was observed in all river systems. Incidence ranged from 97% in the Jones to 61% in the Parker River. Individual intensity of infection was low, with the majority of fish having less than 1% of their erythrocytes affected. The highest intensity for an individual specimen was 4.68%. 相似文献
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A correlation between acoustical nonlinearity, sound absorption, and scattering in a subsurface bubble-saturated layer is established. A model of effective parameters of a bubbly liquid is developed that allows one to obtain results coinciding with experimental field studies. It is shown that “bubbly clouds” under the sea surface increase substantially the sound scattering and the nonlinear acoustic parameter of the seawater.
相似文献16.
The effect of the structural irregularity of an interstellar cloud on the dynamics of its disruption by a shock from a supernova is studied. Irregular clouds are disrupted twice as fast as spherical clouds. However, fragments of irregular clouds preserve their enhanced density for long times without being mixed with the intercloud gas. The fraction of shock energy that is converted to the kinetic energy of the fragments is 50% higher than in the disruption of a spherical cloud. Shocks are not able to trigger the gravitational compression of clouds. 相似文献
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Determining kriging weights to estimate some variable of interest at a given point in the field involves solving a system
of linear equations. The matrix of this linear system is subject to numerical instability, and this instability is measured
by the matrix condition number. Six parameters in the kriging process have been identified which directly affect this condition
number. Analysis of a series of 648 experiments gives some insight on these parameters, and how the condition number relates
to kriging variance. 相似文献
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M. K. Rama Varma Raja G. C. Asnani P. S. Salvekar A. R. Jain D. Narayana Rao S. Venkoba Rao P. Kishore M. Hareesh 《Journal of Earth System Science》1999,108(4):287-295
Contrary to the prevalent belief that tropical region is characterized by convective clouds rather than by layer clouds, we
have suggested that deep convective clouds occur on meso-scale, but layer clouds occur on larger synoptic-scale with a relatively
small region of deep convective clouds. Sustenance of deep convective clouds is inhibited by the presence of inertio-gravity
waves, which have alternating layers of upward and downward motion in the vertical. We have also shown that inertio-gravity
waves generate regions of relatively strong horizontal velocity, vertically separated by layers of relatively weak horizontal
velocity. Layers of strong horizontal velocity are created by inertio-gravity wave system through convergence of vertical
flux of horizontal momentum. We have also suggested that horizontal convergence/divergence of moisture flux is generated by
inertio-gravity waves, giving rise to vertically alternating layers of high/low humidity, and visible or sub-visible clouds.
Layers of high humidity become layers of strong radar reflectivity at frequency of 53 MHz at which MST Radar at Gadanki, near
Tirupati, India, operates. These observations, more than 2,50,000 in number, for vertical grid points, spread over all the
months of the year, have helped us, among other observations, to arrive at these conclusions. Further, the analysis suggests
that the main source of strong MST radar reflectivity is not mechanical turbulence as is commonly believed. 相似文献
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Orography profoundly influences seasonal rainfall amount in several places in south Asia by affecting rain intensity and duration. One of the fundamental questions concerning orographic rainfall is nature of the associated precipitating clouds in the absence of synoptic forcing. It is believed that these clouds are not very deep, however, there is not much information in the literature on their vertical structure. The present study explores the vertical structure of precipitating clouds associated with orographic features in south Asia using data collected with the precipitation radar on board the Tropical Rainfall Measuring Mission satellite. Two types of precipitating clouds have been defined based on cloud echo top height, namely, shallow echo-top cloud and medium echo-top cloud. In both, radar reflectivity factor is at least 30 dBZ at 1.5 km altitude, and tops of shallow and medium echo-top clouds lie below 4.5 km and between 4.5 and 8 km, respectively. The Western Ghats contains the highest fraction of the shallow echo-top clouds followed by the adjacent eastern Arabian Sea, while the Khasi Hills in Meghalaya and Cardamom Mountains in Cambodia contain the least fraction of them. Average vertical profiles of shallow echo-top clouds are similar in different mountainous areas while regional differences are observed in the medium echo-top clouds. Below 3 km, precipitation liquid water content in medium echo-top clouds is the highest over the Western Ghats and the eastern Arabian Sea. The average precipitation liquid water content increases by \(0.16\,\hbox { gm m}^{-3}\) for shallow echo-top clouds between 3 and 1.5 km altitude, while the corresponding increase for medium echo-top clouds is in 0.05–0.08 \(\hbox { gm m}^{-3}\) range. 相似文献