排序方式: 共有22条查询结果,搜索用时 46 毫秒
11.
12.
Jean-Baptiste?RenardEmail author Martyn?P.?Chipperfield Gwena?l?Berthet Fabienne?Goffinont-Taupin Claude?Robert Michel?Chartier Howard?Roscoe Wuhu?Feng Emmanuel?Rivière Michel?Pirre 《Journal of Atmospheric Chemistry》2005,51(1):65-78
Eleven vertical profiles of stratospheric NO3 have been obtained since 1992 using the AMON and SALOMON balloon-borne UV-visible spectrometers. The measurements are compared to the SLIMCAT 3D model and calculations based on the steady-state hypothesis for NO3. The calculations cannot reproduce some parts of the profiles which exhibit strong concentration fluctuations over few kilometres, as a consequence of the dependence of NO3 on local temperature variations. A statistical use of the data allows us to estimate the influence of the temperature dependence of the absorption cross-section on the data analysis, and the validity of the recommended reaction rates available in the literature. Discrepancies exist between the model based on recommended kinetics and observations at warmer temperatures. Nevertheless, the analysis is biased by local temperature inhomogeneities, and only a low-resolution vertical shape of the NO3 profiles can be retrieved. 相似文献
13.
To assess the flood protection capacity of dunes in The Netherlands, a semi-probabilistic dune-erosion prediction method is currently in use in which uncertainties in input parameters of an empirical dune erosion model were taken into account, with the exception of the uncertainty in the extreme surge distribution. Previous research has shown that the surge is by far the most influential parameter affecting erosion in the currently used erosion model, which is due both to the influence of the surge level itself and to the conditional dependence of the wave height and period on the surge level in the probabilistic model used for the assessment. Furthermore, the distribution of extreme surge levels has been shown to contain large statistical uncertainty. The inclusion of uncertainty in input variables into probabilistic models results in more extreme events (in this case erosion) for the same exceedance probability, largely due to the incorporation of higher values of the input variables. The goal of the research described in this paper was to determine the impact of the inclusion of uncertainty in the extreme surge distribution on the estimate of critical erosion (erosion associated with an exceedance frequency of 10− 5 per year). The uncertainty in the surge distributions was estimated and parameterized, and was incorporated into the probabilistic model. A reduction in uncertainty was subsequently imposed to estimate what value a reduction in uncertainty can offer, in terms of the impact on critical erosion. The probabilistic technique first-order reliability method (FORM) was applied to determine the relative contribution of the uncertainty in the surge distribution (as well as the remaining stochastic variables) to the critical erosion. The impact of the inclusion of uncertainty in the surge distribution on the critical retreat distance was found to be substantial with increases ranging from 34% to 93% of the original estimate at five locations along the Dutch coast. The reduced uncertainty showed a more subtle impact, with increases in critical retreat distance ranging from 10% to 26% of the original estimate. The relative importance analysis showed that the uncertainty in the surge distribution has a strong influence, with the relative importance ranging from 10% to 23% for an exceedance frequency of 10− 5 per year. 相似文献
14.
D. F. Roscoe 《Journal of Astrophysics and Astronomy》1997,18(4):407-414
One of the largest rotation curve data bases of spiral galaxies currently available is that provided by Persic& Salucci (1995;
hereafter, PS) which has been derived by them from unreduced rotation curve data of 965 southern sky spirals obtained by Mathewson,
Ford& Buchhorn (1992; hereafter, MFB). Of the original sample of 965 galaxies, the observations on 900 were considered by
PS to be good enough for rotation curve studies, and the present analysis concerns itself with these 900 rotation curves.
The analysis is performed within the context of the hypothesis that velocity fields within spiral discs can be described by
generalized power-laws. Rotation curve data was found to impose an extremely strong and detailed correlation between the free
parameters of the power-law model, and this correlation accounts for virtually all the variation in the pivotal diagram. In
the process, the analysis reveals completely unexpected structure which indicates that rotation curves can be partitioned
into well-defined discrete subclasses. 相似文献
15.
Measurements of stratospheric NO2 by ground-based visible spectrometers rely on laboratory measurements of absorption cross-sections. We review low-temperature laboratory measurements, which disagree by amounts claimed to be significant. Our recalculation of their errors shows that in general disagreements are not significant and that errors in the ratios of cross-sections at low to room temperature are between ±3% and ±8.8%. Of these errors, up to ±3.5% was contributed by errors in the equilibrium constant,K
p, in those measurements where the pressure was above 0.1 mbar.We review measurements and calculations ofK
p, which were accurate to ±5% from 300 to 233 K. Each method was potentially flawed. For example, infrared measurements of the partial pressure of NO2 ignored the dependence of absorption on total pressure. From thermodynamic theory, formulae forK
pcan be derived from expressions for the variation of heat capacity with temperature. Contrary to common belief, coefficients in the formulae used by spectroscopists were not derived from the thermodynamic quantities. Rather, they were fitted to measurements or to calculations. Hence, they are empirical and it is dangerous to extrapolate below 233 K, the lowest temperature of the measurements.There are no measurements of NO2 cross-sections below 230 K. Extrapolation of these cross-sections to analysis of measurements of NO2 at the low temperatures of the Arctic and Antarctic stratosphere is also dangerous. For satisfactory analysis of polar spectra, the NO2 cross-sections should be measured at temperatures down to 190 K with a relative accuracy of ±1%. This difficult experiment would need a cell of minimum length 32 m whose length can be adjusted. Because their effects are circular, many errors cannot be removed simply. Although circular errors also arise in the measurements ofK
pand of the infrared spectrum, their weights differ from those in the visible spectrum. The optimum experiment might therefore simultaneously measure the visible and infrared spectra andK
p. 相似文献
16.
D.F. Roscoe 《Astrophysics and Space Science》2003,285(2):459-470
The work described in this paper has its origins in a speculation on the realization of Mach's Principle – specifically, in the formulation of two questions: (a) Can a globally inertial space &; time be associated with a non-trivial global matter distribution? (b) If so, what are the general properties of such a global distribution?This analysis (Roscoe, [2002a] (astro-ph/0107397)), led us to conclude that a globally inertial space &; time can be associated with a non-trivial global matter distribution, and that this distribution is necessarily fractal with D=2; that is mass ~ R 2. Gravitational processes are then to be understood in terms of perturbations of this equilibrium space-matter-time structure. We give a very brief overview of these gravitational processes, specifically applied to spiral galaxies. These considerations led directly to the discovery of a completely new phenomenology in spiral discs reported in detail in Roscoe [2002b] (astro-ph/0107300). We review this phenomenology, and give a brief account of its theoretical explanation. 相似文献
17.
Ozone depletion at mid-latitudes is caused by reactivehalogens from man-made halocarbons. The stratosphericsulphate aerosol which follows large volcaniceruptions enhances (multiplies) this ozone depletion(it has no effect on ozone without halocarbons). Mid-latitude depletion almost doubled for the twoyears after Mt. Pinatubo. Although the MontrealProtocol is expected to reduce atmospheric amounts ofhalocarbons in the 21st century, stratospheric ozonewill be at risk of depletion enhancement by largeeruptions for the next 50 years. Mechanisms ofvolcanoes suggest that large eruptions are random andthat their global rate is constant for severalcenturies. Measurements of large eruptions during thelast 1000 years in ice cores have a remarkable fit toa Poisson distribution, reinforcing the conclusionthat the global incidence is random and at a constantrate for this period. From this rate, the probabilityof one or more eruptions with at least the ozone-lossenhancement of Pinatubo is 58 % in 50 years. Thisprobability is large enough to be of serious concernfor future mid-latitude ozone loss. 相似文献
18.
Paul W. SchumacherJr. John A. Gaebler Christopher W. T. Roscoe Matthew P. Wilkins Penina Axelrad 《Celestial Mechanics and Dynamical Astronomy》2018,130(9):60
We propose a type of admissible-region analysis for track initiation in multi-satellite problems when angles are the primary observable. Pairs of optical observations are used to calculate candidate orbits via a Lambert solver by hypothesizing range values. The method is attractive because it allows multiple levels of parallelization of the track-initiation process. Orbital element partitions are introduced to divide the admissible region into smaller search spaces to be processed on individual computer nodes. For a specified rectangular partition in the space of orbital elements, constraints are developed to bound the values of range that will lead to initial orbit hypotheses (data association hypotheses) associated with that partition. These bounds allow us to parallelize the generation of candidate orbits, because each element-space partition can be handled independently of the others. Several constraints are developed and shown to limit the range pair hypotheses effectively to the constrained admissible region based on the orbital element partitions. Examples are provided to highlight the topology of the proposed constraints. 相似文献
19.
H. K. Roscoe P. V. Johnston M. Van Roozendael A. Richter A. Sarkissian J. Roscoe K. E. Preston J-C. Lambert C. Hermans W. DeCuyper S. Dzienus T. Winterrath J. Burrows F. Goutail J-P. Pommereau E. D'Almeida J. Hottier C. Coureul R. Didier I. Pundt L. M. Bartlett C. T. McElroy J. E. Kerr A. Elokhov G. Giovanelli F. Ravegnani M. Premuda I. Kostadinov F. Erle T. Wagner K. Pfeilsticker M. Kenntner L. C. Marquard M. Gil O. Puentedura M. Yela D. W. Arlander B. A. Kastad Hoiskar C. W. Tellefsen K. Karlsen Tornkvist B. Heese R. L. Jones S. R. Aliwell R. A. Freshwater 《Journal of Atmospheric Chemistry》1999,32(2):281-314
In June 1996, 16 UV-visible sensors from 11 institutes measured spectra of the zenith sky for more than 10 days. Spectra were analysed in real-time to determine slant column amounts of O3 and NO2. Spectra of Hg lamps and lasers were measured, and the amount of NO2 in a cell was determined by each spectrometer. Some spectra were re-analysed after obvious errors were found. Slant columns were compared in two ways: by examining regression analyses against comparison instruments over the whole range of solar zenith angles; and by taking fractional differences from a comparison instrument at solar zenith angles between 85° and 91°. Regression identified which pairs of instruments were most consistent, and so which could be used as universal comparison instruments. For O3, regression slopes for the whole campaign agreed within 5% for most instruments despite the use of different cross-sections and wavelength intervals, whereas similar agreement was only achieved for NO2 when the same cross-sections and wavelength intervals were used and only one half-day's data was analysed. Mean fractional differences in NO2 from a comparison instrument fall within ±7% (1-sigma) for most instruments, with standard deviations of the mean differences averaging 4.5%. Mean differences in O3 fall within ±2.5% (1- sigma) for most instruments, with standard deviations of the mean differences averaging 2%. Measurements of NO2 in the cell had similar agreement to measurements of NO2 in the atmosphere, but for some instruments measurements with cell and atmosphere relative to a comparison instrument disagreed by more than the error bars. 相似文献
20.
H. K. Roscoe B. J. Kerridge S. Pollitt N. Louisnard J. M. Flaud C. Camy-Peyret C. Alamichel J-P. Pommereau T. Ogawa N. Iwagami M. T. Coffey W. Mankin W. F. J. Evans C. T. McElroy J. Kerr 《Journal of Atmospheric Chemistry》1990,10(2):111-144
During the 1982 and 1983 Balloon Intercomparison Campaigns, the vertical profile of stratospheric NO2 was measured remotely by nine instruments and that of NO by two. Total overhead columns were measured by two more instruments. Between 30 and 35km, where measurements overlapped, agreement between NO profiles was within ±30%, which is better than the accuracies claimed by the experimenters. Between 35 and 40km there was similarly good agreement between NO2 profiles, but below 30km, differences of greater than a factor three were found. In the second Campaign, NO2 values from most instruments agreed within their quoted errors, except that the Oxford radiometer gave much lower values; but the first Campaign and the column measurements show a more uniform spread of results.These differences below 30km could not be resolved, but new laboratory measurements are planned which should do so. 相似文献