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91.
Athena Coustenis Alberto Negrão Alberto Salama Emmanuel Lellouch Pierre Drossart Bernard Schmitt Andrei Nikitin 《Icarus》2006,180(1):176-185
The near-infrared spectrum of Titan, Saturn's largest moon and one of the Cassini/Huygens' space mission primary targets, covers the 0.8 to 5 micron region in which it shows several weak CH4 absorption regions, and in particular one centered near 2.75 micron. Due to the interference of telluric absorption, only part of this window region (2.9-3.1 μm) has previously been observed from the ground [Noll, K.S., Geballe, T.R., Knacke, R., Pendleton, F., Yvonne, J., 1996. Icarus 124, 625-631; Griffith, C.A., Owen, T., Miller, G.A., Geballe, T., 1998. Nature 395, 575-578; Griffith, C.A., Owen, T., Geballe, T.R., Rayner, J., Rannou, P., 2003. Science 300, 628-630; Geballe, T.R., Kim, S.J., Noll, K.S., Griffith, C.A., 2003. Astrophys. J. 583, L39-L42]. We report here on the first spectroscopic observations of Titan covering the whole 2.4-4.9 μm region by two instruments on board the Infrared Space Observatory (ISO) in 1997. These observations show the 2.75-μm window in its complete extent for the first time. In this study we have also used a high-resolution Titan spectrum in the 2.9-3.6 μm region taken with the Keck [Geballe, T.R., Kim, S.J., Noll, K.S., Griffith, C.A., 2003. Astrophys. J. 583, L39-L42; Kim, S.J., Geballe, T.R., Noll, K.S., Courtin, R., 2005. Icarus 173, 522-532] to infer information on the atmospheric parameters (haze extinction, single scattering albedo, methane abundance, etc.) by fitting the methane bands with a detailed microphysical model of Titan's atmosphere (updated from Rannou, P., McKay, C.P., Lorenz, R.D., 2003. Planet. Space Sci. 51, 963-976). We have included in this study an updated version of a database for the CH4 absorption coefficients [STDS, Wenger, Ch., Champion, J.-P., 1998. J. Quant. Spectrosc. Radiat. Transfer 59, 471-480. See also http://www.u-bourgogne.fr/LPUB/TSM/sTDS.html for latest updates; Boudon, V., Champion, J.-P., Gabard, T., Loëte, M., Michelot, F., Pierre, G., Rotger, M., Wenger, Ch., Rey, M., 2004. J. Mol. Spectrosc. 228, 620-634]. For the atmosphere we find that (a) the haze extinction profile that best matches the data is one with higher (by 40%) extinction in the atmosphere with respect to Rannou et al. (2003) down to about 30 km where a complete cut-off occurs; (b) the methane mixing ratio at Titan's surface cannot exceed 3% on a disk-average basis, yielding a maximum CH4 column abundance of 2.27 km-am in Titan's atmosphere. From the derived surface albedo spectrum in the 2.7-3.08 micron region, we bring some constraints on Titan's surface composition. The albedo in the center of the methane window varies from 0.01 to 0.08. These values, compared to others reported in the other methane windows, show a strong compatibility with the water ice spectrum in the near-infrared. Without confirming its existence from this work alone, our data then appear to be compatible with water ice. A variety of other ices, such as CO2, NH3, tholin material or hydrocarbon liquid cannot be excluded from our data, but an additional unidentified component with a signature around 2.74 micron is required to satisfy the data. 相似文献
92.
Rebecca Lemons Andrea Hewitt Gehendra Kharel Cherie New Andrei Kirilenko Xiaodong Zhang 《国际地球制图》2013,28(8):613-626
The climate of the United States Northern Great Plains region is highly variable. Modelling of agriculture in this region and similar locations depends on the availability and quality of satellite and ground data for agro-climate variables. We evaluated tropical rainfall measuring mission (TRMM) multi-satellite preparation analysis (TMPA) precipitation, atmospheric infrared sounder (AIRS) surface air temperature, and AIRS relative air humidity (RH). A significant bias was found within the temperature and RH products and no bias but an insufficient rain event detection skill in the precipitation product (probability of detection ~0.3). A linear correction of the temperature product removed the bias as well as lowered the root mean square deviation (RMSD). The bias-corrections for RH led to increased RMSD or worse correlation. For precipitation, the correlation between the satellite product and ground data improved if cumulative precipitation or only precipitation during the growing season was used. 相似文献
93.
Andrei M. Ionov 《Geophysical Prospecting》2013,61(1):104-119
The dynamic response of a semi‐infinite fluid‐filled borehole embedded in an elastic half‐space under a concentrated normal surface load is analysed in the long‐wavelength limit. The solution of the problem is obtained with integral transforms in the form of a double integral with respect to the slowness and frequency. The partial P‐ and SV‐wave responses are further transformed to path integrals along Cagniard paths in the complex slowness plane. Unlike the traditional Cagniard‐de Hoop technique based on the Laplace transform of time dependence, this paper is based on the Fourier transform. The tube‐wave response is presented as a causal integral over a slowness range. The resultant representation in the time‐domain is suitable for the numerical evaluation of the complete response in the fluid‐filled borehole, especially at large distances. Asymptotic analysis of seismic phases arising in the borehole is performed on the basis of the obtained solution. The complete asymptotic wavefield consists in P‐ and SV‐waves, the Rayleigh wave and the low‐frequency Stoneley (tube) wave. Pressure synthetics obtained by the use of the asymptotic formulas are shown to be in good agreement with straightforward calculations. 相似文献
94.
Raphael Gromig Bernd Wagner Volker Wennrich Grigory Fedorov Larisa Savelieva Elodie Lebas Sebastian Krastel Dominik Brill Andrei Andreev Dmitry Subetto Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):330-348
Lake Ladoga in northwestern Russia is Europe's largest lake. The postglacial history of the Ladoga basin is for the first time documented continuously with high temporal resolution in the upper 13.3 m of a sediment core (Co1309) from the northwestern part of the lake. We applied a multiproxy approach including radiographic imaging, (bio‐)geochemical and granulometric analyses. Age control was established combining radiocarbon dating with varve chronology, the latter anchored to a correlated radiocarbon age from a lake close by. The age‐depth model reveals the onset of glacial varve sedimentation at 13 910±140 cal. a BP, when Lake Ladoga was part of the Baltic Ice Lake. Linear extrapolation of published retreat rates of the Scandinavian Ice Sheet provides a formation age of the Luga moraine close to Lake Ladoga's southern shore of 14.5–15.9 cal. ka BP, older than previously assumed. Varve sedimentation covers the Bølling/Allerød interstadial, the Younger Dryas stadial and the Early Holocene. Varve‐thickness variations, conjoined with grain‐size and geochemical variations, inform about the relative position of the Scandinavian Ice Sheet and the climate during the deglaciation phase. The upper limit of the varved succession marks the change from glaciolacustrine to normal lacustrine sedimentation and post‐dates the drainage of the Baltic Ice Lake as well as the formation of the Salpausselkä II moraine north of Lake Ladoga, by c. 250 years. The Holocene sediment record is divided into three periods in the following order: (i) a lower transition zone between the Holocene boundary and c. 9.5 cal. ka BP, characterized by mostly massive sediments with low organic content, (ii) a phase with increased organic content from c. 9.5 to 4.5 cal. ka BP corresponding to the Holocene Thermal Maximum, and (iii) a phase with relatively stable sedimentation in a lacustrine environment from c. 4.5 cal. ka BP until present. 相似文献
95.
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97.
The Vrancea subcrustal earthquakes of August 30,1986 and May 30,1990 are the two most recent seismic events that have occurred in Romania with moment magnitudes M W ≥ 6.9.The spectral analysis of the strong ground motions recorded in Bucharest reveals that despite small differences in magnitude between the 1986 and 1990 earthquakes,their frequency contents are very different,sometimes even opposing.The main focus of this study is to conduct a comparative analysis of the response spectra in terms of the bi-normalized response spectra(BNRS) proposed by Xu and Xie(2004 and 2007) for strong ground motions recorded in Bucharest during these two seismic events.The mean absolute acceleration and relative velocity response spectra for the two earthquakes are discussed and compared.Furthermore,the mean bi-normalized absolute acceleration and normalized relative velocity response spectra with respect to the control period T C are computed for the ground motions recorded in Bucharest in 1986 and 1990.The predominant period T P is also used in this study for the normalization of the spectral period axis.Subsequently,the methodology proposed by Martinez-Perreira and Bommer(1998) is applied in order to estimate the seismic intensity of the two events.The results are discussed and several conclusions regarding the possibility of using the bi-normalized response spectra(BNRS) are given. 相似文献
98.
Steven R. Furlanetto Andrei Mesinger† 《Monthly notices of the Royal Astronomical Society》2009,394(3):1667-1673
One of the most sought-after signatures of reionization is a rapid increase in the ionizing background (usually measured through the Lyα optical depth towards distant quasars). Conventional wisdom associates this with the 'overlap' phase when ionized bubbles merge, allowing each source to affect a much larger volume. We argue that this picture fails to describe the transition to the post-overlap Universe, where Lyman-limit systems (LLSs) absorb ionizing photons over moderate length-scales (≲20–100 Mpc) . Using an analytic model, we compute the probability distribution of the amplitude of the ionizing background throughout reionization, including both discrete ionized bubbles and LLSs (parametrized by an attenuation length, which we impose rather than attempt to model self-consistently). We show that the overlap does not by itself cause a rapid increase in the ionizing background or a rapid decrease in the mean Lyα transmission towards distant quasars. More detailed seminumeric models support these conclusions. We argue that the rapid changes should instead be interpreted as evolution in the attenuation length itself, which may or may not be directly related to overlap. 相似文献
99.
It is expected that a warmer climate would be beneficial for agriculture in high latitudes. However, this general tendency
is not necessarily true for all northern countries, as a short growing period is not the only factor limiting agriculture.
For Russia, our model shows that the remarkable increase in potential yield in central and northern-forested regions would
not compensate for a sharp drop in yields due to increasing frequency of droughts in the currently most productive southern
European regions. If this scenario is indeed realized, the majority of Russian regions will continue to rely on import of
agricultural products from a few regions with the best soils, and a system of interregional grain trade will remain critical
for food security. However, the basic rules of interregional food market have varied widely over the past century. We have
attempted an analysis of the potential impact of these basic rules on regional food security by describing four basic historical
market scenarios and applying these scenarios to our results for climate change impact on agriculture in the 2020s and 2070s.
We show that the current system, if it continues, would bring the worst results. We also show that the traditionally effective
planned adaptation measures would help little in future climate conditions if the current market system were still in place. 相似文献
100.
Flood risk assessment is usually performed by application of sophisticated mathematical models of river flow. However, there are cases when it is required to assess the risk in the lack of data conditions or a limited time available. In such cases, it is advisable to use some simplifications, which provide reliable results faster. This study proposes a hybrid approach to the flood risk assessment combining quantitative and qualitative indicators. The article describes various methods to assess the flood risk, such as likelihood of flooding, magnitude of the flood, average annual damage, maximum damage and expectation of damage. The authors examined special cases of calculation of the mathematical expectation of harm and zoning in the corresponding indicators. This approach is designed for the conditions of the Russian Federation, but it can be adapted for other regions. It is based on the use of two types of risk maps. The first type of maps is intended to define the mathematical expectation of damage zones for reference building with possibility of risk calculation for other buildings using multiple factors. The second type of maps is designed for the purposes of land use regulation for floodplains based on a priori statistical estimates of flood risk. 相似文献