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11.
Hui Feng Doug Vandemark Yves Quilfen Bertrand Chapron Brian Beckley 《Ocean Engineering》2006,33(11-12):1431-1461
The study presents assessment of an operational wave model (Wavewatch III), focusing upon the model sensitivity to wind-forcing products. Four wind fields are used to drive the model, including the NCEP/NCAR reanalysis and three other products that assimilate various satellite wind measurements having high spatial resolution, including the QuikSCAT scatterometer. Three wave field statistics: significant wave height, mean zero-crossing wave period, and mean square slope are compared with collocated TOPEX altimeter derivatives to gauge the relative skill of differing wind-forced model runs, as well as to demonstrate an extended use of the altimeter beyond simply supplying wave height for wave model validation and assimilation. Results suggest that model output is critically sensitive to choice of the wind field product. Higher spatial resolution in the wind fields does lead to improved agreement for the higher-order wave statistics. 相似文献
12.
The accuracy of the ERA-Interim reanalysis data
on total atmospheric water vapor is assessed using the AMSR2 (Advanced
Microwave Scanning Radiometer 2) measurements. The values of total
column water vapor over the open ocean obtained by applying the improved
algorithm to the ASMR2 data are used as reference ones to evaluate the
quality of water vapor content reproduced by the reanalysis. The
analysis performed for the Arctic region for 2015 and based on the
average daily values demonstrated a high accuracy of ERA-Interim data on
the Arctic water vapor equal to 1.1 kg/m2, which decreases
for the water vapor values above 15 kg/m2. Under such
conditions, the ERA-Interim data underestimate the water vapor content
by several kg/m2. The accuracy of ERA-Interim total water
vapor over the seas of the eastern sector of the Russian Arctic is 30%
lower than for the other Arctic regions. 相似文献
13.
Marion Garçon Catherine Chauvel Emmanuel Chapron Xavier Faïn Mingfang Lin Sylvain Campillo Sarah Bureau Marc Desmet Marie-Christine Bailly-Maître Laurent Charlet 《Applied Geochemistry》2012
High-altitude lake sediments are often used as archives for environmental changes and their chemical and isotopic compositions provide significant constraints on natural and anthropogenic long-term changes that have occurred in their catchment area. Here, trace-element concentrations and Pb isotopes are presented for two sedimentary cores from Lake Blanc Huez in the French Alps, to trace the impact of climate changes and human activities over the Holocene. Lead and Ag contents are very high and clearly dominated by input from a Pb–Ag vein located a few meters from the lakeshore, a vein that also buffers the Pb isotopes. Mining of this vein in medieval times is recorded in the corresponding lake sediments with high Ag content coupled with high Pb/U ratio. These chemical characteristics can be used to constrain the major Holocene climate changes. Significant advances of glaciers next to the lake produced sediments with Ag and Pb concentration peaks and high Pb/U ratios due to accelerated erosion of the Pb–Ag vein, similar to the effects of the medieval mining. In contrast, reduced glacier activity led to the formation of organic-rich sediments with high U and As contents and low Pb/U ratios. More generally, the observed combination of chemical changes could be used elsewhere to decipher environmental changes over long periods of time. 相似文献
14.
Walter Finsinger Daniele Colombaroli Jacques‐Louis De Beaulieu Verushka Valsecchi Boris Vannière Elisa Vescovi Emmanuel Chapron André F. Lotter Michel Magny Willy Tinner 《第四纪科学杂志》2010,25(8):1239-1247
Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
15.
Abstract Ocean backscatter data obtained with a Ku‐band airborne radar are presented along with coincident altimeter and directional wave spectral estimates. These data were collected using one sensor, NASA's radar ocean wave spectrometer (ROWS). The measurements are compared with an electromagnetic scattering model for perfectly conducting Gaussian random surfaces. The normalized radar cross‐section (NRCS) data cover those incidence angles (0–20°) where both quasi‐specular and Bragg scattering mechanisms are expected. Under certain conditions, identification and separation of these two mechanisms is possible. The scanning radar allows observations of the azimuthal variations in NRCS that are at times indicative of short‐scale wave generation in the wind direction. 相似文献
16.
The north‐western corner of Lake Le Bourget is situated along an active fault zone and accommodated a large sediment supply from the Rhone River until the end of the Late Glacial period. On the delta slope, the Holocene sheet drape that covers the largest buried mass wasting deposit (the HDU) shows undulations, small fractures and discontinuities that are attributed to downslope creep. Evidence for episodes of vigorous fluid expulsion is found in association with these discontinuities. All these features are rooted at the top of the HDU and occur along two specific isobaths. These observations indicate a close link between fractures and focused fluid flow. We suggest that focused fluid flow triggered by earthquakes facilitates the formation of small‐scale faults that accommodate part of the downslope movement and eventually link up to form a head‐scarp of a large slide (c. 107 m3). 相似文献
17.
Nicolas Reul Severine Fournier Jaqueline Boutin Olga Hernandez Christophe Maes Bertrand Chapron Gaël Alory Yves Quilfen Joseph Tenerelli Simmon Morisset Yann Kerr Susanne Mecklenburg Steven Delwart 《Surveys in Geophysics》2014,35(3):681-722
While it is well known that the ocean is one of the most important component of the climate system, with a heat capacity 1,100 times greater than the atmosphere, the ocean is also the primary reservoir for freshwater transport to the atmosphere and largest component of the global water cycle. Two new satellite sensors, the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius SAC-D missions, are now providing the first space-borne measurements of the sea surface salinity (SSS). In this paper, we present examples demonstrating how SMOS-derived SSS data are being used to better characterize key land–ocean and atmosphere–ocean interaction processes that occur within the marine hydrological cycle. In particular, SMOS with its ocean mapping capability provides observations across the world’s largest tropical ocean fresh pool regions, and we discuss from intraseasonal to interannual precipitation impacts as well as large-scale river runoff from the Amazon–Orinoco and Congo rivers and its offshore advection. Synergistic multi-satellite analyses of these new surface salinity data sets combined with sea surface temperature, dynamical height and currents from altimetry, surface wind, ocean color, rainfall estimates, and in situ observations are shown to yield new freshwater budget insight. Finally, SSS observations from the SMOS and Aquarius/SAC-D sensors are combined to examine the response of the upper ocean to tropical cyclone passage including the potential role that a freshwater-induced upper ocean barrier layer may play in modulating surface cooling and enthalpy flux in tropical cyclone track regions. 相似文献
18.
Roberto Urrutia Alberto Araneda Fabiola Cruces Laura Torres Luis Chirinos Hans C. Treutler Nathalie Fagel Sebastien Bertrand Ingrid Alvial Ricardo Barra Emmanuel Chapron 《Limnologica》2007,37(1):49-62
Several lakes in Chile are near important volcanic areas where eruption impacts can limit the quality of lacustrine sediments for reconstructing past environmental changes. In this study, we report changes in diatoms, pollen, and chironomids assemblages after a tephra deposition in Lake Galletué (Chilean Andes). A sediment core obtained from Lake Galletué (40 m water depth) was sliced in 1 cm intervals and subsamples were taken to analyze each proxy. 210Pb and 137Cs activities were measured to obtain the geochronology and mineralogical analyses were performed to determine the mineral composition of the tephra. Diatom species composition and productivity were modified when the lake received the tephra; Aulacoseira granulata decreased and was later replaced by Cyclotella af. glomerata. After the tephra input, Aulacoseira granulata abundance increased to pre-disturbance levels and Cyclotella af. glomerata decreased. These changes seem to suggest a momentary increase in lake nutrient levels after the tephra deposition. Chironomid assemblages also decreased in head capsules just after the tephra deposition, but the most important change was the replacement of Ablabesmyia by Parakiefferiella, probably due to the sedimentological changes produced by the input of coarse tephra grains. Furthermore, unlike other studies, chironomid assemblages in Lake Galletué did not show a decrease drastically in diversity within the tephra layer. The pollen analysis indicated that, prior to the volcanic event, the vegetal community was dominated by Nothofagus sp., Araucaria araucana, and Blechnum sp.-type. After the tephra deposition, the same taxa are dominant, indicating that the volcanic event seems not produce changes in the vegetation. Nevertheless, within the tephra layer it is possible to see an increase in Poaceae, which represent – due to the percolation process – the effect of eruption on the vegetation. According to our results, diatoms were the most sensitive proxy for describing the changes produced by tephra deposition into the aquatic ecosystem and, despite the noticeable changes in its sedimentological properties; the lake seems to have a high resilience capacity, allowing it to return to pre-tephra input conditions. 相似文献
19.
Characteristics of short-period internal waves in the Kara Sea inferred from satellite SAR data 总被引：1，自引：0，他引：1
I. E. Kozlov V. N. Kudryavtsev E. V. Zubkova A. V. Zimin B. Chapron 《Izvestiya Atmospheric and Oceanic Physics》2015,51(9):1073-1087
In this paper we present the results of short-period internal wave (SIW) observations in the Kara Sea on the basis of satellite ENVISAT ASAR data between July and October 2007. Altogether, 248 internal wave (IW) packets and solitons are identified in 89 SAR images. Detailed spatial statistics of IW signatures and their properties in the Kara Sea is presented. The primary regions of IW activity are the areas near the Kara Gates Strait, the southeastern part of the Novaya Zemlya Trough, and in the vicinity of Cape Zhelaniya. We identify the regions where large IW packets are observed with wavelengths up to 2–3 km and the front length exceeding 200 km. The mean interpacket distance for observed IWs is about 20 km, but it may reach 50–60 km. Consequent IW packets are observed to travel up to 500 km from the presumed generation points. The results of satellite observations are compared with results of previous studies. 相似文献
20.
Calibration/Validation of an Altimeter Wave Period Model and Application to TOPEX/Poseidon and Jason-1 Altimeters 总被引：1，自引：0，他引：1
The altimeter radar backscatter cross-section is known to be related to the ocean surface wave mean square slope statistics, linked to the mean surface acceleration variance according to the surface wave dispersion relationship. Since altimeter measurements also provide significant wave height estimates, the precedent reasoning was used to derive empirical altimeter wave period models by combining both significant wave height and radar backscatter cross-section measurements. This article follows such attempts to propose new algorithms to derive an altimeter mean wave period parameter using neural networks method. Two versions depending on the required inputs are presented. The first one makes use of Ku-band measurements only as done in previous studies, and the second one exploits the dual-frequency capability of modern altimeters to better account for local environmental conditions. Comparison with in situ measurements show high correlations which give confidence in the derived altimeter wave period parameter. It is further shown that improved mean wave characteristics can be obtained at global and local scales by using an objective interpolation scheme to handle relatively coarse altimeter sampling and that TOPEX/Poseidon and Jason-1 altimeters can be merged to provide altimeter mean wave period fields with a better resolution. Finally, altimeter mean wave period estimates are compared with the WaveWatch-III numerical wave model to illustrate their usefulness for wave models tuning and validation. 相似文献