Dérive à la surface de l'océan sous l'effet des vagues     

Fabrice Ardhuin  François-Régis Martin-Lauzer  Bertrand Chapron  Philippe Craneguy  Fanny Girard-Ardhuin  Tanos Elfouhaily 《Comptes Rendus Geoscience》2004,336(12):1121-1130

We model the drift velocity near the ocean surface separating the motion induced by the local current, itself influenced by winds and waves, and the motion induced by the waves, which are generated by local and remote winds. Application to the drift of ‘tar balls’, following the sinking of the oil tanker Prestige-Nassau in November 2002, shows that waves contribute at least one third of the drift for pollutants floating 1 m below the surface, with a mean direction about 30° to the right of the wind-sea direction. Although not new, this result was previously obtained with specific models, whereas the formalism used here combines classical wave and circulation forecasting models. To cite this article: F. Ardhuin et al., C. R. Geoscience 336 (2004).  相似文献   

Investigation of the climate-driven periodicity of shallow groundwater level fluctuations in a Central-Eastern European agricultural region     

Tamás Garamhegyi  József Kovács  Rita Pongrácz  Péter Tanos  István Gábor Hatvani 《Hydrogeology Journal》2018,26(3):677-688

The distribution and amount of groundwater, a crucial source of Earth’s drinking and irrigation water, is changing due to climate-change effects. Therefore, it is important to understand groundwater behavior in extreme scenarios, e.g. drought. Shallow groundwater (SGW) level fluctuation under natural conditions displays periodic behavior, i.e. seasonal variation. Thus, the study aims to investigate (1) the periodic behavior of the SGW level time series of an agriculturally important and drought-sensitive region in Central-Eastern Europe – the Carpathian Basin, in the north-eastern part of the Great Hungarian Plain, and (2) its relationship to the European atmospheric pressure action centers. Data from 216 SGW wells were studied using wavelet spectrum analysis and wavelet coherence analyses for 1961–2010. Locally, a clear relationship exists between the absence of annual periodic behavior in the SGW level and the periodicity of droughts, as indicated by the self-calibrating Palmer Drought Severity Index and the Aridity Index. During the non-periodic intervals, significant drops in groundwater levels (average 0.5 m) were recorded in 89% of the wells. This result links the meteorological variables to the periodic behavior of SGW, and consequently, drought. On a regional scale, Mediterranean cyclones from the Gulf of Genoa (northwest Italy) were found to be a driving factor in the 8-yr periodic behavior of the SGW wells. The research documents an important link between SGW levels and local/regional climate variables or indices, thereby facilitating the necessary adaptation strategies on national and/or regional scales, as these must take into account the predictions of drought-related climatic conditions.  相似文献   

Formal tilt invariance of the nonlocal curvature approximation and its connection to the integral equation method     

Elfouhaily  T. Guignard  S. Thompson  D.R. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(2):51-56

Tilt invariance is a stringent constraint that second-order scattering models such as the integral equation method (IEM) should satisfy in order to expand their domain of applicability. Moreover, second-order scattering models must reproduce elementary limits such as the small perturbation method (SPM) and the high-frequency Kirchhoff approximation. Tilt invariance is met if and only if a scattering model yields the same asymptotic limit whether the scattering surface is tilted before or after the limiting process. In particular, the tilted SPM coefficients are well determined by simply tilting the reference frame. If it is tilt invariant, a second-order scattering model will reproduce these tilted coefficients by simply tilting the surface explicitly present in the expression of the scattering model before reducing it to the SPM limit. In this letter, we demonstrate that our nonlocal curvature approximation (NLCA) is formally tilt invariant up to first order in the tilting vector. Satisfying the tilt invariance property can extend the applicability of scattering models to account, for example, for scattering from multiscale surfaces and polarization mixing due to out-of-plane tilting. It is also suggested that replacing the field coefficients of IEM by the curvature kernel of NLCA introduces a promising alternative technique that includes multiple scattering up to double reflections from the rough surface, while remaining analytically compact and formally tilt invariant.  相似文献