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Global oceanic precipitation: A joint view by TOPEX and the TOPEX microwave radiometer ArchiMer
Chen, Ge; Chapron, Bertrand; Tournadre, Jean; Katsaros, Kristina; Vandemark, Douglas.
The TOPEX/POSEIDON mission offers the first opportunity to observe rain cells over the ocean by a dual-frequency radar altimeter (TOPEX) and simultaneously observe their natural radiative properties by a three-frequency radiometer (TOPEX microwave radiometer (TMR)). This work is a feasibility study aimed at understanding the capability and potential of the active/passive TOPEX/TMR system for oceanic rainfall detection. On the basis of past experiences in rain flagging, a joint TOPEX/TMR rain probability index is proposed. This index integrates several advantages of the two sensors and provides a more reliable rain estimate than the radiometer alone. One year's TOPEX/TMR TMR data are used to test the performance of the index. The resulting rain frequency...
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Ano: 1997 URL: http://archimer.ifremer.fr/doc/00336/44719/44883.pdf
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Non-tidal aliasing in seasonal sea-level variability and annual Rossby waves as observed by satellite altimetry ArchiMer
Chen, Ge; Ezraty, Robert.
It is becoming well known that aliasing associated with ocean tides could be a major source of systematic error in altimeter sea-level measurements. due to asynoptic sampling and imperfect tide modelling. However, it has been shown that signals of non-tidal origin may also contribute significantly to the observed aliasing. In this paper, numerical simulations are performed to demonstrate the full aliasing potential associated with altimeter observations of seasonal sealevel variability and annual Rossby waves. Our results indicate that ignorance of non-tidal aliasing may lead to the possibility of underestimating the total aliasing and misinterpreting or overlooking existing geophysical phenomena. Therefore, it is argued that an entice aliasing picture...
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Ano: 1997 URL: http://archimer.ifremer.fr/doc/00335/44650/57343.pdf
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Modality of semiannual to multidecadal oscillations in global sea surface temperature variability ArchiMer
Chen, Ge; Shao, Baomin; Han, Yong; Ma, Jun; Chapron, Bertrand.
Repeating the history of study on El Nino-Southern Oscillation (ENSO) in the 1980s, interdecadal oscillation (IDO) in climate variability is currently an area of active research and debate, following the recognition of its emerging significance in nature and science. In this work, a two-dimensional propagating modal extraction technique is applied to a reconstructed global monthly sea surface temperature (SST) data set spanning 1854 through 2007, to examine the spatiotemporal structure of SST variability with an emphasis on the fine modal pattern of IDOs. In the time domain, it is revealed that a canonical modal spectrum of decadal-to-centennial SST variability constitutes four most distinct oscillations with periodicities at 9.0, 13.0, 21.2, and 62.2...
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Ano: 2010 URL: http://archimer.ifremer.fr/doc/00002/11308/7893.pdf
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Limitation of SAR Quasi-Linear Inversion Data on Swell Climate: An Example of Global Crossing Swells ArchiMer
Jiang, Haoyu; Mouche, Alexis; Wang, He; Babanin, Alexander V.; Chapron, Bertrand; Chen, Ge.
Numerical wave models are powerful tools for investigating global wave climate. Here a global wave hindcast is employed to estimate the global pattern of crossing swells. However, the global patterns of crossing swells derived from the model are different from those derived from the synthetic aperture radar (SAR) wave mode products of quasi-linear inversion, indicating one of them is questionable. The comparison shows that the first two most energetic swells inversed by SAR are often not in accordance with the first two most energetic swells in the model, and this will have a large impact on the statistics of the data. Before this problem is solved, SAR wave products of quasi-linear inversion should be treated with care in wave climate studies.
Tipo: Text Palavras-chave: Synthetic aperture radar; Quasi-linear inversion; Crossing swells; Wave climate.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00369/47979/48003.pdf
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Tracking the attenuation and nonbreaking dissipation of swells using altimeters ArchiMer
Jiang, Haoyu; Stopa, Justin; Wang, He; Husson, Romain; Mouche, Alexis; Chapron, Bertrand; Chen, Ge.
A method for systematically tracking swells across oceanic basins is developed by taking advantage of high-quality data from space-borne altimeters and wave model output. The evolution of swells is observed over large distances based on 202 swell events with periods ranging from 12 to 18 s. An empirical attenuation rate of swell energy of about 4 × 10−7 m−1 is estimated using these observations, and the nonbreaking energy dissipation rates of swells far away from their generating areas are also estimated using a point source model. The resulting acceptance range of nonbreaking dissipation rates is −2.5 to 5.0 × 10−7 m−1, which corresponds to a dissipation e-folding scales of at least 2000 km for steep swells, to almost infinite for small-amplitude swells....
Tipo: Text Palavras-chave: Altimeter; Swell dissipation; Swell tracking.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00314/42526/41897.pdf
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Data-Driven Interpolation of Sea Level Anomalies Using Analog Data Assimilation ArchiMer
Lguensat, Redouane; Viet, Phi Huynh; Sun, Miao; Chen, Ge; Fenglin, Tian; Chapron, Bertrand; Fablet, Ronan.
From the recent developments of data-driven methods as a means to better exploit large-scale observation, simulation and reanalysis datasets for solving inverse problems, this study addresses the improvement of the reconstruction of higher-resolution Sea Level Anomaly (SLA) fields using analog strategies. This reconstruction is stated as an analog data assimilation issue, where the analog models rely on patch-based and Empirical Orthogonal Functions (EOF)-based representations to circumvent the curse of dimensionality. We implement an Observation System Simulation Experiment (OSSE) in the South China Sea. The reported results show the relevance of the proposed framework with a significant gain in terms of Root Mean Square Error (RMSE) for scales below 100...
Tipo: Text Palavras-chave: Analog data assimilation; Sea level anomaly; Sea surface height; Interpolation; Data-driven methods.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00489/60078/63402.pdf
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