Quantifying atmosphere and ocean origins of North American precipitation variability     

Zhang  Honghai  Seager  Richard  He  Jie  Diao  Hansheng  Pascale  Salvatore 《Climate Dynamics》2021,56(11):4051-4074

How atmospheric and oceanic processes control North American precipitation variability has been extensively investigated, and yet debates remain. Here we address this question in a 50 km-resolution flux-adjusted global climate model. The high spatial resolution and flux adjustment greatly improve the model’s ability to realistically simulate North American precipitation, the relevant tropical and midlatitude variability and their teleconnections. Comparing two millennium-long simulations with and without an interactive ocean, we find that the leading modes of North American precipitation variability on seasonal and longer timescales exhibit nearly identical spatial and spectral characteristics, explained fraction of total variance and associated atmospheric circulation. This finding suggests that these leading modes arise from internal atmospheric dynamics and atmosphere-land coupling. However, in the fully coupled simulation, North American precipitation variability still correlates significantly with tropical ocean variability, consistent with observations and prior literature. We find that tropical ocean variability does not create its own type of atmospheric variability but excites internal atmospheric modes of variability in midlatitudes. This oceanic impact on North American precipitation is secondary to atmospheric impacts based on correlation. However, relative to the simulation without an interactive ocean, the fully coupled simulation amplifies precipitation variance over southwest North America (SWNA) during late spring to summer by up to 90%. The amplification is caused by a stronger variability in atmospheric moisture content that is attributed to tropical Pacific sea surface temperature variability. Enhanced atmospheric moisture variations over the tropical Pacific are transported by seasonal mean southwesterly winds into SWNA, resulting in larger precipitation variance.

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On the influence of RF absorbing material on the GNSS position     

Wim Aerts  Carine Bruyninx  Pascale Defraigne  Guy A. E. Vandenbosch  Philipp Zeimetz 《GPS Solutions》2016,20(1):1-7

Reflections of the GNSS signal around the antenna induce an error in the measurement of the satellite–receiver distance and therefore should be avoided as much as possible. One solution often used to mitigate these reflections is to apply radio frequency (RF) absorbing material to the antenna, its support or its site. Such material could however alter the antenna phase delay and, in turn, alter the position as calculated from the GNSS observations. We explain under which conditions the RF material will or will not alter the antenna phase delay, and hence in which conditions a re-calibration of the antenna is necessary after the installation of absorbing material. Furthermore, rules of thumb are given to install the material in such a way that re-calibration can be avoided. Some basic theory and measurements of the influence of RF material are reviewed. An application to a real life absorber setup similar to one of the International GNSS Service reference stations is then discussed, and the position offset due to the absorbing material is demonstrated. The topics discussed can serve station managers to limit effects of absorbing material and take precautions to avoid a position bias.  相似文献   

Spatial stabilization and intensification of moistening and drying rate patterns under future climate change     

Yann Chavaillaz  Sylvie Joussaume  Sandrine Bony  Pascale Braconnot 《Climate Dynamics》2016,47(3-4):951-965

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Monitoring of UTC(k)’s using PPP and IGS real-time products     

Pascale Defraigne  Wim Aerts  Eric Pottiaux 《GPS Solutions》2015,19(1):165-172

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Sub‐Permil Interlaboratory Consistency for Solution‐Based Boron Isotope Analyses on Marine Carbonates     

Marcus Gutjahr  Louise Bordier  Eric Douville  Jesse Farmer  Gavin L. Foster  Ed C. Hathorne  Brbel Hnisch  Damien Lemarchand  Pascale Louvat  Malcolm McCulloch  Johanna Noireaux  Nicola Pallavicini  James W. B. Rae  Ilia Rodushkin  Philippe Roux  Joseph A. Stewart  Franois Thil  Chen‐Feng You 《Geostandards and Geoanalytical Research》2021,45(1):59-75

Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO₂ through Earth’s history. While isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the boron isotopic composition (commonly expressed in δ¹¹B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp‐1 (coral Porites) and JCt‐1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre‐treatment, aimed at removing organic material from carbonate, can influence the resulting δ¹¹B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ¹¹B; and (c) to provide well‐constrained consensus δ¹¹B values for JCp‐1 and JCt‐1. The resultant robust mean and associated robust standard deviation (s*) for un‐oxidised JCp‐1 is 24.36 ± 0.45‰ (2s*), compared with 24.25 ± 0.22‰ (2s*) for the same oxidised material. For un‐oxidised JCt‐1, respective compositions are 16.39 ± 0.60‰ (2s*; un‐oxidised) and 16.24 ± 0.38‰ (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement.  相似文献   

Three-dimensional structure of flow at a confluence of river channels with discordant beds   总被引：2，自引：0，他引：2  

Bernard De Serres  Andr G. Roy  Pascale M. Biron  James L. Best 《Geomorphology》1999,26(4):48

This paper presents three-dimensional data of the mean and turbulent structure of flow collected at a natural confluence of rivers with discordant beds to (1) describe the three-dimensional flow field of a natural junction of channels; (2) assess the role of changes in bed morphology occurring during transport-effective events on the structure of flow at a confluence; and (3) examine how the three-dimensional structure of flow varies with changes in the ratio of momentum flux between the two confluent streams. Three-dimensional measurements of velocity were reconstructed from the measurements obtained with an array of four, two-component electromagnetic current meters. Six detailed velocity profiles were taken at five cross-sections in a wide range of flow conditions. The mean field of flow is characterised by (1) the acceleration of flow in the downstream portion of the post-confluence channel, but by lower velocities upstream in the mixing layer area; (2) a stagnation zone at the apex of the junction; (3) a zone of flow deviation, and strong fluid upwelling, close to the avalanche face and at the margin of the tributary mouth bar; and (4) reduced velocities over the depositional bar at the downstream junction corner. The position and extent of these zones vary with changes in the ratio of momentum flux. Very high intensity of turbulence (peaks up to 50%) and turbulent kinetic energy were observed in the mixing layer region. Distortion of the mixing layer, characteristic of flow where bed discordance is present between the two tributary channels, was evident from mean and turbulent flow data. This field study suggests that the effects of bed discordance on flow, sediment transport, and the resultant bed morphology must be incorporated into conceptual and numeric models of these sites of complex flow.  相似文献   

The effects of antecedent moisture conditions on the relationship of hydrology to hydrochemistry in a small forested watershed     

Pascale M. Biron  Andr G. Roy  Franois Courschesne  William H. Hendershot  Benoît Ct  Jim Fyles 《水文研究》1999,13(11):1541-1555

The relationship between stream discharge and the concentration of different solutes reflects the hydrological processes occurring in a catchment, but is also strongly affected by antecedent moisture conditions. In this study, the effects of antecedent conditions were examined for a small forested watershed near Montréal (Québec) by comparing data from sequences of fall events for two years of contrasting antecedent moisture conditions. The relationship between discharge and stream water chemistry was also quantified using cross‐correlation analysis. Results show that concentrations of dissolved organic carbon, nitrate and calcium increased during storm events with dry antecedent conditions but that the relationships were weaker under wet conditions. For both years, concentrations of sulfate, silicon and sodium and the pH were negatively correlated with discharge (cross‐correlations from −0·20 to −0·53). With dry antecedent conditions, there was a general decrease in the concentration of all solutes with time, whereas concentrations remained at about the same level under wet conditions. The concentration–discharge relationships for sulfate shifted frequently from higher concentrations during the rising limb to higher concentrations during the falling limb from one event to another as a result of changing antecedent conditions. Although the contrast in antecedent moisture conditions between the two years was moderate in comparison with that reported in other studies (25% dryer than average in 1995 and 12% wetter than average in 1996), the hydrochemistry of the stream was markedly different. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Impacts of river bank stabilization using riprap on fish habitat in two contrasting environments          下载免费PDF全文

William Massey  Pascale M. Biron  Guénolé Choné 《地球表面变化过程与地形》2017,42(4):635-646

Riverbank stabilization using rock riprap is commonly used for protecting road and bridge structures from fluvial erosion. However, little is known about how streams adjust to such perturbation or how this can affect fish habitat in different fluvial environments, particularly for non‐salmonid species in small streams. The objective of this study is to assess impacts of riprap on fish habitat quantity and quality through a pairwise comparison of 27 stabilized and non‐stabilized stream reaches in two physiographic regions, the Saint Lawrence Lowlands and the Appalachian highlands of Montérégie‐Est (Quebec, Canada). Both quantitative (Hydro‐morphological Index of Diversity, HMID) and qualitative (Qualitative Habitat Evaluation Index, QHEI) fish habitat assessment techniques are applied in order to compare results between methods. For each stream reach depth and velocity were measured to calculate HMID. In‐stream cover (woody debris, overhanging vegetation, undercut banks, aquatic macrophytes) and habitat units (pools, riffles, runs, glides) were also documented and used to determine QHEI. Results show that overall bank stabilization using riprap at bridge and stream crossings alters fish habitat characteristics. Loss of in‐stream covers and riparian vegetation lower QHEI scores at stabilized reaches, especially in more pristine Appalachian streams, but has less impact on already altered straightened Lowlands streams. In this latter context, some positive alterations of fish habitat were observed in riprapped reaches due to the coarsening of the substrate and an induced increase of slope. The two metrics (HMID and QHEI) revealed similar differences between stabilized and non‐stabilized sites for Lowlands sites, but their level of agreement was much less in the Appalachian streams, suggesting caution when interpreting habitat quality results based on a single metric. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Contrasted turbulence intensities in the Indonesian Throughflow: a challenge for parameterizing energy dissipation rate     

Pascale Bouruet-Aubertot  Yannis Cuypers  Bruno Ferron  Denis Dausse  Olivier Ménage  Agus Atmadipoera  Indra Jaya 《Ocean Dynamics》2018,68(7):779-800

Microstructure measurements were performed along two sections through the Halmahera Sea and the Ombai Strait and at a station in the deep Banda Sea. Contrasting dissipation rates (??) and vertical eddy diffusivities (K _z ) were obtained with depth-averaged ranges of \(\sim [9 \times 10^{-10}-10^{-5}]\) W kg^??1 and of \(\sim [1 \times 10^{-5}-2 \times 10^{-3}]\) m² s^??1, respectively. Similarly, turbulence intensity, \(I={\epsilon }/(\nu N^{2})\) with ν the kinematic viscosity and N the buoyancy frequency, was found to vary seven orders of magnitude with values up to \(10^{7}\). These large ranges of variations were correlated with the internal tide energy level, which highlights the contrast between regions close and far from internal tide generations. Finescale parameterizations of ?? induced by the breaking of weakly nonlinear internal waves were only relevant in regions located far from any generation area (“far field”), at the deep Banda Sea station. Closer to generation areas, at the “intermediate field” station of the Halmahera Sea, a modified formulation of MacKinnon and Gregg (2005) was validated for moderately turbulent regimes with 100 < I < 1000. Near generation areas marked by strong turbulent regimes such as “near field” stations within strait and passages, ?? is most adequately inferred from horizontal velocities provided that part of the inertial subrange is resolved, according to Kolmogorov scaling.  相似文献   

On the role of mesoscale eddies in the ventilation of Antarctic intermediate water     

Zouhair Lachkar  James C. Orr  Jean-Claude Dutay  Pascale Delecluse 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(6):909-925

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