Articles de revues : « Climatic tracers »

1

Jull, J. T., G. S. Burr, J. W. Beck, D. J. Donahue, D. Biddulph, A. L. Hatheway, T. E. Lange et L. R. McHargue. « Accelerator Mass Spectrometry at Arizona : Geochronology of the Climatic Record and Connections with the Ocean ». Scientific World JOURNAL 2 (2002) : 1579–93. http://dx.doi.org/10.1100/tsw.2002.349.

Texte intégral

Résumé :

There are many diverse uses of accelerator mass spectrometry (AMS).14C studies at our laboratory include much research related to paleoclimate, with14C as a tracer of past changes in environmental conditions as observed in corals, marine sediments, and many terrestrial records. Terrestrial records can also show the influence of oceanic oscillations, whether they are short term, such as ENSO (El Niño/Southern Oscillation), or on the millennial time scale. In tracer applications, we have developed the use of129I as well as14C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson, AZ, for several of these fields and hope to give some idea of the breadth of these studies.

Styles APA, Harvard, Vancouver, ISO, etc.

2

Krinner, G., et C. Genthon. « Tropospheric transport of continental tracers towards Antarctica under varying climatic conditions ». Tellus B : Chemical and Physical Meteorology 55, n^o 1 (janvier 2003) : 54–70. http://dx.doi.org/10.3402/tellusb.v55i1.16354.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

3

KRINNER, G., et C. GENTHON. « Tropospheric transport of continental tracers towards Antarctica under varying climatic conditions ». Tellus B 55, n^o 1 (février 2003) : 54–70. http://dx.doi.org/10.1034/j.1600-0889.2003.00004.x.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

4

Baker, A. R., W. M. Landing, E. Bucciarelli, M. Cheize, S. Fietz, C. T. Hayes, D. Kadko et al. « Trace element and isotope deposition across the air–sea interface : progress and research needs ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 374, n^o 2081 (28 novembre 2016) : 20160190. http://dx.doi.org/10.1098/rsta.2016.0190.

Texte intégral

Résumé :

The importance of the atmospheric deposition of biologically essential trace elements, especially iron, is widely recognized, as are the difficulties of accurately quantifying the rates of trace element wet and dry deposition and their fractional solubility. This paper summarizes some of the recent progress in this field, particularly that driven by the GEOTRACES, and other, international research programmes. The utility and limitations of models used to estimate atmospheric deposition flux, for example, from the surface ocean distribution of tracers such as dissolved aluminium, are discussed and a relatively new technique for quantifying atmospheric deposition using the short-lived radionuclide beryllium-7 is highlighted. It is proposed that this field will advance more rapidly by using a multi-tracer approach, and that aerosol deposition models should be ground-truthed against observed aerosol concentration data. It is also important to improve our understanding of the mechanisms and rates that control the fractional solubility of these tracers. Aerosol provenance and chemistry (humidity, acidity and organic ligand characteristics) play important roles in governing tracer solubility. Many of these factors are likely to be influenced by changes in atmospheric composition in the future. Intercalibration exercises for aerosol chemistry and fractional solubility are an essential component of the GEOTRACES programme. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Lu, Dawei, Jihua Tan, Xuezhi Yang, Xu Sun, Qian Liu et Guibin Jiang. « Unraveling the role of silicon in atmospheric aerosol secondary formation : a new conservative tracer for aerosol chemistry ». Atmospheric Chemistry and Physics 19, n^o 5 (5 mars 2019) : 2861–70. http://dx.doi.org/10.5194/acp-19-2861-2019.

Texte intégral

Résumé :

Abstract. Aerosol particles are ubiquitous in the atmosphere and affect the quality of human life through their climatic and health effects. The formation and growth of aerosol particles involve extremely complex reactions and processes. Due to limited research tools, the sources and chemistry of aerosols are still not fully understood, and until now have normally been investigated by using chemical species of secondary aerosols (e.g., NH4+, NO3-, SO42-, SOC) as tracers. Here we investigated the role of silicon (Si), an ubiquitous but relatively inert element, during the secondary aerosol formation process. We analyzed the correlation of Si in airborne fine particles (PM2.5) collected in Beijing – a typical pollution region – with the secondary chemical species and secondary particle precursors (e.g., SO2 and NOx). The total mass of Si in PM2.5 was found to be uncorrelated with the secondary aerosol formation process, which suggested that Si is a new conservative tracer for the amount of primary materials in PM2.5 and can be used to estimate the relative amount of secondary and primary compounds in PM2.5. This finding enables the accurate estimation of secondary aerosol contribution to PM2.5 by using Si as a single tracer rather than the commonly used multiple chemical tracers. In addition, we show that the correlation analysis of secondary aerosols with the Si isotopic composition of PM2.5 can further reveal the sources of the precursors of secondary aerosols. Therefore, Si may provide a new tool for aerosol chemistry studies.

Styles APA, Harvard, Vancouver, ISO, etc.

6

Casciotti, Karen L. « Nitrite isotopes as tracers of marine N cycle processes ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 374, n^o 2081 (28 novembre 2016) : 20150295. http://dx.doi.org/10.1098/rsta.2015.0295.

Texte intégral

Résumé :

Nitrite (NO 2 − ) is a key intermediate in the marine nitrogen (N) cycle. It is produced and consumed throughout the ocean by the dominant processes driving the distribution, availability and speciation of N. However, the accumulation of nitrite is typically confined to depths near the base of the sunlit euphotic zone and in oxygen-deficient zones. These features are known as the primary and secondary nitrite maximum (PNM and SNM), respectively. The processes controlling nitrite accumulation in these features are not fully understood, but are thought to depend on the microbial community composition and its response to environmental conditions. A variety of approaches have been applied to understanding these features since their discovery, with the stable N and oxygen (O) isotope measurements of nitrite being added to this toolkit most recently. Large variations in nitrite N isotope ratios ( 15 N/ 14 N) and dramatic depletions in 15 N contrast with more consistent nitrite O isotope ratios ( 18 O/ 16 O) in the SNM. These signals provide unique information about the mechanisms of nitrite consumption in the SNM. By contrast, nitrite in the PNM shows less variation in 15 N/ 14 N, but variations in 18 O/ 16 O that provide insight into the mechanisms and rates of N cycling there. This review presents a synthesis of nitrite isotope measurements in the marine environment, highlighting the insights that have been gained from these measurements. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

Styles APA, Harvard, Vancouver, ISO, etc.

7

Padmaja, Suragani Mohini, Sagiraju Dileep Kumar Varma, Koduri Omkar et Gajula Srinivasa Rao. « Real time performance assessment of utility grid interfaced solar photovoltaic plant ». International Journal of Electrical and Computer Engineering (IJECE) 14, n^o 2 (1 avril 2024) : 1323. http://dx.doi.org/10.11591/ijece.v14i2.pp1323-1333.

Texte intégral

Résumé :

Continuous monitoring of large-scale solar photovoltaic (PV) installations is necessary to check the deterioration and monitor the performance of the PV plant. Fault diagnosis is crucial to ensure the PV plant operates safely and reliably. This paper presents a diagnosis methodology based on current-voltage (I-V) and PV characteristics to monitor and assess the behavior of solar PV. In this paper, I-V curve characterization using an I-V curve tracer is used to check the deterioration and diagnosis of the PV panels. The real-time performance of the 50.4 kWp rooftop solar grid interfaced PV plant is investigated and analyzed using I-V and PV curve tracers in real-time conditions. The overall performance of solar PV is assessed on a real-time test system in different scenarios such as variable climatic conditions, partial shading conditions, aging of solar panels, short circuit conditions, and dust decomposition. Furthermore, the performance assessment of solar PV is evaluated using performance indicators such as open circuit voltage index, short circuit current index, fill factor, and performance ratio.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Tateo, Fabio. « Clay Minerals at the Paleocene–Eocene Thermal Maximum : Interpretations, Limits, and Perspectives ». Minerals 10, n^o 12 (30 novembre 2020) : 1073. http://dx.doi.org/10.3390/min10121073.

Texte intégral

Résumé :

The Paleocene–Eocene Thermal Maximum (PETM) was an “extreme” episode of environmental stress that affected the Earth in the past, and it has numerous affinities concerning the rapid increase in the greenhouse effect. It has left several biological, compositional, and sedimentary facies footprints in sedimentary records. Clay minerals are frequently used to decipher environmental effects because they represent their source areas, essentially in terms of climatic conditions and of transport mechanisms (a more or less fast travel, from the bedrocks to the final site of recovery). Clay mineral variations at the PETM have been studied by several authors in terms of climatic and provenance indicators, but also as tracers of more complicated interplay among different factors requiring integrated interpretation (facies sorting, marine circulation, wind transport, early diagenesis, etc.). Clay minerals were also believed to play a role in the recovery of pre-episode climatic conditions after the PETM exordium, by becoming a sink of atmospheric CO2 that is considered a necessary step to switch off the greenhouse hyperthermal effect. This review aims to consider the use of clay minerals made by different authors to study the effects of the PETM and their possible role as effective (simple) proxy tools for environmental reconstructions.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Pitari, G., et E. Mancini. « Short-term climatic impact of the 1991 volcanic eruption of Mt. Pinatubo and effects on atmospheric tracers ». Natural Hazards and Earth System Sciences 2, n^o 1/2 (30 juin 2002) : 91–108. http://dx.doi.org/10.5194/nhess-2-91-2002.

Texte intégral

Résumé :

Abstract. Large explosive volcanic eruptions are capable of injecting considerable amounts of particles and sulphur gases (mostly sulphur dioxide) above the tropopause, causing increases in the stratospheric aerosol optical depth that may be even larger than one order of magnitude. The e-folding particle lifetime in the stratosphere is much longer than in the troposphere (one year versus a few days) so that climatic perturbations in a timeframe of a few years are produced after major volcanic eruptions. A climate-chemistry coupled model is used here to study the dynamical effects of the radiative forcing due to stratospheric aerosols formed after the June, 1991 cataclysmic eruption of Mt. Pinatubo in the Philippines. It is shown that the dynamical perturbation is twofold: (a) the stratospheric mean meridional circulation is affected by local aerosol radiative heating (mostly located in the tropical lower stratosphere); (b) the planetary wave propagation in the mid- to high-latitude lower stratosphere is altered as a consequence of decreasing atmospheric stability due to the climatic perturbation. Dynamical results of the climate model are compared with available observations; a discussion is made regarding the similarities with the dynamical regime of the easterly phase of the equatorial quasi-biennial oscillation. Major findings of this study are: (a) radiatively forced changes in the stratospheric circulation during the first two years after the eruption may, to a large extent, explain the observed trend decline of long-lived greenhouse gases (CH4 and N2O, in particular); (b) the dynamical perturbation helps explain why simple photochemical studies of the ozone trends during 1991–1993 generally fail in reproducing the satellite observed feature consisting of a 2% additional global ozone depletion during 1993 with respect to 1992. In both cases we conclude that an increase in the mid- to high-latitude downward flux at the tropopause is the key factor for explaining the behaviour of these atmospheric tracers during 1991/92.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Nerushev, A. F., K. N. Visheratin et R. V. Ivangorodsky. « Satellite-derived estimations of the clear-air turbulence in the upper troposphere ». IOP Conference Series : Earth and Environmental Science 1040, n^o 1 (1 juin 2022) : 012025. http://dx.doi.org/10.1088/1755-1315/1040/1/012025.

Texte intégral

Résumé :

Abstract The paper presents the results of a study of turbulence zones in the upper troposphere of the Northern Hemisphere based on measurements from European geostationary meteorological satellites in 2007 - 2018. The essence of the method for determining the zones of turbulence is the use of inhomogeneity’s of concentration of water vapor as tracers and the use of correlation-extremal algorithms. Turbulence zones with a horizontal mesoscale turbulent diffusion coefficient Ked ≥ 104 m2 / s can occupy up to 50% of the Northern Hemisphere area visible from satellites. It is shown that in analyzed time interval there is a significant (by 60-120%) increase in areas occupied by relatively weak and moderate turbulence and a slight decrease (by 6-33%) in areas with strong and very strong turbulence. The temporal variability of these zones and their relationship with the characteristics of jet streams and some climatic parameters are analyzed. A statistical model of the temporal variability of the turbulence zone areas has been built. It is shown that the multiple linear regression model with jet stream characteristics as predictors describes up to 68% of variability of zones of strong turbulence. The use of climatic parameters as predictors makes it possible to describe up to 74% of the temporal variability of strong turbulence zones.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Tomazin, Rok, Saša Simčič, Sanja Stopinšek, Andreja Nataša Kopitar, Andreja Kukec, Tadeja Matos et Janez Mulec. « Effects of Anthropogenic Disturbance and Seasonal Variation on Aerobiota in Highly Visited Show Caves in Slovenia ». Microorganisms 11, n^o 10 (23 septembre 2023) : 2381. http://dx.doi.org/10.3390/microorganisms11102381.

Texte intégral

Résumé :

Aerosols in caves are natural tracers and, together with climatic parameters, provide a detailed insight into atmospheric conditions, responses to climatic changes and anthropogenic influences in caves. Microbiological air monitoring in show caves is becoming increasingly useful to understand changes in cave ecosystems and to implement and review measures for sustainable cave use and tourism development. In 2017 and 2018, air along tourist trails in caves Postojnska jama and Škocjanske jame (Slovenia) was sampled before and after tourist visits. Samples were analysed using culture-dependent methods, flow cytometry, detection of β-D-glucan and lipopolysaccharide and compared with CO2 and temperature data to measure anthropogenic influences and seasonality on aerobiota. While the presence of tourists significantly increased concentrations of airborne microorganisms (p < 0.05), β-D-glucan and CO2 did not show such a trend and were more dependent on seasonal changes. Locally, concentrations of cultivable microorganisms above 1000 CFU/m3 were detected, which could have negative effects on the autochthonous microbiota and possibly on human health. A mixture of bacteria typically associated with humans was found in the air and identified with MALDI-TOF MS. Using MALDI-TOF MS, we achieved a 69.6% success rate in identification. Micrococcus luteus, Streptococcus mitis, Staphylococcus epidermidis and Moraxella spp. were recognized as good indicators of cave anthropisation.

Styles APA, Harvard, Vancouver, ISO, etc.

12

El-Ghazi, Ibrahim, Yousra Ameziane El-Hassani, Fatiha Laziri et Samir El-Jaafari. « Evaluation of Nitrogen Dioxide, Benzene, Toluene, Ethylbenzene and Xylene Concentrations in the Urban Environment of Meknes City, Morocco ». Asian Journal of Advances in Agricultural Research 23, n^o 3 (4 octobre 2023) : 1–24. http://dx.doi.org/10.9734/ajaar/2023/v23i3463.

Texte intégral

Résumé :

The present study focuses on the monitoring and the evaluation of air quality in the city of Meknes, based on the tracers of pollution of proximity cars (NO2 (nitrogen dioxide) and BTEX (Benzene, Toluene, Ethylbenzene, and Xylene). In the absence of a telemetric station and a mobile laboratory within the city, passive diffusion tubes, analyzed offline in the laboratory after exposure, were the most plausible solution. The low cost, ease of implementation of the technique, and the possibility of covering a large geographic area with many samplers all argue for adopting this approach. The coupling of the results of the measurement campaigns and counting sessions under a geographical information system allowed us to determine the most affected areas by automobile pollution and to carry out cartography at a large scale of spatial resolution of the prospected pollutants. The deployment of passive sensors at 14 measurement sites revealed the existence of spatio-temporal variability of the pollutants studied. This variability is due to the climatic conditions that prevailed during the measurement campaigns, notably wind and precipitation, the photochemical nature of the said markers, the proximity to the emission sources, the type of measurement site, and the topography and road infrastructure. The approach developed could be used as a decision-making tool for the competent authorities in this field and adapted for monitoring other types of pollutants (pesticides, tracers generated by industrial units, furan dioxins, etc.).

Styles APA, Harvard, Vancouver, ISO, etc.

13

Delmotte, Marc, Dominique Raynaud, Vin Morgan et Jean Jouzel. « Climatic and glaciological information inferred from air-content measurements of a Law Dome (East Antarctica) ice core ». Journal of Glaciology 45, n^o 150 (1999) : 255–63. http://dx.doi.org/10.1017/s0022143000001751.

Texte intégral

Résumé :

AbstractThe total air content(V)of ice has been measured along the Dome Summit South (DSS) core from Law Dome, East Antarctica. The main features of this record are the very well-preserved sub-annual fluctuations ofV(down to at least 900 m depth) and the significant increase of theVvalues during the last deglaciation. The sub-annual variations reflect changes in close-off porosity, and we interpret theVseasonal peaks as tracers of depth-hoar layers. For the longer time-scale, the largeVfluctuations observed are interpreted in terms of elevation and/or close-off porosity changes under different assumptions. We analyze the possible influence of a different global pressure field and/or a change in seasonal temperature and precipitation cycles during the last glacial period. Our estimates of surface elevation changes derived from theVdata are then compared with independent reconstructions of past elevations.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Delmotte, Marc, Dominique Raynaud, Vin Morgan et Jean Jouzel. « Climatic and glaciological information inferred from air-content measurements of a Law Dome (East Antarctica) ice core ». Journal of Glaciology 45, n^o 150 (1999) : 255–63. http://dx.doi.org/10.3189/s0022143000001751.

Texte intégral

Résumé :

AbstractThe total air content (V) of ice has been measured along the Dome Summit South (DSS) core from Law Dome, East Antarctica. The main features of this record are the very well-preserved sub-annual fluctuations of V (down to at least 900 m depth) and the significant increase of the V values during the last deglaciation. The sub-annual variations reflect changes in close-off porosity, and we interpret the V seasonal peaks as tracers of depth-hoar layers. For the longer time-scale, the large V fluctuations observed are interpreted in terms of elevation and/or close-off porosity changes under different assumptions. We analyze the possible influence of a different global pressure field and/or a change in seasonal temperature and precipitation cycles during the last glacial period. Our estimates of surface elevation changes derived from the V data are then compared with independent reconstructions of past elevations.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Allagui, Asma, Hassouna Bahrouni et Youssef M’Sadak. « Deposition of Pesticide to the Soil and Plant Retention During Crop Spraying : The Art State ». Journal of Agricultural Science 10, n^o 12 (15 novembre 2018) : 104. http://dx.doi.org/10.5539/jas.v10n12p104.

Texte intégral

Résumé :

Environment pollution related to pesticides has been confirmed by the scientific community for a long time, but the available information on the impact of this phenomenon on human health and the ecosystem are still insufficient. Contamination of the environment can occur through various pathways, ground deposits during the application of pesticides to crops are one of those pathways. The retention rate of sprayed droplets is an important factor both for the efficacy of the phytosanitary treatment and the quantities of lost pesticides on the ground. This paper presents an overview of factors that affect spray droplet behavior, involved process in sprayed drop fate and the mainly techniques for measuring pesticide deposits to the ground and plant retention. We present studies that have focused on pesticide retention and soil deposition during crop spraying in relation to sprayer equipment, used formulation and climatic factors. Plant retention and pesticide deposits during spray is a complex problem depending mainly on physical sprayer parameters, climatic conditions, spray properties and chemical formulation. By illustrating the large variety of analytical methods during the recently years, it aims to explain that it is always possible to assess the impact of pesticides in all compartments of the environment. The use of concerned molecules and natural collectors is the safest to evaluate the real situation, but the use of tracers and artificial targets is both very reported and safety for the environment.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Assmann, K. M., M. Bentsen, J. Segschneider et C. Heinze. « An isopycnic ocean carbon cycle model ». Geoscientific Model Development 3, n^o 1 (16 février 2010) : 143–67. http://dx.doi.org/10.5194/gmd-3-143-2010.

Texte intégral

Résumé :

Abstract. The carbon cycle is a major forcing component in the global climate system. Modelling studies, aiming to explain recent and past climatic changes and to project future ones, increasingly include the interaction between the physical and biogeochemical systems. Their ocean components are generally z-coordinate models that are conceptually easy to use but that employ a vertical coordinate that is alien to the real ocean structure. Here, we present first results from a newly-developed isopycnic carbon cycle model and demonstrate the viability of using an isopycnic physical component for this purpose. As expected, the model represents well the interior ocean transport of biogeochemical tracers and produces realistic tracer distributions. Difficulties in employing a purely isopycnic coordinate lie mainly in the treatment of the surface boundary layer which is often represented by a bulk mixed layer. The most significant adjustments of the ocean biogeochemistry model HAMOCC, for use with an isopycnic coordinate, were in the representation of upper ocean biological production. We present a series of sensitivity studies exploring the effect of changes in biogeochemical and physical processes on export production and nutrient distribution. Apart from giving us pointers for further model development, they highlight the importance of preformed nutrient distributions in the Southern Ocean for global nutrient distributions. The sensitivity studies show that iron limitation for biological particle production, the treatment of light penetration for biological production, and the role of diapycnal mixing result in significant changes of nutrient distributions and liniting factors of biological production.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Huang, Hao-Wei, Shiuh-Tsuen Huang, Ruo-Mei Wang, Wen-Fu Chen, Chuan-Hsiung Chung et Chen-Feng You. « Strontium Isotopic Composition as Tracers for Identifying Groundwater Recharge Sources in the Choushui River Alluvial Plain, Western Taiwan ». Water 16, n^o 15 (30 juillet 2024) : 2151. http://dx.doi.org/10.3390/w16152151.

Texte intégral

Résumé :

Groundwater is a vital resource in the Chuoshui River alluvial plain (CSAP), a key agricultural area in Taiwan. Understanding groundwater recharge is crucial for sustainable water management amidst changing climatic conditions and increasing water demand. This study investigates the major ion composition, solute Sr concentrations, and 87Sr/86Sr ratios in groundwater and stream water from the Choushui River (CSR) to trace groundwater recharge sources. The Piper diagram reveals that most groundwater samples are of the freshwater Ca–HCO3 type, aligning with the total dissolved solids (TDS) classification. TDS and major ion compositions indicate that groundwater near Baguashan Terrace (BGT) and Douliu Hill (DLH) primarily derives from stream water and rainwater. Na+ and Cl− enrichment in some aquifers of BGT and DLH is attributed to the dissolution of paleo-sea salt and mixing with paleo-seawater from sedimentary porewater. Elevated dissolved Sr concentrations and lower 87Sr/86Sr ratios in these aquifers further support the intrusion of paleo-seawater. Groundwater in the proximal fan shows high TDS due to intensive weathering, complicating the use of TDS as a tracer. Sr isotopic compositions and solute Sr2+ concentrations effectively distinguish recharge sources, revealing that the CSR mainstream primarily recharges the proximal fan and BGT region, while CSR tributaries and rainwater mainly recharge the DLH region. This study concludes that Sr isotopic compositions and solute Sr2+ concentrations are more reliable than TDS and major ion compositions in identifying groundwater recharge sources, enhancing our understanding of groundwater origins and the processes affecting water quality.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Del Gaudio, Arianna V., Aaron Avery, Gerald Auer, Werner E. Piller et Walter Kurz. « Planktonic foraminiferal assemblages as tracers of paleoceanographic changes within the northern Benguela current system since the Early Pleistocene ». Climate of the Past 20, n^o 10 (9 octobre 2024) : 2237–66. http://dx.doi.org/10.5194/cp-20-2237-2024.

Texte intégral

Résumé :

Abstract. The Benguela Upwelling System (BUS), located in the southeastern Atlantic Ocean, represents one of the world's most productive regions. This system is delimited to the south by the Agulhas retroflection region. The northern boundary of the BUS is, instead, represented by the Angola–Benguela Front (ABF), which is a thermal feature separating warm waters of the Angola Basin (including the South Atlantic Central Water; SACW) from the cooler Benguela Oceanic Current (BOC). We performed statistical analyses on planktonic foraminiferal assemblages in 94 samples from Holes U1575A and U1576A, cored during International Ocean Discovery Program (IODP) Expedition 391. Drilled sites are located along the Tristan–Gough–Walvis Ridge (TGW) seamount track in the northern sector of the BUS (offshore the Namibian continental margin). The analyzed stratigraphic intervals span the Early–Late Pleistocene, marked by the Early–Middle Pleistocene transition (EMPT; 1.40–0.40 Myr), during which important glacial–interglacial sea surface temperature (SST) variabilities occurred. This work provides novel insights on the local paleoceanographic evolution of the northern BUS and associated thermocline variability based on the ecological significance of the foraminiferal assemblages. Specifically, variations in the assemblage content allowed us to characterize the different water masses (BOC, SACW, and Agulhas waters) and reconstruct their interactions during the Quaternary. The interplay of the previously mentioned water masses induced perturbations in the BUS (ABF latitudinal shifts and input of tropical waters from the Agulhas retroflection region). Furthermore, we investigated the possible link between changes in the paleoceanographic conditions and climatic events (e.g., Benguela Niño-/Niña-like phases and deglaciation stages) recorded since the EMPT.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Urrego, D. H., M. F. Sánchez Goñi, A. L. Daniau, S. Lechevrel et V. Hanquiez. « South-western Africa vegetation responses to atmospheric and oceanic changes during the last climatic cycle ». Climate of the Past Discussions 11, n^o 1 (16 février 2015) : 345–76. http://dx.doi.org/10.5194/cpd-11-345-2015.

Texte intégral

Résumé :

Abstract. Terrestrial and marine climatic tracers from marine core MD96-2098 collected in the southwestern African margin and spanning from 194 to 24 (thousand years before present) documented three pronounced expansions of Nama-Karoo and fine-leaved savanna during the last interglacial (Marine Isotopic Stage 5 – MIS 5). Nama-Karoo and fine-leaved savanna expansions were linked to increased aridity during the three warmest substadials of MIS 5. Enhanced aridity potentially resulted from a combination of reduced Benguela Upwelling System (BUS), expanded subtropical high-pressure cells, and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone (ITCZ). Decreased austral-winter precipitation was likely linked to a southern displacement of the westerlies. In contrast, during glacial isotopic stages MIS 6, 4 and 3, Fynbos expanded at the expense of Nama-Karoo and fine-leaved savanna indicating a relative increase in precipitation probably concentrated during the austral winter months. Our record also suggested that warm-cold or cold-warm transitions between isotopic stages and substages were punctuated by short increases in humidity. Increased aridity during MIS 5e, 5c and 5a warm substages coincided with minima in both precessional index and global ice volume. On the other hand, austral-winter precipitation increases were associated with precession maxima at the time of well-developed northern-hemisphere ice caps.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Huang, Yongsong, Bryan Shuman, Yi Wang et Thompson Webb. « Hydrogen isotope ratios of individual lipids in lake sediments as novel tracers of climatic and environmental change : a surface sediment test ». Journal of Paleolimnology 31, n^o 3 (avril 2004) : 363–75. http://dx.doi.org/10.1023/b:jopl.0000021855.80535.13.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

21

Rautio, A., A. L. Kivimäki, K. Korkka-Niemi, M. Nygård, V. P. Salonen, K. Lahti et H. Vahtera. « Vulnerability of groundwater resources to interaction with river water in a boreal catchment ». Hydrology and Earth System Sciences 19, n^o 7 (2 juillet 2015) : 3015–32. http://dx.doi.org/10.5194/hess-19-3015-2015.

Texte intégral

Résumé :

Abstract. A low-altitude aerial infrared (AIR) survey was conducted to identify hydraulic connections between aquifers and rivers and to map spatial surface temperature patterns along boreal rivers. In addition, the stable isotopic compositions (δ18O, δD), dissolved silica (DSi) concentrations and electrical conductivity of water in combination with AIR data were used as tracers to verify the observed groundwater discharge into the river system in a boreal catchment. Based on low temperature anomalies in the AIR survey, around 370 groundwater discharge sites were located along the main river channel and its tributaries (203 km altogether). On the basis of the AIR survey, the longitudinal temperature patterns of the studied rivers differed noticeably. The stable isotopes and DSi composition revealed major differences between the studied rivers. The groundwater discharge locations identified in the proximity of 12 municipal water intake plants during the low-flow seasons should be considered as potential risk areas for water intake plants during flood periods (groundwater quality deterioration due to bank infiltration), and should be taken under consideration in river basin management under changing climatic situations.

Styles APA, Harvard, Vancouver, ISO, etc.

22

Busenberg, Eurybiades, et L. Niel Plummer. « A 17-Year Record of Environmental Tracers in Spring Discharge, Shenandoah National Park, Virginia, USA : Use of Climatic Data and Environmental Conditions to Interpret Discharge, Dissolved Solutes, and Tracer Concentrations ». Aquatic Geochemistry 20, n^o 2-3 (2 octobre 2013) : 267–90. http://dx.doi.org/10.1007/s10498-013-9202-y.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

23

Rontani, J. F., B. Charriere, M. Petit, F. Vaultier, H. J. Heipieper, H. Link, G. Chaillou et R. Sempéré. « Degradation state of organic matter in surface sediments from the Southern Beaufort Sea : a lipid approach ». Biogeosciences 9, n^o 9 (5 septembre 2012) : 3513–30. http://dx.doi.org/10.5194/bg-9-3513-2012.

Texte intégral

Résumé :

Abstract. For the next decades significant climatic changes should occur in the Arctic zone. The expected destabilisation of permafrost and its consequences for hydrology and plant cover should increase the input of terrigenous carbon to coastal seas. Consequently, the relative importance of the fluxes of terrestrial and marine organic carbon to the seafloor will likely change, strongly impacting the preservation of organic carbon in Arctic marine sediments. Here, we investigated the lipid content of surface sediments collected on the Mackenzie basin in the Beaufort Sea. Particular attention was given to biotic and abiotic degradation products of sterols and monounsaturated fatty acids. By using sitosterol and campesterol degradation products as tracers of the degradation of terrestrial higher plant inputs and brassicasterol degradation products as tracers of degradation of phytoplanktonic organisms, it could be observed that autoxidation, photooxidation and biodegradation processes act much more intensively on higher plant debris than on phytoplanktonic organisms. Examination of oxidation products of monounsaturated fatty acids showed that photo- and autoxidation processes act more intensively on bacteria than on phytodetritus. Enhanced damages induced by singlet oxygen (transferred from senescent phytoplanktonic cells) in bacteria were attributed to the lack of an adapted antioxidant system in these microorganisms. The strong oxidative stress observed in the sampled sediments resulted in the production of significant amounts of epoxy acids and unusually high proportions of monounsaturated fatty acids with a trans double bond. The formation of epoxy acids was attributed to peroxygenases (enzymes playing a protective role against the deleterious effects of fatty acid hydroperoxides in vivo), while cis/trans isomerisation was probably induced by thiyl radicals produced during the reaction of thiols with hydroperoxides. Our results confirm the important role played by abiotic oxidative processes in the degradation of marine bacteria and do not support the generally expected refractory character of terrigenous material deposited in deltaic systems.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Assmann, K. M., M. Bentsen, J. Segschneider et C. Heinze. « An isopycnic ocean carbon cycle model ». Geoscientific Model Development Discussions 2, n^o 2 (27 juillet 2009) : 1023–79. http://dx.doi.org/10.5194/gmdd-2-1023-2009.

Texte intégral

Résumé :

Abstract. The carbon cycle is a major forcing component in the global climate system. Modelling studies aiming to explain recent and past climatic changes and to project future ones thus increasingly include the interaction between the physical and biogeochemical systems. Their ocean components are generally z-coordinate models that are conceptually easy to use but that employ a vertical coordinate that is alien to the real ocean structure. Here we present first results from a newly developed isopycnic carbon cycle model and demonstrate the viability of using an isopycnic physical component for this purpose. As expected, the model represents interior ocean transport of biogeochemical tracers well and produces realistic tracer distributions. Difficulties in employing a purely isopycnic coordinate lie mainly in the treatment of the surface boundary layer which is often represented by a bulk mixed layer. The most significant adjustments of the biogeochemical code for use with an isopycnic coordinate are in the representation of upper ocean biological production. We present a series of sensitivity studies exploring the effect of changes in biogeochemical and physical processes on export production and nutrient distribution. Apart from giving us pointers for further model development, they highlight the importance of preformed nutrient distributions in the Southern Ocean for global nutrient distributions. Use of a prognostic slab atmosphere allows us to assess the effect of the changes in export production on global ocean carbon uptake and atmospheric CO2 levels. Sensitivity studies show that iron limitation for biological particle production, the treatment of light penetration for biological production, and the role of diapycnal mixing result in significant changes of modelled air-sea fluxes and nutrient distributions.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Bauziene, Ieva, Jonas Mazeika et Zana Skuratovic. « Fallout 137Cs and natural 40K as tracers of topsoil development during slope processes — a case study from the Daugai environs, Southern Lithuania ». Geochronometria 40, n^o 2 (1 juin 2013) : 126–33. http://dx.doi.org/10.2478/s13386-013-0101-1.

Texte intégral

Résumé :

AbstractInvestigations of soil erosion by 137Cs method brings uncertainties of different nature. The estimation of the 137Cs local inventory is associated with problems of data comparison and instrumental errors. In order to avoid systematic errors, the rate of soil erosion determined by the 137Cs method is compared with the values obtained for other radioactive elements. Soil parameters must be regarded too. The aim of the work was to test the character of 137Cs and 40K distribution in the topsoil vertical section for determination erosion-accumulation type and ratio in different time spans. The topsoil thickened by different types of erosion-accumulation processes was sampled at a 2–3 cm interval. Soil samples were analysed by means of scintillation gamma spectrometry. The relationship between 137Cs and 40K inventories was weakest in the topsoil formed by mixing of soil material during the installation of artificial drains. Based on climatic characteristics, variations of theoretical soil accumulation rate in the last 50 years were calculated for the topsoil accumulated predominantly by water erosion. 40K and 137Cs correlation in the bottom of vertical section of topsoil or arable horizon are closest and this section may be used as a complementary parameter determining the local inventory value.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Rautio, A., A. L. Kivimäki, K. Korkka-Niemi, M. Nygård, V. P. Salonen, K. Lahti et H. Vahtera. « Vulnerability of groundwater resources to interaction with river water in a boreal catchment ». Hydrology and Earth System Sciences Discussions 12, n^o 2 (25 février 2015) : 2435–76. http://dx.doi.org/10.5194/hessd-12-2435-2015.

Texte intégral

Résumé :

Abstract. A low altitude aerial infrared (AIR) survey was conducted to identify hydraulic connections between aquifers and rivers, and to map spatial surface temperature patterns along boreal rivers. In addition, the stable isotopic compositions (δ18O, δD), dissolved silica (DSi) concentrations and electrical conductivity of water in combination with AIR data were used as tracers to verify the observed groundwater discharge into the river system in a boreal catchment. The results of AIR surveys and hydrogeochemical studies performed in the boreal catchment are presented. Based on low temperature anomalies in the AIR survey, around 370 groundwater–surface water interaction sites were located along the main river channel and its tributaries (203 km altogether). On the basis of AIR survey, the longitudinal temperature patterns of the studied rivers differed noticeably. The stable isotopes and DSi composition revealed major differences between the studied rivers. The interaction locations identified in the proximity of 12 municipal water intake plants during the low-flow seasons should be considered as potential risk areas for water intake plants during flood periods (groundwater quality deterioration due to bank infiltration), and should be taken under consideration in river basin management under changing climatic situations.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Schlitzer, Reiner. « Quantifying He fluxes from the mantle using multi-tracer data assimilation ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 374, n^o 2081 (28 novembre 2016) : 20150288. http://dx.doi.org/10.1098/rsta.2015.0288.

Texte intégral

Résumé :

A global, coarse-resolution ocean model previously fitted to geostrophic shear estimates and to data of 10 hydrographic parameters and tracers has been used to simulate the 3 He and 4 He distributions resulting from the release of mantle helium from mid-ocean ridges. The model is in very good agreement with 14 C and chlorofluorocarbon data and has realistic global ocean overturning strength as well as water mass formation and transport rates. It is found that previously published global mantle 3 He fluxes are too high by a factor of about 2. In the model, optimal agreement of modelled δ 3 He with data is achieved for a global flux of 450 ± 50 mol 3 He yr −1 . The formulation of He source strengths proportional to ridge spreading rates appears compatible with data. A model/data misfit analysis shows significant and large-scale δ 3 He underestimation in the southwestern Pacific centred over the Lau Backarc Basin (approx. 179° W/20° S). These misfits disappear in a set-up with 30 of the 450 mol yr −1 global total 3 He flux released in the Lau Basin over a depth range between 1250 and 2500 m. Such He flux contributions are missing in present mantle He source compilations. Hydrothermal fluxes of other trace elements and isotopes (TEI) can be calculated from He fluxes on the basis of TEI : He ratios measured close to the sources. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Zhou, L. Y., Y. S. Li et H. N. Wang. « Glaciochemical study on the surface snow along the traverse route from Zhongshan Station towards Dome A in Antarctica : Glaciochemical tracers of two climatic systems ». Geochimica et Cosmochimica Acta 70, n^o 18 (août 2006) : A751. http://dx.doi.org/10.1016/j.gca.2006.06.1354.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

29

Marchina, Chiara, Valeria Lencioni, Francesca Paoli, Marzia Rizzo et Gianluca Bianchini. « Headwaters’ Isotopic Signature as a Tracer of Stream Origins and Climatic Anomalies : Evidence from the Italian Alps in Summer 2018 ». Water 12, n^o 2 (1 février 2020) : 390. http://dx.doi.org/10.3390/w12020390.

Texte intégral

Résumé :

Glaciers are shrinking due to global warming, resulting in a diminishing contribution of ice and snowmelt to headwaters and subsequent consequences to freshwater ecosystems. Within this context, we tested whether water-stable isotopes are spatio-temporal tracers of (i) water in high altitude periglacial environments, being the isotopic signature of surface water inherited from the snow/icemelt, groundwater, and rainfall; and (ii) regional (year-specific) meteorological conditions, being the isotopic signature of precipitations affected by air temperature, humidity and aqueous vapour origin, ascribing stable isotopes to the list of “essential climate variables″ (ECVs). To this end, we investigated the ionic and isotopic composition (δ18O and δ2H) of six high-altitude streams and one pond in the Italian Alps (Noce and Sarca basins) during the ablation season in 2018. Differences between habitat types (pond, kryal, rhithral, krenal) were detected. More negative values of δ18O and δ2H were recorded in the kryal and glacio-rhithral sites, dominated by ice and snowmelt, in early summer. Less negative values were recorded in these sites in late summer, as well as in the krenal sites, which were dominated by groundwater and rainfall inputs. The isotopic results also show that the complex alpine orography influences air masses and moisture, ultimately resulting in isotopic differences in the precipitations of neighboring but distinct catchments (Sarca and Noce basins). On average, less negative values were recorded in the Sarca basin, characterized by a higher contribution of precipitation of Mediterranean origin. In general, isotopic results of the entire water population appeared to be strongly influenced by the regional climatic anomaly of 2018, which was anomalously warm. Therefore, the study will provide additional information for the climate change debate, proposing water isotopes as ECVs for assessing change in a warmer future.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Urrego, D. H., M. F. Sánchez Goñi, A. L. Daniau, S. Lechevrel et V. Hanquiez. « Increased aridity in southwestern Africa during the warmest periods of the last interglacial ». Climate of the Past 11, n^o 10 (20 octobre 2015) : 1417–31. http://dx.doi.org/10.5194/cp-11-1417-2015.

Texte intégral

Résumé :

Abstract. Terrestrial and marine climatic tracers from marine core MD96-2098 were used to reconstruct glacial–interglacial climate variability in southwestern Africa between 194 and 24 thousand years before present. The pollen record documented three pronounced expansions of Nama-karoo and fine-leaved savanna during the last interglacial (Marine Isotopic Stage 5 – MIS 5). These Nama-karoo and fine-leaved savanna expansions were linked to increased aridity during the three warmest substadials of MIS 5. Enhanced aridity potentially resulted from a combination of reduced Benguela Upwelling, expanded subtropical high-pressure cells, and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone. Decreased austral-winter precipitation was likely linked to a southern displacement of the westerlies. In contrast, during glacial isotopic stages MIS 6, 4 and 3, fynbos expanded at the expense of Nama-karoo and fine-leaved savanna indicating a relative increase in precipitation probably concentrated during the austral winter months. Our record also suggested that warm–cold or cold–warm transitions between isotopic stages and substages were punctuated by short increases in humidity. Increased aridity during MIS 5e, 5c and 5a warm substages coincided with minima in both precessional index and global ice volume. On the other hand, austral-winter precipitation increases were associated with precession maxima at the time of well-developed Northern Hemisphere ice caps.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Lindsay, Keith, Gordon B. Bonan, Scott C. Doney, Forrest M. Hoffman, David M. Lawrence, Matthew C. Long, Natalie M. Mahowald, J. Keith Moore, James T. Randerson et Peter E. Thornton. « Preindustrial-Control and Twentieth-Century Carbon Cycle Experiments with the Earth System Model CESM1(BGC) ». Journal of Climate 27, n^o 24 (10 décembre 2014) : 8981–9005. http://dx.doi.org/10.1175/jcli-d-12-00565.1.

Texte intégral

Résumé :

Abstract Version 1 of the Community Earth System Model, in the configuration where its full carbon cycle is enabled, is introduced and documented. In this configuration, the terrestrial biogeochemical model, which includes carbon–nitrogen dynamics and is present in earlier model versions, is coupled to an ocean biogeochemical model and atmospheric CO2 tracers. The authors provide a description of the model, detail how preindustrial-control and twentieth-century experiments were initialized and forced, and examine the behavior of the carbon cycle in those experiments. They examine how sea- and land-to-air CO2 fluxes contribute to the increase of atmospheric CO2 in the twentieth century, analyze how atmospheric CO2 and its surface fluxes vary on interannual time scales, including how they respond to ENSO, and describe the seasonal cycle of atmospheric CO2 and its surface fluxes. While the model broadly reproduces observed aspects of the carbon cycle, there are several notable biases, including having too large of an increase in atmospheric CO2 over the twentieth century and too small of a seasonal cycle of atmospheric CO2 in the Northern Hemisphere. The biases are related to a weak response of the carbon cycle to climatic variations on interannual and seasonal time scales and to twentieth-century anthropogenic forcings, including rising CO2, land-use change, and atmospheric deposition of nitrogen.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Pratte, Steve, Michelle Garneau et François De Vleeschouwer. « Late-Holocene atmospheric dust deposition in eastern Canada (St. Lawrence North Shore) ». Holocene 27, n^o 1 (28 juillet 2016) : 12–25. http://dx.doi.org/10.1177/0959683616646185.

Texte intégral

Résumé :

Dust deposition in two ombrotrophic peatlands (Baie and Ile du Havre peatland (IDH) bogs) of the Estuary and Gulf of the St. Lawrence in eastern Canada was reconstructed using elemental geochemistry. The rare earth elements (REEs) and other lithogenic element concentrations were measured by ICP-oES and Q-ICP-MS along two peat cores spanning the last 4000 years. Principal component analyses on the geochemical profiles show that REEs display the same behavior as Al, Ti, Sc, and Zr, all conservative elements, which suggests that REEs are immobile in the studied peat bogs and can be used as tracers of dust deposition. Plant macrofossils were also used to infer past environmental and humidity changes. The dust fluxes were reconstructed using the sum of REEs (ΣREE). The range of dust deposition varies from 0.2 to 3.8 g m−2 yr−1 in the Baie bog, while the IDH bog shows lower fluxes ranging between 0.1 and 1.2 g m−2 yr−1. The highest dust fluxes in the Baie bog were recorded from 1750–1000 cal. BP to 600–100 cal. BP and occur at the same time as periods of high variability in the macrofossil record (i.e. successive layers dominated by Sphagnum or Ericaceae). The timing of these events in the dust and macrofossil records also corresponds to documented cold periods. These two periods have been identified as episodes of climatic instability, which could have been caused by changes in the wind regime.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Cramwinckel, Margot J., Lineke Woelders, Emiel P. Huurdeman, Francien Peterse, Stephen J. Gallagher, Jörg Pross, Catherine E. Burgess, Gert-Jan Reichart, Appy Sluijs et Peter K. Bijl. « Surface-circulation change in the southwest Pacific Ocean across the Middle Eocene Climatic Optimum : inferences from dinoflagellate cysts and biomarker paleothermometry ». Climate of the Past 16, n^o 5 (1 septembre 2020) : 1667–89. http://dx.doi.org/10.5194/cp-16-1667-2020.

Texte intégral

Résumé :

Abstract. Global climate cooled from the early Eocene hothouse (∼52–50 Ma) to the latest Eocene (∼34 Ma). At the same time, the tectonic evolution of the Southern Ocean was characterized by the opening and deepening of circum-Antarctic gateways, which affected both surface- and deep-ocean circulation. The Tasmanian Gateway played a key role in regulating ocean throughflow between Australia and Antarctica. Southern Ocean surface currents through and around the Tasmanian Gateway have left recognizable tracers in the spatiotemporal distribution of plankton fossils, including organic-walled dinoflagellate cysts. This spatiotemporal distribution depends on both the physicochemical properties of the water masses and the path of surface-ocean currents. The extent to which climate and tectonics have influenced the distribution and composition of surface currents and thus fossil assemblages has, however, remained unclear. In particular, the contribution of climate change to oceanographic changes, superimposed on long-term and gradual changes induced by tectonics, is still poorly understood. To disentangle the effects of tectonism and climate in the southwest Pacific Ocean, we target a climatic deviation from the long-term Eocene cooling trend: the Middle Eocene Climatic Optimum (MECO; ∼40 Ma). This 500 kyr phase of global warming was unrelated to regional tectonism, and thus provides a test case to investigate the ocean's physicochemical response to climate change alone. We reconstruct changes in surface-water circulation and temperature in and around the Tasmanian Gateway during the MECO through new palynological and organic geochemical records from the central Tasmanian Gateway (Ocean Drilling Program Site 1170), the Otway Basin (southeastern Australia), and the Hampden Beach section (New Zealand). Our results confirm that dinocyst communities track specific surface-ocean currents, yet the variability within the communities can be driven by superimposed temperature change. Together with published results from the east of the Tasmanian Gateway, our new results suggest a shift in surface-ocean circulation during the peak of MECO warmth. Simultaneous with high sea-surface temperatures in the Tasmanian Gateway area, pollen assemblages indicate warm temperate rainforests with paratropical elements along the southeastern margin of Australia. Finally, based on new age constraints, we suggest that a regional southeast Australian transgression might have been coincident with the MECO.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Singh, Nandita, Tirthankar Banerjee, Made P. Raju, Karine Deboudt, Meytar Sorek-Hamer, Ram S. Singh et Rajesh K. Mall. « Aerosol chemistry, transport, and climatic implications during extreme biomass burning emissions over the Indo-Gangetic Plain ». Atmospheric Chemistry and Physics 18, n^o 19 (8 octobre 2018) : 14197–215. http://dx.doi.org/10.5194/acp-18-14197-2018.

Texte intégral

Résumé :

Abstract. The large-scale emissions of airborne particulates from burning of agricultural residues particularly over the upper Indo-Gangetic Plain (IGP) have often been associated with frequent formation of haze, adverse health impacts, and modification in aerosol climatology and thereby aerosol impact on regional climate. In this study, short-term variations in aerosol climatology during extreme biomass burning emissions over the IGP were investigated. Size-segregated particulate concentration was initially measured and submicron particles (PM1.1) were found to dominate particulate mass within the fine mode (PM2.1). Particulate-bound water-soluble ions were mainly secondary in nature and primarily composed of sulfate and nitrate. There was evidence of gaseous NH3 dominating neutralization of acidic aerosol species (SO42-) in submicron particles, in contrast to crustal-dominating neutralization in coarser particulates. Diurnal variation in black carbon (BC) mass ratio was primarily influenced by regional meteorology, while gradual increase in BC concentration was consistent with the increase in Delta-C, referring to biomass burning emissions. The influence of biomass burning emissions was established using specific organic (levoglucosan), inorganic (K+ and NH4+), and satellite-based (UV aerosol index, UVAI) tracers. Levoglucosan was the most abundant species within submicron particles (649±177 ng m−3), with a very high ratio (> 50) to other anhydrosugars, indicating exclusive emissions from burning of agriculture residues. Spatiotemporal distribution of aerosol and a few trace gases (CO and NO2) was evaluated using both spaceborne active and passive sensors. A significant increase in columnar aerosol loading (aerosol optical depth, AOD: 0.98) was evident, with the presence of absorbing aerosols (UVAI > 1.5) having low aerosol layer height (∼ 1.5 km). A strong intraseasonality in the aerosol cross-sectional altitudinal profile was even noted from CALIPSO, referring to the dominance of smoke and polluted continental aerosols across the IGP. A possible transport mechanism of biomass smoke was established using cluster analysis and concentration-weighted air mass back trajectories. Short-wave aerosol radiative forcing (ARF) was further simulated considering intraseasonality in aerosol properties, which resulted in a considerable increase in atmospheric ARF (135 W m−2) and heating rate (4.3 K day−1) during extreme biomass burning emissions compared to the non-dominating period (56 W m−2, 1.8 K day−1). Our analysis will be useful to improve understanding of short-term variation in aerosol chemistry over the IGP and to reduce uncertainties in regional aerosol–climate models.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Mahindawansha, Amani, Marius Jost et Matthias Gassmann. « Spatial and Temporal Variations of Stable Isotopes in Precipitation in the Mountainous Region, North Hesse ». Water 14, n^o 23 (1 décembre 2022) : 3910. http://dx.doi.org/10.3390/w14233910.

Texte intégral

Résumé :

Patterns of stable isotopes of water (18O and 2H) in precipitation have been used as tracers for analyzing environmental processes which can be changed by factors such as the topography or meteorological variables. In this study, we investigated the isotopic data in precipitation for one year in the low mountain range of North Hesse, Germany, and analyzed mainly for altitude, rainfall amount, and air temperature effects on a regional scale. The results indicate that the isotopic composition expressed an altitude effect with a gradient of −0.14‰/100 m for δ18O, −0.28‰/100 m for δ2H and 0.83‰/100 m for Deuterium excess. Patterns of enrichment during warmer months and depletion during colder months were detected. Seasonal correlations were not consistent because the altitude effect was superimposed by other processes such as amount and temperature effects, vapor origins, orographic rainout processes, moisture recycling, and sub-cloud secondary evaporation. Precipitation was mostly affected by secondary evaporation and mixing processes during the summer while depleted moisture-bearing fronts and condensation were more responsible for isotope depletion during winter. In autumn and spring, the amount effect was more prominent in combination with moisture recycling, and large-scale convective processes. The altitude effect was also detected in surface water. The investigated elevation transect with multiple stations provided unique insights into hydrological and climatic processes of North Hesse on a regional scale. The spatial heterogeneity and mixing of different processes suggest that multiple rainfall stations are required when rainfall isotopes serve as forcing data for hydrological applications such as transit time assessments in complex terrains.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Wright, Jonathon S., Adam Sobel et Joseph Galewsky. « Diagnosis of Zonal Mean Relative Humidity Changes in a Warmer Climate ». Journal of Climate 23, n^o 17 (1 septembre 2010) : 4556–69. http://dx.doi.org/10.1175/2010jcli3488.1.

Texte intégral

Résumé :

Abstract The zonal mean relative humidity response to a doubling of CO2 in a climate model is examined using a global climate model and an offline tracer transport model. Offline tracer transport model simulations are driven by the output from two configurations of the climate model, one with 1979 concentrations of atmospheric greenhouse gases and one with doubled CO2. A set of last saturation tracers is applied within the tracer transport model to diagnose the dynamics responsible for features in the water vapor field. Two different methods are used to differentiate the effects of circulation and transport shifts from spatially inhomogeneous temperature changes. The first of these uses the tracer transport model and is achieved by decoupling the input temperature and circulation fields; the second uses the reconstruction of humidity from the last saturation tracers and is achieved by decoupling the tracer concentrations from their saturation specific humidities. The responses of the tropical and subtropical relative humidities are found to be largely dependent on circulation and transport changes, particularly a poleward expansion of the Hadley cell, a deepening of the height of convective detrainment, a poleward shift of the extratropical jets, and an increase in the height of the tropopause. The last saturation tracers are used to illustrate the influence of changes in transport pathways within the GCM on the zonal mean relative humidity, particularly in the tropical upper troposphere and subtropical dry zones. Relative humidity changes near the extratropical tropopause and in the lower troposphere are largely dependent on changes in the distribution and gradients of temperature. Increases in relative humidity near the extratropical tropopause in both hemispheres are coincident with increases in the occurrence of local saturation and high cloud cover.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Lewis, S. C., A. N. LeGrande, M. Kelley et G. A. Schmidt. « Water vapour source impacts on oxygen isotope variability in tropical precipitation during Heinrich events ». Climate of the Past 6, n^o 3 (1 juin 2010) : 325–43. http://dx.doi.org/10.5194/cp-6-325-2010.

Texte intégral

Résumé :

Abstract. Water isotope records such as speleothems provide extensive evidence of past tropical hydrological changes. During Heinrich events, isotopic changes in monsoon regions have been interpreted as implying a widespread drying through the Northern Hemisphere tropics and an anti-phased precipitation response in the south. Here, we examine the sources of this variability using a water isotope-enabled general circulation model, Goddard Institute for Space Studies ModelE. We incorporate a new suite of vapour source distribution tracers to help constrain the impact of precipitation source region changes on the isotopic composition of precipitation and to identify nonlocal amount effects. We simulate a collapse of the North Atlantic meridional overturning circulation with a large freshwater input to the region as an idealised analogue to iceberg discharge during Heinrich events. An increase in monsoon intensity, defined by vertical wind shear, is modelled over the South American domain, with small decreases simulated over Asia. Simulated isotopic anomalies agree well with proxy climate records, with lighter isotopic values simulated over South America and enriched values across East Asia. For this particular abrupt climate event, we identify which climatic change is most likely linked to water isotope change – changes in local precipitation amount, monsoon intensity, water vapour source distributions or precipitation seasonality. We categorise individual sites according to the climate variability that water isotope changes are most closely associated with, and find that the dominant isotopic controls are not consistent across the tropics – simple local explanations, in particular, fall short of explaining water isotope variability at all sites. Instead, the best interpretations appear to be site specific and often regional in scale.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Lewis, S. C., A. N. LeGrande, M. Kelley et G. A. Schmidt. « Water vapour source impacts on oxygen isotope variability in tropical precipitation during Heinrich events ». Climate of the Past Discussions 6, n^o 1 (10 février 2010) : 87–133. http://dx.doi.org/10.5194/cpd-6-87-2010.

Texte intégral

Résumé :

Abstract. Water isotope records such as speleothems provide extensive evidence of past tropical hydrological changes. During Heinrich events, isotopic changes in monsoon regions have been interpreted as implying a widespread drying through the Northern Hemisphere tropics and an anti-phased precipitation response in the south. Here, we examine the sources of this variability using a water isotope-enabled general circulation model, Goddard Institute for Space Studies ModelE. We incorporate a new suite of vapour source distribution tracers to help constrain the impact of precipitation source region changes on the isotopic composition of precipitation and to identify nonlocal amount effects. We simulate a collapse of the North Atlantic meridional overturning circulation with a large freshwater input to the region as an idealised analogue to iceberg discharge during Heinrich events. A decrease in monsoon intensity, defined by vertical wind shear, is modelled over East Asia and an increase over the South American domain. Simulated isotopic anomalies agree well with proxy climate records, with lighter isotopic values simulated over South America and enriched values across East Asia. For this particular abrupt climate event, we identify which climatic change is most likely linked to water isotope change – changes in local precipitation amount, monsoon intensity, water vapour source distributions or precipitation seasonality. We categorise individual sites according to the climate variability that water isotope changes are most closely associated with, and find that the dominant isotopic controls are not consistent across the tropics – simple local explanations, in particular, fall short of explaining water isotope variability at all sites. Instead, the best interpretations appear to be site specific and often regional in scale.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Wiedinmyer, Christine, Xuexi Tie, Alex Guenther, Ron Neilson et Claire Granier. « Future Changes in Biogenic Isoprene Emissions : How Might They Affect Regional and Global Atmospheric Chemistry ? » Earth Interactions 10, n^o 3 (1 janvier 2006) : 1–19. http://dx.doi.org/10.1175/ei174.1.

Texte intégral

Résumé :

Abstract Isoprene is emitted from vegetation to the atmosphere in significant quantities, and it plays an important role in the reactions that control tropospheric oxidant concentrations. As future climatic and land-cover changes occur, the spatial and temporal variations, as well as the magnitude of these biogenic isoprene emissions, are expected to change. This paper presents a study of the change in biogenic isoprene emissions that would result from both anthropogenic land-cover and climate-driven changes. Annual global isoprene emissions were estimated to be 522 Tg yr−1 under current climatological and land-cover conditions. When climate-driven land-cover changes are predicted, but climate does not change, total global emissions did not change significantly, although regional impacts were important. However, the use of future temperature and land-cover drivers to estimate isoprene emissions produced a global estimate of 889 Tg yr−1. Anthropogenic land-cover changes, such as urbanization and changes of natural vegetation to plantation forests, can also have substantial impacts on isoprene emissions (i.e., up to 717 Tg yr−1, a 37% increase, when land-cover changes but temperature remains at current-day values). The Model for Ozone and Related Tracers, version 2 (MOZART-2) was run with the different isoprene emission scenarios to simulate the potential changes in global atmospheric chemical composition. The simulated regional surface ozone concentrations changed as much as −9 to 55 ppbv under certain emission and climate scenarios. These results were used to evaluate changes in the ozone production chemistry under different emission scenarios. As expected, the impacts of changing isoprene emissions are regionally dependent, with large changes in China, the Amazon, and the United States.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Wozniak, Matthew C., et Allison L. Steiner. « A prognostic pollen emissions model for climate models (PECM1.0) ». Geoscientific Model Development 10, n^o 11 (13 novembre 2017) : 4105–27. http://dx.doi.org/10.5194/gmd-10-4105-2017.

Texte intégral

Résumé :

Abstract. We develop a prognostic model called Pollen Emissions for Climate Models (PECM) for use within regional and global climate models to simulate pollen counts over the seasonal cycle based on geography, vegetation type, and meteorological parameters. Using modern surface pollen count data, empirical relationships between prior-year annual average temperature and pollen season start dates and end dates are developed for deciduous broadleaf trees (Acer, Alnus, Betula, Fraxinus, Morus, Platanus, Populus, Quercus, Ulmus), evergreen needleleaf trees (Cupressaceae, Pinaceae), grasses (Poaceae; C3, C4), and ragweed (Ambrosia). This regression model explains as much as 57 % of the variance in pollen phenological dates, and it is used to create a climate-flexible phenology that can be used to study the response of wind-driven pollen emissions to climate change. The emissions model is evaluated in the Regional Climate Model version 4 (RegCM4) over the continental United States by prescribing an emission potential from PECM and transporting pollen as aerosol tracers. We evaluate two different pollen emissions scenarios in the model using (1) a taxa-specific land cover database, phenology, and emission potential, and (2) a plant functional type (PFT) land cover, phenology, and emission potential. The simulated surface pollen concentrations for both simulations are evaluated against observed surface pollen counts in five climatic subregions. Given prescribed pollen emissions, the RegCM4 simulates observed concentrations within an order of magnitude, although the performance of the simulations in any subregion is strongly related to the land cover representation and the number of observation sites used to create the empirical phenological relationship. The taxa-based model provides a better representation of the phenology of tree-based pollen counts than the PFT-based model; however, we note that the PFT-based version provides a useful and climate-flexible emissions model for the general representation of the pollen phenology over the United States.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Erath, Christoph, Mark A. Taylor et Ramachandran D. Nair. « Two conservative multi-tracer efficient semi-Lagrangian schemes for multiple processor systems integrated in a spectral element (climate) dynamical core ». Communications in Applied and Industrial Mathematics 7, n^o 3 (1 septembre 2016) : 74–98. http://dx.doi.org/10.1515/caim-2016-0023.

Texte intégral

Résumé :

Abstract In today’s atmospheric numerical modeling, scalable and highly accurate numerical schemes are of particular interest. To address these issues Galerkin schemes, such as the spectral element method, have received more attention in the last decade. They also provide other state-of-the-art capabilities such as improved conservation. However, the tracer transport of hundreds of tracers, e.g., in the chemistry version of the Community Atmosphere Model, is still a performance bottleneck. Therefore, we consider two conservative semi-Lagrangian schemes. Both are designed to be multi-tracer efficient, third order accurate, and allow significantly longer time steps than explicit Eulerian formulations. We address the difficulties arising on the cubed-sphere projection and on parallel computers and show the high scalability of our approach. Additionally, we use the two schemes for the transport of passive tracers in a dynamical core and compare our results with a current spectral element tracer transport advection used by the High-Order Method Modeling Environment.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Mason, R. H., M. Si, J. Li, C. Chou, R. Dickie, D. Toom-Sauntry, C. Pöhlker et al. « Ice nucleating particles at a coastal marine boundary layer site : correlations with aerosol type and meteorological conditions ». Atmospheric Chemistry and Physics 15, n^o 21 (10 novembre 2015) : 12547–66. http://dx.doi.org/10.5194/acp-15-12547-2015.

Texte intégral

Résumé :

Abstract. Information on what aerosol particle types are the major sources of ice nucleating particles (INPs) in the atmosphere is needed for climate predictions. To determine which aerosol particles are the major sources of immersion-mode INPs at a coastal site in Western Canada, we investigated correlations between INP number concentrations and both concentrations of different atmospheric particles and meteorological conditions. We show that INP number concentrations are strongly correlated with the number concentrations of fluorescent bioparticles between −15 and −25 °C, and that the size distribution of INPs is most consistent with the size distribution of fluorescent bioparticles. We conclude that biological particles were likely the major source of ice nuclei at freezing temperatures between −15 and −25 °C at this site for the time period studied. At −30 °C, INP number concentrations are also well correlated with number concentrations of the total aerosol particles ≥ 0.5 μm, suggesting that non-biological particles may have an important contribution to the population of INPs active at this temperature. As we found that black carbon particles were unlikely to be a major source of ice nuclei during this study, these non-biological INPs may include mineral dust. Furthermore, correlations involving chemical tracers of marine aerosols and marine biological activity, sodium and methanesulfonic acid, indicate that the majority of INPs measured at the coastal site likely originated from terrestrial rather than marine sources. Finally, six existing empirical parameterizations of ice nucleation were tested to determine if they accurately predict the measured INP number concentrations. We found that none of the parameterizations selected are capable of predicting INP number concentrations with high accuracy over the entire temperature range investigated. This finding illustrates that additional measurements are needed to improve parameterizations of INPs and their subsequent climatic impacts.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Thurnherr, Iris, Anna Kozachek, Pascal Graf, Yongbiao Weng, Dimitri Bolshiyanov, Sebastian Landwehr, Stephan Pfahl et al. « Meridional and vertical variations of the water vapour isotopic composition in the marine boundary layer over the Atlantic and Southern Ocean ». Atmospheric Chemistry and Physics 20, n^o 9 (15 mai 2020) : 5811–35. http://dx.doi.org/10.5194/acp-20-5811-2020.

Texte intégral

Résumé :

Abstract. Stable water isotopologues (SWIs) are useful tracers of moist diabatic processes in the atmospheric water cycle. They provide a framework to analyse moist processes on a range of timescales from large-scale moisture transport to cloud formation, precipitation and small-scale turbulent mixing. Laser spectrometric measurements on research vessels produce high-resolution time series of the variability of the water vapour isotopic composition in the marine boundary layer. In this study, we present a 5-month continuous time series of such ship-based measurements of δ2H and δ18O from the Antarctic Circumnavigation Expedition (ACE) in the Atlantic and the Southern Ocean in the time period from November 2016 to April 2017. We analyse the drivers of meridional SWI variations in the marine boundary layer across diverse climate zones in the Atlantic and Southern Ocean using Lagrangian moisture source diagnostics and relate vertical SWI differences to near-surface wind speed and ocean surface state. The median values of δ18O, δ2H and deuterium excess during ACE decrease continuously from low to high latitudes. These meridional SWI distributions reflect climatic conditions at the measurement and moisture source locations, such as air temperature, specific humidity and relative humidity with respect to sea surface temperature. The SWI variability at a given latitude is highest in the extratropics and polar regions with decreasing values equatorwards. This meridional distribution of SWI variability is explained by the variability in moisture source locations and its associated environmental conditions as well as transport processes. The westward-located moisture sources of water vapour in the extratropics are highly variable in extent and latitude due to the frequent passage of cyclones and thus widen the range of encountered SWI values in the marine boundary layer. Moisture loss during transport further contributes to the high SWI variability in the extratropics. In the subtropics and tropics, persistent anticyclones lead to well-confined narrow easterly moisture source regions, which is reflected in the weak SWI variability in these regions. Thus, the expected range of SWI signals at a given latitude strongly depends on the large-scale circulation. Furthermore, the ACE SWI time series recorded at 8.0 and 13.5 m above the ocean surface provide estimates of vertical SWI gradients in the lowermost marine boundary layer. On average, the vertical gradients with height found during ACE are -0.1‰m-1 for δ18O, -0.5‰m-1 for δ2H and 0.3 ‰ m−1 for deuterium excess. Careful calibration and post-processing of the SWI data and a detailed uncertainty analysis provide a solid basis for the presented gradients. Using sea spray concentrations and sea state conditions, we show that the vertical SWI gradients are particularly large during high wind speed conditions with increased contribution of sea spray evaporation or during low wind speed conditions due to weak vertical turbulent mixing. Although further SWI measurements at a higher vertical resolution are required to validate these findings, the simultaneous SWI measurements at several heights during ACE show the potential of SWIs as tracers for vertical mixing and sea spray evaporation in the lowermost marine boundary layer.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Griffies, S. M., A. Gnanadesikan, K. W. Dixon, J. P. Dunne, R. Gerdes, M. J. Harrison, A. Rosati et al. « Formulation of an ocean model for global climate simulations ». Ocean Science 1, n^o 1 (12 septembre 2005) : 45–79. http://dx.doi.org/10.5194/os-1-45-2005.

Texte intégral

Résumé :

Abstract. This paper summarizes the formulation of the ocean component to the Geophysical Fluid Dynamics Laboratory's (GFDL) climate model used for the 4th IPCC Assessment (AR4) of global climate change. In particular, it reviews the numerical schemes and physical parameterizations that make up an ocean climate model and how these schemes are pieced together for use in a state-of-the-art climate model. Features of the model described here include the following: (1) tripolar grid to resolve the Arctic Ocean without polar filtering, (2) partial bottom step representation of topography to better represent topographically influenced advective and wave processes, (3) more accurate equation of state, (4) three-dimensional flux limited tracer advection to reduce overshoots and undershoots, (5) incorporation of regional climatological variability in shortwave penetration, (6) neutral physics parameterization for representation of the pathways of tracer transport, (7) staggered time stepping for tracer conservation and numerical efficiency, (8) anisotropic horizontal viscosities for representation of equatorial currents, (9) parameterization of exchange with marginal seas, (10) incorporation of a free surface that accomodates a dynamic ice model and wave propagation, (11) transport of water across the ocean free surface to eliminate unphysical ``virtual tracer flux" methods, (12) parameterization of tidal mixing on continental shelves. We also present preliminary analyses of two particularly important sensitivities isolated during the development process, namely the details of how parameterized subgridscale eddies transport momentum and tracers.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Williams, Richard G., Anna Katavouta et Vassil Roussenov. « Regional Asymmetries in Ocean Heat and Carbon Storage due to Dynamic Redistribution in Climate Model Projections ». Journal of Climate 34, n^o 10 (mai 2021) : 3907–25. http://dx.doi.org/10.1175/jcli-d-20-0519.1.

Texte intégral

Résumé :

AbstractProjected changes in ocean heat and carbon storage are assessed in terms of the added and redistributed tracer using a transport-based framework, which is applied to an idealized climate model and a suite of six CMIP5 Earth system models following an annual 1% rise in atmospheric CO2. Heat and carbon budgets for the added and redistributed tracer are used to explain opposing regional patterns in the storage of ocean heat and carbon anomalies, such as in the tropics and subpolar North Atlantic, and the relatively reduced storage within the Southern Ocean. Here the added tracer takes account of the net tracer source and the advection of the added tracer by the circulation, while the redistributed tracer takes account of the time-varying circulation advecting the preindustrial tracer distribution. The added heat and carbon often have a similar sign to each other with the net source usually acting to supply the tracer. In contrast, the redistributed heat and carbon consistently have an opposing sign to each other due to the opposing gradients in the preindustrial temperature and carbon. These different signs in heat and carbon redistribution can lead to regional asymmetries in the climate-driven changes in ocean heat and carbon storage. For a weakening in the Atlantic overturning and strengthening in the Southern Ocean residual circulation, the high latitudes are expected to have heat anomalies of variable sign and carbon anomalies of a consistently positive sign, since added and redistributed tracers are opposing in sign for heat and the same sign for carbon there.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Ala-aho, Pertti, Doerthe Tetzlaff, James P. McNamara, Hjalmar Laudon et Chris Soulsby. « Using isotopes to constrain water flux and age estimates in snow-influenced catchments using the STARR (Spatially distributed Tracer-Aided Rainfall–Runoff) model ». Hydrology and Earth System Sciences 21, n^o 10 (9 octobre 2017) : 5089–110. http://dx.doi.org/10.5194/hess-21-5089-2017.

Texte intégral

Résumé :

Abstract. Tracer-aided hydrological models are increasingly used to reveal fundamentals of runoff generation processes and water travel times in catchments. Modelling studies integrating stable water isotopes as tracers are mostly based in temperate and warm climates, leaving catchments with strong snow influences underrepresented in the literature. Such catchments are challenging, as the isotopic tracer signals in water entering the catchments as snowmelt are typically distorted from incoming precipitation due to fractionation processes in seasonal snowpack. We used the Spatially distributed Tracer-Aided Rainfall–Runoff (STARR) model to simulate fluxes, storage, and mixing of water and tracers, as well as estimating water ages in three long-term experimental catchments with varying degrees of snow influence and contrasting landscape characteristics. In the context of northern catchments the sites have exceptionally long and rich data sets of hydrometric data and – most importantly – stable water isotopes for both rain and snow conditions. To adapt the STARR model for sites with strong snow influence, we used a novel parsimonious calculation scheme that takes into account the isotopic fractionation through snow sublimation and snowmelt. The modified STARR setup simulated the streamflows, isotope ratios, and snow pack dynamics quite well in all three catchments. From this, our simulations indicated contrasting median water ages and water age distributions between catchments brought about mainly by differences in topography and soil characteristics. However, the variable degree of snow influence in catchments also had a major influence on the stream hydrograph, storage dynamics, and water age distributions, which was captured by the model. Our study suggested that snow sublimation fractionation processes can be important to include in tracer-aided modelling for catchments with seasonal snowpack, while the influence of fractionation during snowmelt could not be unequivocally shown. Our work showed the utility of isotopes to provide a proof of concept for our modelling framework in snow-influenced catchments.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Haertel, Patrick. « A Lagrangian Ocean Model for Climate Studies ». Climate 7, n^o 3 (15 mars 2019) : 41. http://dx.doi.org/10.3390/cli7030041.

Texte intégral

Résumé :

Most weather and climate models simulate circulations by numerically approximating a complex system of partial differential equations that describe fluid flow. These models also typically use one of a few standard methods to parameterize the effects of smaller-scale circulations such as convective plumes. This paper discusses the continued development of a radically different modeling approach. Rather than solving partial differential equations, the author’s Lagrangian models predict the motions of individual fluid parcels using ordinary differential equations. They also use a unique convective parameterization, in which the vertical positions of fluid parcels are rearranged to remove convective instability. Previously, a global atmospheric model and basin-scale ocean models were developed with this approach. In the present study, components of these models are combined to create a new global Lagrangian ocean model (GLOM), which will soon be coupled to a Lagrangian atmospheric model. The first simulations conducted with the GLOM examine the contribution of interior tracer mixing to ocean circulation, stratification, and water mass distributions, and they highlight several special model capabilities: (1) simulating ocean circulations without numerical diffusion of tracers; (2) modeling deep convective transports at low resolution; and (3) identifying the formation location of ocean water masses and water pathways.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Lucas-Picher, Philippe, Daniel Caya, Sébastien Biner et René Laprise. « Quantification of the Lateral Boundary Forcing of a Regional Climate Model Using an Aging Tracer ». Monthly Weather Review 136, n^o 12 (1 décembre 2008) : 4980–96. http://dx.doi.org/10.1175/2008mwr2448.1.

Texte intégral

Résumé :

Abstract The present work introduces a new and useful tool to quantify the lateral boundary forcing of a regional climate model (RCM). This tool, an aging tracer, computes the time the air parcels spend inside the limited-area domain of an RCM. The aging tracers are initialized to zero when the air parcels enter the domain and grow older during their migrations through the domain with each time step in the integration of the model. This technique was employed in a 10-member ensemble of 10-yr (1980–89) simulations with the Canadian RCM on a large domain covering North America. The residency time is treated and archived as the other simulated meteorological variables, therefore allowing computation of its climate diagnostics. These diagnostics show that the domain-averaged residency time is shorter in winter than in summer as a result of the faster winter atmospheric circulation. The residency time decreases with increasing height above the surface because of the faster atmospheric circulation at high levels dominated by the jet stream. Within the domain, the residency time increases from west to east according to the transportation of the aging tracer with the westerly general atmospheric circulation. A linear relation is found between the spatial distribution of the internal variability—computed with the variance between the ensemble members—and residency time. This relation indicates that the residency time can be used as a quantitative indicator to estimate the level of control exerted by the lateral boundary conditions on the RCM simulations.

Styles APA, Harvard, Vancouver, ISO, etc.

49

Schröter, Jennifer, Daniel Rieger, Christian Stassen, Heike Vogel, Michael Weimer, Sven Werchner, Jochen Förstner et al. « ICON-ART 2.1 : a flexible tracer framework and its application for composition studies in numerical weather forecasting and climate simulations ». Geoscientific Model Development 11, n^o 10 (5 octobre 2018) : 4043–68. http://dx.doi.org/10.5194/gmd-11-4043-2018.

Texte intégral

Résumé :

Abstract. Atmospheric composition studies on weather and climate timescales require flexible, scalable models. The ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) provides such an environment. Here, we introduce the most up-to-date version of the flexible tracer framework for ICON-ART and explain its application in one numerical weather forecast and one climate related case study. We demonstrate the implementation of idealised tracers and chemistry tendencies of different complexity using the ART infrastructure. Using different ICON physics configurations for weather and climate with ART, we perform integrations on different timescales, illustrating the model's performance. First, we present a hindcast experiment for the 2002 ozone hole split with two different ozone chemistry schemes using the numerical weather prediction physics configuration. We compare the hindcast with observations and discuss the confinement of the vortex split using an idealised tracer diagnostic. Secondly, we study AMIP-type integrations using a simplified chemistry scheme in conjunction with the climate physics configuration. We use two different simulations: the interactive simulation, where modelled ozone is coupled back to the radiation scheme, and the non-interactive simulation that uses a default background climatology of ozone. Additionally, we introduce changes of water vapour by methane oxidation for the interactive simulation. We discuss the impact of stratospheric ozone and water vapour variations in the interactive and non-interactive integrations on the water vapour tape recorder, as a measure of tropical upwelling changes. Additionally we explain the seasonal evolution and latitudinal distribution of the age of air. The age of air is a measure of the strength of the meridional overturning circulation with young air in the tropical upwelling region and older air in polar winter downwelling regions. We conclude that our flexible tracer framework allows for tailor-made configurations of ICON-ART in weather and climate applications that are easy to configure and run well.

Styles APA, Harvard, Vancouver, ISO, etc.

50

Meliyev, H. O. « INFLUENCE OF SOIL AND CLIMATIC CONDITIONS ON THE OPERATION OF UNIVERSAL PLOUGHING TRACTORS IN AGRICULTURE ». International Journal of Advance Scientific Research 02, n^o 12 (1 décembre 2022) : 166–74. http://dx.doi.org/10.37547/ijasr-02-12-24.

Texte intégral

Résumé :

The article analyzes the operation of universal mowers in soil and climatic conditions, changes in dust content, air temperature in the regions and cultivation processes, as well as a negative impact on the quality of transmission oil.

Styles APA, Harvard, Vancouver, ISO, etc.

Articles de revues sur le sujet « Climatic tracers »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres