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Aldo Fedele - One of the best experts on this subject based on the ideXlab platform.
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water masses in the humboldt current system properties distribution and the nitrate deficit as a Chemical water mass Tracer for equatorial subsurface water off chile
Deep-sea Research Part Ii-topical Studies in Oceanography, 2009Co-Authors: Nelson R F A Silva, Nora Rojas, Aldo FedeleAbstract:Abstract Three sections are used to analyze the physical and Chemical characteristics of the water masses in the eastern South Pacific and their distributions. Oceanographic data were taken from the SCORPIO (May–June 1967), PIQUERO (May–June 1969), and KRILL (June 1974) cruises. Vertical sections of temperature, salinity, σθ, dissolved oxygen, nitrate, nitrite, phosphate, and silicate were used to analyze the water column structure. Five water masses were identified in the zone through T–S diagrams: Subantarctic Water, Subtropical Water, Equatorial Subsurface Water, Antarctic Intermediate Water, and Pacific Deep Water. Their proportions in the sea water mixture are calculated using the mixing triangle method. Vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m. Several characteristic oceanographic features in the study area were analyzed: the shallow salinity minimum displacement towards the equator, the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south, and the equatorward intermediate Antarctic salinity minimum associated with a dissolved oxygen maximum. The nitrate deficit generated in the denitrification area off Peru and northern Chile is proposed as a conservative Chemical Tracer for the Equatorial Subsurface Waters off the coast of Chile, south of 25°S.
Nelson R F A Silva - One of the best experts on this subject based on the ideXlab platform.
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water masses in the humboldt current system properties distribution and the nitrate deficit as a Chemical water mass Tracer for equatorial subsurface water off chile
Deep-sea Research Part Ii-topical Studies in Oceanography, 2009Co-Authors: Nelson R F A Silva, Nora Rojas, Aldo FedeleAbstract:Abstract Three sections are used to analyze the physical and Chemical characteristics of the water masses in the eastern South Pacific and their distributions. Oceanographic data were taken from the SCORPIO (May–June 1967), PIQUERO (May–June 1969), and KRILL (June 1974) cruises. Vertical sections of temperature, salinity, σθ, dissolved oxygen, nitrate, nitrite, phosphate, and silicate were used to analyze the water column structure. Five water masses were identified in the zone through T–S diagrams: Subantarctic Water, Subtropical Water, Equatorial Subsurface Water, Antarctic Intermediate Water, and Pacific Deep Water. Their proportions in the sea water mixture are calculated using the mixing triangle method. Vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m. Several characteristic oceanographic features in the study area were analyzed: the shallow salinity minimum displacement towards the equator, the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south, and the equatorward intermediate Antarctic salinity minimum associated with a dissolved oxygen maximum. The nitrate deficit generated in the denitrification area off Peru and northern Chile is proposed as a conservative Chemical Tracer for the Equatorial Subsurface Waters off the coast of Chile, south of 25°S.
Andrew Tangborn - One of the best experts on this subject based on the ideXlab platform.
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A Wavelet based Suboptimal Kalman Filter for Assimilation of Stratospheric Chemical Tracer Observations
2020Co-Authors: Andrew Tangborn, Ludovic AugerAbstract:A suboptimal Kalman filter system which evolves error covariances in terms of a truncated set of wavelet coefficients has been developed for the assimilation of Chemical Tracer observations of CH4. This scheme projects the discretized covariance propagation equations and covariance matrix onto an orthogonal set of compactly supported wavelets. Wavelet representation is localized in both location and scale, which allows for efficient representation of the inherently anisotropic structure of the error covariances. The truncation is carried out in such a way that the resolution of the error covariance is reduced only in the zonal direction, where gradients are smaller. Assimilation experiments which last 24 days, and used different degrees of truncation were carried out. These reduced the covariance size by 90, 97 and 99 % and the computational cost of covariance propagation by 80, 93 and 96 % respectively. The difference in both error covariance and the Tracer field between the truncated and full systems over this period were found to be not growing in the first case, and growing relatively slowly in the later two cases. The largest errors in the Tracer fields were found to occur in regions of largest zonal gradients in the constituent field. This results indicate that propagation of error covariances for a global two-dimensional data assimilation system are currently feasible. Recommendations for further reduction in computational cost are made with the goal of extending this technique to three-dimensional global assimilation systems.
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a wavelet based reduced rank kalman filter for assimilation of stratospheric Chemical Tracer observations
Monthly Weather Review, 2004Co-Authors: Ludovic Auger, Andrew TangbornAbstract:A suboptimal Kalman filter system that evolves error covariances in terms of a truncated set of wavelet coefficients has been developed for the assimilation of Chemical Tracer observations of CH4. The truncation is carried out in such a way that the resolution of the error covariance is reduced only in the zonal direction, where gradients are smaller. Assimilation experiments, which lasted 24 days and used different degrees of truncation, were carried out. These experiments reduced the number of elements in the covariance matrix by 90%, 97%, and 99% and the computational cost of covariance propagation by 80%, 93%, and 96%, respectively. The difference in both error covariance and the Tracer field between the truncated and full systems over this period was not found to be growing after about 5 days of assimilation. The largest errors in the Tracer fields were found to occur in regions of largest zonal gradients at times when observations were made in the immediate vicinity.
Michael J Prather - One of the best experts on this subject based on the ideXlab platform.
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reply to comment on tropospheric oh in a three dimensional Chemical Tracer model an assessment based on observations of ch3ccl3 by c m spivakovsky et al
Journal of Geophysical Research, 1991Co-Authors: C M Spivakovsky, Rose M Yevich, Jennifer A Logan, S C Wofsy, Michael B Mcelroy, Michael J PratherAbstract:JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 96, NO. D9, PAGES 17,389-17,390, SEPTEMBER 20, 1991 Reply C.M. SPIVAKOVSKY, R. YEVICH. J.A. LOGAN. S.C. WOFSY, AND M.B. MCELROY Division of Applied Science and Department of Earth and Planetary Sciences, Harvard University, Cambridge M. J. PRATHER NASA Goddard Institute for Space Studies, New York concurrent data for CC12F2, CFCI•, Hartley and Prinn [this issue] misrepresent the objectives, pro- years of yet-to-be-published cedures, and results of our work [Spivakovsky et al., 1990, and CHzCC13. As emphasized in our paper, observations of hereinafter referred to as S90]. In addition, their analysis is longer-lived species (e.g., CC12Fa and CFClz) provide invaluable plagued by a number of conceptual errors and misuse of statistics. additional constraints on the relative influences of Chemical and The objective of S90 was to compute the global three- dynamical processes in controlling the distribution of CHzCClz. dimensional field of tropospheric OH, based on our understanding Besides, the ancillary information tells a different tale. of atmospheric chemistry and the climatologies of precursors, and The observations at Samoa available to S90 provide evidence then to assess the results using available observations. This work for an annual cycle in CFCs which is satisfactorily reproduced by also included an extensive analysis of observations of CFCs and our model. Important differences were noted in S90 between the CH3CC13 in order to identify and compare annual cycles of these seasonal behavior of CFCs and CHzCC13 observed at Samoa. species. Comparisons of seasonal variations of Chemically passive Observations of CH•CClz, unlike those for CFCs, did not display Tracers (CFCs) with those for CH3CCI5, which is destroyed by a significant annual cycle. We suggested that the differences reaction with OH, were intended to distinguish annual cycles asso- could reflect cancellation (for CHzCCI•) between the Chemical ciated with transport from those due to chemistry. We concluded and dynamical components of the variations which appeared to be that seasonal variations of CH3CC13 are dominated by chemistry of opposite phase and comparable amplitude (see Figure 24 in only at southern mid-latitudes and that only for this region can S90). Hartley and Prinn could have made a useful contribution in they provide constraints for OH. this context. Do the 11-year records for CFCs and CH3CClz sup- Hartley and Prinn seem to believe that the primary purpose of a port our suggestion? modeling study is to allow an adjustment of model sources and We were pleased to see that the 11-year record for CH•CCI• sinks either by trial and error or by an inverse method until the displays an annual cycle at Barbados similar to the one we showed model agrees with data. This was never the intent of our studies. for the published data. Apparently, our coarse-resolution global Data for most Uace species are inadequate to allow unambiguous model reproduces the magnitude and, approximately, the phase of determination of either sources or sinks, except on a hemispheric or global scale. Indeed, the purpose of S90 was to explore what could be learned about OH from analysis of the ALE/GAGE data. We concluded that competitive effects of transport and chemistry were such that concentrations of OH could be constrained only in a global-average sense with somewhat greater detail for southern mid-latitudes. In particular, the latitudinal distribution of OH can- not be constrained on the basis of data from the five ALE/GAGE the fall minimum. Our simulations suggested that this seasonal decrease is determined by a dynamical rather than a Chemical sig- n fl. However, observations of CFCs at Barbados available to S90 do not display a significant annual cycle. Do the 11 years of observations of CFCs define a cycle at Barbados similar to that for CH•CC137 It is incorrect to expect a single model year (or, for that matter, a single year of observations) to fall within the standard error of stations. the mean of observations as implied by Hartley and Prinn. The Hartley and Prinn address their attention to a peripheral com- results shown in S90 do not represent averaged seasonal variations ponent of our paper, the month-to-month variability of CH•CC13 but rather typical seasonal variations, since the simulations were in the tropics. The resolution of the model employed in our study, based on a single year of GCM statistics. Hartley and Prinn state combined with use of a single year of dynamical output from the that the interannual variabilifies ... for Samoa are in fact multimo- general circulation model (GCM), precluded adequate simulation dal. How then should one interpret the standard deviations in of the movement of the intertropical convergence zone (1TCZ) or Figures 4a and 5a? What fraction of the observations is expected simulation of the interannual variability of tropical meteorology to fall within one standard deviation of the mean? Is there reason (related for example to E1 Nino Southem Oscillation (ENSO). to expect that the intra-annual variations simulated for Samoa The assumptions used in our simulations are clearly stated in S90. should agree with observations averaged over 11 years given that Hartley and Prinn ereate and demolish a straw man adding little to observed seasonal variations appear to be nonrecurrent, i.e., indis- our understanding of tropical meteorology. tinguishable from random (the appropriate autocorrelation coeffi- Regrettably, Hartley and Prinn restrict their discussion to the cient is equal to -0.1 as shown in Figure 3b of the comment)? use of data for CHa CCla, unfortunate in light of authors' access to Hartley and Prinn in their calculation of correlation coefficients Copyright 1991 by the American Geophysical Union. Paper number 91JD01670. 0148-0227/91/91JD-01670502.00 for the different ENSO phases appear to have treated the separated 12-month periods as continuous. This is likely to produce spuri- ous correlations or anticorrelations; consequently, results for ENSO warm events, ENSO cold events, and intermediate years are suspect (Figure 3b in the comment).
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tropospheric oh in a three dimensional Chemical Tracer model an assessment based on observations of ch3ccl3
Journal of Geophysical Research, 1990Co-Authors: C M Spivakovsky, Rose M Yevich, Jennifer A Logan, S C Wofsy, Michael B Mcelroy, Michael J PratherAbstract:The three-dimensional global distribution of OH over a year is calculated as a function of temperature, ultraviolet irradiance, and densities of H2O, CO, O3, CH4, and NOt, (defined as NO + NO2 + NO3 + 2N2O5 + HNO2 + HNO4). The concentration of OH is computed within a Chemical Tracer model (CTM) with an accuracy comparable to that of a detailed photoChemical model. Distributions of CO, NOt, O3, CH4, and the density of O3 column were specified on the basis of observations. Meteorological fields were derived from the general circulation model developed at the Goddard Institute for Space Studies. The numerical method for parametrization of chemistry is described in Spivakovsky et al. (this issue). The CTM is used to simulate the global distribution of CH3CCl3. The computed distribution of OH implies a lifetime of 5.5 years for CH3CCl3 (obtained by relating the global burden of CH3CCl3 to the global loss, integrated using simulated three-dimensional distributions). Analysis of the long-term trend in CH3CCl3 as defined by observations suggests a lifetime of 6.2 years (consistent with Prinn et al. (1987)), indicating that model levels of OH may be too high by about 13%. This estimate for the lifetime depends on industry data for global emissions and on the absolute calibration of observations. It is argued that seasonal variations of CH3CCl3 provide an independent test for computed OH fields that is insensitive to the uncertainties in the budget of CH3CCl3. The annual cycle of CH3CCl3 from about 25°S to the South Pole is dominated by seasonal changes in OH. Observed seasonal variations of CH3CCl3 indicate that the OH field south of 20°S±4° should be scaled by 0.75±0.25 from computed values, consistent with the result based on long-term trends. Reactions involving non-methane hydrocarbons were not included in the current model. These reactions could account for lower concentrations of OH than computed. Seasonal variations of CH3CCl3 in the tropics and in the northern mid-latitudes are dominated by effects of transport. If use of CH3CCl3 is phased out (as envisioned by the Montreal protocol), the dynamically driven seasonal variations of CH3CCl3 will decrease dramatically, whereas the Chemically driven variations will remain proportional to the concentration of CH3CCl3; then the annual cycle of CH3CCl3 in northern mid-latitudes will provide a measure of OH as does at present the annual cycle in southern mid-latitudes. The influence of chemistry on the latitudinal distribution of CH3CCl3 is small and at present does not provide a constraint for the globally averaged OH or for the latitudinal distribution of OH. However, if emissions of CH3CCl3 were to cease, the tropical depression in the concentration of CH3CCl3 caused by high levels of OH in the tropics may provide an additional means to test OH models.
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Stratospheric chemistry and transport
1990Co-Authors: Michael J Prather, Maria M. GarciaAbstract:A Chemical Tracer Model (CTM) that can use wind field data generated by the General Circulation Model (GCM) is developed to implement chemistry in the three dimensional GCM of the middle atmosphere. Initially, Chemical Tracers with simple first order losses such as N2O are used. Successive models are to incorporate more complex ozone chemistry.
Truls Norby - One of the best experts on this subject based on the ideXlab platform.
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Chemical Tracer diffusion of sr and co in polycrystalline ca deficient camno3 δ with camn2o4 precipitates
Physical Chemistry Chemical Physics, 2018Co-Authors: Temesgen Debelo Desissa, Nikola Kanas, Sathya Prakash Singh, Kjell Wiik, Mariann Einarsrud, Truls NorbyAbstract:Diffusivity on the A- and B-site of polycrystalline perovskite CaMnO3−δ with Ca deficiency and spinel CaMn2O4 (marokite) as a secondary phase was studied using Chemical Tracers and secondary ion mass spectrometry (SIMS) complemented by electron probe microanalysis (EPMA). Thin films containing Sr and Co Chemical Tracers were deposited on the polished surface of the polycrystalline composite sample followed by annealing at 800–1200 °C for 96 h. Diffusion profiles for each Tracer were determined with SIMS, followed by calculation of diffusion coefficients by fitting to appropriate models. The Sr Tracer showed mainly lattice diffusion, with an activation energy of 210 ± 30 kJ mol−1, whereas the Co Tracer showed a combination of lattice and enhanced grain-boundary diffusion, with activation energies of 270 ± 30 kJ mol−1 and 380 ± 40 kJ mol−1, respectively. The diffusivities may be used to predict interdiffusion and lifetime of junctions between n-type CaMnO3−δ or CaMnO3−δ/CaMn2O4 composites and metallization interlayers or p-type leg materials in oxide thermoelectrics. In particular, the relatively high effective diffusivity of Co in polycrystalline CaMnO3−δ may play a role in the reported fast formation of the secondary phase (Ca3Co2−yMnyO6) between p-type Ca3Co3.92O9+δ and n-type CaMnO3−δ in a direct p–n thermoelectric junction.
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Chemical Tracer diffusion of Sr and Co in polycrystalline Ca-deficient CaMnO3−δ with CaMn2O4 precipitates
Physical Chemistry Chemical Physics, 2018Co-Authors: Temesgen Debelo Desissa, Nikola Kanas, Sathya Prakash Singh, Kjell Wiik, Mariann Einarsrud, Truls NorbyAbstract:Diffusivity on the A- and B-site of polycrystalline perovskite CaMnO3−δ with Ca deficiency and spinel CaMn2O4 (marokite) as a secondary phase was studied using Chemical Tracers and secondary ion mass spectrometry (SIMS) complemented by electron probe microanalysis (EPMA). Thin films containing Sr and Co Chemical Tracers were deposited on the polished surface of the polycrystalline composite sample followed by annealing at 800–1200 °C for 96 h. Diffusion profiles for each Tracer were determined with SIMS, followed by calculation of diffusion coefficients by fitting to appropriate models. The Sr Tracer showed mainly lattice diffusion, with an activation energy of 210 ± 30 kJ mol−1, whereas the Co Tracer showed a combination of lattice and enhanced grain-boundary diffusion, with activation energies of 270 ± 30 kJ mol−1 and 380 ± 40 kJ mol−1, respectively. The diffusivities may be used to predict interdiffusion and lifetime of junctions between n-type CaMnO3−δ or CaMnO3−δ/CaMn2O4 composites and metallization interlayers or p-type leg materials in oxide thermoelectrics. In particular, the relatively high effective diffusivity of Co in polycrystalline CaMnO3−δ may play a role in the reported fast formation of the secondary phase (Ca3Co2−yMnyO6) between p-type Ca3Co3.92O9+δ and n-type CaMnO3−δ in a direct p–n thermoelectric junction.
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determination of Chemical Tracer diffusion coefficients for the la and ni site in la2nio4 δ studied by sims
Journal of the American Ceramic Society, 2012Co-Authors: Nebojsa Cebasek, Reidar Haugsrud, Zuoan Li, Truls NorbyAbstract:Chemical (impurity) Tracer diffusion of Pr, Nd, and Co into polycrystalline La2NiO4+δ was done at 950°C–1350°C in air, argon, and intermediate pO2 (5.5 × 10−3 atm O2), and diffusion coefficients were extracted from depth profiles determined by Secondary Ion Mass Spectrometry (SIMS). The Pr and Nd profiles have only one broad region, corresponding to bulk diffusion, whereas the Co Tracer depth profile has two distinct regions with different slopes, where the outer shallow region represents bulk diffusion and the inner region with deep penetration depths represents grain-boundary diffusion. It is thus concluded that the diffusivity on the Ni-site is enhanced by grain-boundary diffusion. The bulk diffusion was evaluated using the solution of Fick's second law for thin-film source, and the grain-boundary diffusion was evaluated according to Whipple-Le Claire's equation. The average apparent activation energies for Pr and Nd bulk diffusion are 165 ± 15 kJ/mol, for Co bulk diffusion 295 ± 15 kJ/mol, and for Co grain-boundary diffusion 380 ± 20 kJ/mol. Qualitatively, the diffusivities and activation energies follow levels and trends in agreement with those from other experimental techniques. The apparent lack of—in fact reverse—correlation between activation energy and level of diffusivity is discussed in terms of a possibility that the faster species (Ni) reach equilibrium defect concentrations while the slower (La) is in effect frozen in.