Journal articles on the topic 'Transport timescales'
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Vercruysse, Kim, Robert C. Grabowski, Tim Hess, and Irantzu Lexartza-Artza. "Linking temporal scales of suspended sediment transport in rivers: towards improving transferability of prediction." Journal of Soils and Sediments 20, no. 12 (May 29, 2020): 4144–59. http://dx.doi.org/10.1007/s11368-020-02673-5.
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Abstract Purpose Suspended sediment (SS) transport in rivers is highly variable, making it challenging to develop predictive models that are applicable across timescales and rivers. Previous studies have identified catchment and hydro-meteorological variables controlling SS concentrations. However, due to the lack of long-term, high-frequency SS monitoring, it remains difficult to link SS transport dynamics during high-flow events with annual or decadal trends in SS transport. This study investigated how processes driving SS transport during high-flow events impact SS transport dynamics and trends observed over longer timescales. Methods Suspended sediment samples from the River Aire (UK) (1989–2017) were used to (i) statistically identify factors driving SS transport over multiple timescales (high-flow events, intra- and inter-annual) and (ii) conceptualize SS transport as a fractal system to help link and interpret the effect of short-term events on long-term SS transport dynamics. Results and discussion Antecedent moisture conditions were a dominant factor controlling event-based SS transport, confirming results from previous studies. Findings also showed that extreme high-flow events (in SS concentration or discharge) mask factors controlling long-term trends. This cross-timescale effect was conceptualized as high fractal power, indicating that quantifying SS transport in the River Aire requires a multi-timescale approach. Conclusion Characterizing the fractal power of a SS transport system presents a starting point in developing transferrable process-based approaches to quantify and predict SS transport, and develop management strategies. A classification system for SS transport dynamics in river systems in terms of fractal power could be developed which expresses the dominant processes underlying SS transport.
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Hasanloo, Davood, and Amir Etemad-Shahidi. "On the estimation of transport timescales – case study: the Dez reservoir." Journal of Hydroinformatics 13, no. 2 (April 29, 2010): 217–28. http://dx.doi.org/10.2166/hydro.2010.161.
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The purpose of this study is to demonstrate an application of a hydroinformatics methodology for analysis of transport timescales in a large reservoir. Therefore, a laterally averaged two-dimensional numerical model was used to estimate the transit time, flushing times and combination of these two timescales by modeling about 230 scenarios in the Dez reservoir. The model was calibrated using temperature profiles and then executed for a period of two years (2002–2004). A possible characterization of the flushing time as e-folding time was investigated and the results revealed that the e-folding time, which is simpler to estimate, can be used in place of the flushing time in the Dez reservoir. The effects of the location of the outlet on each of these timescales were also investigated. Results indicated that the mean residence and flushing times have their smallest value when the outlet is set in the middle of the Dez dam. The mean flushing times were also less sensitive to thermal structures of the Dez reservoir than the transit times. Finally, the temporal patterns of these timescales were elucidated. It was found that no single transport timescale can be used for all conditions.
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Bravo, Hector R., Sajad A. Hamidi, Eric J. Anderson, J. Val Klump, and Bahram Khazaei. "Timescales of transport through Lower Green Bay." Journal of Great Lakes Research 46, no. 5 (October 2020): 1292–306. http://dx.doi.org/10.1016/j.jglr.2020.06.010.
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de Vries, S., H. N. Southgate, W. Kanning, and R. Ranasinghe. "Dune behavior and aeolian transport on decadal timescales." Coastal Engineering 67 (September 2012): 41–53. http://dx.doi.org/10.1016/j.coastaleng.2012.04.002.
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Jackson, Nicholas E., Lin X. Chen, and Mark A. Ratner. "Charge transport network dynamics in molecular aggregates." Proceedings of the National Academy of Sciences 113, no. 31 (July 20, 2016): 8595–600. http://dx.doi.org/10.1073/pnas.1601915113.
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Due to the nonperiodic nature of charge transport in disordered systems, generating insight into static charge transport networks, as well as analyzing the network dynamics, can be challenging. Here, we apply time-dependent network analysis to scrutinize the charge transport networks of two representative molecular semiconductors: a rigid n-type molecule, perylenediimide, and a flexible p-type molecule, bBDT(TDPP)2. Simulations reveal the relevant timescale for local transfer integral decorrelation to be ∼100 fs, which is shown to be faster than that of a crystalline morphology of the same molecule. Using a simple graph metric, global network changes are observed over timescales competitive with charge carrier lifetimes. These insights demonstrate that static charge transport networks are qualitatively inadequate, whereas average networks often overestimate network connectivity. Finally, a simple methodology for tracking dynamic charge transport properties is proposed.
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Frajka-Williams, E., C. S. Meinen, W. E. Johns, D. A. Smeed, A. Duchez, A. J. Lawrence, D. A. Cuthbertson, et al. "Compensation between meridional flow components of the Atlantic MOC at 26° N." Ocean Science 12, no. 2 (April 1, 2016): 481–93. http://dx.doi.org/10.5194/os-12-481-2016.
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Abstract. From ten years of observations of the Atlantic meridional overturning circulation (MOC) at 26° N (2004–2014), we revisit the question of flow compensation between components of the circulation. Contrasting with early results from the observations, transport variations of the Florida Current (FC) and upper mid-ocean (UMO) transports (top 1000 m east of the Bahamas) are now found to compensate on sub-annual timescales. The observed compensation between the FC and UMO transports is associated with horizontal circulation and means that this part of the correlated variability does not project onto the MOC. A deep baroclinic response to wind-forcing (Ekman transport) is also found in the lower North Atlantic Deep Water (LNADW; 3000–5000 m) transport. In contrast, co-variability between Ekman and the LNADW transports does contribute to overturning. On longer timescales, the southward UMO transport has continued to strengthen, resulting in a continued decline of the MOC. Most of this interannual variability of the MOC can be traced to changes in isopycnal displacements on the western boundary, within the top 1000 m and below 2000 m. Substantial trends are observed in isopycnal displacements in the deep ocean, underscoring the importance of deep boundary measurements to capture the variability of the Atlantic MOC.
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Frajka-Williams, E., C. S. Meinen, W. E. Johns, D. A. Smeed, A. Duchez, A. J. Lawrence, D. A. Cuthbertson, et al. "Compensation between meridional flow components of the AMOC at 26° N." Ocean Science Discussions 12, no. 6 (November 13, 2015): 2705–41. http://dx.doi.org/10.5194/osd-12-2705-2015.
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Abstract. From ten years of observations of the Atlantic meridional overturning circulation at 26° N (MOC, 2004–2014), we revisit the question of flow compensation between components of the circulation. Contrasting with early results from the observations, transport variations of the Florida Current (FC) and upper mid-ocean transports (UMO, top 1000 m east of the Bahamas) are now found to compensate on sub-annual timescales. A deep baroclinic response to wind-forcing (Ekman transport) is also found in the lower North Atlantic Deep Water (LNADW, 3000–5000 m) transport. The observed compensation between the FC and UMO transports is associated with horizontal circulation and means that their individual variability does not project onto the MOC. In contrast, covariability between Ekman and the LNADW transports does contribute to overturning. On longer timescales, the southward UMO transport has continued to strengthen, resulting in a continued decline of the MOC. Most of this interannual variability of the MOC can be traced to changes in isopycnal displacements on the western boundary, within the top 1000 m and below 2000 m. Substantial trends are observed in isopycnal displacements in the deep ocean, underscoring the importance of deep boundary measurements to capture the variability of the Atlantic MOC.
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Hughes, C. W., Joanne Williams, A. C. Coward, and B. A. de Cuevas. "Antarctic circumpolar transport and the southern mode: a model investigation of interannual to decadal timescales." Ocean Science 10, no. 2 (April 10, 2014): 215–25. http://dx.doi.org/10.5194/os-10-215-2014.
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Abstract. It is well-established that, at periods shorter than a year, variations in Antarctic circumpolar transport are reflected in a barotropic mode, known as the southern mode, in which sea level and bottom pressure varies coherently around Antarctica. Here, we use two multidecadal ocean model runs to investigate the behaviour of the southern mode at timescales on which density changes become important, leading to a baroclinic component to the adjustment. We find that the concept of a southern mode in bottom pressure remains valid, and remains a direct measure of the circumpolar transport, with changes at the northern boundary playing only a small role even on decadal timescales. However, at periods longer than about 5 years, density changes start to play a role, leading to a surface intensification of the vertical profile of the transport. We also find that barotropic currents on the continental slope account for a significant fraction of the variability, and produce surface intensification in the meridional-integral flow. Circumpolar sea level and transport are related at all investigated timescales. However, the role of density variations results in a ratio of sea level change to transport which becomes larger at longer timescales. This means that any long-term transport monitoring strategy based on present measurement systems must involve multiplying the observed quantity by a factor which depends on frequency.
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Hoor, P., H. Wernli, and M. I. Hegglin. "Transport timescales and tracer properties in the extratropical UTLS." Atmospheric Chemistry and Physics Discussions 10, no. 5 (May 20, 2010): 12953–91. http://dx.doi.org/10.5194/acpd-10-12953-2010.
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Abstract. A comprehensive evaluation of seasonal backward trajectories initialized in the Northern Hemisphere lowermost stratosphere (LMS) has been performed to investigate the origin of air parcels and the main mechanisms determining characteristic structures in H2O and CO within the LMS. In particular we explain the fundamental role of the transit time since last tropopause crossing (tTST) for the chemical structure of the LMS as well as the feature of the extra-tropical tropopause transition layer (ExTL) as identified from CO profiles. The distribution of H2O in the background LMS above Θ=320 K and 340 K in northern winter and summer, respectively, is found to be governed mainly by the saturation mixing ratio, which in turn is determined by the Lagrangian Cold Point (LCP) encountered by each trajectory. Most of the backward trajectories from this region in the LMS experienced their LCP in the tropics and sub-tropics. The transit time since crossing the tropopause from the troposphere to the stratosphere (tTST) is independent of the H2O value of the air parcel. TST often occurs 20 days after trajectories have encountered their LCP. CO, on the other hand, depends strongly on tTST due to its finite lifetime. The ExTL as identified from CO measurements is then explained as a layer of air just above the tropopause, which on average encountered TST fairly recently.
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Hoor, P., H. Wernli, M. I. Hegglin, and H. Bönisch. "Transport timescales and tracer properties in the extratropical UTLS." Atmospheric Chemistry and Physics 10, no. 16 (August 25, 2010): 7929–44. http://dx.doi.org/10.5194/acp-10-7929-2010.
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Abstract. A comprehensive evaluation of seasonal backward trajectories initialized in the northern hemisphere lowermost stratosphere (LMS) has been performed to investigate the factors that determine the temporal and spatial structure of troposphere-to-stratosphere-transport (TST) and it's impact on the LMS. In particular we explain the fundamental role of the transit time since last TST (tTST) for the chemical composition of the LMS. According to our results the structure of the LMS can be characterized by a layer with tTST<40 days forming a narrow band around the local tropopause. This layer extends about 30 K above the local dynamical tropopause, corresponding to the extratropical tropopause transition layer (ExTL) as identified by CO. The LMS beyond this layer shows a relatively well defined separation as marked by an aprupt transition to longer tTST indicating less frequent mixing and a smaller fraction of tropospheric air. Thus the LMS constitutes a region of two well defined regimes of tropospheric influence. These can be characterized mainly by different transport times from the troposphere and different fractions of tropospheric air. Carbon monoxide (CO) mirrors this structure of tTST due to it's finite lifetime on the order of three months. Water vapour isopleths, on the other hand, do not uniquely indicate TST and are independent of tTST, but are determined by the Lagrangian Cold Point (LCP) of air parcels. Most of the backward trajectories from the LMS experienced their LCP in the tropics and sub-tropics, and TST often occurs 20 days after trajectories have encountered their LCP. Therefore, ExTL properties deduced from CO and H2O provide totally different informations on transport and particular TST for the LMS.
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Charlesworth, Edward J., Ann-Kristin Dugstad, Frauke Fritsch, Patrick Jöckel, and Felix Plöger. "Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model." Atmospheric Chemistry and Physics 20, no. 23 (December 8, 2020): 15227–45. http://dx.doi.org/10.5194/acp-20-15227-2020.
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Abstract. We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and results from the two transport schemes (Lagrangian critical Lyapunov scheme and flux-form semi-Lagrangian, respectively) were compared. Advection in CLaMS was driven by the EMAC simulation winds, and thereby the only differences in transport between the two sets of results were caused by differences in the transport schemes. To analyze the timescales of large-scale transport, multiple tropical-surface-emitted tracer pulses were performed to calculate age of air spectra, while smaller-scale transport was analyzed via idealized, radioactively decaying tracers emitted in smaller regions (nine grid cells) within the stratosphere. The results show that stratospheric transport barriers are significantly stronger for Lagrangian EMAC-CLaMS transport due to reduced numerical diffusion. In particular, stronger tracer gradients emerge around the polar vortex, at the subtropical jets, and at the edge of the tropical pipe. Inside the polar vortex, the more diffusive EMAC flux-form semi-Lagrangian transport scheme results in a substantially higher amount of air with ages from 0 to 2 years (up to a factor of 5 higher). In the lowermost stratosphere, mean age of air is much smaller in EMAC, owing to stronger diffusive cross-tropopause transport. Conversely, EMAC-CLaMS shows a summertime lowermost stratosphere age inversion – a layer of older air residing below younger air (an “eave”). This pattern is caused by strong poleward transport above the subtropical jet and is entirely blurred by diffusive cross-tropopause transport in EMAC. Potential consequences from the choice of the transport scheme on chemistry–climate and geoengineering simulations are discussed.
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Zhang, J., J. Liu, S. Tao, and G. A. Ban-Weiss. "Long-range transport of black carbon to the Pacific Ocean and its dependence on aging timescale." Atmospheric Chemistry and Physics Discussions 15, no. 12 (June 22, 2015): 16945–83. http://dx.doi.org/10.5194/acpd-15-16945-2015.
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Abstract. Improving the ability of global models to predict concentrations of black carbon (BC) over the Pacific Ocean is essential to evaluate the impact of BC on marine climate. In this study, we tag BC tracers from 13 source regions around the globe in a global chemical transport model MOZART-4. Numerous sensitivity simulations are carried out varying the aging timescale of BC emitted from each source region. The aging timescale for each source region is optimized by minimizing errors in vertical profiles of BC mass mixing ratios between simulations and HIAPER Pole-to-Pole Observations (HIPPO). For most HIPPO deployments, in the Northern Hemisphere, optimized aging timescales are less than half a day for BC emitted from tropical and mid-latitude source regions, and about 1 week for BC emitted from high latitude regions in all seasons except summer. We find that East Asian emissions contribute most to the BC loading over the North Pacific, while South American, African and Australian emissions dominate BC loadings over the South Pacific. Dominant source regions contributing to BC loadings in other parts of the globe are also assessed. The lifetime of BC originating from East Asia (i.e., the world's largest BC emitter) is found to be only 2.2 days, much shorter than the global average lifetime of 4.9 days, making East Asia's contribution to global burden only 36 % of BC from the second largest emitter, Africa. Thus, evaluating only relative emission rates without accounting for differences in aging timescales and deposition rates is not predictive of the contribution of a given source region to climate impacts. Our simulations indicate that lifetime of BC increases nearly linearly with aging timescale for all source regions. When aging rate is fast, the lifetime of BC is largely determined by factors that control local deposition rates (e.g. precipitation). The sensitivity of lifetime to aging timescale depends strongly on the initial hygroscopicity of freshly emitted BC. Our findings suggest that the aging timescale of BC varies significantly by region and season, and can strongly influence the contribution of source regions to BC burdens around the globe. Improving parameterizations of the aging process for BC is important for enhancing the predictive skill of air quality and climate models. Future observations that investigate the evolution of hygroscopicity of BC as it ages from different source regions to the remote atmosphere are urgently needed.
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Zhang, J., J. Liu, S. Tao, and G. A. Ban-Weiss. "Long-range transport of black carbon to the Pacific Ocean and its dependence on aging timescale." Atmospheric Chemistry and Physics 15, no. 20 (October 20, 2015): 11521–35. http://dx.doi.org/10.5194/acp-15-11521-2015.
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Abstract. Improving the ability of global models to predict concentrations of black carbon (BC) over the Pacific Ocean is essential to evaluate the impact of BC on marine climate. In this study, we tag BC tracers from 13 source regions around the globe in a global chemical transport model, Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4). Numerous sensitivity simulations are carried out varying the aging timescale of BC emitted from each source region. The aging timescale for each source region is optimized by minimizing errors in vertical profiles of BC mass mixing ratios between simulations and HIAPER Pole-to-Pole Observations (HIPPO). For most HIPPO deployments, in the Northern Hemisphere, optimized aging timescales are less than half a day for BC emitted from tropical and midlatitude source regions and about 1 week for BC emitted from high-latitude regions in all seasons except summer. We find that East Asian emissions contribute most to the BC loading over the North Pacific, while South American, African and Australian emissions dominate BC loadings over the South Pacific. Dominant source regions contributing to BC loadings in other parts of the globe are also assessed. The lifetime of BC originating from East Asia (i.e., the world's largest BC emitter) is found to be only 2.2 days, much shorter than the global average lifetime of 4.9 days, making the contribution from East Asia to the global BC burden only 36 % of that from the second largest emitter, Africa. Thus, evaluating only relative emission rates without accounting for differences in aging timescales and deposition rates is not predictive of the contribution of a given source region to climate impacts. Our simulations indicate that the lifetime of BC increases nearly linearly with aging timescale for all source regions. When the aging rate is fast, the lifetime of BC is largely determined by factors that control local deposition rates (e.g., precipitation). The sensitivity of lifetime to aging timescale depends strongly on the initial hygroscopicity of freshly emitted BC. Our findings suggest that the aging timescale of BC varies significantly by region and season and can strongly influence the contribution of source regions to BC burdens around the globe. Therefore, improving parameterizations of the aging process for BC is important for enhancing the predictive skill of global models. Future observations that investigate the evolution of the hygroscopicity of BC as it ages from different source regions to the remote atmosphere are urgently needed.
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Barnes, Jeffrey R., Thomas D. Walsh, and James R. Murphy. "Transport timescales in the Martian atmosphere: General circulation model simulations." Journal of Geophysical Research: Planets 101, E7 (July 1, 1996): 16881–89. http://dx.doi.org/10.1029/96je00500.
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Itoh, K., S. I. Itoh, K. Ida, S. Inagaki, Y. Kamada, K. Kamiya, J. Q. Dong, et al. "Hysteresis and fast timescales in transport relations of toroidal plasmas." Nuclear Fusion 57, no. 10 (July 28, 2017): 102021. http://dx.doi.org/10.1088/1741-4326/aa796a.
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Stohl, Andreas, Sabine Eckhardt, Caroline Forster, Paul James, and Nicole Spichtinger. "On the pathways and timescales of intercontinental air pollution transport." Journal of Geophysical Research: Atmospheres 107, no. D23 (December 4, 2002): ACH 6–1—ACH 6–17. http://dx.doi.org/10.1029/2001jd001396.
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Cucco, Andrea, Angelo Perilli, Gianni De Falco, Michol Ghezzo, and Georg Umgiesser. "Water circulation and transport timescales in the Gulf of Oristano." Chemistry and Ecology 22, sup1 (August 2006): S307—S331. http://dx.doi.org/10.1080/02757540600670364.
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Brett, Genevieve Jay, Daniel B. Whitt, Matthew C. Long, Frank Bryan, Kate Feloy, and Kelvin J. Richards. "Sensitivity of 21st-century projected ocean new production changes to idealized biogeochemical model structure." Biogeosciences 18, no. 10 (May 25, 2021): 3123–45. http://dx.doi.org/10.5194/bg-18-3123-2021.
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Abstract. While there is agreement that global warming over the 21st century is likely to influence the biological pump, Earth system models (ESMs) display significant divergence in their projections of future new production. This paper quantifies and interprets the sensitivity of projected changes in new production in an idealized global ocean biogeochemistry model. The model includes two tracers that explicitly represent nutrient transport, light- and nutrient-limited nutrient uptake by the ecosystem (new production), and export via sinking organic particles. Globally, new production declines with warming due to reduced surface nutrient availability, as expected. However, the magnitude, seasonality, and underlying dynamics of the nutrient uptake are sensitive to the light and nutrient dependencies of uptake, which we summarize in terms of a single biological timescale that is a linear combination of the partial derivatives of production with respect to light and nutrients. Although the relationships are nonlinear, this biological timescale is correlated with several measures of biogeochemical function: shorter timescales are associated with greater global annual new production and higher nutrient utilization. Shorter timescales are also associated with greater declines in global new production in a warmer climate and greater sensitivity to changes in nutrients than light. Future work is needed to characterize more complex ocean biogeochemical models in terms of similar timescale generalities to examine their climate change implications.
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Stone, Daniel, Tomás Sherwen, Mathew J. Evans, Stewart Vaughan, Trevor Ingham, Lisa K. Whalley, Peter M. Edwards, et al. "Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives." Atmospheric Chemistry and Physics 18, no. 5 (March 12, 2018): 3541–61. http://dx.doi.org/10.5194/acp-18-3541-2018.
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Abstract. The chemistry of the halogen species bromine and iodine has a range of impacts on tropospheric composition, and can affect oxidising capacity in a number of ways. However, recent studies disagree on the overall sign of the impacts of halogens on the oxidising capacity of the troposphere. We present simulations of OH and HO2 radicals for comparison with observations made in the remote tropical ocean boundary layer during the Seasonal Oxidant Study at the Cape Verde Atmospheric Observatory in 2009. We use both a constrained box model, using detailed chemistry derived from the Master Chemical Mechanism (v3.2), and the three-dimensional global chemistry transport model GEOS-Chem. Both model approaches reproduce the diurnal trends in OH and HO2. Absolute observed concentrations are well reproduced by the box model but are overpredicted by the global model, potentially owing to incomplete consideration of oceanic sourced radical sinks. The two models, however, differ in the impacts of halogen chemistry. In the box model, halogen chemistry acts to increase OH concentrations (by 9.8 % at midday at the Cape Verde Atmospheric Observatory), while the global model exhibits a small increase in OH at the Cape Verde Atmospheric Observatory (by 0.6 % at midday) but overall shows a decrease in the global annual mass-weighted mean OH of 4.5 %. These differences reflect the variety of timescales through which the halogens impact the chemical system. On short timescales, photolysis of HOBr and HOI, produced by reactions of HO2 with BrO and IO, respectively, increases the OH concentration. On longer timescales, halogen-catalysed ozone destruction cycles lead to lower primary production of OH radicals through ozone photolysis, and thus to lower OH concentrations. The global model includes more of the longer timescale responses than the constrained box model, and overall the global impact of the longer timescale response (reduced primary production due to lower O3 concentrations) overwhelms the shorter timescale response (enhanced cycling from HO2 to OH), and thus the global OH concentration decreases. The Earth system contains many such responses on a large range of timescales. This work highlights the care that needs to be taken to understand the full impact of any one process on the system as a whole.
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Krol, Maarten, Marco de Bruine, Lars Killaars, Huug Ouwersloot, Andrea Pozzer, Yi Yin, Frederic Chevallier, et al. "Age of air as a diagnostic for transport timescales in global models." Geoscientific Model Development 11, no. 8 (August 3, 2018): 3109–30. http://dx.doi.org/10.5194/gmd-11-3109-2018.
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Abstract. This paper presents the first results of an age-of-air (AoA) inter-comparison of six global transport models. Following a protocol, three global circulation models and three chemistry transport models simulated five tracers with boundary conditions that grow linearly in time. This allows for an evaluation of the AoA and transport times associated with inter-hemispheric transport, vertical mixing in the troposphere, transport to and in the stratosphere, and transport of air masses between land and ocean. Since AoA is not a directly measurable quantity in the atmosphere, simulations of 222Rn and SF6 were also performed. We focus this first analysis on averages over the period 2000–2010, taken from longer simulations covering the period 1988–2014. We find that two models, NIES and TOMCAT, show substantially slower vertical mixing in the troposphere compared to other models (LMDZ, TM5, EMAC, and ACTM). However, while the TOMCAT model, as used here, has slow transport between the hemispheres and between the atmosphere over land and ocean, the NIES model shows efficient horizontal mixing and a smaller latitudinal gradient in SF6 compared to the other models and observations. We find consistent differences between models concerning vertical mixing of the troposphere, expressed as AoA differences and modelled 222Rn gradients between 950 and 500 hPa. All models agree, however, on an interesting asymmetry in inter-hemispheric mixing, with faster transport from the Northern Hemisphere surface to the Southern Hemisphere than vice versa. This is attributed to a rectifier effect caused by a stronger seasonal cycle in boundary layer venting over Northern Hemispheric land masses, and possibly to a related asymmetric position of the intertropical convergence zone. The calculated AoA in the mid–upper stratosphere varies considerably among the models (4–7 years). Finally, we find that the inter-model differences are generally larger than differences in AoA that result from using the same model with a different resolution or convective parameterisation. Taken together, the AoA model inter-comparison provides a useful addition to traditional approaches to evaluate transport timescales. Results highlight that inter-model differences associated with resolved transport (advection, reanalysis data, nudging) and parameterised transport (convection, boundary layer mixing) are still large and require further analysis. For this purpose, all model output and analysis software are available.
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Tang, J. Y., W. J. Riley, C. D. Koven, and Z. M. Subin. "CLM4-BeTR, a generic biogeochemical transport and reaction module for CLM4: model development, evaluation, and application." Geoscientific Model Development 6, no. 1 (January 29, 2013): 127–40. http://dx.doi.org/10.5194/gmd-6-127-2013.
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Abstract. To improve regional and global biogeochemistry modeling and climate predictability, we have developed a generic reactive transport module for the land model CLM4 (called CLM4-BeTR (Biogeochemical Transport and Reactions)). CLM4-BeTR represents the transport, interactions, and biotic and abiotic transformations of an arbitrary number of tracers (aka chemical species) in an arbitrary number of phases (e.g., dissolved, gaseous, sorbed, aggregate). An operator splitting approach was employed and consistent boundary conditions were derived for each modeled sub-process. Aqueous tracer fluxes, associated with hydrological processes such as surface run-on and run-off, belowground drainage, and ice to liquid conversion were also computed consistently with the bulk water fluxes calculated by the soil physics module in CLM4. The transport code was evaluated and found in good agreement with several analytical test cases using a time step of 30 min. The model was then applied at the Harvard Forest site with a representation of depth-dependent belowground biogeochemistry. The results indicated that, at this site, (1) CLM4-BeTR was able to simulate soil–surface CO2 effluxes and soil CO2 profiles accurately; (2) the transient surface CO2 effluxes calculated based on the tracer transport mechanism were in general not equal to the belowground CO2 production rates with the magnitude of the difference being a function of averaging timescale and site conditions: differences were large (−20 ~ 20%) on hourly, smaller (−5 ~ 5%) at daily timescales, and persisted to the monthly timescales with a smaller magnitude (<4%); (3) losses of CO2 through processes other than surface gas efflux were less than 1% of the overall soil respiration; and (4) the contributions of root respiration and heterotrophic respiration have distinct temporal signals in surface CO2 effluxes and soil CO2 concentrations. The development of CLM4-BeTR will allow detailed comparisons between ecosystem observations and predictions and insights to the modeling of terrestrial biogeochemistry.
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Ziemke, J. R., A. R. Douglass, L. D. Oman, S. E. Strahan, and B. N. Duncan. "Tropospheric ozone variability in the tropics from ENSO to MJO and shorter timescales." Atmospheric Chemistry and Physics Discussions 15, no. 5 (March 5, 2015): 6373–401. http://dx.doi.org/10.5194/acpd-15-6373-2015.
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Abstract. Aura OMI and MLS measurements are combined to produce daily maps of tropospheric ozone beginning October 2004. We show that El Ni no Southern Oscillation (ENSO) related inter-annual change in tropospheric ozone in the tropics is small compared to combined intra-seasonal/Madden–Julian Oscillation (MJO) and shorter timescale variability by a factor ~ 3–10 (largest in the Atlantic). Outgoing Longwave Radiation (OLR) indicates further that deep convection is the primary driver of the observed tropospheric ozone variability from ENSO down to weekly timescales. We compare tropospheric ozone and OLR satellite observations with two simulations: (1) the Goddard Earth Observing System (GEOS) chemistry-climate model (CCM) that uses observed sea surface temperatures and is otherwise free-running, and (2) the NASA Global Modeling Initiative (GMI) chemical transport model (CTM) that is driven by Modern-Era Retrospective Analysis for Research and Applications (MERRA) analyses. It is shown that the CTM-simulated ozone accurately matches measurements for timescales from ENSO to intra-seasonal/MJO and even 1–2 week periods; however (though not unexpected) the CCM simulation reproduces ENSO variability but not shorter timescales. These analyses suggest that using a model to delineate temporal/spatial properties of tropospheric ozone and convection in the tropics will require that the model reproduce the non-ENSO variability that dominates.
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Pulupa, Joan, Manas Rachh, Michael D. Tomasini, Joshua S. Mincer, and Sanford M. Simon. "A coarse-grained computational model of the nuclear pore complex predicts Phe-Gly nucleoporin dynamics." Journal of General Physiology 149, no. 10 (September 8, 2017): 951–66. http://dx.doi.org/10.1085/jgp.201711769.
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The phenylalanine-glycine–repeat nucleoporins (FG-Nups), which occupy the lumen of the nuclear pore complex (NPC), are critical for transport between the nucleus and cytosol. Although NPCs differ in composition across species, they are largely conserved in organization and function. Transport through the pore is on the millisecond timescale. Here, to explore the dynamics of nucleoporins on this timescale, we use coarse-grained computational simulations. These simulations generate predictions that can be experimentally tested to distinguish between proposed mechanisms of transport. Our model reflects the conserved structure of the NPC, in which FG-Nup filaments extend into the lumen and anchor along the interior of the channel. The lengths of the filaments in our model are based on the known characteristics of yeast FG-Nups. The FG-repeat sites also bind to each other, and we vary this association over several orders of magnitude and run 100-ms simulations for each value. The autocorrelation functions of the orientation of the simulated FG-Nups are compared with in vivo anisotropy data. We observe that FG-Nups reptate back and forth through the NPC at timescales commensurate with experimental measurements of the speed of cargo transport through the NPC. Our results are consistent with models of transport where FG-Nup filaments are free to move across the central channel of the NPC, possibly informing how cargo might transverse the NPC.
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Williams, I. N., W. J. Riley, M. S. Torn, S. C. Biraud, and M. L. Fischer. "Biases in regional carbon budgets from covariation of surface fluxes and weather in transport model inversions." Atmospheric Chemistry and Physics 14, no. 3 (February 12, 2014): 1571–85. http://dx.doi.org/10.5194/acp-14-1571-2014.
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Abstract. Recent advances in atmospheric transport model inversions could significantly reduce uncertainties in land carbon uptake through the assimilation of CO2 concentration measurements at weekly and shorter timescales. The potential of these measurements for reducing biases in estimated land carbon sinks depends on the strength of covariation between surface fluxes and atmospheric transport at these timescales and how well transport models represent this covariation. Daily to seasonal covariation of surface fluxes and atmospheric transport was estimated in observations at the US Southern Great Plains Atmospheric Radiation Measurement Climate Research Facility, and compared to an atmospheric transport model inversion (CarbonTracker). Covariation of transport and surface fluxes was stronger in CarbonTracker than in observations on synoptic (daily to weekly) timescales, with a wet year (2007) having significant covariation compared to a dry year (2006). Differences between observed and CarbonTracker synoptic covariation resulted in a 0.3 ppm CO2 enhancement in boundary layer concentrations during the growing season, and a corresponding enhancement in carbon uptake by 13% of the seasonal cycle amplitude in 2007, as estimated by an offline simplified transport model. This synoptic rectification of surface flux variability was of similar magnitude to the interannual variability in carbon sinks alone, and indicates that interannual variability in the inversions can be affected by biases in simulated synoptic rectifier effects. The most significant covariation of surface fluxes and transport had periodicities of 10 days and greater, suggesting that surface flux inversions would benefit from improved simulations of the effects of soil moisture on boundary layer heights and surface CO2 fluxes. Soil moisture remote sensing could be used along with CO2 concentration measurements to further constrain atmospheric transport model inversions.
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Li, Ying, and Manabu Shiraiwa. "Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humidities." Atmospheric Chemistry and Physics 19, no. 9 (May 7, 2019): 5959–71. http://dx.doi.org/10.5194/acp-19-5959-2019.
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Abstract. Secondary organic aerosols (SOA) account for a substantial fraction of air particulate matter, and SOA formation is often modeled assuming rapid establishment of gas–particle equilibrium. Here, we estimate the characteristic timescale for SOA to achieve gas–particle equilibrium under a wide range of temperatures and relative humidities using a state-of-the-art kinetic flux model. Equilibration timescales were calculated by varying particle phase state, size, mass loadings, and volatility of organic compounds in open and closed systems. Model simulations suggest that the equilibration timescale for semi-volatile compounds is on the order of seconds or minutes for most conditions in the planetary boundary layer, but it can be longer than 1 h if particles adopt glassy or amorphous solid states with high glass transition temperatures at low relative humidity. In the free troposphere with lower temperatures, it can be longer than hours or days, even at moderate or relatively high relative humidities due to kinetic limitations of bulk diffusion in highly viscous particles. The timescale of partitioning of low-volatile compounds into highly viscous particles is shorter compared to semi-volatile compounds in the closed system, as it is largely determined by condensation sink due to very slow re-evaporation with relatively quick establishment of local equilibrium between the gas phase and the near-surface bulk. The dependence of equilibration timescales on both volatility and bulk diffusivity provides critical insights into thermodynamic or kinetic treatments of SOA partitioning for accurate predictions of gas- and particle-phase concentrations of semi-volatile compounds in regional and global chemical transport models.
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Wan, Shiming, Youbin Sun, and Kana Nagashima. "Asian dust from land to sea: processes, history and effect from modern observation to geological records." Geological Magazine 157, no. 5 (May 2020): 701–6. http://dx.doi.org/10.1017/s0016756820000333.
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AbstractProduction, transport and deposition of aeolian dust from land to sea closely interact with regional environment and global climate. This Special Issue addresses transport of aeolian dust from the Asian inland to the Loess Plateau and North Pacific Ocean and their possible links to oceanic ecosystem, global climate and even human activity, over various timescales. The papers in this volume are multidisciplinary in nature and include sedimentology, mineralogy, geochemistry, environmental magnetism and climate modelling on multi-timescales from interannual, glacial–interglacial to tectonic timescales. Based on modern observation, geological records and modelling, this Special Issue offers new insights especially into aeolian provenance, dynamics controls on dust production, a novel marine aeolian proxy, as well as long-term aeolian input to the marginal basins of NE Asia and its influence on oceanic productivity. This issue provides a good example for future comprehensive studies of source-to-sink processes of Asian dust from land to sea.
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Shi, Huabin, and Xiping Yu. "Application of transport timescales to coastal environmental assessment: A case study." Journal of Environmental Management 130 (November 2013): 176–84. http://dx.doi.org/10.1016/j.jenvman.2013.08.062.
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Sun, Jian, Zijun Xiao, Binliang Lin, Bing Yuan, and Xiaofeng Zhang. "Longitudinal transport timescales in a large dammed river - The Changjiang River." Science of The Total Environment 771 (June 2021): 144886. http://dx.doi.org/10.1016/j.scitotenv.2020.144886.
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Strypsteen, Houthuys, and Rauwoens. "Dune Volume Changes at Decadal Timescales and Its Relation with Potential Aeolian Transport." Journal of Marine Science and Engineering 7, no. 10 (October 8, 2019): 357. http://dx.doi.org/10.3390/jmse7100357.
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Long-term changes in dune volume at the Belgian coast are analyzed based on measured data by airborne surveys available from 1979. For most of the 65 km long coastal stretch, dune volume increases linearly in time at a constant rate. Dune growth varies between 0–12.3 m³/m/year with an average dune growth of 6.2 m³/m/year, featuring large variations in longshore directions. Based on a wind data set from 2000–2017, it is found that potential aeolian sediment transport has its main drift from the west to southwest direction (onshore to oblique onshore). Based on a modified Bagnold model, onshore potential aeolian sediment transport ranges to a maximum of 9 m³/m/year, while longshore potential aeolian sediment transport could reach up to 20 m³/m/year. We found an important correlation between observed and predicted dune development at decadal timescales when zones with dune management activities are excluded. Most of the predicted data are within a factor of two of the measured values. The variability in potential transport is well related to the variability in dune volume changes at the considered spatial–temporal scale, suggesting that natural dune growth is primarily caused by aeolian sediment transport from the beach. It also suggests that annual differences in forcing and transport limiting conditions (wind and moisture) only have a modest effect on the overall variability of dune volume trends.
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Rossby, T., C. Flagg, and K. Donohue. "On the variability of Gulf Stream transport from seasonal to decadal timescales." Journal of Marine Research 68, no. 3 (May 1, 2010): 503–22. http://dx.doi.org/10.1357/002224010794657128.
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Hall, Timothy M. "Path histories and timescales in stratospheric transport: Analysis of an idealized model." Journal of Geophysical Research: Atmospheres 105, no. D18 (September 1, 2000): 22811–23. http://dx.doi.org/10.1029/2000jd900329.
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Andutta, Fernando P., Fernanda Helfer, Luiz Bruner de Miranda, Eric Deleersnijder, Christopher Thomas, and Charles Lemckert. "An assessment of transport timescales and return coefficient in adjacent tropical estuaries." Continental Shelf Research 124 (August 2016): 49–62. http://dx.doi.org/10.1016/j.csr.2016.05.006.
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Sandery, Paul A., and Jochen Kämpf. "Transport timescales for identifying seasonal variation in Bass Strait, south-eastern Australia." Estuarine, Coastal and Shelf Science 74, no. 4 (September 2007): 684–96. http://dx.doi.org/10.1016/j.ecss.2007.05.011.
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Kabbe, Gabriel, Christian Dreßler, and Daniel Sebastiani. "Proton mobility in aqueous systems: combining ab initio accuracy with millisecond timescales." Physical Chemistry Chemical Physics 19, no. 42 (2017): 28604–9. http://dx.doi.org/10.1039/c7cp05632j.
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Turowski, Jens Martin. "Mass balance, grade, and adjustment timescales in bedrock channels." Earth Surface Dynamics 8, no. 1 (February 13, 2020): 103–22. http://dx.doi.org/10.5194/esurf-8-103-2020.
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Abstract. Rivers are dynamical systems that are thought to evolve towards a steady-state configuration. Then, geomorphic parameters, such as channel width and slope, are constant over time. In the mathematical description of the system, the steady state corresponds to a fixed point in the dynamic equations in which all time derivatives are equal to zero. In alluvial rivers, steady state is characterized by grade. This can be expressed as a so-called order principle: an alluvial river evolves to achieve a state in which sediment transport is constant along the river channel and is equal to transport capacity everywhere. In bedrock rivers, steady state is thought to be achieved with a balance between channel incision and uplift. The corresponding order principle is the following: a bedrock river evolves to achieve a vertical bedrock incision rate that is equal to the uplift rate or base-level lowering rate. In the present work, considerations of process physics and of the mass balance of a bedrock channel are used to argue that bedrock rivers evolve to achieve both grade and a balance between channel incision and uplift. As such, bedrock channels are governed by two order principles. As a consequence, the recognition of a steady state with respect to one of them does not necessarily imply an overall steady state. For further discussion of the bedrock channel evolution towards a steady state, expressions for adjustment timescales are sought. For this, a mechanistic model for lateral erosion of bedrock channels is developed, which allows one to obtain analytical solutions for the adjustment timescales for the morphological variables of channel width, channel bed slope, and alluvial bed cover. The adjustment timescale to achieve steady cover is of the order of minutes to days, while the adjustment timescales for width and slope are of the order of thousands of years. Thus, cover is adjusted quickly in response to a change in boundary conditions to achieve a graded state. The resulting change in vertical and lateral incision rates triggers a slow adjustment of width and slope, which in turn affects bed cover. As a result of these feedbacks, it can be expected that a bedrock channel is close to a graded state most of the time, even when it is transiently adjusting its bedrock channel morphology.
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Gao, Xueping, Yuanyuan Chen, and Chen Zhang. "Water renewal timescales in an ecological reconstructed lagoon in China." Journal of Hydroinformatics 15, no. 3 (January 29, 2013): 991–1001. http://dx.doi.org/10.2166/hydro.2013.136.
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To improve water quality and construct a landscape lagoon in China, an ecological reconstruction plan for the Qilihai Lagoon (Changli County, Hebei) is proposed. A three-dimensional numerical model (EFDC) was used to study the water renewal capacity in the reconstructed lagoon by using residence time, exposure time and connectivity as timescales. The influences of wind and the depth of the tidal inlet of the lagoon on water renewal capacity were also investigated. The results show that the transport and diffusion processes in the lagoon were strongly influenced by wind and the modification of the tidal inlet. The lagoon under a no wind condition exhibited a low water renewal capacity, especially at the end areas (exposure time, 700–1,000 days). The wind action notably enhanced the water renewal capacity in the lagoon, and the exposure times were all lower than 400 days in the whole region. The optimal inlet depth for the water renewal in the lagoon was predicted to be 4.0 m. The connectivity matrices identified which areas of the domain would be most affected by a pollution source under different conditions. This study examines transport and diffusion processes in a reconstructed lagoon, which could be informative for ecological reconstruction planning.
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Rannik, Üllar, Luxi Zhou, Putian Zhou, Rosa Gierens, Ivan Mammarella, Andrey Sogachev, and Michael Boy. "Aerosol dynamics within and above forest in relation to turbulent transport and dry deposition." Atmospheric Chemistry and Physics 16, no. 5 (March 9, 2016): 3145–60. http://dx.doi.org/10.5194/acp-16-3145-2016.
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Abstract. A 1-D atmospheric boundary layer (ABL) model coupled with a detailed atmospheric chemistry and aerosol dynamical model, the model SOSAA, was used to predict the ABL and detailed aerosol population (characterized by the number size distribution) time evolution. The model was applied over a period of 10 days in May 2013 to a pine forest site in southern Finland. The period was characterized by frequent new particle formation events and simultaneous intensive aerosol transformation. The aim of the study was to analyze and quantify the role of aerosol and ABL dynamics in the vertical transport of aerosols. It was of particular interest to what extent the fluxes above the canopy deviate from the particle dry deposition on the canopy foliage due to the above-mentioned processes. The model simulations revealed that the particle concentration change due to aerosol dynamics frequently exceeded the effect of particle deposition by even an order of magnitude or more. The impact was, however, strongly dependent on particle size and time. In spite of the fact that the timescale of turbulent transfer inside the canopy is much smaller than the timescales of aerosol dynamics and dry deposition, leading us to assume well-mixed properties of air, the fluxes at the canopy top frequently deviated from deposition inside the forest. This was due to transformation of aerosol concentration throughout the ABL and resulting complicated pattern of vertical transport. Therefore we argue that the comparison of timescales of aerosol dynamics and deposition defined for the processes below the flux measurement level do not unambiguously describe the importance of aerosol dynamics for vertical transport above the canopy. We conclude that under dynamical conditions reported in the current study the micrometeorological particle flux measurements can significantly deviate from the dry deposition into the canopy. The deviation can be systematic for certain size ranges so that the time-averaged particle fluxes can be also biased with respect to deposition sink.
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Good, P., C. Giannakopoulos, F. M. O’Connor, S. R. Arnold, M. de Reus, and H. Schlager. "Constraining tropospheric mixing timescales using airborne observations and numerical models." Atmospheric Chemistry and Physics Discussions 3, no. 2 (March 5, 2003): 1213–45. http://dx.doi.org/10.5194/acpd-3-1213-2003.
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Abstract. A technique is demonstrated for estimating atmospheric mixing time-scales from in-situ data, using a Lagrangian model initialised from an Eulerian chemical transport model (CTM). This method is applied to airborne tropospheric CO observations taken during seven flights of the Mediterranean Intensive Oxidant Study (MINOS) campaign, of August 2001. The time-scales derived, correspond to mixing applied at the spatial scale of the CTM grid. Specifically, they are upper bound estimates of the mix-down lifetime that should be imposed for a Lagrangian model to reproduce the observed small-scale tracer structure. They are relevant to the family of hybrid Lagrangian-Eulerian models, which impose Eulerian grid mixing to an underlying Lagrangian model. The method uses the fact that in Lagrangian tracer transport modelling, the mixing spatial and temporal scales are decoupled: the spatial scale is determined by the resolution of the initial tracer field, and the time scale by the trajectory length. The chaotic nature of lower-atmospheric advection results in the continuous generation of smaller spatial scales, a process terminated in the real atmosphere by mixing. Thus, a mix-down lifetime can be estimated by varying trajectory length so that the model reproduces the observed amount of small-scale tracer structure. Selecting a trajectory length is equivalent to choosing a mixing timescale. For the cases studied, the results are very insensitive to CO photochemical change calculated along the trajectories. The method is most appropriate for relatively homogeneous regions, i.e. it is not too important to account for changes in aircraft altitude or the positioning of stratospheric intrusions, so that small scale structure is easily distinguished. The chosen flights showed a range of mix-down time upper limits: 1 and 3 days for 8 August and 3 August, due to recent convective and boundary layer mixing respectively, and 7–9 days for 16, 17, 22a, 22c and 24 August. For the flight of 3 August, the observed concentrations result from a complex set of transport histories, and the models are used to interpret the observed structure, while illustrating where more caution is required with this method of estimating mix-down lifetimes.
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Oldham, C. E., D. E. Farrow, and S. Peiffer. "A generalized Damköhler number for classifying material processing in hydrological systems." Hydrology and Earth System Sciences 17, no. 3 (March 15, 2013): 1133–48. http://dx.doi.org/10.5194/hess-17-1133-2013.
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Abstract. Assessing the potential for transfer of pollutants and nutrients across catchments is of primary importance under changing land use and climate. Over the past decade the connectivity/disconnectivity dynamic of a catchment has been related to its potential to export material; however, we continue to use multiple definitions of connectivity, and most have focused strongly on physical (hydrological or hydraulic) connectivity. In contrast, this paper constantly focuses on the dynamic balance between transport and material transformation, and defines material connectivity as the effective transfer of material between elements of the hydrological cycle. The concept of exposure timescales is developed and used to define three distinct regimes: (i) which is hydrologically connected and transport is dominated by advection; (ii) which is hydrologically connected and transport is dominated by diffusion; and (iii) which is materially isolated. The ratio of exposure timescales to material processing timescales is presented as the non-dimensional number, NE, where NE is reaction-specific and allows estimation of relevant spatial scales over which the reactions of interest take place. Case studies within each regime provide examples of how NE can be used to characterise systems according to their sensitivity to shifts in hydrology and gain insight into the biogeochemical processes that are signficant under the specified conditions. Finally, we explore the implications of the NE framework for improved water management, and for our understanding of biodiversity, resilience and chemical competitiveness under specified conditions.
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Froeschlé, Ch, P. Michel, and C. Froeschlé. "Dynamical transport mechanisms of planet-crossing bodies." International Astronomical Union Colloquium 173 (1999): 87–96. http://dx.doi.org/10.1017/s0252921100031274.
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AbstractIn this paper we review the most important dynamical mechanisms for transporting material from the asteroid belt to the vicinity of the inner planets. Most of these mechanisms are associated with secular or/and mean motion resonances. From numerical integrations on timescales of hundreds Myr, new quantitative results on the dynamical lifetimes of bodies injected in the main resonances have been obtained. These new results are not consistent with the observed population of Earth-crossers of large diameter. At the light of these results a new scenario for the origin of large Earth-crossers has recently been proposed.
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Pnyushkov, Andrey V., Igor V. Polyakov, Robert Rember, Vladimir V. Ivanov, Matthew B. Alkire, Igor M. Ashik, Till M. Baumann, Genrikh V. Alekseev, and Arild Sundfjord. "Heat, salt, and volume transports in the eastern Eurasian Basin of the Arctic Ocean from 2 years of mooring observations." Ocean Science 14, no. 6 (November 2, 2018): 1349–71. http://dx.doi.org/10.5194/os-14-1349-2018.
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Abstract. This study discusses along-slope volume, heat, and salt transports derived from observations collected in 2013–2015 using a cross-slope array of six moorings ranging from 250 to 3900 m in the eastern Eurasian Basin (EB) of the Arctic Ocean. These observations demonstrate that in the upper 780 m layer, the along-slope boundary current advected, on average, 5.1±0.1 Sv of water, predominantly in the eastward (shallow-to-right) direction. Monthly net volume transports across the Laptev Sea slope vary widely, from ∼0.3±0.8 in April 2014 to ∼9.9±0.8 Sv in June 2014; 3.1±0.1 Sv (or 60 %) of the net transport was associated with warm and salty intermediate-depth Atlantic Water (AW). Calculated heat transport for 2013–2015 (relative to −1.8 ∘C) was 46.0±1.7 TW, and net salt transport (relative to zero salinity) was 172±6 Mkg s−1. Estimates for AW heat and salt transports were 32.7±1.3 TW (71 % of net heat transport) and 112±4 Mkg s−1 (65 % of net salt transport). The variability of currents explains ∼90 % of the variability in the heat and salt transports. The remaining ∼10 % is controlled by temperature and salinity anomalies together with the temporal variability of the AW layer thickness. The annual mean volume transports decreased by 25 % from 5.8±0.2 Sv in 2013–2014 to 4.4±0.2 Sv in 2014–2015, suggesting that changes in the transports at interannual and longer timescales in the eastern EB may be significant.
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Armitage, John J. "Short communication: flow as distributed lines within the landscape." Earth Surface Dynamics 7, no. 1 (January 17, 2019): 67–75. http://dx.doi.org/10.5194/esurf-7-67-2019.
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Abstract. Landscape evolution models (LEMs) aim to capture an aggregation of the processes of erosion and deposition within the earth's surface and predict the evolving topography. Over long timescales, i.e. greater than 1 million years, the computational cost is such that numerical resolution is coarse and all small-scale properties of the transport of material cannot be captured. A key aspect, therefore, of such a long timescale LEM is the algorithm chosen to route water down the surface. I explore the consequences of two end-member assumptions of how water flows over the surface of an LEM – either down a single flow direction (SFD) or down multiple flow directions (MFDs) – on model sediment flux and valley spacing. I find that by distributing flow along the edges of the mesh cells, node to node, the resolution dependence of the evolution of an LEM is significantly reduced. Furthermore, the flow paths of water predicted by this node-to-node MFD algorithm are significantly closer to those observed in nature. This reflects the observation that river channels are not necessarily fixed in space, and a distributive flow captures the sub-grid-scale processes that create non-steady flow paths. Likewise, drainage divides are not fixed in time. By comparing results between the distributive transport-limited LEM and the stream power model “Divide And Capture”, which was developed to capture the sub-grid migration of drainage divides, I find that in both cases the approximation for sub-grid-scale processes leads to resolution-independent valley spacing. I would, therefore, suggest that LEMs need to capture processes at a sub-grid-scale to accurately model the earth's surface over long timescales.
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Plake, D., M. Sörgel, P. Stella, A. Held, and I. Trebs. "Influence of meteorology and anthropogenic pollution on chemical flux divergence of the NO–NO<sub>2</sub>–O<sub>3</sub> triad above and within a natural grassland canopy." Biogeosciences 12, no. 4 (February 17, 2015): 945–59. http://dx.doi.org/10.5194/bg-12-945-2015.
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Abstract. The detailed understanding of surface–atmosphere exchange fluxes of reactive trace gases is a crucial precondition for reliable modelling of processes in atmospheric chemistry. Plant canopies significantly impact the atmospheric budget of trace gases. In the past, many studies focused on taller forest canopies or crops, where the bulk plant material is concentrated in the uppermost canopy layer. However, within grasslands, a land-cover class that globally covers vast terrestrial areas, the canopy structure is fundamentally different, as the main biomass is concentrated in the lowest part of the canopy. This has obvious implications for aerodynamic in-canopy transport, and consequently also impacts on global budgets of key species in atmospheric chemistry such as nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3). This study presents for the first time a comprehensive data set of directly measured in-canopy transport times and aerodynamic resistances, chemical timescales, Damköhler numbers, trace gas and micrometeorological measurements for a natural grassland canopy (canopy height = 0.6 m). Special attention is paid to the impact of contrasting meteorological and air chemical conditions on in-canopy transport and chemical flux divergence. Our results show that the grassland canopy is decoupled throughout the day. In the lowermost canopy layer, the measured transport times are fastest during nighttime, which is due to convection during nighttime and a stable stratification during daytime in this layer. The inverse was found in the layers above. During periods of low wind speed and high NOx (NO+NO2) levels, the effect of canopy decoupling on trace gas transport was found to be especially distinct. The aerodynamic resistance in the lowermost canopy layer (0.04–0.2 m) was around 1000 s m−1, which is as high as values determined previously for the lowest metre of an Amazonian rain forest canopy. The aerodynamic resistance representing the bulk canopy was found to be more than 3–4 times higher than in forests. Calculated Damköhler numbers (ratio of transport and chemical timescales) suggest a strong flux divergence for the NO–NO2–O3 triad within the canopy during daytime. During that time, the timescale of NO2 uptake by plants ranged from 90 to 160 s and was the fastest relevant timescale, i.e. faster than the reaction of NO and O3. Thus, our results reveal that grassland canopies of similar structure exhibit a strong potential to retain soil-emitted NO due to oxidation and subsequent uptake of NO2 by plants. Furthermore, photo-chemical O3 production was observed above the canopy, which was attributed to a deviation from the NO–NO2–O3 photostationary state by a surplus of NO2 due to oxidation of NO, by e.g. peroxy radicals. The O3 production was one order of magnitude higher during high NOx than during low NOx periods and resulted in an underestimation of the O3 deposition flux measured with the EC method.
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Plake, D., M. Sörgel, P. Stella, A. Held, and I. Trebs. "Influence of meteorology and anthropogenic pollution on chemical flux divergence of the NO-NO<sub>2</sub>-O<sub>3</sub> triad above and within a natural grassland canopy." Biogeosciences Discussions 11, no. 7 (July 14, 2014): 10737–77. http://dx.doi.org/10.5194/bgd-11-10737-2014.
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Abstract. The detailed understanding of surface–atmosphere exchange of reactive trace gas species is a crucial precondition for reliable modeling of processes in atmospheric chemistry. Plant canopies significantly impact the atmospheric budget of trace gases. In the past, many studies focused on taller forest canopies or crops, where the bulk plant material is concentrated in the uppermost canopy layer. However, within grasslands, a land-cover class that globally covers vast terrestrial areas, the canopy structure is fundamentally different, as the main biomass is concentrated in the lowest canopy part. This has obvious implications for aerodynamic in-canopy transport, and consequently also impacts on global budgets of key species in atmospheric chemistry such as nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3). This study presents for the first time a~comprehensive data set of directly measured in-canopy transport times and aerodynamic resistances, chemical timescales, Damköhler numbers, trace gas and micrometeorological measurements for a natural grassland canopy (canopy height = 0.6 m). Special attention is paid to the impact of contrasting meteorological and air chemical conditions on in-canopy transport and chemical flux divergence. Our results show that the grassland canopy is decoupled throughout the day. In the lower canopy, the measured transport times are fastest during nighttime, which is due to convection during nighttime and stable stratification during daytime in this layer. The inverse was found in the layers above. During periods of low wind speed and high NOx (NO+NO2) levels, the effect of canopy decoupling on trace gas transport was found especially distinct. The aerodynamic resistance in the lower canopy (0.04–0.2 m) was around 1000 s m−1, thus as high as values from literature representing the lowest meter of an Amazonian rain forest canopy. The aerodynamic resistance representing the bulk canopy was found to be more than 3–4 times higher as in forests. Calculated Damköhler numbers (ratio of transport and chemical timescales) suggested a strong flux divergence for the NO-NO2-O3 triad within the canopy during daytime. At that time, the timescale of NO2 plant uptake ranged from 90 to 160 s and was the fastest relevant timescale, i.e. faster than the reaction of NO and O3. Thus, our results clearly reveal that grassland canopies of similar structure have a strong potential to retain soil emitted NO by uptake of NO2 by the plants. Furthermore, a photo-chemical O3 production above the canopy was observed, which resulted from a~surplus of NO2 from the NO-NO2-O3 photostationary state. The O3 production was one order of magnitude higher during high NOx than during low NOx periods and resulted in an O3 flux underestimation, which was observed for the first time.
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Ziemke, J. R., A. R. Douglass, L. D. Oman, S. E. Strahan, and B. N. Duncan. "Tropospheric ozone variability in the tropics from ENSO to MJO and shorter timescales." Atmospheric Chemistry and Physics 15, no. 14 (July 22, 2015): 8037–49. http://dx.doi.org/10.5194/acp-15-8037-2015.
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Abstract. Aura OMI and MLS measurements are combined to produce daily maps of tropospheric ozone beginning October 2004. We show that El Niño-Southern Oscillation (ENSO) related inter-annual change in tropospheric ozone in the tropics is small in relation to combined intra-seasonal/Madden–Julian Oscillation (MJO) and shorter timescale variability by a factor of ~ 3–10 (largest in the Atlantic). Outgoing longwave radiation (OLR), taken as a proxy for convection, suggests that convection is a dominant driver of large-scale variability of tropospheric ozone in the Pacific from inter-annual (e.g., ENSO) to weekly periods. We compare tropospheric ozone and OLR satellite observations with two simulations: (1) the Goddard Earth Observing System (GEOS) chemistry-climate model (CCM) that uses observed sea surface temperatures and is otherwise free-running, and (2) the NASA Global Modeling Initiative (GMI) chemical transport model (CTM) that is driven by Modern Era Retrospective-Analysis for Research and Applications (MERRA) analyses. It is shown that the CTM-simulated ozone accurately matches measurements for timescales from ENSO to intra-seasonal/MJO and even 1–2-week periods. The CCM simulation reproduces ENSO variability but not shorter timescales. These analyses suggest that a model used to delineate temporal and/or spatial properties of tropospheric ozone and convection in the tropics must reproduce both ENSO and non-ENSO variability.
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Good, P., C. Giannakopoulos, F. M. O’Connor, S. R. Arnold, M. de Reus, and H. Schlager. "Constraining tropospheric mixing timescales using airborne observations and numerical models." Atmospheric Chemistry and Physics 3, no. 4 (July 16, 2003): 1023–35. http://dx.doi.org/10.5194/acp-3-1023-2003.
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Abstract. A technique is demonstrated for estimating atmospheric mixing time-scales from in-situ data, using a Lagrangian model initialised from an Eulerian chemical transport model (CTM). This method is applied to airborne tropospheric CO observations taken during seven flights of the Mediterranean Intensive Oxidant Study (MINOS) campaign, of August 2001. The time-scales derived, correspond to mixing applied at the spatial scale of the CTM grid. They are relevant to the family of hybrid Lagrangian-Eulerian models, which impose Eulerian grid mixing to an underlying Lagrangian model. The method uses the fact that in Lagrangian tracer transport modelling, the mixing spatial and temporal scales are decoupled: the spatial scale is determined by the resolution of the initial tracer field, and the time scale by the trajectory length. The chaotic nature of lower-atmospheric advection results in the continuous generation of smaller spatial scales, a process terminated in the real atmosphere by mixing. Thus, a mix-down lifetime can be estimated by varying trajectory length so that the model reproduces the observed amount of small-scale tracer structure. Selecting a trajectory length is equivalent to choosing a mixing timescale. For the cases studied, the results are very insensitive to CO photochemical change calculated along the trajectories. That is, it was found that if CO was treated as a passive tracer, this did not affect the mix-down timescales derived, since the slow CO photochemistry does not have much influence at small spatial scales. The results presented correspond to full photochemical calculations. The method is most appropriate for relatively homogeneous regions, i.e. it is not too important to account for changes in aircraft altitude or the positioning of stratospheric intrusions, so that small scale structure is easily distinguished. The chosen flights showed a range of mix-down time upper limits: a very short timescale of 1 day for 8 August, due possibly to recent convection or model error, 3 days for 3 August, probably due to recent convective and boundary layer mixing, and 6-9 days for 16, 17, 22a, 22c and 24 August. These numbers refer to a mixing spatial scale of 2.8°, defined here by the resolution of the Eulerian grid from which tracer fields were interpolated to initialise the Lagrangian model. For the flight of 3 August, the observed concentrations result from a complex set of transport histories, and the models are used to interpret the observed structure, while illustrating where more caution is required with this method of estimating mix-down lifetimes.
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Robinson, Heather K., and Elizabeth A. Hasenmueller. "Transport of road salt contamination in karst aquifers and soils over multiple timescales." Science of The Total Environment 603-604 (December 2017): 94–108. http://dx.doi.org/10.1016/j.scitotenv.2017.05.244.
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Furbish, David Jon, Siobhan L. Fathel, Mark W. Schmeeckle, Douglas J. Jerolmack, and Rina Schumer. "The elements and richness of particle diffusion during sediment transport at small timescales." Earth Surface Processes and Landforms 42, no. 1 (December 19, 2016): 214–37. http://dx.doi.org/10.1002/esp.4084.
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Berthier, Ludovic, Patrick Charbonneau, Yuliang Jin, Giorgio Parisi, Beatriz Seoane, and Francesco Zamponi. "Growing timescales and lengthscales characterizing vibrations of amorphous solids." Proceedings of the National Academy of Sciences 113, no. 30 (July 8, 2016): 8397–401. http://dx.doi.org/10.1073/pnas.1607730113.
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Low-temperature properties of crystalline solids can be understood using harmonic perturbations around a perfect lattice, as in Debye’s theory. Low-temperature properties of amorphous solids, however, strongly depart from such descriptions, displaying enhanced transport, activated slow dynamics across energy barriers, excess vibrational modes with respect to Debye’s theory (i.e., a boson peak), and complex irreversible responses to small mechanical deformations. These experimental observations indirectly suggest that the dynamics of amorphous solids becomes anomalous at low temperatures. Here, we present direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former. We provide a real-space description of this transition and of the rapidly growing time- and lengthscales that accompany it. Our results provide the seed for a universal understanding of low-temperature glass anomalies within the theoretical framework of the recently discovered Gardner phase transition.
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Sonnewald, M., J. J. M. Hirschi, and R. Marsh. "Oceanic dominance of interannual subtropical North Atlantic heat content variability." Ocean Science Discussions 10, no. 1 (January 10, 2013): 27–53. http://dx.doi.org/10.5194/osd-10-27-2013.
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Abstract. Ocean heat content varies on a range of timescales. Traditionally the atmosphere is seen to dominate the oceanic heat content variability. However, this variability can be driven either by oceanic or atmospheric heat fluxes. To diagnose the relative contributions and respective timescales, this study uses a box model forced with output from an ocean general circulation model (OGCM) to investigate the heat content variability of the upper 800 m of the subtropical North Atlantic from 26° N to 36° N. The ocean and air-sea heat flux data needed to force the box model is taken from a 19 yr (1988 to 2006) simulation performed with the 1/12° version of the OCCAM OGCM. The box model heat content is compared to the corresponding heat content in OCCAM for verification. The main goal of the study is to identify to what extent the seasonal to interannual ocean heat content variability is of atmospheric or oceanic origin. To this end, the box model is subjected to a range of scenarios forced either with the full (detrended) ocean and air-sea fluxes, or their deseasoned counterparts. Results show that in all cases, the seasonal variability is dominated by the seasonal component of the air-sea fluxes, which produce a seasonal range in mean temperature of the upper 800 m of ~ 0.42 °C. However, on longer timescales oceanic heat transport dominates, with changes of up to ~ 0.30 °C over 4 yr. The technique is subsequently applied to observational data. For the ocean heat fluxes, we use data from the RAPID program at 26° N from April 2004 to January 2011. At 36° N heat transport is inferred using a linear regression model based on the oceanic low-frequency transport in OCCAM. The air-sea flux from OCCAM is used for the period 2004 to 2006 when the RAPID timeseries and the OCCAM simulation overlap, and a climatology is used for the air-sea flux from 2006 onwards. The results confirm that on longer (> 2 yr) timescales the ocean dominates the ocean heat content variability, which is further verified using data from the ARGO project. This work illustrates that oceanic divergence significantly impacts the ocean heat content variability on timescales relevant for applications such as seasonal hurricane forecasts.