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1
Gyasi-Agyei, Yeboah. "Evaluation of the effects of temperature changes on fine timescale rainfall." Water Resources Research 49, no. 7 (July 2013): 4379–98. http://dx.doi.org/10.1002/wrcr.20369.
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Mancillas, Brisa, Pierre-Alain Duc, Françoise Combes, Frédéric Bournaud, Eric Emsellem, Marie Martig, and Leo Michel-Dansac. "Probing the merger history of red early-type galaxies with their faint stellar substructures." Astronomy & Astrophysics 632 (December 2019): A122. http://dx.doi.org/10.1051/0004-6361/201936320.
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Several detailed observations, such as those carried out at the Canada-France-Hawaii Telescope (CFHT), have revealed prominent Low Surface Brightness (LSB) fine structures that lead to a change in the apparent morphology of galaxies. Previous photometry surveys have developed observational techniques which make use of the diffuse light detected in the external regions of galaxies. In these studies, the outer perturbations have been identified and classified. These include tidal tails, stellar streams, and shells. These structures serve as tracers for interacting events and merging events and retain some memory of the mass assembly of galaxies. Cosmological numerical simulations are required to estimate their visibility timescale, among other properties, in order to reconstruct the merger history of galaxies. In the present work, we analyze a hydrodynamical cosmological simulation to build up a comprehensive interpretation of the properties of fine structures. We present a census of several types of LSB fine structures compiled using a visual inspection of individual snapshots at various points in time. We reconstruct the evolution of the number of fine structures detected around an early-type galaxy and we compare it with the merger history of the galaxy. We find that most fine structures are associated with major and intermediate mass merger events. Their survival timescale ranges between 0.7 and 4 Gyr. Shells and streams remain visible for a longer time, while tidal tails have a shorter lifetime. These estimates for the survival time of collisional debris provide clues for the interpretation of the shape and frequency of fine structures observed in deep images with regard to their mass assembly. We find that the detectability of stellar streams is most sensitive at the surface brightness limit, demonstrating greater visibility at the deepest surface brightness level used in our simulation. We see between two and three times more streams based on a surface brightness cut of 33 mag arcsec−2 than with 29 mag arcsec−2. We find that the detection of shells is strongly dependent upon the projection angle.
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Barth, Anders, Jelle Hendrix, Daniel Fried, Yoav Barak, Edward A. Bayer, and Don C. Lamb. "Dynamic interactions of type I cohesin modules fine-tune the structure of the cellulosome ofClostridium thermocellum." Proceedings of the National Academy of Sciences 115, no. 48 (November 14, 2018): E11274—E11283. http://dx.doi.org/10.1073/pnas.1809283115.
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Efficient degradation of plant cell walls by selected anaerobic bacteria is performed by large extracellular multienzyme complexes termed cellulosomes. The spatial arrangement within the cellulosome is organized by a protein called scaffoldin, which recruits the cellulolytic subunits through interactions between cohesin modules on the scaffoldin and dockerin modules on the enzymes. Although many structural studies of the individual components of cellulosomal scaffoldins have been performed, the role of interactions between individual cohesin modules and the flexible linker regions between them are still not entirely understood. Here, we report single-molecule measurements using FRET to study the conformational dynamics of a bimodular cohesin segment of the scaffoldin protein CipA ofClostridium thermocellum. We observe compacted structures in solution that persist on the timescale of milliseconds. The compacted conformation is found to be in dynamic equilibrium with an extended state that shows distance fluctuations on the microsecond timescale. Shortening of the intercohesin linker does not destabilize the interactions but reduces the rate of contact formation. Upon addition of dockerin-containing enzymes, an extension of the flexible state is observed, but the cohesin–cohesin interactions persist. Using all-atom molecular-dynamics simulations of the system, we further identify possible intercohesin binding modes. Beyond the view of scaffoldin as “beads on a string,” we propose that cohesin–cohesin interactions are an important factor for the precise spatial arrangement of the enzymatic subunits in the cellulosome that leads to the high catalytic synergy in these assemblies and should be considered when designing cellulosomes for industrial applications.
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Asatrian, Norayr S. "Hour-timescale profile variations in the broad Balmer lines of the Seyfert galaxy Hour-timescale profile variations in the broad Balmer lines of the Seyfert galaxy Markarian 6." Proceedings of the International Astronomical Union 9, S304 (October 2013): 407–8. http://dx.doi.org/10.1017/s1743921314004426.
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AbstractPart of results of the multi-epoch intranight optical spectroscopic monitoring of the Markarian 6 nucleus carried out at the telescopes of 6-m of the Special Astrophysical Observatory (Russia), 2.6-m of the Byurakan Astrophysical Observatory (Armenia) and 2-m of the Tautenburg Observatory (Germany) is presented.Observations were made in 1979, 1986, 1988-1991 and 2007-2009 during a total of 33 nights with an average sampling rate of 4 spectra per night. TV-scanner and long-slit spectrographs equipped with Image Tube and CCD detector arrays were used. Altogether we analyzed 110 Hβ and 58 Hα region spectra to search for intranight variability in the broad hydrogen emission line profiles. The typical spectral resolutions were 4 Å for scanner spectra, 6 Å for photographic spectra, and 5 Å and 10 Å for CCD spectra. The S/N ratio at the continuum level near the Hβ and Hα lines was in the range 15–50.The purpose of the search was to look for the characteristic variability signatures of different kinematical models of the broad emission-line region. We considered the centering and guiding errors which can result in differences between spectra.We found variations in the broad Balmer line difference profiles on time scale of hour with the level of significance of 3.6 σ to 5.0 σ. Variations take the form of narrow, small bumps located at the blue and red sides or only at the blue side of the lines. In the intermediate level of broad line flux, the Hβ and Hα profiles show fine structure. Detected profile changes occurred at the same radial velocity shifts as the details in the fine structure.The variability is at least 2 orders of magnitude more rapid than any observed for broad Balmer line profiles in AGNs that we are aware of in the literature.Discovered extremely rapid line-profile variability may be associated with reverberation effects. Two-sided profile changes may indicate the response of circularly rotating hydrogen clouds in the BLR to a light pulse from a central source. One-sided profile variations may be attributed to a response of a non-disk component: the subarcsec scale region of the jet.
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An, Zhisheng, Ru-Jin Huang, Renyi Zhang, Xuexi Tie, Guohui Li, Junji Cao, Weijian Zhou, et al. "Severe haze in northern China: A synergy of anthropogenic emissions and atmospheric processes." Proceedings of the National Academy of Sciences 116, no. 18 (April 15, 2019): 8657–66. http://dx.doi.org/10.1073/pnas.1900125116.
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Regional severe haze represents an enormous environmental problem in China, influencing air quality, human health, ecosystem, weather, and climate. These extremes are characterized by exceedingly high concentrations of fine particulate matter (smaller than 2.5 µm, or PM2.5) and occur with extensive temporal (on a daily, weekly, to monthly timescale) and spatial (over a million square kilometers) coverage. Although significant advances have been made in field measurements, model simulations, and laboratory experiments for fine PM over recent years, the causes for severe haze formation have not yet to be systematically/comprehensively evaluated. This review provides a synthetic synopsis of recent advances in understanding the fundamental mechanisms of severe haze formation in northern China, focusing on emission sources, chemical formation and transformation, and meteorological and climatic conditions. In particular, we highlight the synergetic effects from the interactions between anthropogenic emissions and atmospheric processes. Current challenges and future research directions to improve the understanding of severe haze pollution as well as plausible regulatory implications on a scientific basis are also discussed.
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Pao, Chih-Wen, Jeng-Lung Chen, Jyh-Fu Lee, Meng-Che Tsai, Chi-Yi Huang, Chao-Chih Chiu, Chao-Yu Chang, Liang-Chih Chiang, and Yu-Shan Huang. "The new X-ray absorption fine-structure beamline with sub-second time resolution at the Taiwan Photon Source." Journal of Synchrotron Radiation 28, no. 3 (March 12, 2021): 930–38. http://dx.doi.org/10.1107/s1600577521001740.
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The new TPS 44A beamline at the Taiwan Photon Source, located at the National Synchrotron Radiation Research Center, is presented. This beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans (s-scans) and on-the-fly scans (q-scans) for X-ray absorption fine-structure (XAFS) spectroscopy experiments, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectral measurements. Ti and Te K-edge XAFS spectra were used to demonstrate the capability of collecting spectra at the limits of the working energy range. The Ni and Cu K-edge XAFS spectra for a Cu-doped Pt/Ni nanocomposite were acquired to test the performance of the newly commissioned beamline. Pt L 3- and Ru K-edge quick-scanning XAFS (QXAFS) spectra for standard Pt and Ru foils, respectively, revealed the stability of the q-scan technique. The results also demonstrated the beamline's ability to collect XAFS spectra on a sub-second timescale. Furthermore, a Zn(s)|Zn2+ (aq)|Cu(s) system was tested to indicate that the states of the Zn electrode could be observed in real time for charging and discharging conditions using an in situ/operando setup combined with QXAFS measurements.
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Fasoli, Benjamin, John C. Lin, David R. Bowling, Logan Mitchell, and Daniel Mendoza. "Simulating atmospheric tracer concentrations for spatially distributed receptors: updates to the Stochastic Time-Inverted Lagrangian Transport model's R interface (STILT-R version 2)." Geoscientific Model Development 11, no. 7 (July 13, 2018): 2813–24. http://dx.doi.org/10.5194/gmd-11-2813-2018.
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Abstract. The Stochastic Time-Inverted Lagrangian Transport (STILT) model is comprised of a compiled Fortran executable that carries out advection and dispersion calculations as well as a higher-level code layer for simulation control and user interaction, written in the open-source data analysis language R. We introduce modifications to the STILT-R code base with the aim to improve the model's applicability to fine-scale (< 1 km) trace gas measurement studies. The changes facilitate placement of spatially distributed receptors and provide high-level methods for single- and multi-node parallelism. We present a kernel density estimator to calculate influence footprints and demonstrate improvements over prior methods. Vertical dilution in the hyper near field is calculated using the Lagrangian decorrelation timescale and vertical turbulence to approximate the effective mixing depth. This framework provides a central source repository to reduce code fragmentation among STILT user groups as well as a systematic, well-documented workflow for users. We apply the modified STILT-R to light-rail measurements in Salt Lake City, Utah, United States, and discuss how results from our analyses can inform future fine-scale measurement approaches and modeling efforts.
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Skyllakou, K., B. N. Murphy, A. G. Megaritis, C. Fountoukis, and S. N. Pandis. "Contributions of local and regional sources to fine PM in the megacity of Paris." Atmospheric Chemistry and Physics Discussions 13, no. 10 (October 8, 2013): 25769–99. http://dx.doi.org/10.5194/acpd-13-25769-2013.
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Abstract. The Particulate Matter Source Apportionment Technology (PSAT) is used together with PMCAMx, a regional chemical transport model, to estimate how local emissions and pollutant transport affect primary and secondary particulate matter mass concentration levels in Paris. During the summer and the winter periods examined, only 13% of the PM2.5 is predicted to be due to local Paris emissions, with 36% coming from mid range (50–500 km from the center of the Paris) sources and 51% from long range transport (more than 500 km from Paris). The local emissions contribution to predicted elemental carbon (EC) is significant, with almost 60% of the EC originating from local sources during both summer and winter. Approximately 50% of the predicted fresh primary organic aerosol (POA) originated from local sources and another 45% from areas 100–500 km from the receptor region during summer. Regional sources dominated the secondary PM components. During summer more than 70% of the predicted sulfate originated from SO2 emitted more than 500 km away from the center of the Paris. Also more than 45% of secondary organic aerosol (SOA) was due to the oxidation of VOC precursors that were emitted 100–500 km from the center of the Paris. The model predicts more contribution from long range secondary PM sources during winter because the timescale for its production is longer due to the slower photochemical activity. PSAT results for contributions of local and regional sources were compared with observation-based estimates from field campaigns that took place during the MEGAPOLI project. PSAT predictions are in general consistent (within 20%) with these estimates for OA and sulfate. The only exception is that PSAT predicts higher local EC contribution during the summer compared to that estimated from observations.
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Skyllakou, K., B. N. Murphy, A. G. Megaritis, C. Fountoukis, and S. N. Pandis. "Contributions of local and regional sources to fine PM in the megacity of Paris." Atmospheric Chemistry and Physics 14, no. 5 (March 6, 2014): 2343–52. http://dx.doi.org/10.5194/acp-14-2343-2014.
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Abstract. The particulate matter source apportionment technology (PSAT) is used together with PMCAMx, a regional chemical transport model, to estimate how local emissions and pollutant transport affect primary and secondary particulate matter mass concentration levels in Paris. During the summer and the winter periods examined, only 13% of the PM2.5 is predicted to be due to local Paris emissions, with 36% coming from mid-range (50–500 km from the center of the Paris) sources and 51% from long range transport (more than 500 km from Paris). The local emissions contribution to simulated elemental carbon (EC) is significant, with almost 60% of the EC originating from local sources during both summer and winter. Approximately 50% of the simulated fresh primary organic aerosol (POA) originated from local sources and another 45% from areas 100–500 km from the receptor region during summer. Regional sources dominated the secondary PM components. During summer more than 70% of the simulated sulfate originated from SO2 emitted more than 500 km away from the center of the Paris. Also more than 45% of secondary organic aerosol (SOA) was due to the oxidation of VOC precursors that were emitted 100–500 km from the center of the Paris. The model simulates more contribution from long range secondary PM sources during winter because the timescale for its production is longer due to the slower photochemical activity. PSAT results for contributions of local and regional sources were compared with observation-based estimates from field campaigns that took place during the MEGAPOLI project. PSAT simulations are in general consistent (within 20%) with these estimates for OA and sulfate. The only exception is that PSAT simulates higher local EC contribution during the summer compared to that estimated from observations.
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Sandora, McCullen. "Multiverse Predictions for Habitability: The Number of Stars and Their Properties." Universe 5, no. 6 (June 13, 2019): 149. http://dx.doi.org/10.3390/universe5060149.
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In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, any of which could falsify the multiverse scenario.
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Neppl, Stefan, Johannes Mahl, Anton S. Tremsin, Bruce Rude, Ruimin Qiao, Wanli Yang, Jinghua Guo, and Oliver Gessner. "Towards efficient time-resolved X-ray absorption studies of electron dynamics at photocatalytic interfaces." Faraday Discussions 194 (2016): 659–82. http://dx.doi.org/10.1039/c6fd00125d.
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We present a picosecond time-resolved X-ray absorption spectroscopy (tr-XAS) setup designed for synchrotron-based studies of interfacial photochemical dynamics. The apparatus combines a high power, variable repetition rate picosecond laser system with a time-resolved X-ray fluorescence yield detection technique. Time-tagging of the detected fluorescence signals enables the parallel acquisition of X-ray absorption spectra at a variety of pump–probe delays employing the well-defined time structure of the X-ray pulse trains. The viability of the setup is demonstrated by resolving dynamic changes in the fine structure near the O1s X-ray absorption edge of cuprous oxide (Cu2O) after photo-excitation with a 355 nm laser pulse. Two distinct responses are detected. A pronounced, quasi-static, reversible change of the Cu2O O1s X-ray absorption spectrum by up to ∼30% compared to its static line shape corresponds to a redshift of the absorption edge by ∼1 eV. This value is small compared to the 2.2 eV band gap of Cu2O but in agreement with previously published results. The lifetime of this effect exceeds the laser pulse-to-pulse period of 8 μs, resulting in a quasi-static spectral change that persists as long as the sample is exposed to the laser light, and completely vanishes once the laser is blocked. Additionally, a short-lived response corresponding to a laser-induced shift of the main absorption line by ∼2 eV to lower energies appears within <200 ps and decays with a characteristic timescale of 43 ± 5 ns. Both the picosecond rise and nanosecond decay of this X-ray response are simultaneously captured by making use of a time-tagging approach – highlighting the prospects of the experimental setup for efficient probing of the electronic and structural dynamics in photocatalytic systems on multiple timescales.
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Metman, Maurits C., Philip W. Livermore, Jonathan E. Mound, and Ciarán D. Beggan. "Modelling decadal secular variation with only magnetic diffusion." Geophysical Journal International 219, Supplement_1 (February 17, 2019): S58—S82. http://dx.doi.org/10.1093/gji/ggz089.
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SUMMARY Secular variation (SV) of Earth’s internal magnetic field is the sum of two contributions, one resulting from core fluid flow and the other from magnetic diffusion. Based on the millenial diffusive timescale of global-scale structures, magnetic diffusion is widely perceived to be too weak to significantly contribute to decadal SV, and indeed is entirely neglected in the commonly adopted end-member of frozen-flux. Such an argument however lacks consideration of radially fine-scaled magnetic structures in the outermost part of the liquid core, whose diffusive timescale is much shorter. Here we consider the opposite end-member model to frozen flux, that of purely diffusive evolution associated with the total absence of fluid flow. Our work is based on a variational formulation, where we seek an optimized full-sphere initial magnetic field structure whose diffusive evolution best fits, over various time windows, a time-dependent magnetic field model. We present models that are regularized based on their magnetic energy, and consider how well they can fit the COV-OBS.x1 ensemble mean using a global error bound based on the standard deviation of the ensemble. With these regularized models, over time periods of up to 30 yr, it is possible to fit COV-OBS.x1 within one standard deviation at all times. For time windows up to 102 yr we show that our models can fit COV-OBS.x1 when adopting a time-averaged global uncertainty. Our modelling is sensitive only to magnetic structures in approximately the top 10 per cent of the liquid core, and show an increased surface area of reversed flux at depth. The diffusive models recover fundamental characteristics of field evolution including the historical westward drift, the recent acceleration of the North Magnetic Pole and reversed-flux emergence. Based on a global time-averaged residual, our diffusive models fit the evolution of the geomagnetic field comparably, and sometimes better than, frozen-flux models within short time windows.
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Morrison, Sara E., Vincent B. McGinty, Johann du Hoffmann, and Saleem M. Nicola. "Limbic-motor integration by neural excitations and inhibitions in the nucleus accumbens." Journal of Neurophysiology 118, no. 5 (November 1, 2017): 2549–67. http://dx.doi.org/10.1152/jn.00465.2017.
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The nucleus accumbens (NAc) has often been described as a “limbic-motor interface,” implying that the NAc integrates the value of expected rewards with the motor planning required to obtain them. However, there is little direct evidence that the signaling of individual NAc neurons combines information about predicted reward and behavioral response. We report that cue-evoked neural responses in the NAc form a likely physiological substrate for its limbic-motor integration function. Across task contexts, individual NAc neurons in behaving rats robustly encode the reward-predictive qualities of a cue, as well as the probability of behavioral response to the cue, as coexisting components of the neural signal. In addition, cue-evoked activity encodes spatial and locomotor aspects of the behavioral response, including proximity to a reward-associated target and the latency and speed of approach to the target. Notably, there are important limits to the ability of NAc neurons to integrate motivational information into behavior: in particular, updating of predicted reward value appears to occur on a relatively long timescale, since NAc neurons fail to discriminate between cues with reward associations that change frequently. Overall, these findings suggest that NAc cue-evoked signals, including inhibition of firing (as noted here for the first time), provide a mechanism for linking reward prediction and other motivationally relevant factors, such as spatial proximity, to the probability and vigor of a reward-seeking behavioral response. NEW & NOTEWORTHY The nucleus accumbens (NAc) is thought to link expected rewards and action planning, but evidence for this idea remains sparse. We show that, across contexts, both excitatory and inhibitory cue-evoked activity in the NAc jointly encode reward prediction and probability of behavioral responding to the cue, as well as spatial and locomotor properties of the response. Interestingly, although spatial information in the NAc is updated quickly, fine-grained updating of reward value occurs over a longer timescale.
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Omukai, K., R. Nishi, H. Uehara, and H. Susa. "Evolution of Primordial Protostellar Clouds." Symposium - International Astronomical Union 183 (1999): 161. http://dx.doi.org/10.1017/s0074180900132413.
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The formation of stars in proto-galactic clouds can be viewed as two step processes i.e. the fragmentation of proto-galactic clouds and evolution of these fragments into stars. We consider here the latter process, the contraction of protosteller clouds (∼ 1M⊙) which consist of primordial gas. We investigate cooling processes by calculating the radiative transfer of H2 rotational/vibrational lines. We consider clouds in hydrostatic equilibrium as initial conditions. Comparing two timescales, the freefall time and the timescale of quasi-static contraction (∼ tcool, the cooling time) of these clouds, we find that as the clouds contract, the ratio of two timescales tff/tqsc, i.e. the efficiency of cooling, becomes larger even under the existence of cold and opaque envelope. Especially for the fragments of primordial filamentary clouds (tff ∼ tqsc initially), they collapse dynamically in the freefall timescale. This efficiency of cooling is utterly peculiar to the line cooling.
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Moni, C., D. Derrien, P. J. Hatton, B. Zeller, and M. Kleber. "Density fractions versus size separates: does physical fractionation isolate functional soil compartments?" Biogeosciences 9, no. 12 (December 17, 2012): 5181–97. http://dx.doi.org/10.5194/bg-9-5181-2012.
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Abstract. Physical fractionation is a widely used methodology to study soil organic matter (SOM) dynamics, but concerns have been raised that the available fractionation methods do not well describe functional SOM pools. In this study we explore whether physical fractionation techniques isolate soil compartments in a meaningful and functionally relevant way for the investigation of litter-derived nitrogen dynamics at the decadal timescale. We do so by performing aggregate density fractionation (ADF) and particle size-density fractionation (PSDF) on mineral soil samples from two European beech forests a decade after application of 15N labelled litter. Both density and size-based fractionation methods suggested that litter-derived nitrogen became increasingly associated with the mineral phase as decomposition progressed, within aggregates and onto mineral surfaces. However, scientists investigating specific aspects of litter-derived nitrogen dynamics are pointed towards ADF when adsorption and aggregation processes are of interest, whereas PSDF is the superior tool to research the fate of particulate organic matter (POM). Some methodological caveats were observed mainly for the PSDF procedure, the most important one being that fine fractions isolated after sonication can not be linked to any defined decomposition pathway or protective mechanism. This also implies that historical assumptions about the "adsorbed" state of carbon associated with fine fractions need to be re-evaluated. Finally, this work demonstrates that establishing a comprehensive picture of whole soil OM dynamics requires a combination of both methodologies and we offer a suggestion for an efficient combination of the density and size-based approaches.
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Münch, Thomas, and Thomas Laepple. "What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?" Climate of the Past 14, no. 12 (December 20, 2018): 2053–70. http://dx.doi.org/10.5194/cp-14-2053-2018.
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Abstract. Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of climate and non-climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, we find an increase in the SNR by nearly 1 order of magnitude (∼0.2 at decadal and ∼1.0 at multi-centennial scales). The estimated spectrum of climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent climate variations, which is applicable to a large set of palaeoclimate records.
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Meru, Farzana, and Matthew R. Bate. "Non-convergence of the critical cooling timescale for fragmentation of self-gravitating discs." Proceedings of the International Astronomical Union 6, S276 (October 2010): 438–40. http://dx.doi.org/10.1017/s1743921311020709.
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AbstractWe carry out a resolution study on the fragmentation boundary of self-gravitating discs. We perform three-dimensional Smoothed Particle Hydrodynamics (SPH) simulations of discs to determine whether the critical value of the cooling timescale in units of the orbital timescale, βcrit, converges with increasing resolution. Using particle numbers ranging from 31,250 to 16 million (the highest resolution simulations to date) we do not find convergence. Instead, fragmentation occurs for longer cooling timescales as the resolution is increased. These results certainly suggest that βcrit is larger than previously thought. However, the absence of convergence also questions whether or not a critical value exists. In light of these results, we caution against using cooling timescale or gravitational stress arguments to deduce whether gravitational instability may or may not have been the formation mechanism for observed planetary systems.
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Stephens, Greg J., Christopher J. Honey, and Uri Hasson. "A place for time: the spatiotemporal structure of neural dynamics during natural audition." Journal of Neurophysiology 110, no. 9 (November 1, 2013): 2019–26. http://dx.doi.org/10.1152/jn.00268.2013.
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We use functional magnetic resonance imaging (fMRI) to analyze neural responses to natural auditory stimuli. We characterize the fMRI time series through the shape of the voxel power spectrum and find that the timescales of neural dynamics vary along a spatial gradient, with faster dynamics in early auditory cortex and slower dynamics in higher order brain regions. The timescale gradient is observed through the unsupervised clustering of the power spectra of individual brains, both in the presence and absence of a stimulus, and is enhanced in the stimulus-locked component that is shared across listeners. Moreover, intrinsically faster dynamics occur in areas that respond preferentially to momentary stimulus features, while the intrinsically slower dynamics occur in areas that integrate stimulus information over longer timescales. These observations connect the timescales of intrinsic neural dynamics to the timescales of information processing, suggesting a temporal organizing principle for neural computation across the cerebral cortex.
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CUSTÓDIO, P. S., and J. E. HORVATH. "COSMOLOGICAL QUINTESSENCE ACCRETION ONTO PRIMORDIAL BLACK HOLES: CONDITIONS FOR THEIR GROWTH TO THE SUPERMASSIVE SCALE." International Journal of Modern Physics D 14, no. 02 (February 2005): 257–73. http://dx.doi.org/10.1142/s0218271805006043.
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In this work we revisit the growth of small primordial black holes (PBHs) immersed in a quintessential field and/or radiation to the supermassive black hole (SMBHs) scale. We show the difficulties of scenarios in which such huge growth is possible. For that purpose we evaluated analytical solutions of the differential equations (describing mass evolution) and point out the strong fine tuning for the conclusions. The timescale for growth in a model with a constant quintessence flux is calculated and we show that it is much bigger than the Hubble time. The fractional gain of the mass is further evaluated in other forms, including quintessence and/or radiation. We calculate the cosmological density Ω due to quintessence necessary to grow BHs to the supermassive range and show it to be much bigger than one. We also describe the set of complete equations analyzing the evolution of the BH + quintessence universe, showing some interesting effects such the quenching of the BH mass growth due to the evolution of the background energy. Additional constraints obtained by using the Holographic Bound are also described. The general equilibrium conditions for evaporating/accreting black holes evolving in a quintessence/radiation universe are discussed in Appendix.
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Helinski, Matthew, Martin Fahey, and Andy Fourie. "Coupled two-dimensional finite element modelling of mine backfilling with cemented tailings." Canadian Geotechnical Journal 47, no. 11 (November 2010): 1187–200. http://dx.doi.org/10.1139/t10-020.
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Mine backfilling is a process whereby mine tailings mixed with small amounts of cement are placed hydraulically into mined-out voids (“stopes”) to stabilize the rockmass and allow full extraction of adjacent ore. A containment barricade is constructed to block the access point at the base of the stope, the design of which requires calculation of the total stress on the barricade during and following filling. For fine-grained backfill containing cement, the rate of development of stresses is governed by the rates of filling, consolidation, and cement hydration, each with its own timescale. As “consolidation” in backfill undergoing hydration can be dominated by “self-desiccation”, this mechanism must also be incorporated. Interaction between the backfill and the stope walls (“arching”) also has an influence. The paper describes a finite element (FE) model (“Minefill-2D”) that can model these interactions, although only in a two-dimensional (plane–strain or axisymmetric) fashion. It is shown that arching significantly influences the total stress distribution in a typical stope during filling, but only if and when effective stress develops. For cemented backfill, arching sometimes does not fully mobilize the cement bond strength, so that assessment of arching using traditional limit equilibrium methods is often not appropriate.
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Chatterjee, Tapan K. "Nuclear Activity in Interacting Galaxies." Symposium - International Astronomical Union 159 (1994): 499. http://dx.doi.org/10.1017/s0074180900176727.
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Dynamical studies of galactic collisions, conducted previously (Chatterjee, 1992, 1993a, b), indicated that most of the mergers take place in two to three shrinking orbital periods. We extend this line of research work to study induced nuclear activity. We study the binary evolution of a spiral galaxy perturbed by a compact elliptical galaxy of comparable mass and find that each time the perturber penetrates the disk of the spiral, the disk is subjected to an appropriate perturbation, causing inflow of gas towards its nucleus due to loss of angular momentum; there it could activate an inert black hole (consistent with previous studies; e.g. Naguchi, 1988). However a new feature that we find is that repeated episodes of disk penetration by the perturber occur in gradually shorter timescales, causing an overlap of the activity timescale and the dynamical timescale. In fact if the elliptical is very compact and the spiral has a massive bulge, subsequent dynamical timescales reduce by more than an order of magnitude. This periodic increase in the activity of the nucleus is of a secular nature (in contrast to a reactivation process), and could lead to the evolution of the spiral along the following lines, Starburst → Seyfert 2 → Seyfert 1, as interpenetrations follow.
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Wang, Y., M. Notaro, Z. Liu, R. Gallimore, S. Levis, and J. E. Kutzbach. "Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models." Climate of the Past Discussions 3, no. 4 (July 25, 2007): 961–75. http://dx.doi.org/10.5194/cpd-3-961-2007.
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Abstract. Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte-Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.
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Wang, Y., M. Notaro, Z. Liu, R. Gallimore, S. Levis, and J. E. Kutzbach. "Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models." Climate of the Past 4, no. 1 (March 31, 2008): 59–67. http://dx.doi.org/10.5194/cp-4-59-2008.
Full textAbstract:
Abstract. Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte-Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.
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Konijnendijk, T. Y. M., S. L. Weber, E. Tuenter, and M. van Weele. "Methane variations on orbital timescales: a transient modeling experiment." Climate of the Past Discussions 7, no. 1 (January 6, 2011): 47–77. http://dx.doi.org/10.5194/cpd-7-47-2011.
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Abstract. Methane (CH4) variations on orbital timescales are often associated with variations in wetland coverage, most notably in the summer monsoon areas of the Northern Hemisphere. Here we test this assumption by simulating orbitally forced variations in global wetland emissions, using a simple wetland distribution and CH4 emissions model that was coupled off-line to a climate model containing atmosphere, ocean and vegetation components. The transient climate modeling simulation extends over the last 650 000 yrs and includes variations in land-ice distribution and greenhouse gases. Tropical temperature and global vegetation are found to be the dominant controls for global CH4 emissions and thus atmospheric concentrations. The relative importance of wetland coverage, vegetation coverage, and emission temperatures depends on the specific climatic zone (boreal, tropics and Indian/Asian monsoon area) and timescale (precession, obliquity and glacial-interglacial timescales). Simulated variations in emissions agree well with those in measured concentrations, both in their time series and spectra. The simulated lags with respect to the orbital forcing also show close agreement with those found in measured data, both on the precession and obliquity timescale. We only find covariance between monsoon precipitation and CH4 concentrations, however we find causal links between atmospheric concentrations and tropical temperatures and global vegetation. The primary importance of these two factors explains the lags found in the CH4 record from ice cores.
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Du, Andrew, Andrew M. Zipkin, Kevin G. Hatala, Elizabeth Renner, Jennifer L. Baker, Serena Bianchi, Kallista H. Bernal, and Bernard A. Wood. "Pattern and process in hominin brain size evolution are scale-dependent." Proceedings of the Royal Society B: Biological Sciences 285, no. 1873 (February 21, 2018): 20172738. http://dx.doi.org/10.1098/rspb.2017.2738.
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A large brain is a defining feature of modern humans, yet there is no consensus regarding the patterns, rates and processes involved in hominin brain size evolution. We use a reliable proxy for brain size in fossils, endocranial volume (ECV), to better understand how brain size evolved at both clade- and lineage-level scales. For the hominin clade overall, the dominant signal is consistent with a gradual increase in brain size. This gradual trend appears to have been generated primarily by processes operating within hypothesized lineages—64% or 88% depending on whether one uses a more or less speciose taxonomy, respectively. These processes were supplemented by the appearance in the fossil record of larger-brained Homo species and the subsequent disappearance of smaller-brained Australopithecus and Paranthropus taxa. When the estimated rate of within-lineage ECV increase is compared to an exponential model that operationalizes generation-scale evolutionary processes, it suggests that the observed data were the result of episodes of directional selection interspersed with periods of stasis and/or drift; all of this occurs on too fine a timescale to be resolved by the current human fossil record, thus producing apparent gradual trends within lineages. Our findings provide a quantitative basis for developing and testing scale-explicit hypotheses about the factors that led brain size to increase during hominin evolution.
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Cong, Linxiao, Jianchao Mu, Qian Liu, Hao Wang, Linlin Wang, Yonggui Li, and Congfeng Qiao. "Thermal Noise Decoupling of Micro-Newton Thrust Measured in a Torsion Balance." Symmetry 13, no. 8 (July 27, 2021): 1357. http://dx.doi.org/10.3390/sym13081357.
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The space gravitational wave detection and drag free control requires the micro-thruster to have ultra-low thrust noise within 0.1 mHz–0.1 Hz, which brings a great challenge to calibration on the ground because it is impossible to shield any spurious couplings due to the asymmetry of torsion balance. Most thrusters dissipate heat during the test, making the rotation axis tilt and components undergo thermal drift, which is hysteretic and asymmetric for micro-Newton thrust measurement. With reference to LISA’s research and coming up with ideas inspired from proportional-integral-derivative (PID) control and multi-timescale (MTS), this paper proposes to expand the state space of temperature to be applied on the thrust prediction based on fine tree regression (FTR) and to subtract the thermal noise filtered by transfer function fitted with z-domain vector fitting (ZDVF). The results show that thrust variation of diurnal asymmetry in temperature is decoupled from 24 μN/Hz1/2 to 4.9 μN/Hz1/2 at 0.11 mHz. Additionally, 1 μN square wave modulation of electrostatic force is extracted from the ambiguous thermal drift background of positive temperature coefficient (PTC) heater. The PID-FTR validation is performed with experimental data in thermal noise decoupling, which can guide the design of thermal control and be extended to other physical quantities for noise decoupling.
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Lystrup, M. B., S. Miller, T. Stallard, C. G. A. Smith, and A. Aylward. "Variability of Jovian ion winds: an upper limit for enhanced Joule heating." Annales Geophysicae 25, no. 4 (May 8, 2007): 847–53. http://dx.doi.org/10.5194/angeo-25-847-2007.
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Abstract. It has been proposed that short-timescale fluctuations about the mean electric field can significantly increase the upper atmospheric energy inputs at Jupiter, which may help to explain the high observed thermospheric temperatures. We present data from the first attempt to detect such variations in the Jovian ionosphere. Line-of-sight ionospheric velocity profiles in the Southern Jovian auroral/polar region are shown, derived from the Doppler shifting of H3+ infrared emission spectra. These data were recently obtained from the high-resolution CSHELL spectrometer at the NASA Infrared Telescope Facility. We find that there is no variability within this data set on timescales of the order of one minute and spatial scales of 640 km, putting upper limits on the timescales of fluctuations that would be needed to enhance Joule heating.
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Steiger, Nathan, and Gregory Hakim. "Multi-timescale data assimilation for atmosphere–ocean state estimates." Climate of the Past 12, no. 6 (June 24, 2016): 1375–88. http://dx.doi.org/10.5194/cp-12-1375-2016.
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Abstract. Paleoclimate proxy data span seasonal to millennial timescales, and Earth's climate system has both high- and low-frequency components. Yet it is currently unclear how best to incorporate multiple timescales of proxy data into a single reconstruction framework and to also capture both high- and low-frequency components of reconstructed variables. Here we present a data assimilation approach that can explicitly incorporate proxy data at arbitrary timescales. The principal advantage of using such an approach is that it allows much more proxy data to inform a climate reconstruction, though there can be additional benefits. Through a series of offline data-assimilation-based pseudoproxy experiments, we find that atmosphere–ocean states are most skillfully reconstructed by incorporating proxies across multiple timescales compared to using proxies at short (annual) or long (∼ decadal) timescales alone. Additionally, reconstructions that incorporate long-timescale pseudoproxies improve the low-frequency components of the reconstructions relative to using only high-resolution pseudoproxies. We argue that this is because time averaging high-resolution observations improves their covariance relationship with the slowly varying components of the coupled-climate system, which the data assimilation algorithm can exploit. These results are consistent across the climate models considered, despite the model variables having very different spectral characteristics. Our results also suggest that it may be possible to reconstruct features of the oceanic meridional overturning circulation based on atmospheric surface temperature proxies, though here we find such reconstructions lack spectral power over a broad range of frequencies.
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Schepper, Rob, Rafael Almar, Erwin Bergsma, Sierd de Vries, Ad Reniers, Mark Davidson, and Kristen Splinter. "Modelling Cross-Shore Shoreline Change on Multiple Timescales and Their Interactions." Journal of Marine Science and Engineering 9, no. 6 (May 27, 2021): 582. http://dx.doi.org/10.3390/jmse9060582.
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In this paper, a new approach to model wave-driven, cross-shore shoreline change incorporating multiple timescales is introduced. As a base, we use the equilibrium shoreline prediction model ShoreFor that accounts for a single timescale only. High-resolution shoreline data collected at three distinctly different study sites is used to train the new data-driven model. In addition to the direct forcing approach used in most models, here two additional terms are introduced: a time-upscaling and a time-downscaling term. The upscaling term accounts for the persistent effect of short-term events, such as storms, on the shoreline position. The downscaling term accounts for the effect of long-term shoreline modulations, caused by, for example, climate variability, on shorter event impacts. The multi-timescale model shows improvement compared to the original ShoreFor model (a normalized mean square error improvement during validation of 18 to 59%) at the three contrasted sandy beaches. Moreover, it gains insight in the various timescales (storms to inter-annual) and reveals their interactions that cause shoreline change. We find that extreme forcing events have a persistent shoreline impact and cause 57–73% of the shoreline variability at the three sites. Moreover, long-term shoreline trends affect short-term forcing event impacts and determine 20–27% of the shoreline variability.
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Adams, Keith L. "Insights into the evolution of duplicate gene expression in polyploids from GossypiumThis paper is one of a selection of papers published in the Special Issue on Systematics Research." Botany 86, no. 8 (August 2008): 827–34. http://dx.doi.org/10.1139/b08-042.
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Polyploidy is a prominent mechanism of speciation in plants that can lead to novel phenotypes. Polyploidy is characterized by novel genetic and genomic consequences that provide raw material for morphological evolution. Polyploids often exhibit changes in genome organization and gene expression compared with their diploid progenitors. The five allopolyploid cotton (Gossypium) species and newly created cotton neopolyploids have been developed as a useful group for studies of duplicated gene expression in polyploids. Here I review recent studies on the evolution of duplicate gene expression in polyploid cotton. In addition I present new expression data from cotton neopolyploids that address the effects on expression of adding a third genome in an allohexaploid, and that provide insights into fine scale organ-specific silencing. Substantial changes in gene expression have occurred in homoeologous genes (gene pairs duplicated by polyploidy), including organ-specific gene silencing and subfunctionalization. Many of the changes in gene expression have occurred on an evolutionary timescale, whereas others occur immediately after genome merger and within a few generations. Abiotic stress can affect the expression of homoeologous gene expression, causing expression partitioning between homoeologs. To examine the effects of interspecific hybridization, without chromosome doubling, on gene expression, interspecific hybrids have been studied. Extensive variation in allelic expression was observed upon hybridization that varied by gene, organ, and genotype. Several hypotheses have been proposed for why gene expression is altered in allopolyploids and interspecific hybrids.
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Zamani Esfahlani, Farnaz, Youngheun Jo, Joshua Faskowitz, Lisa Byrge, Daniel P. Kennedy, Olaf Sporns, and Richard F. Betzel. "High-amplitude cofluctuations in cortical activity drive functional connectivity." Proceedings of the National Academy of Sciences 117, no. 45 (October 22, 2020): 28393–401. http://dx.doi.org/10.1073/pnas.2005531117.
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Resting-state functional connectivity is used throughout neuroscience to study brain organization and to generate biomarkers of development, disease, and cognition. The processes that give rise to correlated activity are, however, poorly understood. Here we decompose resting-state functional connectivity using a temporal unwrapping procedure to assess the contributions of moment-to-moment activity cofluctuations to the overall connectivity pattern. This approach temporally resolves functional connectivity at a timescale of single frames, which enables us to make direct comparisons of cofluctuations of network organization with fluctuations in the blood oxygen level-dependent (BOLD) time series. We show that surprisingly, only a small fraction of frames exhibiting the strongest cofluctuation amplitude are required to explain a significant fraction of variance in the overall pattern of connection weights as well as the network’s modular structure. These frames coincide with frames of high BOLD activity amplitude, corresponding to activity patterns that are remarkably consistent across individuals and identify fluctuations in default mode and control network activity as the primary driver of resting-state functional connectivity. Finally, we demonstrate that cofluctuation amplitude synchronizes across subjects during movie watching and that high-amplitude frames carry detailed information about individual subjects (whereas low-amplitude frames carry little). Our approach reveals fine-scale temporal structure of resting-state functional connectivity and discloses that frame-wise contributions vary across time. These observations illuminate the relation of brain activity to functional connectivity and open a number of directions for future research.
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Goodwin, Philip, and B. B. Cael. "Bayesian estimation of Earth's climate sensitivity and transient climate response from observational warming and heat content datasets." Earth System Dynamics 12, no. 2 (June 17, 2021): 709–23. http://dx.doi.org/10.5194/esd-12-709-2021.
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Abstract. Future climate change projections, impacts, and mitigation targets are directly affected by how sensitive Earth's global mean surface temperature is to anthropogenic forcing, expressed via the climate sensitivity (S) and transient climate response (TCR). However, the S and TCR are poorly constrained, in part because historic observations and future climate projections consider the climate system under different response timescales with potentially different climate feedback strengths. Here, we evaluate S and TCR by using historic observations of surface warming, available since the mid-19th century, and ocean heat uptake, available since the mid-20th century, to constrain a model with independent climate feedback components acting over multiple response timescales. Adopting a Bayesian approach, our prior uses a constrained distribution for the instantaneous Planck feedback combined with wide-ranging uniform distributions of the strengths of the fast feedbacks (acting over several days) and multi-decadal feedbacks. We extract posterior distributions by applying likelihood functions derived from different combinations of observational datasets. The resulting TCR distributions when using two preferred combinations of historic datasets both find a TCR of 1.5 (1.3 to 1.8 at 5–95 % range) ∘C. We find the posterior probability distribution for S for our preferred dataset combination evolves from S of 2.0 (1.6 to 2.5) ∘C on a 20-year response timescale to S of 2.3 (1.4 to 6.4) ∘C on a 140-year response timescale, due to the impact of multi-decadal feedbacks. Our results demonstrate how multi-decadal feedbacks allow a significantly higher upper bound on S than historic observations are otherwise consistent with.
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Konijnendijk, T. Y. M., S. L. Weber, E. Tuenter, and M. van Weele. "Methane variations on orbital timescales: a transient modeling experiment." Climate of the Past 7, no. 2 (June 17, 2011): 635–48. http://dx.doi.org/10.5194/cp-7-635-2011.
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Abstract. Methane (CH4) variations on orbital timescales are often associated with variations in wetland coverage, most notably in the summer monsoon areas of the Northern Hemisphere. Here we test this assumption by simulating orbitally forced variations in global wetland emissions, using a simple wetland distribution and CH4 emissions model that has been run on the output of a climate model (CLIMBER-2) containing atmosphere, ocean and vegetation components. The transient climate modeling simulation extends over the last 650 000 yr and includes variations in land-ice distribution and greenhouse gases. Tropical temperature and global vegetation are found to be the dominant controls for global CH4 emissions and therefore atmospheric concentrations. The relative importance of wetland coverage, vegetation coverage, and emission temperatures depends on the specific climatic zone (boreal, tropics and Indian/Asian monsoon area) and timescale (precession, obliquity and glacial-interglacial timescales). Despite the low spatial resolution of the climate model and crude parameterizations for methane production and release, simulated variations in CH4 emissions agree well with those in measured concentrations, both in their time series and spectra. The simulated lags between emissions and orbital forcing also show close agreement with those found in measured data, both on the precession and obliquity timescale. We find causal links between atmospheric CH4 concentrations and tropical temperatures and global vegetation, but only covariance between monsoon precipitation and CH4 concentrations. The primary importance of the first two factors explains the lags found in the CH4 record from ice cores. Simulation of the dynamical vegetation response to climate variation on orbital timescales would be needed to reduce the uncertainty in these preliminary attributions.
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Chandan, Deepak, and W. Richard Peltier. "On the mechanisms of warming the mid-Pliocene and the inference of a hierarchy of climate sensitivities with relevance to the understanding of climate futures." Climate of the Past 14, no. 6 (June 18, 2018): 825–56. http://dx.doi.org/10.5194/cp-14-825-2018.
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Abstract. We present results from our investigation into the physical mechanisms through which the mid-Pliocene, with a pCO2 of only ∼ 400 ppmv, could have supported the same magnitude of global warmth as has been projected for the climate at the end of the 21st century when pCO2 is expected to be 3 times higher. These mechanisms allow us to understand the warming in terms of changes to the radiative properties of the surface, the clouds, greenhouse gases, and changes to the meridional heat transport. We find that two-thirds of the warming pervasive during the mid-Pliocene, compared to the preindustrial, could be attributed to the reduction in the planetary emissivity owing to the higher concentrations of the greenhouse gases CO2 and water vapor, and the remaining one-third to the reduction in planetary albedo. We also find that changes to the orography and the pCO2 are the leading causes of the warming with each contributing in roughly equal parts to a total of 87 % of the warming and changes to the polar ice sheets responsible for the remaining warming. Furthermore, we provide a mid-Pliocene perspective on ongoing efforts to understand the climate system's sensitivity at various timescales and using multiple lines of evidence. The similarities in the boundary conditions between the mid-Pliocene and the present day, together with the globally elevated temperatures, make the mid-Pliocene an ideal paleo time period from which to derive inferences of climate sensitivity and assess the impacts of various timescale-dependent feedback processes. We assess a hierarchy of climate sensitivities of increasing complexity in order to explore the response of the climate over a very large range of timescales. The picture that emerges is as follows: on the short timescale, owing to the influence of fast feedback processes, the climate sensitivity is 3.25 °C per doubling of CO2; sensitivity increases to 4.16 °C per doubling of CO2 on an intermediate timescale as the ice–albedo feedback becomes active, and then sensitivity further increases to 7.0 °C per doubling of CO2 on long timescales due to the feedback from the glacial isostatic adjustment of the Earth's surface in response to the melting of the polar ice sheets. Finally, once the slow feedbacks have stabilized, the sensitivity of the system drops to 3.35 °C per doubling of CO2. Our inference of the intermediate-timescale climate sensitivity suggests that the projected warming by 2300 CE, inferred using Earth system models of intermediate complexity on the basis of an extension to the RCP4.5 emission scenario in which atmospheric pCO2 stabilizes at roughly twice the PI level in year 2150 CE, could be underestimated by ∼ 1 °C due to the absence of ice-sheet-based feedbacks in those models.
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Neish, C. D., R. D. Lorenz, and D. P. O'Brien. "The potential for prebiotic chemistry in the possible cryovolcanic dome Ganesa Macula on Titan." International Journal of Astrobiology 5, no. 1 (January 2006): 57–65. http://dx.doi.org/10.1017/s1473550406002898.
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New observations of Titan by the Cassini spacecraft suggest the presence of cryovolcanism on the surface. Cryovolcanism has important astrobiological implications, as it provides a means of exposing Titan's organics to liquid water, transforming hydrocarbons and nitriles into more evolved and oxidized prebiotic species. One possible cryovolcano – the 180 km structure Ganesa Macula – resembles the pancake domes seen on Venus by the Magellan spacecraft. To assess the potential of Ganesa Macula for prebiotic chemistry, we estimate its height using radarclinometry and other methods, and calculate the freezing timescale assuming an initially completely liquid dome. Given height constraints of ~200 m to 4 km, we find that liquid water or water–ammonia environments could be sustained in Ganesa Macula for timescales of the order of 102–105 years. These timescales open a window for prebiotic chemistry far wider than can be explored in terrestrial laboratory experiments.
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Smith, Matthew A., Xiaoxuan Jia, Amin Zandvakili, and Adam Kohn. "Laminar dependence of neuronal correlations in visual cortex." Journal of Neurophysiology 109, no. 4 (February 15, 2013): 940–47. http://dx.doi.org/10.1152/jn.00846.2012.
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Neuronal responses are correlated on a range of timescales. Correlations can affect population coding and may play an important role in cortical function. Correlations are known to depend on stimulus drive, behavioral context, and experience, but the mechanisms that determine their properties are poorly understood. Here we make use of the laminar organization of cortex, with its variations in sources of input, local circuit architecture, and neuronal properties, to test whether networks engaged in similar functions but with distinct properties generate different patterns of correlation. We find that slow timescale correlations are prominent in the superficial and deep layers of primary visual cortex (V1) of macaque monkeys, but near zero in the middle layers. Brief timescale correlation (synchrony), on the other hand, was slightly stronger in the middle layers of V1, although evident at most cortical depths. Laminar variations were also apparent in the power of the local field potential, with a complementary pattern for low frequency (<10 Hz) and gamma (30–50 Hz) power. Recordings in area V2 revealed a laminar dependence similar to V1 for synchrony, but slow timescale correlations were not different between the input layers and nearby locations. Our results reveal that cortical circuits in different laminae can generate remarkably different patterns of correlations, despite being tightly interconnected.
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van Ramshorst, Justus G. V., Miriam Coenders-Gerrits, Bart Schilperoort, Bas J. H. van de Wiel, Jonathan G. Izett, John S. Selker, Chad W. Higgins, Hubert H. G. Savenije, and Nick C. van de Giesen. "Revisiting wind speed measurements using actively heated fiber optics: a wind tunnel study." Atmospheric Measurement Techniques 13, no. 10 (October 13, 2020): 5423–39. http://dx.doi.org/10.5194/amt-13-5423-2020.
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Abstract. Near-surface wind speed is typically only measured by point observations. The actively heated fiber-optic (AHFO) technique, however, has the potential to provide high-resolution distributed observations of wind speeds, allowing for better spatial characterization of fine-scale processes. Before AHFO can be widely used, its performance needs to be tested in a range of settings. In this work, experimental results on this novel observational wind-probing technique are presented. We utilized a controlled wind tunnel setup to assess both the accuracy and the precision of AHFO under a range of operational conditions (wind speed, angles of attack and temperature difference). The technique allows for wind speed characterization with a spatial resolution of 0.3 m on a 1 s timescale. The flow in the wind tunnel was varied in a controlled manner such that the mean wind ranged between 1 and 17 m s−1. The AHFO measurements are compared to sonic anemometer measurements and show a high coefficient of determination (0.92–0.96) for all individual angles, after correcting the AHFO measurements for the angle of attack. Both the precision and accuracy of the AHFO measurements were also greater than 95 % for all conditions. We conclude that AHFO has the potential to measure wind speed, and we present a method to help choose the heating settings of AHFO. AHFO allows for the characterization of spatially varying fields of mean wind. In the future, the technique could potentially be combined with conventional distributed temperature sensing (DTS) for sensible heat flux estimation in micrometeorological and hydrological applications.
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Rousseau, D. D., P. Antoine, N. Gerasimenko, A. Sima, M. Fuchs, C. Hatté, O. Moine, and L. Zöller. "North Atlantic abrupt climatic events of the Last Glacial period recorded in Ukrainian loess deposits." Climate of the Past Discussions 6, no. 5 (October 1, 2010): 1959–90. http://dx.doi.org/10.5194/cpd-6-1959-2010.
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Abstract. Loess deposits are widely distributed in the Northern Hemisphere, where they have recorded not only the glacial-interglacial cycles, but also millennial-timescale changes resembling those in marine and ice cores. Such abrupt variations are clearly marked in Western European series, but have not yet been evidenced in the east of the continent. Here we present results of the high-resolution investigation of a Weichselian Upper Pleniglacial loess sequence (~38–15 ka) from Stayky, Ukraine. The stratigraphy shows an alternation of loess horizons and embryonic soils, similar to sequences from Western Europe. Similarities are also found between variations of a grain-size index (ratio between coarse and fine material fractions) in Stayky and in Western European profiles. Based on these similarities, and in agreement with the luminescence dates, the embryonic soils are associated to the Greenland interstadials (GIS) 7 to 2, and the Vytachiv paleosol at the base of the sequence, to GIS 8. Pollen analysis indicates a wetter climate for these interstadials, allowing the development of arboreal vegetation, than for the stadials, marked by loess formation. The grain-size index reaches the highest values for intervals correlated with the Heinrich events 3 and 2. Thus, it appears that the North Atlantic abrupt climate changes have extended their influence and modulated the loess sedimentation at least as far as in Eastern Europe. This result is supported by recent climate modeling experiments, and recommends the Stayky sequence as a reference for further comparisons between profiles along the Eurasian loess belt centered at 50° N.
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Rousseau, D. D., P. Antoine, N. Gerasimenko, A. Sima, M. Fuchs, C. Hatté, O. Moine, and L. Zoeller. "North Atlantic abrupt climatic events of the last glacial period recorded in Ukrainian loess deposits." Climate of the Past 7, no. 1 (March 8, 2011): 221–34. http://dx.doi.org/10.5194/cp-7-221-2011.
Full textAbstract:
Abstract. Loess deposits are widely distributed in the Northern Hemisphere, where they have recorded not only the glacial-interglacial cycles, but also millennial-timescale changes resembling those in marine and ice cores. Such abrupt variations are clearly marked in western European series, but have not yet been evidenced in the East of the continent. Here we present results of the high-resolution investigation of a Weichselian Upper Pleniglacial loess sequence (~38–15 ka) from Stayky, Ukraine. The stratigraphy shows an alternation of loess horizons and embryonic soils, similar to sequences from western Europe. Similarities are also found between variations of a grain-size index (ratio between coarse and fine material fractions) in Stayky and in western European profiles. Based on these similarities and in agreement with the luminescence dates, the embryonic soils are associated with the Greenland interstadials (GIS) 7 to 2, and the Vytachiv paleosol at the base of the sequence, with GIS 8. Pollen analysis indicates a wetter climate for these interstadials, allowing the development of arboreal vegetation, than for the stadials, which are marked by loess formation. The grain-size index reaches the highest values for intervals correlated with the Heinrich events 3 and 2. Thus, it appears that the North Atlantic abrupt climate changes have extended their influence and modulated the loess sedimentation at least as far as eastern Europe. This result is supported by recent climate modeling experiments and recommends the Stayky sequence as a reference for further comparisons between profiles along the Eurasian loess belt centered at 50° N.
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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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Martínez-de la Torre, Alberto, Eleanor Blyth, and Emma Robinson. "Evaluation of Drydown Processes in Global Land Surface and Hydrological Models Using Flux Tower Evapotranspiration." Water 11, no. 2 (February 20, 2019): 356. http://dx.doi.org/10.3390/w11020356.
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A key aspect of the land surface response to the atmosphere is how quickly it dries after a rainfall event. It is key because it will determine the intensity and speed of the propagation of drought and also affects the atmospheric state through changes in the surface heat exchanges. Here, we test the theory that this response can be studied as an inherent property of the land surface that is unchanging over time unless the above- and below-ground structures change. This is important as a drydown metric can be used to evaluate a landscape and its response to atmospheric drivers in models used in coupled land–atmosphere mode when the forcing is often not commensurate with the actual atmosphere. We explore whether the speed of drying of a land unit can be quantified and how this can be used to evaluate models. We use the most direct observation of drying: the rate of change of evapotranspiration after a rainfall event using eddy-covariance observations, or commonly referred to as flux tower data. We analyse the data and find that the drydown timescale is characteristic of different land cover types, then we use that to evaluate a suite of global hydrological and land surface models. We show that, at the site level, the data suggest that evapotranspiration decay timescales are longer for trees than for grasslands. The studied model’s accuracy to capture the site drydown timescales depends on the specific model, the site, and the vegetation cover representation. A more robust metric is obtained by grouping the modeled data by vegetation type and, using this, we find that land surface models capture the characteristic timescale difference between trees and grasslands, found using flux data, better than large-scale hydrological models. We thus conclude that the drydown metric has value in understanding land–atmosphere interactions and model evaluation.
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Roe, Gerard H., and Michael A. O’Neal. "The response of glaciers to intrinsic climate variability: observations and models of late-Holocene variations in the Pacific Northwest." Journal of Glaciology 55, no. 193 (2009): 839–54. http://dx.doi.org/10.3189/002214309790152438.
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AbstractDiscriminating between glacier variations due to natural climate variability and those due to true climate change is crucial for the interpretation and attribution of past glacier changes, and for the expectations of future changes. We explore this issue for the well-documented glaciers of Mount Baker in the Cascades Mountains of Washington State, USA, using glacier histories, glacier modeling, weather data and numerical weather model output. We find that natural variability alone is capable of producing kilometer-scale excursions in glacier length on multi-decadal and centennial timescales. Such changes are similar in magnitude to those attributed to a global Little Ice Age. The null hypothesis, that no climate change is required to explain the glacier fluctuations in this setting, cannot be rejected. These results for Mount Baker glaciers are also consistent with an earlier study analyzing individual glaciers in Scandinavia and the Alps. The principle that long-timescale fluctuations of glacier length can be driven by short-timescale fluctuations in climate reflects a robust and fundamental property of stochastically forced physical systems with memory. It is very likely that this principle also applies to other Alpine glaciers and that it therefore complicates interpretations of the relationship between glacier and climate history. However, the amplitude and timescale of the length fluctuations depends on the details of the particular glacier geometry and climatic setting, and this remains largely unevaluated for most glaciers.
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Brick, Tim. "SEQUENCE MINING FOR COMPLEX PATTERN FINDING." Innovation in Aging 3, Supplement_1 (November 2019): S377. http://dx.doi.org/10.1093/geroni/igz038.1383.
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Abstract The processes of aging play out across multiple variables and multiple timescales, with patterns of daily, and weekly behavior that may be influenced by each other and by changes across the aging process. Further, many of these patterns do not fit neatly into the linear modeling approaches common in the field. Sequence mining, an approach from the data mining literature, provides a means of identifying commonalities and differences in these sequences in ways that can begin to handle the multivariate and multi-timescale nature of behaviors in aging. In this talk, I present an example of sequence mining to illustrate its ability to find arbitrarily complex patterns of behavior that characterize and distinguish groups and individuals.
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Steimer, S. S., M. Lampimäki, E. Coz, G. Grzinic, and M. Ammann. "The influence of physical state on shikimic acid ozonolysis: a case for in situ microspectroscopy." Atmospheric Chemistry and Physics 14, no. 19 (October 13, 2014): 10761–72. http://dx.doi.org/10.5194/acp-14-10761-2014.
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Abstract. Atmospheric soluble organic aerosol material can become solid or semi-solid. Due to increasing viscosity and decreasing diffusivity, this can impact important processes such as gas uptake and reactivity within aerosols containing such substances. This work explores the dependence of shikimic acid ozonolysis on humidity and thereby viscosity. Shikimic acid, a proxy for oxygenated reactive organic material, reacts with O3 in a Criegee-type reaction. We used an environmental microreactor embedded in a scanning transmission X-ray microscope (STXM) to probe this oxidation process. This technique facilitates in situ measurements with single micron-sized particles and allows to obtain near-edge X-ray absorption fine structure (NEXAFS) spectra with high spatial resolution. Thus, the chemical evolution of the interior of the particles can be followed under reaction conditions. The experiments show that the overall degradation rate of shikimic acid is depending on the relative humidity in a way that is controlled by the decreasing diffusivity of ozone with decreasing humidity. This decreasing diffusivity is most likely linked to the increasing viscosity of the shikimic acid–water mixture. The degradation rate was also depending on particle size, most congruent with a reacto-diffusion limited kinetic case where the reaction progresses only in a shallow layer within the bulk. No gradient in the shikimic acid concentration was observed within the bulk material at any humidity indicating that the diffusivity of shikimic acid is still high enough to allow its equilibration throughout the particles on the timescale of hours at higher humidity and that the thickness of the oxidized layer under dry conditions, where the particles are solid, is beyond the resolution of STXM.
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Shin, Nagai, Taku M. Saitoh, and Kenlo Nishida Nasahara. "How did the characteristics of the growing season change during the past 100 years at a steep river basin in Japan?" PLOS ONE 16, no. 7 (July 30, 2021): e0255078. http://dx.doi.org/10.1371/journal.pone.0255078.
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The effects of climate change on plant phenological events such as flowering, leaf flush, and leaf fall may be greater in steep river basins than at the horizontal scale of countries and continents. This possibility is due to the effect of temperature on plant phenology and the difference between vertical and horizontal gradients in temperature sensitivities. We calculated the dates of the start (SGS) and end of the growing season (EGS) in a steep river basin located in a mountainous region of central Japan over a century timescale by using a degree-day phenological model based on long-term, continuous, in situ observations. We assessed the generality and representativeness of the modelled SGS and EGS dates by using phenological events, live camera images taken at multiple points in the basin, and satellite observations made at a fine spatial resolution. The sensitivity of the modelled SGS and EGS dates to elevation changed from 3.29 days (100 m)−1 (−5.48 days °C−1) and −2.89 days (100 m)−1 (4.81 days °C−1), respectively, in 1900 to 2.85 days (100 m)−1 (−4.75 days °C−1) and −2.84 day (100 m)−1 (4.73 day °C−1) in 2019. The long-term trend of the sensitivity of the modelled SGS date to elevation was −0.0037 day year−1 per 100 m, but the analogous trend in the case of the modelled EGS date was not significant. Despite the need for further studies to improve the generality and representativeness of the model, the development of degree-day phenology models in multiple, steep river basins will deepen our ecological understanding of the sensitivity of plant phenology to climate change.
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Drury, Jonathan P., Madeline C. Cowen, and Gregory F. Grether. "Competition and hybridization drive interspecific territoriality in birds." Proceedings of the National Academy of Sciences 117, no. 23 (May 26, 2020): 12923–30. http://dx.doi.org/10.1073/pnas.1921380117.
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Costly interactions between species that arise as a by-product of ancestral similarities in communication signals are expected to persist only under specific evolutionary circumstances. Territorial aggression between species, for instance, is widely assumed to persist only when extrinsic barriers prevent niche divergence or selection in sympatry is too weak to overcome gene flow from allopatry. However, recent theoretical and comparative studies have challenged this view. Here we present a large-scale, phylogenetic analysis of the distribution and determinants of interspecific territoriality. We find that interspecific territoriality is widespread in birds and strongly associated with hybridization and resource overlap during the breeding season. Contrary to the view that territoriality only persists between species that rarely breed in the same areas or where niche divergence is constrained by habitat structure, we find that interspecific territoriality is positively associated with breeding habitat overlap and unrelated to habitat structure. Furthermore, our results provide compelling evidence that ancestral similarities in territorial signals are maintained and reinforced by selection when interspecific territoriality is adaptive. The territorial signals linked to interspecific territoriality in birds depend on the evolutionary age of interacting species, plumage at shallow (within-family) timescales, and song at deeper (between-family) timescales. Evidently, territorial interactions between species have persisted and shaped phenotypic diversity on a macroevolutionary timescale.
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Day, Jonathan J., Steffen Tietsche, Mat Collins, Helge F. Goessling, Virginie Guemas, Anabelle Guillory, William J. Hurlin, et al. "The Arctic Predictability and Prediction on Seasonal-to-Interannual TimEscales (APPOSITE) data set version 1." Geoscientific Model Development 9, no. 6 (June 29, 2016): 2255–70. http://dx.doi.org/10.5194/gmd-9-2255-2016.
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Abstract. Recent decades have seen significant developments in climate prediction capabilities at seasonal-to-interannual timescales. However, until recently the potential of such systems to predict Arctic climate had rarely been assessed. This paper describes a multi-model predictability experiment which was run as part of the Arctic Predictability and Prediction On Seasonal to Interannual Timescales (APPOSITE) project. The main goal of APPOSITE was to quantify the timescales on which Arctic climate is predictable. In order to achieve this, a coordinated set of idealised initial-value predictability experiments, with seven general circulation models, was conducted. This was the first model intercomparison project designed to quantify the predictability of Arctic climate on seasonal to interannual timescales. Here we present a description of the archived data set (which is available at the British Atmospheric Data Centre), an assessment of Arctic sea ice extent and volume predictability estimates in these models, and an investigation into to what extent predictability is dependent on the initial state. The inclusion of additional models expands the range of sea ice volume and extent predictability estimates, demonstrating that there is model diversity in the potential to make seasonal-to-interannual timescale predictions. We also investigate whether sea ice forecasts started from extreme high and low sea ice initial states exhibit higher levels of potential predictability than forecasts started from close to the models' mean state, and find that the result depends on the metric. Although designed to address Arctic predictability, we describe the archived data here so that others can use this data set to assess the predictability of other regions and modes of climate variability on these timescales, such as the El Niño–Southern Oscillation.
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Linscheid, Nora, Lina M. Estupinan-Suarez, Alexander Brenning, Nuno Carvalhais, Felix Cremer, Fabian Gans, Anja Rammig, Markus Reichstein, Carlos A. Sierra, and Miguel D. Mahecha. "Towards a global understanding of vegetation–climate dynamics at multiple timescales." Biogeosciences 17, no. 4 (February 24, 2020): 945–62. http://dx.doi.org/10.5194/bg-17-945-2020.
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Abstract. Climate variables carry signatures of variability at multiple timescales. How these modes of variability are reflected in the state of the terrestrial biosphere is still not quantified or discussed at the global scale. Here, we set out to gain a global understanding of the relevance of different modes of variability in vegetation greenness and its covariability with climate. We used >30 years of remote sensing records of the normalized difference vegetation index (NDVI) to characterize biosphere variability across timescales from submonthly oscillations to decadal trends using discrete Fourier decomposition. Climate data of air temperature (Tair) and precipitation (Prec) were used to characterize atmosphere–biosphere covariability at each timescale. Our results show that short-term (intra-annual) and longer-term (interannual and longer) modes of variability make regionally highly important contributions to NDVI variability: short-term oscillations focus in the tropics where they shape 27 % of NDVI variability. Longer-term oscillations shape 9 % of NDVI variability, dominantly in semiarid shrublands. Assessing dominant timescales of vegetation–climate covariation, a natural surface classification emerges which captures patterns not represented by conventional classifications, especially in the tropics. Finally, we find that correlations between variables can differ and even invert signs across timescales. For southern Africa for example, correlation between NDVI and Tair is positive for the seasonal signal but negative for short-term and longer-term oscillations, indicating that both short- and long-term temperature anomalies can induce stress on vegetation dynamics. Such contrasting correlations between timescales exist for 15 % of vegetated areas for NDVI with Tair and 27 % with Prec, indicating global relevance of scale-specific climate sensitivities. Our analysis provides a detailed picture of vegetation–climate covariability globally, characterizing ecosystems by their intrinsic modes of temporal variability. We find that (i) correlations of NDVI with climate can differ between scales, (ii) nondominant subsignals in climate variables may dominate the biospheric response, and (iii) possible links may exist between short-term and longer-term scales. These heterogeneous ecosystem responses on different timescales may depend on climate zone and vegetation type, and they are to date not well understood and do not always correspond to transitions in dominant vegetation types. These scale dependencies can be a benchmark for vegetation model evaluation and for comparing remote sensing products.
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Penaud, Aurélie, Frédérique Eynaud, Antje Helga Luise Voelker, and Jean-Louis Turon. "Palaeohydrological changes over the last 50 ky in the central Gulf of Cadiz: complex forcing mechanisms mixing multi-scale processes." Biogeosciences 13, no. 18 (September 27, 2016): 5357–77. http://dx.doi.org/10.5194/bg-13-5357-2016.
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Abstract. New dinoflagellate cyst (dinocyst) analyses were carried out at high resolution in core MD99-2339, retrieved from a contouritic field in the central part of the Gulf of Cadiz, for the Marine Isotope Stage (MIS) 3 interval, allowing for discussion of palaeohydrological changes over the last 50 ky in the subtropical NE Atlantic Ocean. Some index dinocyst taxa, according to their (palaeo)ecological significance, shed light on significant sea-surface changes. Superimposed on the general decreasing pattern of dinocyst export to the seafloor over the last 50 ky, paralleling the general context of decreasing aeolian dust fertilization, a complex variability in dinocyst assemblages was detected at the millennial timescale. Enhanced fluvial discharges occurred during Greenland Interstadials (GIs), especially GI 1, 8 and 12, while enhanced upwelling cell dynamics were suggested during the Last Glacial Maximum and Heinrich Stadials. Finally, during the early Holocene, and more specifically during the Sapropel 1 interval (around 7–9 ka BP), we evidenced a strong decrease in dinocyst fluxes, which occurred synchronously to a strong reduction in Mediterranean Outflow Water strength and which we attributed to an advection of warm and nutrient-poor subtropical North Atlantic Central Waters. Over the last 50 ky, our study thus allows for capturing and documenting the fine tuning existing between terrestrial and marine realms in North Atlantic subtropical latitudes, in response to not only the regional climate pattern but also monsoonal forcing interfering during precession-driven Northern Hemisphere insolation maxima. This mechanism, well expressed during the Holocene, is superimposed on the pervasive role of the obliquity as a first major trigger for explaining migration of dinocyst productive centres in the NE Atlantic margin to the subtropical (temperate) latitudes during glacial (interglacial) periods.