High-resolution paleoclimatology is the study of climate variability and change on interannual to multi-century time scales. Its primary focus is the past few millennia, a period lacking major shifts ...in external climate forcing and earth system configuration. Large arrays of proxy climate records derived from natural archives have been used to reconstruct aspects of climate in recent centuries. The main approaches used have been empirical and statistical, albeit informed by prior knowledge both of the physics of the climate, and of the processes imprinting climate information in the natural archives. We propose a new direction, in which emerging tools are used to formalize the combination of process knowledge and proxy climate records to better illuminate past climate variability on these time scales of great relevance to human concerns.
We present an automated dynamic chamber system which is optimised for continuous unattended flux measurements of multiple non-reactive and reactive trace gases on grassland ecosystems. Main design ...features of our system are (a) highly transparent chamber walls consisting of chemically inert material, (b) individual purging flow units for each chamber, and (c) a movable lid for automated opening and closing of the chamber. The purging flow rate was chosen high enough to keep the mean residence time of the chamber air below one minute. This guarantees a proven efficient mixing of the chamber volume and a fast equilibration after lid closing. The dynamic chamber system is able to measure emission as well as deposition fluxes of trace gases. For the latter case, the modification of the turbulent transport by the chamber (compared to undisturbed ambient conditions) is quantitatively described by a bulk resistance concept. Beside a detailed description of the design and functioning of the system, results of field applications at two grassland sites are presented. In the first experiment, fluxes of five trace gases (CO2, H2O, NO, NO2, O3) were measured simultaneously on small grassland plots. It showed that the dynamic chamber system is able to detect the characteristic diurnal cycles with a sufficient temporal resolution. The results also demonstrated the importance of considering the chemical source/sink in the chamber due to gas phase reactions for the reactive compounds of the NO-NO2-O3 triad. In a second field experiment, chamber flux measurements of CO2 and methanol were compared to simultaneous independent eddy covariance flux measurements on the field scale. The fluxes obtained with the two methods showed a very good agreement indicating a minimal disturbance of the chambers on the physiological activity of the enclosed vegetation.
Observations indicate that the height of the tropopause-the boundary between the stratosphere and troposphere-has increased by several hundred meters since 1979. Comparable increases are evident in ...climate model experiments. The latter show that human-induced changes in ozone and well-mixed greenhouse gases account for ~80% of the simulated rise in tropopause height over 1979-1999. Their primary contributions are through cooling of the stratosphere (caused by ozone) and warming of the troposphere (caused by well-mixed greenhouse gases). A model-predicted fingerprint of tropopause height changes is statistically detectable in two different observational ("reanalysis") data sets. This positive detection result allows us to attribute overall tropopause height changes to a combination of anthropogenic and natural external forcings, with the anthropogenic component predominating.
The climate system is continuously affected by forcings that add to its inherent variability. Recently, the dominant influence shifted from mostly natural factors to the rapidly increasing ...anthropogenic greenhouse gas and aerosol forcing. Climate change simulations for the 21st and 22nd centuries then employ possible story lines of human socio‐economic development with associated radiative forcing that exclusively explore the potential human influence on climate. None of the scenarios, however, include natural factors that dominated climate variations prior to the large anthropogenic emissions. This leads to a discontinuity at the transition between the historical and the future projection period. Similarly, studies of transient climate variations before the last 1–2 millennia generally use only the well‐known, slowly varying forcings such as orbital or greenhouse forcing derived from ice cores. While past solar irradiance variations can be reasonably estimated from cosmogenic isotope data, no well‐dated, high‐resolution information exists before about A.D. 500 that would allow for an implementation of forcing from explosive volcanism. Here, we present a statistical approach to generate statistically (and geophysically) realistic scenarios of volcanic forcing that are based on the properties of the longest available volcanic forcing series derived from ice cores. The resulting scenarios do not carry direct temporally predictive or hindcast capabilities, but they allow for an appropriate evaluation of natural uncertainty on various timescales. These series can be applied to ensure a seamless integration of an important natural forcing factor for climate change simulations of periods where such forcing is not available.
A system for fast ammonia (NH3) measurements with chemical ionisation mass spectrometry (CIMS) based on a commercial Proton Transfer Reaction-Mass Spectrometer (PTR-MS) is presented. It uses electron ...transfer reaction as ionisation pathway and features a drift tube of polyetheretherketone (PEEK) and silica-coated steel. Heating the instrumental inlet and the drift tube to 180 °C enabled an effective time resolution of ~1 s and made it possible to apply the instrument for eddy covariance (EC) measurements. EC fluxes of NH3 were measured over two agricultural fields in Oensingen, Switzerland, following fertilisations with cattle slurry. Air was aspirated close to a sonic anemometer at a flow of 100 STP L min−1 and was directed through a 23 m long 1/2" PFA tube heated to 150 °C to an air-conditioned trailer where the gas was sub-sampled from the large bypass stream. This setup minimised damping of fast NH3 concentration changes between the sampling point and the actual measurement. High-frequency attenuation loss of the NH3 fluxes of 20 to 40% was quantified and corrected for using an empirical ogive method. The instrumental NH3 background signal showed a minor interference with H2O which was characterised in the laboratory. The resulting correction of the NH3 flux after slurry spreading was less than 1‰. The flux detection limit of the EC system was about 5 ng m−2 s−1 while the accuracy of individual flux measurements was estimated 16% for the high-flux regime during these experiments. The NH3 emissions after broad spreading of the slurry showed an initial maximum of 150 μg m−2 s−1 with a fast decline in the following hours.
The (net) exchange of reactive nitrogen (Nr) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne Nr includes various trace ...compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds. Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all Nr compounds (∑Nr). Measurements were performed over a managed grassland field with phases of net emission and net deposition of ∑Nr and alternating dominance of oxidized (NOX) and reduced species (NH3). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19%–26% for a low measurement height of 1.2 m and to about 10% for 4.8 m measurement height. ∑Nr concentrations and fluxes were compared to parallel NO and NO2 measurements by dynamic chambers and NH3 measurements by the aerodynamic gradient technique. The average concentration results indicate that the main compounds NO2 and NH3 were converted by the TRANC system with an efficiency of near 100%. With an optimised sample inlet also the fluxes of these compounds were recovered reasonably well including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen.
There is increasing evidence for the beneficial effects of exercise training in stroke survivors. In order to reach the desired training effects, exercise training principles must be considered as ...this ensures the prescription of adequate exercises at an adequate dose. Moreover, exercise training interventions must be designed in a way that maximizes patients' adherence to the prescribed exercise regimen. The objectives of this systematic review were (1) to investigate whether training principles for physical exercise interventions are reported in RCTs for sub-acute and chronic stroke survivors, (2) to evaluate whether the RCTs reported the prescription of the FITT components of the exercise interventions as well as (3) patients' adherence to this prescription, and (4) to assess the risk of bias of the included studies.
We performed a systematic review of RCTs with exercise training as the primary intervention and muscular strength and/or endurance as primary outcomes. The Cochrane library's risk of bias (ROB) tool was used to judge the methodological quality of RCTs.
Thirty-seven RCTs were included in this systematic review. Eighteen studies (48.7%) focused on aerobic, 8 (21.6%) on resistance and 11 (29.7%) on combined interventions of aerobic and resistive strength exercise. Twenty-nine studies (78.4%) included only chronic stroke survivors, 5 studies (13.5%) only sub-acute stroke survivors whilst 3 studies (8.1%) included both. In terms of principle of exercise training, 89% reported specificity, 75.7% progression, 48.7% overload, 37.8% initial values, 32.4% reversibility and 13.5% diminishing returns. One RCT described all principles of physical exercise training and 19 (51.4%) all FITT components. Patients' adherence to exercise prescription was accounted for in 3 studies (8.1%). Failure to report blinding in patients and participants and failure to report allocation concealment were the most prevalent methodological shortcomings.
Incomplete and inconsistent reporting of (1) training components, (2) underlying exercise training principles and (3) patient adherence together with (4) a broad variation in the methodological quality of the included RCTs limit both the utility and reproducibility of physical exercise programs in stroke patients.
Nitrogen dioxide (NO2 ) plays an important role in atmospheric pollution, in particular for tropospheric ozone production. However, the removal processes involved in NO2 deposition to terrestrial ...ecosystems are still the subject of ongoing discussion. This study reports NO2 flux measurements made over a meadow using the eddy covariance method. The measured NO2 deposition fluxes during daytime were about a factor of two lower than a priori calculated fluxes using the Surfatm model without taking into account an internal (also called mesophyllic or sub-stomatal) resistance. Neither an underestimation of the measured NO2 deposition flux due to chemical divergence or an in-canopy NO2 source nor an underestimation of the resistances used to model the NO2 deposition explained the large difference between measured and modelled NO2 fluxes. Thus, only the existence of the internal resistance could account for this large discrepancy between model and measurements. The median internal resistance was estimated to be 300 s m-1 during daytime, but exhibited a large variability (100-800 s m-1 ). In comparison, the stomatal resistance was only around 100 s m-1 during daytime. Hence, the internal resistance accounted for 50-90% of the total leaf resistance to NO2 . This study presents the first clear evidence and quantification of the internal resistance using the eddy covariance method; i.e. plant functioning was not affected by changes of microclimatological (turbulent) conditions that typically occur when using enclosure methods.
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