Methane flux, vertical gradient and mixing ratio measurements in a tropical forest

Measurements of CH<sub>4</sub> mixing ratio, vertical gradients and turbulent fluxes were carried out in a tropical forest (Reserva Biológica Cuieiras), about 60 km north of Manaus, Brazil. The methane mixing ratio and flux measurements were performed at a height of 53 m (canopy height 35 m). In addition, vertical CH<sub>4</sub> gradients were measured within the canopy using custom made air samplers at levels of 2, 16 and 36 m above ground. The methane gradients within the canopy reveal that there is a continuous methane source at the surface. No clear evidence for aerobic methane emission from the canopy was found. The methane fluxes above the canopy are small but consistently upwards with a maximum early in the morning. The measured fluxes are in agreement with the observed CH<sub>4</sub> gradient in the canopy. In the morning hours, a strong canopy venting peak is observed for both CH<sub>4</sub> and CO<sub>2</sub>, but for CO<sub>2</sub> this peak is then superimposed by photosynthetic uptake, whereas the peak lasts longer for CH<sub>4</sub>. Monthly averaged diurnal cycles of the CH<sub>4</sub> mixing ratio show a decrease during daytime and increase during nighttime. The magnitude of the difference in CH<sub>4</sub> mixing ratio between day and night gradually increases throughout the wet season. The fluxes required to explain the nighttime increase are in agreement with the nighttime fluxes measured above the canopy, which implies that the CH<sub>4</sub> increase in the nighttime boundary layer originates from local sources

Vertical profiles of CO\u3csub\u3e2\u3c/sub\u3e above eastern Amazonia suggest a net carbon flux to the atmosphere and balanced biosphere between 2000 and 2009

From 2000 until January 2010 vertical profiles were collected above eastern Amazonia to help determine regional-scale (∼105–106 km2) fluxes of carbon cycle-related greenhouse gases. Samples were collected aboard light aircraft between the surface and 4.3 km and a column integration technique was used to determine the CO2 flux. Measured CO2 profiles were differenced from the CO2 background determined from measurements in the tropical Atlantic. The observed annual flux between the coast and measurement sites was 0.40 ± 0.27 gC m−2 d−1 (90% confidence interval using a bootstrap analysis). The wet season (January–June) mean flux was 0.44 ± 0.38 gC m−2 d−1 (positive fluxes defined as a source to the atmosphere) and the dry season mean flux was 0.35 ± 0.17 gC m−2 d−1 (July–December). The observed flux variability is high, principally in the wet season. The influence of biomass burning has been removed using co-measured CO, and revealed the presence of a significant dry season sink. The annual mean vegetation flux, after the biomass burning correction, was 0.02 ± 0.27 gC m−2 d−1, and a clear sink was observed between August and November of −0.70 ± 0.21 gC m−2 d−1 where for all of the dry season it was −0.24 ± 0.17 gC m−2 d−1

Vertical profiles of CO2 above eastern Amazonia suggest a net carbon flux to the atmosphere and balanced biosphere between 2000 and 2009

From 2000 until January 2010 vertical profiles were collected above eastern Amazonia to help determine regional-scale (∼105–106 km2) fluxes of carbon cycle-related greenhouse gases. Samples were collected aboard light aircraft between the surface and 4.3 km and a column integration technique was used to determine the CO2 flux. Measured CO2 profiles were differenced from the CO2 background determined from measurements in the tropical Atlantic. The observed annual flux between the coast and measurement sites was 0.40 ± 0.27 gC m−2 d−1 (90% confidence interval using a bootstrap analysis). The wet season (January–June) mean flux was 0.44 ± 0.38 gC m−2 d−1 (positive fluxes defined as a source to the atmosphere) and the dry season mean flux was 0.35 ± 0.17 gC m−2 d−1 (July–December). The observed flux variability is high, principally in the wet season. The influence of biomass burning has been removed using co-measured CO, and revealed the presence of a significant dry season sink. The annual mean vegetation flux, after the biomass burning correction, was 0.02 ± 0.27 gC m−2 d−1, and a clear sink was observed between August and November of −0.70 ± 0.21 gC m−2 d−1 where for all of the dry season it was −0.24 ± 0.17 gC m−2 d−1.Earth and Planetary Science

Spannungsverlauf eines Volumenelements im Freilauf-Wälzkontakt

Der Freilauf ist ein Maschinenelement, welches die Funktion der richtungsabhängigen Drehmomenttransmission erfüllt. Die Übertragung des Drehmoments erfolgt über das Abwälzen des Klemmelements zwischen den An- und Abtriebskomponenten. Für den Fall des Klemmrollenfreilaufs beträgt das überwälzte Volumen während dieses Wälzvorgangs in der Regel nur wenige Millimeter. Das gleiche Volumen wird sowohl in Belastungsrichtung als auch in Entlastungsrichtung beansprucht. In der Berechnung der Lebensdauer von Freiläufen wird angenommen, dass durch diesen Zustand das Volumen doppelt belastet wird. Werden die zeitlich abhängigen Spannungsverläufe einzelner Volumen unterhalb der Oberfläche betrachtet, ist zu erkennen, dass diese Annahme nicht für jedes Volumenelement gilt: einige weisen ein doppeltes Schwingspiel je Belastung auf, andere wiederum nur ein einfaches Schwingspiel. Es wird die Möglichkeit geboten die Beanspruchung des Materials unterhalb der Oberfläche für die Optimierung der Berechnungsansätze neu zu quantifizieren.The freewheel clutch is a machine element that fulfills the function of directiondependent torque transmission. The special geometry of the freewheel enables an almost friction-free overtaking operation. In the opposite direction of rotation a torque is transmitted through a frictional rolling process. The traveled distance of the roller during the loading and unloading process is generally only a few millimeters. When calculating the service life of freewheels, it is assumed that the volume underneath the rolling contact is rolled-over twice and thus a load cycle has also to be counted twice. Considering the time-dependent stress curves of individual volume elements, it can be seen that this assumption does not apply to every volume element. It is possible to re-quantify the subsurface-stresses for the calculation approaches

Drought sensitivity of Amazonian carbon balance revealed by atmospheric measurements

Feedbacks between land carbon pools and climate provide one of the largest sources of uncertainty in our predictions of global climate(1,2). Estimates of the sensitivity of the terrestrial carbon budget to climate anomalies in the tropics and the identification of the mechanisms responsible for feedback effects remain uncertain(3,4). The Amazon basin stores a vast amount of carbon(5), and has experienced increasingly higher temperatures and more frequent floods and droughts over the past two decades(6). Here we report seasonal and annual carbon balances across the Amazon basin, based on carbon dioxide and carbon monoxide measurements for the anomalously dry and wet years 2010 and 2011, respectively. We find that the Amazon basin lost 0.48 +/- 0.18 petagrams of carbon per year (Pg C yr(-1)) during the dry year but was carbon neutral (0.06 +/- 0.1 Pg C yr(-1)) during the wet year. Taking into account carbon losses from fire by using carbon monoxide measurements, we derived the basin net biome exchange (that is, the carbon flux between the non-burned forest and the atmosphere) revealing that during the dry year, vegetation was carbon neutral. During the wet year, vegetation was a net carbon sink of 0.25 +/- 0.14 Pg C yr(-1), which is roughly consistent with the mean long-term intact-forest biomass sink of 0.39 +/- 0.10 Pg C yr(-1) previously estimated from forest censuses(7). Observations from Amazonian forest plots suggest the suppression of photosynthesis during drought as the primary cause for the 2010 sink neutralization. Overall, our results suggest that moisture has an important role in determining the Amazonian carbon balance. If the recent trend of increasing precipitation extremes persists(6), the Amazon may become an increasing carbon source as a result of both emissions from fires and the suppression of net biome exchange by drought