The charge excess and momentum spectrum of cosmic ray muons in the vertical direction

The charge excess and momentum spectrum of cosmic ray muons have been measured at 60 m above sea-level by means of the "Vertical Durham Spectrograph" which had been modi-fied in many respects (e.g. by the addition of a solid iron plug of thickness 45 cm) and re-aligned and calibrated. The effect of the multiple scattering in the magnet is found to be the most serious limitation of the instrument and methods of coping with it are investigated, among others a new statistical method. The values obtained for the charge ratio are 1.240 + 0.036 at 12 GeV/c, 1.262 + 0.031 at 23 GeV/c, 1.279 + 0.038 at 31 GeV/c, 1.208 + O.O69 at 47 GeV/c, 1.269 + u.085 at 66 GeV/c, and 1.324 + 0.111 at 102 GeV/c. These results have been combined with the results of previous workers. The best estimates thus obtained are compared with the theoretical expectations calculated by kacKeown et al. (1965a). The expectations are calculated for an empirical model of nuclear interactions including kaons, for the isobar model (Peters, 1963; Yash Pal, I963), and for the peripheral collision model (Narayan, 1964; Crossland and Powler, 1965), including the empirical low-energy pionization in the two latter models. A qualitative agreement is found between the experiments and theory in each case but quantitative conclusions cannot be drawn because of the statistical errors of the experimental results and because of uncertainty in the parameters of the models. The momentum spectrum observed agrees well with the spectrum given by Osborne et al. (1964) within the accuracy of the instrument. The underground muon spectrum observed by Vernov et al. (1965) and the spectrum of primary nuclei measured by the satellite Proton I (Grigorov et al., 1965; Vernov, 1965) disagree with the present results

Carbon dioxide fluxes and vegetation structure in rewetted and pristine peatlands in Finland and Estonia

Vast areas of peatlands have been drained for forestry endangering their carbon sink function. Peatland rewetting aims at mitigating the situation through restoring the hydrology and vegetation of these areas. We compared the carbon dioxide (CO2) fluxes and phy-tomass on four pairs of rewetted and pristine peatland sites in Finland and Estonia, and described correlations between phytomass and CO2 fluxes. We measured the net ecosystem exchange of CO2 (NEE), respiration and photosynthesis over one growing season using manual chambers, and biomass of plant functional types (PFT) on rewetted sites and their pristine counterparts. Although pair-wise differences in the vegetation were small, pristine sites were on average stronger CO2 sinks than rewetted sites. Respiration was higher in hummocks while no differences were found in photosynthesis between hummocks and hollows. No clear relationship between the biomasses of PFTs and NEE was found. Generally, however, CO2 uptake decreased with increase in Sphagnum biomass. © 2019, Finnish Environment Institute. All rights reserved.Peer reviewe

Interpreting eddy covariance data from heterogeneous Siberian tundra : land-cover-specific methane fluxes and spatial representativeness

The non-uniform spatial integration, an inherent feature of the eddy covariance (EC) method, creates a challenge for flux data interpretation in a heterogeneous environment, where the contribution of different land cover types varies with flow conditions, potentially resulting in biased estimates in comparison to the areally averaged fluxes and land cover attributes. We modelled flux footprints and characterized the spatial scale of our EC measurements in Tiksi, a tundra site in northern Siberia. We used leaf area index (LAI) and land cover class (LCC) data, derived from very-high-spatial-resolution satellite imagery and field surveys, and quantified the sensor location bias. We found that methane (CH4) fluxes varied strongly with wind direction (-0.09 to 0.59 mu gCH(4)m(-2) s(-1) on average) during summer 2014, reflecting the distribution of different LCCs. Other environmental factors had only a minor effect on short-term flux variations but influenced the seasonal trend. Using footprint weights of grouped LCCs as explanatory variables for the measured CH4 flux, we developed a multiple regression model to estimate LCC group-specific fluxes. This model showed that wet fen and graminoid tundra patches in locations with topography-enhanced wetness acted as strong sources (1.0 mu gCH(4) m(-2) s(-1) during the peak emission period), while mineral soils were significant sinks (-0.13 mu gCH(4) m(-2) s(-1)). To assess the representativeness of measurements, we upscaled the LCC group-specific fluxes to different spatial scales. Despite the landscape heterogeneity and rather poor representativeness of EC data with respect to the areally averaged LAI and coverage of some LCCs, the mean flux was close to the CH4 balance upscaled to an area of 6.3 km(2), with a location bias of 14 %. We recommend that EC site descriptions in a heterogeneous environment should be complemented with footprint-weighted high-resolution data on vegetation and other site characteristics.Peer reviewe

Detecting northern peatland vegetation patterns at ultra-high spatial resolution

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Chemical composition of boundary layer aerosol over the Atlantic Ocean and at an Antarctic site

International audienceAerosol chemical composition was measured over the Atlantic Ocean in November?December 1999 and at the Finnish Antarctic research station Aboa in January 2000. The concentrations of all anthropogenic aerosol compounds decreased clearly from north to south. An anthropogenic influence was still evident in the middle of the tropical South Atlantic, background values were reached south of Cape Town. Chemical mass balance was calculated for high volume filter samples (Dp80% in the Southern Ocean, and 10% in most samples, also at Aboa. The correlation of biomass-burning-related aerosol components with 210Pb was very high compared with that between nss calcium and 210Pb which suggests that 210Pb is a better tracer for biomass burning than for Saharan dust. The ratio of the two clear tracers for biomass burning, nss potassium and oxalate, was different in European and in African samples, suggesting that this ratio could be used as an indicator of biomass burning type. The concentrations of continent-related particles decreased exponentially with the distance from Africa. The shortest half-value distance, ~100 km, was for nss calcium. The half-value distance of particles that are mainly in the submicron particles was ~700±200 km. The MSA to nss sulfate ratio, R, increased faster than MSA concentration with decreasing anthropogenic influence, indicating that the R increase could largely be explained by the decrease of anthropogenic sulfate

Impact of coordinate rotation on eddy covariance fluxes at complex sites

The choice of coordinate system to calculate eddy covariance fluxes becomes particularly relevant at complex measurement sites. The traditional way is to perform double rotation (DR) of the coordinate system i.e., to calculate turbulent fluxes in a coordinate system that is aligned with the flow streamlines within the flux averaging period (e.g., Kaimal and Finnigan, 1994). The second approach, the so-called planar-fitted (PF) coordinate system, averages the flow over a longer period of time, in practice a month or more. The PF method allows to derive an intercept coefficient of the vertical wind speed which can be attributed to the offset of the sonic anemometer or the average vertical flow related to meteorological conditions. We evaluated the variants of the PF methods using data from a variety of sites ranging from complex urban and forest sites to nearly ideal forest and peatland sites. At complex sites, we found that the intercept of the vertical wind speed derived from the PF method is a function of wind direction, time of day and/or stability. The sector-wise PF (SPF) method frequently led to insignificant statistical relationships. We tested a continuous PF (CPF) method where the relationship establishing the coordinate frame was represented as the continuous function in the form of Fourier series. The method enabled to obtain the PF with lower uncertainty as compared to the SPF method, by selecting necessary number of harmonics for each site based on confidence intervals of estimated parameters. Therefore, we recommend to use the CPF method in cases when the number of observations in some wind direction interval is low or the obtained SPF is insignificant due to large variance in measurements. We also showed that significant systematic difference can exist in cumulative turbulent fluxes between the DR and PF methods over a longer period of time. Derived vertical advection of carbon dioxide exhibited large variability with wind direction due to topography at complex sites and therefore, without considering horizontal advection, cannot be used to improve the net ecosystem exchange estimation during nocturnal, low turbulence conditions.Peer reviewe

CO2 fluxes and ecosystem dynamics at five European treeless peatlands – merging data and process oriented modeling

The carbon dioxide (CO2) exchange of five different peatland systems across Europe with a wide gradient in land use intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out whether CO2 fluxes, measured at different sites, can be explained by common processes and parameters or to what extend a site specific configuration is needed. The model was calibrated to fit measured CO2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analyzed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data. Seasonal variability in the major fluxes was well captured, when a site independent configuration was utilized for most of the parameters. Parameters that differed between sites included the rate of soil organic decomposition, photosynthetic efficiency, and regulation of the mobile carbon (C) pool from senescence to shooting in the next year. The largest difference between sites was the rate coefficient for heterotrophic respiration. Setting it to a common value would lead to underestimation of mean total respiration by a factor of 2.8 up to an overestimation by a factor of 4. Despite testing a wide range of different responses to soil water and temperature, rate coefficients for heterotrophic respiration were consistently the lowest on formerly drained sites and the highest on the managed sites. Substrate decomposability, pH and vegetation characteristics are possible explanations for the differences in decomposition rates. Specific parameter values for the timing of plant shooting and senescence, the photosynthesis response to temperature, litter fall and plant respiration rates, leaf morphology and allocation fractions of new assimilates, were not needed, even though the gradient in site latitude ranged from 48° N (southern Germany) to 68° N (northern Finland) differed largely in their vegetation. This was also true for common parameters defining the moisture and temperature response for decomposition, leading to the conclusion that a site specific interpretation of these processes is not necessary. In contrast, the rate of soil organic decomposition, photosynthetic efficiency, and the regulation of the mobile carbon pool need to be estimated from available information on specific soil conditions, vegetation and management of the ecosystems, to be able to describe CO2 fluxes under different condition

Assessing seasonality of biochemical CO2 exchange model parameters from micrometeorological flux observations at boreal coniferous forest

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