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The vernal equinox total solar eclipse of 20 March 2015 produced a maximum occultation of 65.8 to 70.1 % over Switzerland during the morning hours (09:22 to 11:48 CET). Skies were generally clear over the Swiss Alps due to a persistent high-pressure band between the UK and Russia associated with a rather weak pressure gradient over the continent. To assess the effects of penumbral shading on near-surface meteorology across Switzerland, air temperature data measured at 10-minute intervals at 184 MeteoSwiss weather stations that reported air temperature at 10-minute intervals were used. Wind speed and direction data were available from 165 of these stations. Additionally, six Swiss FluxNet eddy covariance flux (ECF) sites provided turbulent measurements at 20 Hz resolution. During maximum occultation the temperature drop was up to 5.8 K at a mountain site where cold air can pool in the topographic depression of the weather station. The bootstrapped average of the maximum temperature drops of all 184 MeteoSwiss sites during the solar eclipse was 1.51 ± 0.02 K (mean ± SE). A detailed comparison with literature values since 1834 showed a temperature decrease by 2.6 ± 1.7 K (average of all reports) with extreme values up to 11 K. On fair weather days under weak larger scale pressure gradients, local thermo-topographic wind systems develop that are driven by small-scale pressure and temperature gradients. At one ECF site, the penumbral shading delayed the morning transition from down-valley to up-valley wind conditions, and at another site, it prevented this transition from occurring at all. Data from the 165 MeteoSwiss sites measuring wind direction did not show a consistent pattern of wind direction response to the passing of the penumbral shadow. These results suggest that the local topographic setting had an important influence on the temperature drop and the wind flow patterns during the eclipse. Still, results tend to lend support to a recent theory that the anticyclonic cold-air outflow from the center of the eclipse only extends ≈ 1600 km outwards, with cyclonic flow beyond that distance. This contrasts with an earlier theory that the anticyclonic outflow should reach as far as ≈ 2400 km from the center of the eclipse, which would have included all of Switzerland during the 2015 eclipse. Nevertheless, a significant cyclonic effect of the passing penumbral shadow was found in the elevation range ≈ 1700–2700 m a.s.l., but not at lower elevations of the Swiss Plateau. Thus, measurable effects of penumbral shading on the local wind system could be even found at ≈ 2000 km from the path of the eclipse (that is, Switzerland during the 2015 eclipse)., Atmospheric Chemistry and Physics Discussions, ISSN:1680-7375, ISSN:1680-7367

Agricultural and Forest Meteorology, 247, ISSN:0168-1923, ISSN:1873-2240

Environmental Science: Processes & Impacts, 19 (10), ISSN:2050-7887, ISSN:2050-7895

Atmospheric inverse modelling has the potential to provide observation-based esti-mates of greenhouse gas emissions at the country scale, thereby allowing for an inde-pendent validation of national emission inventories. Here, we present a regional scaleinverse modelling study to quantify the emissions of methane (CH4) from Switzerland, making use of the newly established CarboCount-CH measurement network and a highresolution Lagrangian transport model. Overall we estimate national CH4emissions tobe 196±18 Gg yr−1for the year 2013 (1σuncertainty). This result is in close agree-ment with the recently revised “bottom-up” estimate of 206±33 Gg yr−1published bythe Swiss Federal Office for the Environment as part of the Swiss Greenhouse Gas Inventory (SGHGI). Results from sensitivity inversions using alternative prior emissions,covariance settings, baseline treatments, two different inverse algorithms (Bayesianand extended Kalman Filter), and two different transport models confirms the robust-ness and independent character of our estimate. According to the latest “bottom-up”inventory the main CH4source categories in Switzerland are agriculture (78 %), waste handling (15 %) and natural gas distribution and combustion (6 %). The spatial distri-bution and seasonal variability of our posterior emissions suggest an overestimation ofagricultural CH4emissions by 10 to 20 % in the most recent national inventory, whichis likely due to an overestimation of emissions from manure handling. Urban areas donot appear as emission hotspots in our posterior results suggesting that leakages from natural gas disribution are only a minor source of CH4in Switzerland. This is consis-tent with rather low emissions of 8.4 Gg yr−1reported by the SGHGI but inconsistentwith the much higher value of 32 Gg yr−1implied by the EDGARv4.2 inventory for thissector. Increased CH4emissions (up to 30 % compared to the prior) were deduced forthe north-eastern parts of Switzerland. This feature was common to most sensitivity inversions, which rules out an artefact of the transport model and the inversion system.However, it was not possible to assign an unambiguous source process to the region.The observations of the CarboCount-CH network provided invaluable and independent information for the validation of the national bottom-up inventory. Similar systems needto be sustained to provide independent monitoring of future climate agreements. ISSN:1680-7375 ISSN:1680-7367

Summer droughts projected to increase in central Europe due to climate changes strongly influence the carbon cycle of ecosystems. Persistent respiration activities during drought periods are responsible for a significant carbon loss, which may turn the ecosystem from a sink into a source of carbon. There are still gaps in our knowledge regarding the characteristic changes taking place in the respiration of the different components of the ecosystem in response to drought events. In the present study, we combined a physical separation of soil respiration components with continuous measurements of soil CO2 efflux and its isotopic (13C) signals at a dry grassland site in Hungary. The physical separation of soil respiration components was performed by means of inox meshes and tubes inserted into the soil. The root-excluded and root- and mycorrhiza-excluded treatments served to measure the isotopic signals of the rhizospheric, mycorrhizal fungi and heterotrophic components, respectively. In the dry grassland investigated in the study the three components of the soil CO2 efflux decreased at different rates under drought conditions. During drought the contribution made by the heterotrophic components was the highest (54±8%; mean ±SE). Rhizospheric component was the most sensitive to soil drying with its relative contribution to the total soil respiration dropping from 66±7 (non-stressed) to 35±17% (mean ±SE) under drought conditions. According to our results the heterotrophic component of soil respiration is the major contributor to the respiration activities during drought events in the dry grassland ecosystem studied, Biogeosciences Discussions, 12, ISSN:1810-6277, ISSN:1810-6285

ISSN:1680-7375 ISSN:1680-7367

Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring `green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future., Biogeosciences Discussions, 12 (20), ISSN:1810-6277, ISSN:1810-6285

Atmospheric Chemistry and Physics Discussions, 15, ISSN:1680-7375, ISSN:1680-7367

Aims Our aim was to study the effect of potential biotic drivers, including evapotranspiration (ET) and gross primary production (GPP), on the soil CO2 production and efflux on the diel time scale. Methods Eddy covariance, soil respiration and soil CO2 gradient systems were used to measure the CO2 and H2O fluxes in a dry, sandy grassland in Hungary. The contribution of CO2 production from three soil layers to plot-scale soil respiration was quantified. CO2 production and efflux residuals after subtracting the effects of the main abiotic and biotic drivers were analysed. Results Soil CO2 production showed a strong negative correlation with ET rates with a time lag of 0.5 h in the two upper layers, whereas less strong, but still significant time-lagged and positive correlations were found between GPP and soil CO2 production. Our results suggest a rapid negative response of soil CO2 production rates to transpiration changes, and a delayed positive response to GPP. Conclusions We found evidence for a combined effect of soil temperature and transpiration that influenced the diel changes in soil CO2 production. A possible explanation for this pattern could be that a significant part of CO2 produced in the soil may be transported across soil layers via the xylem., Plant and Soil, 388 (1-2), ISSN:0032-079X, ISSN:1573-5036

Net CO2 exchange data of legume crops at 17 flux tower sites in North America and 3 sites in Europe representing 29 site-years of measurements were partitioned into gross photosynthesis and ecosystem respiration by using nonrectangular hyperbolic light-response function method. The analyses produced net CO2 exchange data and new ecosystem-scale ecophysiological parameter estimates for of legume crops determined at the diurnal and weekly time steps. Dynamics and annual totals of gross photosynthesis, ecosystem respiration, and net ecosystem production were calculated by gap-filling with multivariate nonlinear regression. Comparison with the data from grain crops obtained with the same method demonstrated that CO2 exchange rates and ecophysiological parameters of legumes were lower than for maize, but higher than for wheat crops. Year-round annual legume crops demonstrated a broad range of net ecosystem production, from sinks of +760 g CO2 m-2 yr-1 to sources of –2100 g CO2 m-2 yr-1, with average of –330 g CO2 m-2 yr-1, indicating overall moderate CO2-source activity related to shorter period of photosynthetic uptake and metabolic costs of nitrogen fixation. Perennial legumes (alfalfa) were strong sinks for atmospheric CO2 with average NEP of +980 (range 550 to 1200) g CO2 m-2 yr-1

Environmental Research Letters, 9 (8), ISSN:1748-9326, ISSN:1748-9318

This paper aims to assess the spatial variability in the response of CO2 exchange to irradiance across the Arctic tundra during peak season using light response curve (LRC) parameters. This investigation allows us to better understand the future response of Arctic tundra under climatic change. Peak season data were collected during different years (between 1998 and 2010) using the micrometeorological eddy covariance technique from 12 circumpolar Arctic tundra sites, in the range of 64–74° N. The LRCs were generated for 14 days with peak net ecosystem exchange (NEE) using an NEE–irradiance model. Parameters from LRCs represent site-specific traits and characteristics describing the following: (a) NEE at light saturation (Fcsat), (b) dark respiration (Rd), (c) light use efficiency (α), (d) NEE when light is at 1000 μmol m−2 s−1 (Fc1000), (e) potential photosynthesis at light saturation (Psat) and (f) the light compensation point (LCP). Parameterization of LRCs was successful in predicting CO2 flux dynamics across the Arctic tundra. We did not find any trends in LRC parameters across the whole Arctic tundra but there were indications for temperature and latitudinal differences within sub-regions like Russia and Greenland. Together, leaf area index (LAI) and July temperature had a high explanatory power of the variance in assimilation parameters (Fcsat, Fc1000 and Psat, thus illustrating the potential for upscaling CO2 exchange for the whole Arctic tundra. Dark respiration was more variable and less correlated to environmental drivers than were assimilation parameters. This indicates the inherent need to include other parameters such as nutrient availability, substrate quantity and quality in flux monitoring activities.

ISSN:1810-6277 ISSN:1810-6285