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  • 1
    Unknown
    Basel, Boston, Berlin : Birkhäuser
    Keywords: chemical composition of dew ; fog microphysics ; fog simulations ; remote sensing ; temporal and spatial variation of fog
    Description / Table of Contents: This topical issue of the Journal of Pure and Applied Geophysics focuses on research related to dew and various types of fog occurring around the globe which was presented on July 25-30, 2010, at the 5th International Conference on Fog, Fog Collection, and Dew in Münster, Germany. The areas of knowledge in this field include surface in-situ and remote sensing observations of fog, dew, fog collection, applications of the various fog models (such as 1D, 2D, and 3D fog and forecasting models), microphysical parameterizations, and climatology. This volume gives a very good review of the existing knowledge and highlights the remaining difficulties in predicting and measuring fog at various scales of time and space. It also represents an important step in the direction of addressing new scientific challenges in fog and dew related research, teaching, and operational applications. Students as well as researchers, who are interested either in fog, in association with cloud physics, physical meteorology, aviation meteorology, climatology, weather forecasting and nowcasting, or in other adjacent disciplines like hydrometeorology, environment, and agriculture, will benefit from consulting and reading this topical issue. This publication was significantly supported by the Canadian National Search And Rescue (SAR) Secretariat by funding the Fog Remote Sensing and Modeling (FRAM) Project led by Dr. Ismail Gultepe since 2005.
    Pages: Online-Ressource (VI, 408 Seiten)
    ISBN: 9783034804561
    Language: English
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Studies and models of trace-gas flux in the Arctic consider temperature and moisture to be the dominant controls over land–atmosphere exchange,, with little attention having been paid to the effects of different substrates. Likewise, current Arctic vegetation maps for models of vegetation ...
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Synthesis of results from several Arctic and boreal research programmes provides evidence for the strong role of high-latitude ecosystems in the climate system. Average surface air temperature has increased 0.3 °C per decade during the twentieth century in the western North American Arctic and boreal forest zones. Precipitation has also increased, but changes in soil moisture are uncertain. Disturbance rates have increased in the boreal forest; for example, there has been a doubling of the area burned in North America in the past 20 years. The disturbance regime in tundra may not have changed. Tundra has a 3–6-fold higher winter albedo than boreal forest, but summer albedo and energy partitioning differ more strongly among ecosystems within either tundra or boreal forest than between these two biomes. This indicates a need to improve our understanding of vegetation dynamics within, as well as between, biomes. If regional surface warming were to continue, changes in albedo and energy absorption would likely act as a positive feedback to regional warming due to earlier melting of snow and, over the long term, the northward movement of treeline. Surface drying and a change in dominance from mosses to vascular plants would also enhance sensible heat flux and regional warming in tundra. In the boreal forest of western North America, deciduous forests have twice the albedo of conifer forests in both winter and summer, 50–80% higher evapotranspiration, and therefore only 30–50% of the sensible heat flux of conifers in summer. Therefore, a warming-induced increase in fire frequency that increased the proportion of deciduous forests in the landscape, would act as a negative feedback to regional warming.Changes in thermokarst and the aerial extent of wetlands, lakes, and ponds would alter high-latitude methane flux. There is currently a wide discrepancy among estimates of the size and direction of CO2 flux between high-latitude ecosystems and the atmosphere. These discrepancies relate more strongly to the approach and assumptions for extrapolation than to inconsistencies in the underlying data. Inverse modelling from atmospheric CO2 concentrations suggests that high latitudes are neutral or net sinks for atmospheric CO2, whereas field measurements suggest that high latitudes are neutral or a net CO2 source. Both approaches rely on assumptions that are difficult to verify. The most parsimonious explanation of the available data is that drying in tundra and disturbance in boreal forest enhance CO2 efflux. Nevertheless, many areas of both tundra and boreal forests remain net sinks due to regional variation in climate and local variation in topographically determined soil moisture. Improved understanding of the role of high-latitude ecosystems in the climate system requires a concerted research effort that focuses on geographical variation in the processes controlling land–atmosphere exchange, species composition, and ecosystem structure. Future studies must be conducted over a long enough time-period to detect and quantify ecosystem feedbacks.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This paper presents results of 1 year (from March 25, 2003 to March 24, 2004, 366 days) of continuous measurements of net ecosystem CO2 exchange (NEE) above a steppe in Mongolia using the eddy covariance technique. The steppe, typical of central Mongolia, is dominated by C3 plants adapted to the continental climate. The following two questions are addressed: (1) how do NEE and its components: gross ecosystem production (GEP) and total ecosystem respiration (Reco) vary seasonally? (2) how do NEE, GEP, and Reco respond to biotic and abiotic factors? The hourly minimal NEE and the hourly maximal Reco were −3.6 and 1.2 μmol m−2 s−1, respectively (negative values denoting net carbon uptake by the canopy from the atmosphere). Peak daily sums of NEE, GEP, and Reco were −2.3, 3.5, and 1.5 g C m−2 day−1, respectively. The annual sums of GEP, Reco, and NEE were 179, 138, and −41 g C m−2, respectively. The carbon removal by sheep was estimated to range between 10 and 82 g C m−2 yr−1 using four different approaches. Including these estimates in the overall carbon budget yielded net ecosystem productivity of −23 to +20 g C m−2 yr−1. Thus, within the remaining experimental uncertainty the carbon budget at this steppe site can be considered to be balanced. For the growing period (from April 23 to October 21, 2003), 26% and 53% of the variation in daily NEE and GEP, respectively, could be explained by the changes in leaf area index. Seasonality of GEP, Reco, and NEE was closely associated with precipitation, especially in the peak growing season when GEP and Reco were largest. Water stress was observed in late July to early August, which switched the steppe from a carbon sink to a carbon source. For the entire growing period, the light response curves of daytime NEE showed a rather low apparent quantum yield (α=−0.0047 μmol CO2 μmol−1 photons of photosynthetically active radiation). However, the α values varied with air temperature (Ta), vapor pressure deficit, and soil water content.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 74 (1995), S. 321-340 
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A correction model for eddy correlation flux measurements is developed and applied to nitrogen dioxide flux measurements obtained from a SOLENT sonic anemometer and a Scintrex Luminox LMA-3 analyser for NO2. Four field campaigns were carried out near the village of Merenschwand in Central Switzerland from which two were selected for further analysis in this paper. The need for the correction of measured eddy covariance fluxes arises due to the damping loss of the NO2 analyser at high frequencies. This damping loss is described by an analogy to inductance in an electronical alternating current circuit. The independent variables in the correction model are:z (measuring height above zero-plane displacement), $$\bar u$$ (mean horizontal wind speed), ζ (Monin-Obukhov stability parameter),f (natural frequency) and inductanceL. The value for inductanceL can be derived from spectral and cospectral analysis. The theoretical cospectrum of an ideal measurement is taken from Kaimalet al. (1972) and extended with a damping term in order to describe the real measurements of the cospectrum. The inductanceL of the LMA-3 with a 0.6 cm teflon aspiration tube of 5 m length lies in the order of 0.30 to 0.35 for the dataset from Merenschwand. With this inductance, a correction factor of 1.17 in August/September 1992 and of 1.18 in May 1993 was determined for the NO2 flux maxima during daytime. The range of the correction factor is 1.05 to 1.31 for the mean daily cycles of both datasets.
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2010-11-10
    Type: paper
    Format: application/pdf
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  • 7
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    Unknown
    Univ. of Iceland, School of Engineering and Natural Sciences
    In:  [Talk] In: 14th Workshop on Physical Processes in Natural Waters, 28.06.-01.07.2010, Reykjavik, Iceland . Conference Proceedings / 14th Workshop on Physical Processes in Natural Waters, Reykjavik, Iceland, June 28 - July 1 2010 / Ed.: ; pp. 143-144 .
    Publication Date: 2012-02-23
    Description: Methane (CH4) is one of the most important greenhouse gases (IPCC, 2005). Lakes and reservoirs have been identified as important, but overlooked, sources to the global CH4 budget. CH4 emission pathways include dissolved gas exchange at the water surface, bubble transport (ebullition), and degassing at the turbines of a hydropower dam or further downstream (Soumis, et al., 2005). Ebullition is an extremely effective pathway as bubbles mostly bypass oxidation at the sediment surface or in the water column and directly emit CH4. The stochastic nature of ebullition, however, makes it incredibly difficult to estimate; thus the aim of this study was to compare the traditional funnel method for measuring ebullition with a mass balance system analysis, atmospheric CH4 measurements, and hydroacoustic surveying. A yearlong CH4 survey was conducted at 2.5 km2 Lake Wohlen, a 90-yr-old run-of-river hydropower reservoir along the Aare River downstream of Bern, Switzerland. Dissolved CH4 ([CH4]d) profiles were measured monthly at the river inflow and at the dam. Sediment surface and water surface CH4 diffusion and CH4 oxidation in the water column were measured and/or calculated. Gas trap funnels measured ebullition near the seabed; drifting chambers captured total surface CH4 emissions. A bubble dissolution model was used to assess fractions of CH4 dissolving into the water and emitted to the atmosphere from bubbles. Complete method details in DelSontro, et al. (2010). Drifting chamber campaigns were accompanied by hydroacoustic surveys using an echosounder (Simrad EK60, 120 kHz). Eddy covariance measurements of atmospheric CH4 fluxes (EC/CH4) over the lake were made in conjunction with a cavity ringdown laser spectrometer (Los Gatos Research DLT-100). For details, see Eugster and Plüss (in press). It was discovered that [CH4]d increased by an order of magnitude along the reservoir and the [CH4]d accumulation was exponentially correlated with water temperature (T) (Figure 1a). The bubble dissolution model predicted that 70% of bubble-conveyed CH4 would reach the atmosphere, resulting in ~470 mg CH4 m-2 d-1 emitted to the atmosphere at T=17°C. Sediment and surface diffusions did not vary much with season and played a much lesser role in CH4 emissions than ebullition. Methane oxidation was negligible in this oxic reservoir with an average 2-day residence time. A system analysis was developed to better constrain the stochastic pattern of ebullition. Assuming no ebullition in winter (T〈10°C), sediment diffusion was estimated based on [CH4]d accumulation in water at a given flow rate. The [CH4]d accumulation and T regression was used to estimate [CH4]d from dissolving bubbles at various T regimes which, at T=17°C, agreed well with funnel measurements (140 and 220 mg CH4 m-2 d-1, respectively). Using the bubble dissolution model results, sediment ebullition and atmospheric emissions were calculated and agreed well with empirical results. Considering all CH4 dissolved into the water from rising bubbles will either degas at the turbines or further downstream, Lake Wohlen thus emits ~156 mg CH4 m-2 d-1 on average throughout the year (140 tons/yr; Figure 1b), the highest recorded for a temperate reservoir to date (Soumis, et al., 2005) and of which ~80% is from ebullition. Drifting chambers captured emissions (mean, 855 mg CH4 m-2 d-1) much higher than those estimated with the system analysis at 17°C, but chambers were deployed in a highly active ebullition area. The chamber emissions agreed, however, with the peak CH4 emissions measured by EC/CH4 in the same region and are comparable to emissions estimated via hydroacoustics. These findings further highlight the importance in a potentially warming climate of (1) temperature-correlated CH4 ebullition emissions from temperate water bodies, and (2) these promising techniques for quantifying them.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 9
    Publication Date: 2007-02-01
    Description: The effects of historical land-use and land-cover changes on the climate of the Swiss Plateau in the different seasons were investigated. In the 19th century, a civil engineering project was initiated to reshape the lake and river system on the Swiss Plateau in order to ban the frequent flooding during extreme weather events. The landscape modifications consisted primarily of a conversion of wetlands with extended peat soils into a highly productive agricultural landscape. Historical maps (1800–1850) served as a basis for the reconstruction of the past land use. The “Lokal-Modell” of the Consortium for Small-Scale Modelling was used to conduct eight one-month long high-resolution simulations (1.5 × 1.5 km2) with present and past landscape conditions. The modified soil and surface properties led to distinctly altered energy and moisture exchanges at the surface and as a consequence affected the local and regional climate. The climatic changes show different characteristics and magnitudes in the cold (October – March) as compared to the warm season (April – September). The landscape modifications led to an average daytime cooling between −0.12 °C (January) and −0.61 °C (April) and a night-time warming of 0.19 °C−0.34 °C. The differences in the mean monthly temperatures show a warming of 0.1 °C−0.2 °C in the cold season and a cooling of similar magnitude in most of the study area in the warm season. The modification of the radiation budget and the surface energy balance distinctly affected the convective activity in the study area in the warm season, but had only a weak effect on convectivity in the cold season. The cloud coverage in the warm season is therefore distinctly reduced compared to the past. ©2006 Springer Science+Business Media B.V.
    Print ISSN: 0165-0009
    Electronic ISSN: 1573-1480
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2005-04-26
    Description: The influence of agricultural management on the CO2 budget of a typical subalpine grassland was investigated at the Swiss CARBOMONT site at Rigi-Seebodenalp (1025 m a.s.l.) in Central Switzerland. Eddy covariance flux measurements obtained during the first growing season from the mid of spring until the first snow fall (17 Mai to 25 September 2002) are reported. With respect to the 10-year average 1992–2001, we found that this growing season had started 10 days earlier than normal, but was close to average temperature with above-normal precipitation (100–255% depending on month). Using a footprint model we found that a simple approach using wind direction sectors was adequate to classify our CO2 fluxes as being controlled by either meadow or pasture. Two significantly different light response curves could be determined: one for periods with external interventions (grass cutting, cattle grazing) and the other for periods without external interventions. Other than this, meadow and pasture were similar, with a net carbon gain of −128 ± 17 g C m−2 on the undisturbed meadow, and a net carbon loss of 79 ± 17 g C m−2 on the managed meadow, and 270 ± 24 g C m−2 on the pasture during 131 days of the growing season, respectively. The grass cut in June reduced the gross CO2 uptake of the meadow by 50 ± 2% until regrowth of the vegetation. Cattle grazing reduced gross uptake over the whole vegetation period (37 ± 2%), but left respiration at a similar level as observed in the meadow. ©2004 Springer-Verlag/Wien
    Print ISSN: 0177-798X
    Electronic ISSN: 1434-4483
    Topics: Geosciences , Physics
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