Extension of the Averaging Time in Eddy-Covariance Measurements and Its Effect on the Energy Balance Closure   总被引：1，自引：0，他引：1  

Doojdao Charuchittipan  Wolfgang Babel  Matthias Mauder  Jens-Peter Leps  Thomas Foken 《Boundary-Layer Meteorology》2014,152(3):303-327

The modified ogive analysis and the block ensemble average were employed to investigate the impact of the averaging time extension on the energy balance closure over six land-use types. The modified ogive analysis, which requires a steady-state condition, can extend the averaging time up to a few hours and suggests that an averaging time of 30 min is still overall sufficient for eddy-covariance measurements over low vegetation. The block ensemble average, which does not require a steady-state condition, can extend the averaging time to several days. However, it can improve the energy balance closure for some sites during specific periods, when secondary circulations exist in the vicinity of the sensor. These near-surface secondary circulations mainly transport sensible heat, and when near-ground warm air is transported upward, the sensible heat flux observed by the block ensemble average will increase at longer averaging times. These findings suggest an alternative energy balance correction for a ground-based eddy-covariance measurement, in which the attribution of the residual depends on the ratio of sensible heat flux to the buoyancy flux. The fraction of the residual attributed to the sensible heat flux by this energy balance correction is larger than in the energy balance correction that preserves the Bowen ratio.  相似文献   

A 16-ka δ18O record of lacustrine sugar biomarkers from the High Himalaya reflects Indian Summer Monsoon variability     

Michael Zech  Mario Tuthorn  Roland Zech  Frank Schlütz  Wolfgang Zech  Bruno Glaser 《Journal of Paleolimnology》2014,51(2):241-251

We investigated a late glacial–Holocene lacustrine sediment archive located at 4,050 m a.s.l. in the small carbonate-free catchment of Lake Panch Pokhari, Helambu Himal, Nepal. A δ¹⁸O sugar biomarker record was established by applying novel compound-specific δ¹⁸O analysis of plant sugar biomarkers (Zech and Glaser in Rapid Commun Mass Spectrom 23:3522–3532, 2009). This method overcomes analytical challenges such as extraction and purification faced by previous methods aimed at using δ¹⁸O of aquatic cellulose as a paleoclimate proxy. The δ¹⁸O results for sugar biomarkers arabinose, xylose and fucose agree well and reveal a pronounced trend towards lower δ¹⁸O values during the deglaciation and the onset of the Bølling/Allerød interstadial. By contrast, the period of the Younger Dryas is characterized by higher δ¹⁸O values. The early Holocene again reveals lower δ¹⁸O values. We suggest that our lacustrine δ¹⁸O record reflects coupled hydrological and thermal control. It is strongly related to changes in the oxygen isotopic composition of paleo-precipitation and resembles the δ¹⁸O records of Asian speleothems. With respect to the ‘amount effect,’ the record is interpreted as reflecting the Indian Summer Monsoon intensity. The precipitation signal is, however, amplified in our record by evaporative ¹⁸O enrichment that is controlled by the ratio of precipitation to evaporation. We suggest that our δ¹⁸O record reflects the variability of the Indian Summer Monsoon, which was strong during the Bølling/Allerød interstadial and early Holocene, but weak during the Younger Dryas stadial. This interpretation is corroborated by a pollen-based index for Lake Panch Pokhari that estimated the strength of the Indian Summer Monsoon versus the strength of the Westerlies. Millennial-scale synchronicity with the Greenland δ¹⁸O temperature records highlights the previously suggested strong teleconnections between the Asian Monsoon system and North Atlantic climate variability.  相似文献   

A 3-year dataset of sensible and latent heat fluxes from the Tibetan Plateau,derived using eddy covariance measurements     

Maoshan Li  Wolfgang Babel  Xuelong Chen  Lang Zhang  Fanglin Sun  Binbin Wang  Yaoming Ma  Zeyong Hu  Thomas Foken 《Theoretical and Applied Climatology》2015,122(3-4):457-469

  相似文献   

The need for data: natural disasters and the challenges of database management   总被引：2，自引：2，他引：0  

Angelika Wirtz  Wolfgang Kron  Petra Löw  Markus Steuer 《Natural Hazards》2014,70(1):135-157

Hundreds of natural catastrophes occur worldwide every year—there were 780 loss events per year on average over the last 10 years. Since 1980, these disasters have claimed over two million lives and caused losses worth US$ 3,000 billion. The deadliest disasters were caused by earthquakes: the tsunami following the Sumatra quake (2004) and the Haiti earthquake (2010) claimed more than 220,000 lives each. The Great East Japan Earthquake of 11 March 2011 was the costliest natural disaster of all times, with total losses of US$ 210 billion. Hurricane Katrina, in 2005, was the second costliest disaster, with total losses of US$ 140 billion (in 2010 values). To ensure that high-quality natural disaster analyses can be performed, the data have to be collected, checked and managed with a high degree of expertise and professionality. Scientists, governmental and non-governmental organisations and the finance industry make use of global databases that contain losses attributable to natural catastrophes. At present, there are three global and multi-peril loss databases: NatCatSERVICE (Munich Re), Sigma (Swiss Re) and EM-Dat (Centre for Research on the Epidemiology of Disasters). They are supplemented by numerous databases focusing on national or regional issues, certain hazards and specific sectors. This paper outlines the criteria and definitions relating to how global and multi-peril databases are operated, and the efforts being made to ensure consistent and internationally recognised standards of data management. In addition, it presents the concept and methodology underlying the NatCatSERVICE database, and points out the many challenges associated with data acquisition and data management.  相似文献   

Morphology and geology of the continental shelf and upper slope of southern Central Chile (33°S–43°S)     

David Völker  Jacob Geersen  Eduardo Contreras-Reyes  Javier Sellanes  Silvio Pantoja  Wolfgang Rabbel  Martin Thorwart  Christian Reichert  Martin Block  Wilhelm Reimer Weinrebe 《International Journal of Earth Sciences》2014,103(7):1765-1787

The continental shelf and slope of southern Central Chile have been subject to a number of international as well as Chilean research campaigns over the last 30 years. This work summarizes the geologic setting of the southern Central Chilean Continental shelf (33°S–43°S) using recently published geophysical, seismological, sedimentological and bio-geochemical data. Additionally, unpublished data such as reflection seismic profiles, swath bathymetry and observations on biota that allow further insights into the evolution of this continental platform are integrated. The outcome is an overview of the current knowledge about the geology of the southern Central Chilean shelf and upper slope. We observe both patches of reduced as well as high recent sedimentation on the shelf and upper slope, due to local redistribution of fluvial input, mainly governed by bottom currents and submarine canyons and highly productive upwelling zones. Shelf basins show highly variable thickness of Oligocene-Quaternary sedimentary units that are dissected by the marine continuations of upper plate faults known from land. Seismic velocity studies indicate that a paleo-accretionary complex that is sandwiched between the present, relatively small active accretionary prism and the continental crust forms the bulk of the continental margin of southern Central Chile.  相似文献   

Constraining input and output fluxes of the southern-central Chile subduction zone: water,chlorine and sulfur     

David Völker  Heidi Wehrmann  Steffen Kutterolf  Karthik Iyer  Wolfgang Rabbel  Jacob Geersen  Kaj Hoernle 《International Journal of Earth Sciences》2014,103(7):2129-2153

In this paper, we constrain the input and output fluxes of H₂O, Cl and S into the southern-central Chilean subduction zone (31°S–46°S). We determine the input flux by calculating the amounts of water, chlorine and sulfur that are carried into the subduction zone in subducted sediments, igneous crust and hydrated lithospheric mantle. The applied models take into account that latitudinal variations in the subducting Nazca plate impact the crustal porosity and the degree of upper mantle serpentinization and thus water storage in the crust and mantle. In another step, we constrain the output fluxes of the subduction zone both to the subcontinental lithospheric mantle and to the atmosphere–geosphere–ocean by the combined use of gas flux determinations at the volcanic arc, volume calculations of volcanic rocks and the combination of mineralogical and geothermal models of the subduction zone. The calculations indicate that about 68 Tg/m/Ma of water enters the subduction zone, as averaged over its total length of 1,480 km. The volcanic output on the other hand accounts for 2 Tg/m/Ma or 3 % of that input. We presume that a large fraction of the volatiles that are captured within the subducting sediments (which accounts for roughly one-third of the input) are cycled back into the ocean through the forearc. This assumption is however questioned by the present lack of evidence for major venting systems of the submarine forearc. The largest part of the water that is carried into the subduction zone in the crust and hydrated mantle (accounting for two-thirds of the input) appears to be transported beyond the volcanic arc.  相似文献   

Impacts of large-scale climatic disturbances on the terrestrial carbon cycle     

Tim Erbrecht  Wolfgang Lucht 《Carbon balance and management》2006,1(1):7-7

Background

The amount of carbon dioxide in the atmosphere steadily increases as a consequence of anthropogenic emissions but with large interannual variability caused by the terrestrial biosphere. These variations in the CO₂ growth rate are caused by large-scale climate anomalies but the relative contributions of vegetation growth and soil decomposition is uncertain. We use a biogeochemical model of the terrestrial biosphere to differentiate the effects of temperature and precipitation on net primary production (NPP) and heterotrophic respiration (Rh) during the two largest anomalies in atmospheric CO₂ increase during the last 25 years. One of these, the smallest atmospheric year-to-year increase (largest land carbon uptake) in that period, was caused by global cooling in 1992/93 after the Pinatubo volcanic eruption. The other, the largest atmospheric increase on record (largest land carbon release), was caused by the strong El Niño event of 1997/98.

Results

We find that the LPJ model correctly simulates the magnitude of terrestrial modulation of atmospheric carbon anomalies for these two extreme disturbances. The response of soil respiration to changes in temperature and precipitation explains most of the modelled anomalous CO₂ flux.

Conclusion

Observed and modelled NEE anomalies are in good agreement, therefore we suggest that the temporal variability of heterotrophic respiration produced by our model is reasonably realistic. We therefore conclude that during the last 25 years the two largest disturbances of the global carbon cycle were strongly controlled by soil processes rather then the response of vegetation to these large-scale climatic events.  相似文献   

High resolution climate simulations over the Arctic   总被引：1，自引：0，他引：1  

Annette Rinke  Klaus Dethloff  Arne Spekat  Wolfgang Enke  Jens Hesselbjerg Christensen 《Polar research》1999,18(2):143-150

The regional atmospheric climate model HIRHAM has been applied to the Arctic. Simulations for the whole year 1990 and for an ensemble of winter months (January of 1985-1995) have been performed. The comparison of the simulations with observational data analyses shows that the general spatial patterns are in good agreement with the data, in both the vertical structure and the annual cycle. For an additional validation of the model results, a multivariate classification of large-scale circulation patterns has been applied to the January ensemble model simulations.  相似文献   

Physical laboratory analyses of intergravel flow through brown trout redds (Salmo trutta fario) in response to coarse sand infiltration          下载免费PDF全文

Wolfgang Obruca  Christoph Hauer 《地球表面变化过程与地形》2017,42(4):670-680

In the spawning environment of salmonids, the quality of the intergravel flow is an essential abiotic requirement for the survival success of incubated embryos. As one of the most frequently investigated anthropogenic environmental impacts, the enhanced mobilization of fine sediments (<1 mm) and their entry into riverine ecosystems is considered as a major cause for the degradation of a variety of biological processes and habitats, including the spawning habitats of salmonids. In catchments draining crystalline bedrock, however, like the Bohemian Massif in the northern part of Austria, the excessive loading of river channels with coarse sand and fine gravel sediments (D = 1–10 mm) and less cohesive than fines is common as a consequence of altered catchment land use. Here, far less understanding exists of the mechanism and the possible implications of coarse sand infiltration on the functioning of the intergravel flow in salmonid redds. To investigate the intergravel flow hydraulics in response to coarse sand infiltration (D₅₀ = 2 mm) in brown trout spawning redds (Salmo trutta fario ) under controlled conditions, a laboratory flume experiment with three infiltration scenarios was conducted: (1) no infiltration; (2) segmental infiltration; and (3) full section infiltration. A more than two times drop in the average intergravel flow velocity was documented from scenario 1 (5.85 cms^?1) to scenario 2 (2.53 cms^?1) and another clear reduction was seen from scenario 2 (2.53 cms^?1) to scenario 3 (1.61 cms^?1). Moreover, in scenario 3, a clear reduction of the intergravel flow distance traveled was observed. Based on the findings we conclude that future considerations regarding the sustainable catchment management of salmonid fisheries should include programs to reduce not only the excessive entry of fines, but, in the relevant catchments, also the entry of excessive coarse sand into the riverine ecosystem. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Design considerations for using Distributed Acoustic Sensing for cross-well seismics: A case study for CO2 storage     

Andreas Wuestefeld  Wolfgang Weinzierl 《Geophysical Prospecting》2020,68(6):1893-1905

Downhole monitoring with fibre-optic Distributed Acoustic Sensing (DAS) systems offers unprecedented spatial resolution. At the same time, costs are reduced since repeated wireline surveys can be replaced by the permanent installation of comparatively cheap fibre cables. However, the single component nature of fibre data requires novel approaches when designing a monitoring project such as cross-well seismics. At the example of the shallow CO₂ injection test site in Svelvik, Norway, we model the evolution of velocity changes during CO₂ injection based on rock physics theory. Different cross-well seismic design scenarios are then considered to evaluate the best design and the limits of this method to detect containment breach. We present a series of evaluation tools to compare the effect of different well spacings for cross-well seismic tomography. In addition to travel-times, we also consider characteristic amplitude changes along the fibre unique to DAS strain measurements, which might add a constraint to the inversion. We also compare the effect of using helical fibres instead of classical straight fibres. We thus present a toolbox to evaluate and compare different monitoring design options for fibre optic downhole installations for cross-well monitoring.  相似文献