Spatial observations of large eddies and cross-canopy coupling with joint fiber-optic distributed sensing and eddy covariance flux measurements

2020 ◽  
Author(s):  
Olli Peltola ◽  
Karl Lapo ◽  
Christoph Thomas ◽  
Timo Vesala
Keyword(s):  
Eddy Covariance ◽  
Wind Shear ◽  
Fiber Optic ◽  
Distributed Sensing ◽  
Carbon Dioxide Transport ◽  
Stable Conditions ◽  
Sonic Anemometers ◽  
Flux Measurements ◽  
Large Eddies

<p>Air flows above forest canopies are typically governed by large coherent eddies generated mechanically by inflected mean wind velocity profile or thermally by buoyancy in the convective regime. A significant body of research have been devoted to the role of these eddies on ecosystem scalar (gases and heat) exchange since they are likely related to the energy balance closure problem observed at the eddy covariance (EC) stations and turbulent flux divergence under stable stratification. Here we utilize fiber-optic distributed sensing on a tall mast to observe the turbulent fluctuations of air temperature with high spatial (25 cm) and temporal resolution (1 Hz) from the forest floor up to 120 m above the ground. These unique measurements resolved the continuous vertical profile of scalar turbulence and hence enabled us to study the topology (height – time space) of the turbulent eddies in different stability regimes. For example, the inclination angle of the eddies changed with stability and the scalar ramps often observed in canopy flows were evident only close to the canopy top, whereas higher up thermal eddies dominated the flow. Furthermore, the measurements permitted the identification of coupled air layers and hence analysis on the dynamics of below-canopy decoupling. During stable conditions with wind shear large eddies and the related inverted ramps in the temperature time series were observed at the top of the decoupling layer, however when the wind shear decreased the flow switched to submeso regime with canopy waves. These analyses were then combined with concurrent turbulence measurements with 3D sonic anemometers at several heights and EC gas flux measurements at one height to gain new insights on the role of these eddies on gas (e.g. carbon dioxide) transport. The measurements were conducted during summer 2019 at the Hyytiälä SMEAR II station located in central Finland and the permanent ICOS measurements at the site were utilized to the fullest.</p>

scholarly journals Uncertainty analysis of eddy covariance CO<sub>2</sub> flux measurements for different EC tower distances using an extended two-tower approach

2015 ◽  
Vol 12 (4) ◽  
pp. 1205-1221 ◽  
Author(s):  
H. Post ◽  
H. J. Hendricks Franssen ◽  
A. Graf ◽  
M. Schmidt ◽  
H. Vereecken
Keyword(s):  
Eddy Covariance ◽  
Reference Method ◽  
Co2 Flux ◽  
Weather Conditions ◽  
Data Set ◽  
Random Uncertainty ◽  
Extended Approach ◽  
Uncertainty Estimates ◽  
Flux Measurements

Abstract. The use of eddy covariance (EC) CO2 flux measurements in data assimilation and other applications requires an estimate of the random uncertainty. In previous studies, the (classical) two-tower approach has yielded robust uncertainty estimates, but care must be taken to meet the often competing requirements of statistical independence (non-overlapping footprints) and ecosystem homogeneity when choosing an appropriate tower distance. The role of the tower distance was investigated with help of a roving station separated between 8 m and 34 km from a permanent EC grassland station. Random uncertainty was estimated for five separation distances with the classical two-tower approach and an extended approach which removed systematic differences of CO2 fluxes measured at two EC towers. This analysis was made for a data set where (i) only similar weather conditions at the two sites were included, and (ii) an unfiltered one. The extended approach, applied to weather-filtered data for separation distances of 95 and 173 m gave uncertainty estimates in best correspondence with an independent reference method. The introduced correction for systematic flux differences considerably reduced the overestimation of the two-tower based uncertainty of net CO2 flux measurements and decreased the sensitivity of results to tower distance. We therefore conclude that corrections for systematic flux differences (e.g., caused by different environmental conditions at both EC towers) can help to apply the two-tower approach to more site pairs with less ideal conditions.

scholarly journals The Sensible Heat Flux in the Course of the Year at Ny-Ålesund, Svalbard: Characteristics of Eddy Covariance Data and Corresponding Model Results

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
Georg Jocher ◽  
Alexander Schulz ◽  
Christoph Ritter ◽  
Roland Neuber ◽  
Klaus Dethloff ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Friction Velocity ◽  
Sensible Heat Flux ◽  
Quality Criterion ◽  
Eddy Covariance Method ◽  
Stable Conditions ◽  
Flux Measurements ◽  
One Year ◽  
Good Agreement ◽  
Model Approach

In this paper we present one year of meteorological and flux measurements obtained near Ny-Ålesund, Spitsbergen. Fluxes are derived by the eddy covariance method and by a hydrodynamic model approach (HMA) as well. Both methods are compared and analyzed with respect to season and mean wind direction. Concerning the wind field we find a clear distinction between 3 prevailing regimes (which have influence on the flux behavior) mainly caused by the topography at the measurement site. Concerning the fluxes we find a good agreement between the HMA and the eddy covariance method in cases of turbulent mixing in summer but deviations at stable conditions, when the HMA almost always shows negative fluxes. Part of the deviation is based on a dependence of HMA fluxes on friction velocity and the influence of the molecular boundary layer. Moreover, the flagging system of the eddy covariance software package TK3 is briefly revised. A new quality criterion for the use of fluxes obtained by the eddy covariance method, which is based on integral turbulence characteristics, is proposed.

scholarly journals Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

2010 ◽  
Vol 3 (4) ◽  
pp. 2961-2993 ◽  
Author(s):  
B. Tuzson ◽  
R. V. Hiller ◽  
K. Zeyer ◽  
W. Eugster ◽  
A. Neftel ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Best Practice ◽  
Field Evaluation ◽  
Methane Flux ◽  
Fast Response ◽  
Similar Data ◽  
Mixing Ratios ◽  
Data Treatment ◽  
Sonic Anemometers ◽  
Flux Measurements

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane flux. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

scholarly journals Technical Note: Novel triple O<sub>2</sub>-sensor aquatic eddy covariance instrument with improved time-shift correction reveals central role of microphytobenthos for carbon cycling in coral reef sands

2021 ◽  
Author(s):  
Alireza Merikhi ◽  
Peter Berg ◽  
Markus Huettel
Keyword(s):  
Coral Reef ◽  
Eddy Covariance ◽  
Organic Content ◽  
Utilization Efficiency ◽  
Time Shift ◽  
Overlying Water ◽  
Coral Sand ◽  
New Instrument ◽  
Flux Measurements

Abstract. The aquatic eddy covariance technique stands out as a method for benthic O2-flux measurements because it measures non-invasively, but in the conventional instruments, the spatial separation of the measuring locations of the velocity and O2 sensors causes a time-shift that can be substantial and difficult to correct. Here we introduce a triple O2-sensor-eddy covariance instrument (3OEC) that by positioning of the O2-sensors around the flow measuring volume allows eliminating these time-shifts through signal averaging. The new instrument was used to determine O2-production and consumption in an energetic coastal environment with highly permeable coral reef sands colonized by microphytobenthos. The measurement at ~10 m water depth revealed O2-fluxes that range among the highest reported for marine sediments despite relatively low organic content of the water and coarse sediment, indicating a central role of microphytobenthos for the carbon and nutrient cycling in the coral sand. High light utilization efficiency of the microphytobenthos and bottom currents increasing pore water exchange facilitated the high benthic production and respiration. The measurements documented a gradual transfer of the flux signal from the small turbulence generated at the sediment water interface to the larger wave-dominated eddies of the overlying water column with a delay influenced by the memory effect of eddies. These results demonstrate that the 3OEC can improve the precision of the flux measurements, including measurements in environments considered challenging for this technique, and thereby produce novel insights into the mechanisms that control flux. We consider the fluxes produced by this instrument for the permeable reef sands the most realistic achievable with present day technology.

scholarly journals Characterisation of ozone deposition to a mixed oak-hornbeam forest. Flux measurements at 5 levels above and inside the canopy and their interactions with nitric oxide

2018 ◽  
Author(s):  
Angelo Finco ◽  
Mhairi Coyle ◽  
Eiko Nemitz ◽  
Riccardo Marzuoli ◽  
Maria Chiesa ◽  
...  
Keyword(s):  
Photochemical Reactions ◽  
Field Campaign ◽  
Climate Conditions ◽  
Dynamic Chamber ◽  
Sonic Anemometers ◽  
Flux Measurements ◽  
Ozone Fluxes ◽  
Reactive Gases ◽  
No Fluxes

Abstract. In the framework of the European FP7 project ECLAIRE a joint field campaign was run in Marmirolo, in the northern part of the Italy, one of the most polluted areas in Europe due to intense industrial activities and peculiar climate conditions promoting high ozone formation by photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds. The studied ecosystem is a mixed oak-hornbeam forest and the aim of this field campaign was to investigate the processes regulating the gas exchange between the forest and the atmosphere with a focus on ozone flux measurements and the interaction with reactive gases. Measurements were run on a 40 m tower equipped with sonic anemometers and fast ozone analyzers for eddy covariance at five different heights: one at canopy height, two above canopy and two below canopy. NO fluxes were measured above canopy and NOx fluxes were measured with a dynamic chamber system at the soil level. Ozone fluxes measured at different levels above the canopy showed a good agreement between each other, while fluxes at 24 m were surprisingly higher than the above ones. In this paper we discuss the possible reasons for this discrepancies shedding light on the role of NOx and of the coupling between forest and atmosphere will be explained. A partition of the ozone fluxes will be shown too to identify the most relevant sinks in the soil-plant continuum.

scholarly journals Field intercomparison of two optical analyzers for CH<sub>4</sub> eddy covariance flux measurements

2010 ◽  
Vol 3 (6) ◽  
pp. 1519-1531 ◽  
Author(s):  
B. Tuzson ◽  
R. V. Hiller ◽  
K. Zeyer ◽  
W. Eugster ◽  
A. Neftel ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Best Practice ◽  
Field Evaluation ◽  
Fast Response ◽  
Similar Data ◽  
Mixing Ratios ◽  
Data Treatment ◽  
Sonic Anemometers ◽  
Flux Measurements ◽  
Field Intercomparison

Abstract. Fast response optical analyzers based on laser absorption spectroscopy are the preferred tools to measure field-scale mixing ratios and fluxes of a range of trace gases. Several state-of-the-art instruments have become commercially available and are gaining in popularity. This paper aims for a critical field evaluation and intercomparison of two compact, cryogen-free and fast response instruments: a quantum cascade laser based absorption spectrometer from Aerodyne Research, Inc., and an off-axis integrated cavity output spectrometer from Los Gatos Research, Inc. In this paper, both analyzers are characterized with respect to precision, accuracy, response time and also their sensitivity to water vapour. The instruments were tested in a field campaign to assess their behaviour under various meteorological conditions. The instrument's suitability for eddy covariance flux measurements was evaluated by applying an artificial flux of CH4 generated above a managed grassland with otherwise very low methane exchange. This allowed an independent verification of the flux measurements accuracy, including the overall eddy covariance setup and data treatment. The retrieved fluxes were in good agreement with the known artificial emission flux, which is more than satisfactory, given that the analyzers were attached to separate sonic anemometers placed on individual eddy towers with different data acquisition systems but similar data treatment that are specific to the best practice used by the involved research teams.

scholarly journals Uncertainty analysis of eddy covariance CO<sub>2</sub> flux measurements for different EC tower distances using an extended two-tower approach

2014 ◽  
Vol 11 (8) ◽  
pp. 11943-11983
Author(s):  
H. Post ◽  
H. J. Hendricks Franssen ◽  
A. Graf ◽  
M. Schmidt ◽  
H. Vereecken
Keyword(s):  
Eddy Covariance ◽  
Reference Method ◽  
Co2 Flux ◽  
Weather Conditions ◽  
Co2 Fluxes ◽  
Random Uncertainty ◽  
Extended Approach ◽  
Uncertainty Estimates ◽  
Flux Measurements

Abstract. The use of eddy covariance CO2 flux measurements in data assimilation and other applications requires an estimate of the random uncertainty. In previous studies, the two-tower approach has yielded robust uncertainty estimates, but care must be taken to meet the often competing requirements of statistical independence (non-overlapping footprints) and ecosystem homogeneity when choosing an appropriate tower distance. The role of the tower distance was investigated with help of a roving station separated between 8 m and 34 km from a permanent EC grassland station. Random uncertainty was estimated for five separation distances with an extended two-tower approach which removed systematic differences of CO2 fluxes measured at two EC towers. This analysis was made for a dataset where (i) only similar weather conditions at the two sites were included and (ii) an unfiltered one. The extended approach, applied to weather-filtered data for separation distances of 95 m and 173 m gave uncertainty estimates in best correspondence with the independent reference method The introduced correction for systematic flux differences considerably reduced the overestimation of the two-tower based uncertainty of net CO2 flux measurements, e.g. caused by different environmental conditions at both EC towers. It is concluded that the extension of the two-tower approach can help to receive more reliable uncertainty estimates because systematic differences of measured CO2 fluxes which are not part of random error are filtered out.

The ROLE OF CHINA-PAK ECONOMIC CORRIDOR (CPEC) IN LOGISTIC SYSTEM OF PAKISTAN’S AND CHINA’S

2019 ◽  
Vol 6 (1) ◽  
pp. 48-50
Author(s):  
Ikram Uddin
Keyword(s):  
Persian Gulf ◽  
Lead Time ◽  
Fiber Optic ◽  
Delivery Time ◽  
Fiber Optic Cable ◽  
Total Cost ◽  
Economic Complexity ◽  
Shipping Cost ◽  
The Impact

This study will explain the impact of China-Pak Economic Corridor (CPEC) on logistic system of China and Pakistan. This project is estimated investment of US $90 billion, CPEC project is consists of various sub-projects including energy, road, railway and fiber optic cable but major portion will be spent on energy. This project will start from Kashgar port of china to Gwadar port of Pakistan. Transportation is sub-function of logistic that consists of 44% total cost of logistic system and 20% total cost of production of manufacturing and mainly shipping cost and transit/delivery time are critical for logistic system. According to OEC (The Observing Economic Complexity) currently, china is importing crude oil which 13.4% from Persian Gulf. CPEC will china for lead time that will be reduced from 45 days to 10 days and distance from 2500km to 1300km. This new route will help to china for less transit/deliver time and shipping cost in terms of logistic of china. Pakistan’s transportation will also improve through road, railway and fiber optic cabal projects from Karachi-Peshawar it will have speed 160km per hour and with help of pipeline between Gwadar to Nawabshah gas will be transported from Iran. According to (www.cpec.inf.com) Pakistan logistic industry will grow by US $30.77 billion in the end of 2020.

scholarly journals Atlantic Hurricanes and Climate Change. Part II: Role of Thermodynamic Changes in Decreased Hurricane Frequency

2013 ◽  
Vol 26 (21) ◽  
pp. 8513-8528 ◽  
Author(s):  
Megan S. Mallard ◽  
Gary M. Lackmann ◽  
Anantha Aiyyer
Keyword(s):  
Case Studies ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Effect Of Temperature ◽  
Physical Processes ◽  
Thermodynamic Conditions ◽  
Atlantic Hurricanes ◽  
Reduced Activity

Abstract A method of downscaling that isolates the effect of temperature and moisture changes on tropical cyclone (TC) activity was presented in Part I of this study. By applying thermodynamic modifications to analyzed initial and boundary conditions from past TC seasons, initial disturbances and the strength of synoptic-scale vertical wind shear are preserved in future simulations. This experimental design allows comparison of TC genesis events in the same synoptic setting, but in current and future thermodynamic environments. Simulations of both an active (September 2005) and inactive (September 2009) portion of past hurricane seasons are presented. An ensemble of high-resolution simulations projects reductions in ensemble-average TC counts between 18% and 24%, consistent with previous studies. Robust decreases in TC and hurricane counts are simulated with 18- and 6-km grid lengths, for both active and inactive periods. Physical processes responsible for reduced activity are examined through comparison of monthly and spatially averaged genesis-relevant parameters, as well as case studies of development of corresponding initial disturbances in current and future thermodynamic conditions. These case studies show that reductions in TC counts are due to the presence of incipient disturbances in marginal moisture environments, where increases in the moist entropy saturation deficits in future conditions preclude genesis for some disturbances. Increased convective inhibition and reduced vertical velocity are also found in the future environment. It is concluded that a robust decrease in TC frequency can result from thermodynamic changes alone, without modification of vertical wind shear or the number of incipient disturbances.

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