scholarly journals Spatial variability in airborne surface flux measurements during HAPEX-Sahel

1997 ◽  
Vol 188-189 ◽  
pp. 878-911 ◽  
Author(s):  
F. Saïd ◽  
J.L. Attié ◽  
B. Bénech ◽  
A. Druilhet ◽  
P. Durand ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Surface Flux ◽  
Flux Measurements

scholarly journals Precipitation Sensitivity to the Uncertainty of Terrestrial Water Flow in WRF-Hydro: An Ensemble Analysis for Central Europe

2018 ◽  
Vol 19 (6) ◽  
pp. 1007-1025 ◽  
Author(s):  
Joël Arnault ◽  
Thomas Rummler ◽  
Florian Baur ◽  
Sebastian Lerch ◽  
Sven Wagner ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Spatial Variability ◽  
Central Europe ◽  
Water Flow ◽  
Daily Precipitation ◽  
Three Dimensional ◽  
Wrf Model ◽  
Vertical Direction ◽  
Surface Flux ◽  
Terrestrial Water

Abstract Precipitation is affected by soil moisture spatial variability. However, this variability is not well represented in atmospheric models that do not consider soil moisture transport as a three-dimensional process. This study investigates the sensitivity of precipitation to the uncertainty in the representation of terrestrial water flow. The tools used for this investigation are the Weather Research and Forecasting (WRF) Model and its hydrologically enhanced version, WRF-Hydro, applied over central Europe during April–October 2008. The model grid is convection permitting, with a horizontal spacing of 2.8 km. The WRF-Hydro subgrid employs a 280-m resolution to resolve lateral terrestrial water flow. A WRF/WRF-Hydro ensemble is constructed by modifying the parameter controlling the partitioning between surface runoff and infiltration and by varying the planetary boundary layer (PBL) scheme. This ensemble represents terrestrial water flow uncertainty originating from the consideration of resolved lateral flow, terrestrial water flow uncertainty in the vertical direction, and turbulence parameterization uncertainty. The uncertainty of terrestrial water flow noticeably increases the normalized ensemble spread of daily precipitation where topography is moderate, surface flux spatial variability is high, and the weather regime is dominated by local processes. The adjusted continuous ranked probability score shows that the PBL uncertainty improves the skill of an ensemble subset in reproducing daily precipitation from the E-OBS observational product by 16%–20%. In comparison to WRF, WRF-Hydro improves this skill by 0.4%–0.7%. The reproduction of observed daily discharge with Nash–Sutcliffe model efficiency coefficients generally above 0.3 demonstrates the potential of WRF-Hydro in hydrological science.

scholarly journals Spatial variability of CO<sub>2</sub> uptake in polygonal tundra: assessing low-frequency disturbances in eddy covariance flux estimates

2017 ◽  
Vol 14 (12) ◽  
pp. 3157-3169 ◽  
Author(s):  
Norbert Pirk ◽  
Jakob Sievers ◽  
Jordan Mertes ◽  
Frans-Jan W. Parmentier ◽  
Mikhail Mastepanov ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Eddy Covariance ◽  
Low Frequency ◽  
Optimization Method ◽  
Co2 Exchange ◽  
Aerial Photographs ◽  
Strong Increase ◽  
Vulnerability To Climate Change ◽  
Flux Measurements ◽  
Ice Wedge

Abstract. The large spatial variability in Arctic tundra complicates the representative assessment of CO2 budgets. Accurate measurements of these heterogeneous landscapes are, however, essential to understanding their vulnerability to climate change. We surveyed a polygonal tundra lowland on Svalbard with an unmanned aerial vehicle (UAV) that mapped ice-wedge morphology to complement eddy covariance (EC) flux measurements of CO2. The analysis of spectral distributions showed that conventional EC methods do not accurately capture the turbulent CO2 exchange with a spatially heterogeneous surface that typically features small flux magnitudes. Nonlocal (low-frequency) flux contributions were especially pronounced during snowmelt and introduced a large bias of −46 gC m−2 to the annual CO2 budget in conventional methods (the minus sign indicates a higher uptake by the ecosystem). Our improved flux calculations with the ogive optimization method indicated that the site was a strong sink for CO2 in 2015 (−82 gC m−2). Due to differences in light-use efficiency, wetter areas with low-centered polygons sequestered 47 % more CO2 than drier areas with flat-centered polygons. While Svalbard has experienced a strong increase in mean annual air temperature of more than 2 K in the last few decades, historical aerial photographs from the site indicated stable ice-wedge morphology over the last 7 decades. Apparently, warming has thus far not been sufficient to initiate strong ice-wedge degradation, possibly due to the absence of extreme heat episodes in the maritime climate on Svalbard. However, in Arctic regions where ice-wedge degradation has already initiated the associated drying of landscapes, our results suggest a weakening of the CO2 sink in polygonal tundra.

Interpretation of surface flux measurements in heterogeneous terrain during the Monsoon '90 experiment

1994 ◽  
Vol 30 (5) ◽  
pp. 1227-1239 ◽  
Author(s):  
D. I. Stannard ◽  
J. H. Blanford ◽  
W. P. Kustas ◽  
W. D. Nichols ◽  
S. A. Amer ◽  
...  
Keyword(s):  
Surface Flux ◽  
Heterogeneous Terrain ◽  
Flux Measurements

Variability of total soil respiration in a Mediterranean vineyard

Soil Research ◽  
2015 ◽  
Vol 53 (5) ◽  
pp. 531 ◽  
Author(s):  
Egidio Lardo ◽  
Assunta Maria Palese ◽  
Vitale Nuzzo ◽  
Cristos Xiloyannis ◽  
Giuseppe Celano
Keyword(s):  
Soil Respiration ◽  
Spatial Variability ◽  
Co2 Emissions ◽  
Temporal Dynamics ◽  
Non Invasive ◽  
Total Soil ◽  
Greenhouse Gas Flux ◽  
Flux Measurements ◽  
Total Soil Respiration

Total soil respiration (TSR) is the major component of the CO2 global flux. The knowledge of the temporal-spatial variability of TSR allows for a better interpretation of a critical component of global greenhouse gas flux measurements. The objective of the research was to evaluate the TSR dynamic over a long measurement period in a vineyard in the South of Italy. A static home-made automatic system was used to measure TSR for a three year period. A portable gas analyser (Li-Cor 6400-09) was used to study TSR spatial variability. A non-invasive geophysical technique (Electromagnetic Induction – EMI) was applied to search for a significant relationship between apparent soil electrical conductivity (ECa), the EMI signal and TSR. Long-term measurements of TSR enabled to study its temporal dynamics. CO2 rates ranged from 0.78 to 43.7 g CO2 m–2 day–1. TSR increased during spring and decreased by 45–50% during the mid-summer. The daily trend of TSR showed differences between the seasons studied reporting a clearly variation among TSR measured on row and inter-row positions. The supplemental irrigation significantly affected (P < 0.001) CO2 soil effluxes which showed a weekly mean increase of 300%. Significant inverse relationships were found by interpolating TSR values and ECa (coefficient of correlation ranging from –0.43 to –0.83 at P < 0.001). The spatialisation of TSR at field scale was performed using the linear regression between TSR values and EMI signals. TSR spatialisation gave a more detailed view of CO2 emissions distribution within the vineyard. EMI technique could be a useful tool to compute accurately the global CO2 emissions which are a complex and hard to measure component of the agrosystem carbon balance.

scholarly journals Measured and Estimated Water Vapor Advection in the Atmospheric Surface Layer

2013 ◽  
Vol 14 (6) ◽  
pp. 1966-1972 ◽  
Author(s):  
Chad W. Higgins ◽  
Eric Pardyjak ◽  
Martin Froidevaux ◽  
Valentin Simeonov ◽  
Marc B. Parlange
Keyword(s):  
Water Vapor ◽  
Land Surface ◽  
Field Measurements ◽  
Surface Flux ◽  
Energy Deficit ◽  
Surface Transition ◽  
Measurement Height ◽  
Flux Measurements ◽  
Field Deployment ◽  
The Impact

Abstract The flux of water vapor due to advection is measured using high-resolution Raman lidar that was orientated horizontally across a land–lake transition. At the same time, a full surface energy balance is performed to assess the impact of scalar advection on energy budget closure. The flux of water vapor due to advection is then estimated with analytical solutions to the humidity transport equation that show excellent agreement with the field measurements. Although the magnitude of the advection was not sufficient to account for the total energy deficit for this field site, the analytical approach is used to explore situations where advection would be the dominant transport mechanism. The authors find that advection is at maximum when the measurement height is 0.036 times the distance to a land surface transition. The framework proposed in this paper can be used to predict the potential impact of advection on surface flux measurements prior to field deployment and can be used as a data analysis algorithm to calculate the flux of water vapor due to advection from field measurements.

Novel meteorological methods for measuring trace gas fluxes

1995 ◽  
Vol 351 (1696) ◽  
pp. 383-396 ◽  
Keyword(s):  
Diffusion Theory ◽  
Animal Experiments ◽  
Surface Flux ◽  
Test Plot ◽  
Plant Canopies ◽  
Gradient Diffusion ◽  
Gas Fluxes ◽  
Trace Gas Fluxes ◽  
Flux Measurements ◽  
Source Sink

The paper deals with flux measurements in two contexts: small plots and plant canopies. Mass balance methods have been developed for small experimental plots with lateral dimensions of tens of metres rather than the 1 m typical of chambers or the hundreds of metres required for conventional micrometeorological estimates. The general method relies on the conservation of mass to equate the differences in horizontal fluxes across upwind and downwind boundaries of a test plot with the surface flux within the plot along the line of the wind. Applications to soil and animal experiments are discussed. Lagrangian descriptions of transport now supplant older, but inappropriate gradient-diffusion theory for inferring fluxes and source-sink distributions of scalars in plant canopies. An inverse Lagrangian theory due to M. R. Raupach provides a relatively simple observational and computational scheme for making such inferences from measurements of mean concentration profiles and canopy turbulence. The scheme and a range of applications are described.

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