Using Spatial Eddy Covariance to Investigate Energy Balance Closure over a Heterogeneous Ecosystem

2020 ◽  
Author(s):  
Brian Butterworth ◽  
Ankur Desai ◽  
Sreenath Paleri ◽  
Stefan Metzger ◽  
David Durden ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Energy Balance ◽  
Surface Energy ◽  
Atmospheric Boundary Layer ◽  
Eddy Covariance ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Land Surface Heterogeneity

<p>Land surface heterogeneity influences patterns of sensible and latent heat flux, which in turn affect processes in the atmospheric boundary layer. However, gridded atmospheric models often fail to incorporate the influence of land surface heterogeneity due to differences between the temporal and spatial scales of models compared to the local, sub-grid processes. Improving models requires the scaling of surface flux measurements; a process made difficult by the fact that surface measurements usually find an imbalance in the energy budget.</p><p>The Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors (CHEESEHEAD19) was an observational experiment designed to investigate how the atmospheric boundary layer responds to scales of spatial heterogeneity in surface-atmosphere heat and water exchanges. The campaign was conducted from June – October 2019, measuring surface energy fluxes over a heterogeneous forest ecosystem as fluxes transitioned from latent heat-dominated summer through sensible heat-dominated fall. Observations were made by ground, airborne, and satellite platforms within the 10 x 10 km study region, which was chosen to match the scale of a typical model grid cell. The spatial distribution of energy fluxes was observed by an array of 20 eddy covariance towers and a low-flying aircraft. Mesoscale atmospheric properties were measured by a suite of LiDAR and sounding instruments, measuring winds, water vapor, temperature, and boundary layer development. Plant phenology was measured in-situ and mapped remotely using hyperspectral imaging.</p><p>The dense set of multi-scale observations of land-atmosphere exchange collected during the CHEESEHEAD field campaign permits combining the spatial and temporal distribution of energy fluxes with mesoscale surface and atmospheric properties. This provides an unprecedented data foundation to evaluate theoretical explanations of energy balance non-closure, as well as to evaluate methods for scaling surface energy fluxes for improved model-data comparison. Here we show how fluxes calculated using a spatial eddy covariance technique across the 20-tower network compare to those of standard temporal eddy covariance fluxes in order to characterize of the spatial representativeness of single tower eddy covariance measurements. Additionally, we show how spatial EC fluxes can be used to better understand the energy balance over heterogeneous ecosystems.</p>

scholarly journals CONNECTING LAND-ATMOSPHERE INTERACTIONS TO SURFACE HETEROGENEITY IN CHEESEHEAD19

2020 ◽  
pp. 1-71
Author(s):  
BRIAN J. BUTTERWORTH ◽  
ANKUR R. DESAI ◽  
STEFAN METZGER ◽  
PHILIP A. TOWNSEND ◽  
MARK D. SCHWARTZ ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Energy ◽  
Atmospheric Boundary Layer ◽  
Spatial Heterogeneity ◽  
Regional Scale ◽  
Surface Heterogeneity ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

CAPSULE SUMMARYA regional-scale observational experiment designed to address how the atmospheric boundary layer responds to spatial heterogeneity in surface energy fluxes.

scholarly journals Upscaling surface energy fluxes over the North Slope of Alaska using airborne eddy-covariance measurements and environmental response functions

2018 ◽  
Author(s):  
Andrei Serafimovich ◽  
Stefan Metzger ◽  
Jörg Hartmann ◽  
Katrin Kohnert ◽  
Donatella Zona ◽  
...  
Keyword(s):  
Surface Energy ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Land Surface ◽  
Response Functions ◽  
Sensible Heat ◽  
Environmental Response ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Eddy Covariance Measurements

Abstract. The objective of this study was to upscale airborne flux measurements of sensible heat and latent heat and to develop high resolution flux maps. In order to support the evaluation of coupled atmospheric/land–surface models we investigated spatial patterns of energy fluxes in relation to land–surface properties. We used airborne eddy-covariance measurements acquired by the POLAR 5 research aircraft in June–July 2012 to analyze surface fluxes. Footprint-weighted surface properties were then related to 21 529 sensible heat flux observations and 25 608 latent heat flux observations using both remote sensing and modelled data. A boosted regression tree technique was used to estimate environmental response functions between spatially and temporally resolved flux observations and corresponding biophysical and meteorological drivers. In order to improve the spatial coverage and spatial representativeness of energy fluxes we used relationships extracted across heterogeneous Arctic landscapes to infer high-resolution surface energy flux maps, thus directly upscaling the observational data. These maps of projected sensible heat and latent heat fluxes were used to assess energy partitioning in northern ecosystems and to determine the dominant energy exchange processes in permafrost areas. This allowed us to estimate energy fluxes for specific types of land cover, taking into account meteorological conditions. Airborne and modelled fluxes were then compared with measurements from an eddy-covariance tower near Atqasuk. Our results are an important contribution for the advanced, scale-dependent quantification of surface energy fluxes and provide new insights into the processes affecting these fluxes for the main vegetation types in high-latitude permafrost areas.

scholarly journals Upscaling surface energy fluxes over the North Slope of Alaska using airborne eddy-covariance measurements and environmental response functions

2018 ◽  
Vol 18 (13) ◽  
pp. 10007-10023 ◽  
Author(s):  
Andrei Serafimovich ◽  
Stefan Metzger ◽  
Jörg Hartmann ◽  
Katrin Kohnert ◽  
Donatella Zona ◽  
...  
Keyword(s):  
Surface Energy ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Land Surface ◽  
Response Functions ◽  
Sensible Heat ◽  
Environmental Response ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Eddy Covariance Measurements

Abstract. The objective of this study was to upscale airborne flux measurements of sensible heat and latent heat and to develop high-resolution flux maps. In order to support the evaluation of coupled atmospheric–land-surface models we investigated spatial patterns of energy fluxes in relation to land-surface properties. We used airborne eddy-covariance measurements acquired by the Polar 5 research aircraft in June–July 2012 to analyze surface fluxes. Footprint-weighted surface properties were then related to 21 529 sensible heat flux observations and 25 608 latent heat flux observations using both remote sensing and modeled data. A boosted regression tree technique was used to estimate environmental response functions between spatially and temporally resolved flux observations and corresponding biophysical and meteorological drivers. In order to improve the spatial coverage and spatial representativeness of energy fluxes we used relationships extracted across heterogeneous Arctic landscapes to infer high-resolution surface energy flux maps, thus directly upscaling the observational data. These maps of projected sensible heat and latent heat fluxes were used to assess energy partitioning in northern ecosystems and to determine the dominant energy exchange processes in permafrost areas. This allowed us to estimate energy fluxes for specific types of land cover, taking into account meteorological conditions. Airborne and modeled fluxes were then compared with measurements from an eddy-covariance tower near Atqasuk. Our results are an important contribution for the advanced, scale-dependent quantification of surface energy fluxes and they provide new insights into the processes affecting these fluxes for the main vegetation types in high-latitude permafrost areas.

Modelling Regional Water and Energy balance in East Africa

2020 ◽  
Author(s):  
Sopan Patil ◽  
John Musau ◽  
Michael Marshall
Keyword(s):  
Surface Water ◽  
Energy Balance ◽  
Land Cover ◽  
Vegetation Structure ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Time Varying ◽  
Energy Fluxes ◽  
Vegetation Parameters ◽  
Land Surface Heterogeneity

<p>Effective modeling of surface water and energy balance is crucial in planning and management of regional resources. However, the heterogeneous and clumped vegetation structure controls the portioning of land surface water and energy fluxes, which leads to large variations of local radiative and hydrological processes. The aim of this study is to characterize the land surface heterogeneity in East Africa and examine the impact of the spatially and temporally varying vegetation parameters on energy and water balance in the region.  We used MODIS datasets on Leaf Area Index (LAI), Enhanced Vegetation Index (EVI) and albedo to derive time-varying vegetation parameters for the period 2001 – 2011 period at 0.05° resolution. These parameters were integrated with the Variable Infiltration Capacity (VIC) model to characterize the effects of varying vegetation properties on surface water and energy fluxes. A twin simulation was also carried based on seasonally averaged vegetation parameters to isolate the effects of time-varying and spatially heterogeneous parameters on the water and energy fluxes. The simulation results were compared to rigorously validated global datasets on evapotranspiration and sensible heat. Results showed that the time-varying and spatially heterogeneous vegetation parameters provided surface water and energy fluxes which were more consistent with the validation datasets. The simulated evapotranspiration matched reasonably well with the observed values particularly in areas characterized by sparse vegetation and which are more prone to human influence. The improvements were highly noticeable in grassland and savanna land cover types. However, due to intensive human activities in region which affect not only the lad cover but also the vegetation structure, there is need for characterization of the land cover parameters based on high resolution data which can better capture the land surface heterogeneity in the region.</p>

scholarly journals The Diurnal Behavior of Evaporative Fraction in the Soil–Vegetation–Atmospheric Boundary Layer Continuum

2011 ◽  
Vol 12 (6) ◽  
pp. 1530-1546 ◽  
Author(s):  
Pierre Gentine ◽  
Dara Entekhabi ◽  
Jan Polcher
Keyword(s):  
Boundary Layer ◽  
Energy Balance ◽  
Surface Energy ◽  
Atmospheric Boundary Layer ◽  
Land Surface ◽  
Radiative Forcing ◽  
Surface Energy Balance ◽  
Heat Fluxes ◽  
Physical Factors ◽  
Phase Lag

Abstract The components of the land surface energy balance respond to periodic incoming radiation forcing with different amplitude and phase characteristics. Evaporative fraction (EF), the ratio of latent heat to available energy at the land surface, supposedly isolates surface control (soil moisture and vegetation) from radiation and turbulent factors. EF is thus supposed to be a diagnostic of the surface energy balance that is constant or self-preserved during daytime. If this holds, EF can be an effective way to estimate surface characteristics from temperature and energy flux measurements. Evidence for EF diurnal self-preservation is based on limited-duration field measurements. The daytime EF self-preservation using both long-term measurements and a model of the soil–vegetation–atmosphere continuum is reexamined here. It is demonstrated that EF is rarely constant and that its temporal power spectrum is wide; thus emphasizing the role of all diurnal frequencies associated with reduced predictability in its daylight response. Oppositely, surface turbulent heat fluxes are characterized by a strong response to the principal daily frequencies (daily and semi-daily) of the solar radiative forcing. It is shown that the phase lag and bias between the turbulent flux components of the surface energy balance are key to the shape of the daytime EF. Therefore, an understanding of the physical factors that affect the phase lag and bias in the response of the components of the surface energy balance to periodic radiative forcing is needed. A linearized model of the soil–vegetation–atmosphere continuum is used that can be solved in terms of harmonics to explore the physical factors that determine the phase characteristics. The dependency of these phase and offsets on environmental parameters—friction velocity, water availability, solar radiation intensity, relative humidity, and boundary layer entrainment—is then analyzed using the model that solves the dynamics of subsurface and atmospheric boundary layer temperatures and heat fluxes in a continuum. Additionally, the asymptotical diurnal lower limit of EF is derived as a function of these surface parameters and shown to be an important indicator of the self-preservation value when the conditions (also identified) for such behavior are present.

scholarly journals Remotely sensed land-surface energy fluxes at sub-field scale in heterogeneous agricultural landscape and coniferous plantation

2014 ◽  
Vol 11 (3) ◽  
pp. 4857-4908 ◽  
Author(s):  
R. Guzinski ◽  
H. Nieto ◽  
R. Jensen ◽  
G. Mendiguren
Keyword(s):  
Surface Energy ◽  
Eddy Covariance ◽  
Spatial Resolution ◽  
Land Surface ◽  
Agricultural Landscape ◽  
Remotely Sensed ◽  
Energy Fluxes ◽  
Surface Energy Fluxes ◽  
Coniferous Plantation ◽  
Agricultural Site

Abstract. In this study we evaluate a methodology for disaggregating land surface energy fluxes estimated with the Dual Time Difference (DTD) model which uses the day and night polar orbiting satellites observations of Land Surface Temperature (LST) as a remotely sensed input. The DTD model is run with MODIS input data at a spatial resolution of around 1 km while the disaggregation uses Landsat observations of LST to produce fluxes at a nominal spatial resolution of 30 m. The higher resolution modeled fluxes can be directly compared against eddy-covariance based flux tower measurements to ensure more accurate model validation and also provide a better visualization of fluxes' spatial patterns in heterogeneous areas allowing for development of, for example, more efficient irrigation practices. The disaggregation technique is evaluated in an area covered by the Danish Hydrological Observatory (HOBE), in the west of the Jutland peninsula, and the modeled fluxes are compared against measurements from two flux towers: first one in a heterogeneous agricultural landscape and second one in a homogeneous conifer plantation. The results indicate that the disaggregated fluxes have greatly improved accuracy as compared to high resolution fluxes derived directly with Landsat data without the disaggregation. At the agricultural site the disaggregated fluxes display negligible bias and almost perfect correlation (r > 0.90) with Eddy Covariance based measurements, while at the plantation site the results are encouraging but not ideal. In addition we introduce a modification to the DTD model by replacing the "parallel" configuration of the resistances to sensible heat exchange by the "series" configuration. The later takes into account the in-canopy air temperature and substantially improves the accuracy of the DTD model.

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