scholarly journals Multi-Scale Evaluation of the TSEB Model over a Complex Agricultural Landscape in Morocco

2020 ◽  
Vol 12 (7) ◽  
pp. 1181
Author(s):  
Jamal Elfarkh ◽  
Jamal Ezzahar ◽  
Salah Er-Raki ◽  
Vincent Simonneaux ◽  
Bouchra Ait Hssaine ◽  
...  
Keyword(s):  
Latent Heat ◽  
Complex Terrain ◽  
Large Scale ◽  
Agricultural Landscape ◽  
Local Scale ◽  
Heat Fluxes ◽  
Balance Model ◽  
Modis Data ◽  
Multi Scale ◽  
Basin Scale

An accurate assessment of evapotranspiration (ET) is crucially needed at the basin scale for studying the hydrological processes and water balance especially from upstream to downstream. In the mountains, this term is poorly understood because of various challenges, including the vegetation complexity, plant diversity, lack of available data and because the in situ direct measurement of ET is difficult in complex terrain. The main objective of this work was to investigate the potential of a Two-Source-Energy-Balance model (TSEB) driven by the Landsat and MODIS data for estimating ET over a complex mountain region. The complexity is associated with the type of the vegetation canopy as well as the changes in topography. For validating purposes, a large-aperture scintillometer (LAS) was set up over a heterogeneous transect of about 1.4 km to measure sensible (H) and latent heat (LE) fluxes. Additionally, two towers of eddy covariance (EC) systems were installed along the LAS transect. First, the model was tested at the local scale against the EC measurements using multi-scale remote sensing (MODIS and Landsat) inputs at the satellite overpasses. The obtained averaged values of the root mean square error (RMSE) and correlation coefficient (R) were about 72.4 Wm−2 and 0.79 and 82.0 Wm−2 and 0.52 for Landsat and MODIS data, respectively. Secondly, the potential of the TSEB model for evaluating the latent heat fluxes at large scale was investigated by aggregating the derived parameters from both satellites based on the LAS footprint. As for the local scale, the comparison of the latent heat fluxes simulated by TSEB driven by Landsat data performed well against those measured by the LAS (R = 0.69, RMSE = 68.0 Wm−2), while slightly more scattering was observed when MODIS products were used (R = 0.38, RMSE = 99.8 Wm−2). Based on the obtained results, it can be concluded that (1) the TSEB model can be fairly used to estimate the evapotranspiration over the mountain regions; and (2) medium- to high-resolution inputs are a better option than coarse-resolution products for describing this kind of complex terrain.

scholarly journals Air-Sea Interactions over Eddies in the Brazil-Malvinas Confluence

2021 ◽  
Vol 13 (7) ◽  
pp. 1335
Author(s):  
Ronald Souza ◽  
Luciano Pezzi ◽  
Sebastiaan Swart ◽  
Fabrício Oliveira ◽  
Marcelo Santini
Keyword(s):  
Latent Heat ◽  
Large Scale ◽  
Surface Wind ◽  
Heat Fluxes ◽  
Lower Atmosphere ◽  
Meteorological Variables ◽  
Global Ocean ◽  
Study Region ◽  
Cold Core

The Brazil–Malvinas Confluence (BMC) is one of the most dynamical regions of the global ocean. Its variability is dominated by the mesoscale, mainly expressed by the presence of meanders and eddies, which are understood to be local regulators of air-sea interaction processes. The objective of this work is to study the local modulation of air-sea interaction variables by the presence of either a warm (ED1) and a cold core (ED2) eddy, present in the BMC, during September to November 2013. The translation and lifespans of both eddies were determined using satellite-derived sea level anomaly (SLA) data. Time series of satellite-derived surface wind data, as well as these and other meteorological variables, retrieved from ERA5 reanalysis at the eddies’ successive positions in time, allowed us to investigate the temporal modulation of the lower atmosphere by the eddies’ presence along their translation and lifespan. The reanalysis data indicate a mean increase of 78% in sensible and 55% in latent heat fluxes along the warm eddy trajectory in comparison to the surrounding ocean of the study region. Over the cold core eddy, on the other hand, we noticed a mean reduction of 49% and 25% in sensible and latent heat fluxes, respectively, compared to the adjacent ocean. Additionally, a field campaign observed both eddies and the lower atmosphere from ship-borne observations before, during and after crossing both eddies in the study region during October 2013. The presence of the eddies was imprinted on several surface meteorological variables depending on the sea surface temperature (SST) in the eddy cores. In situ oceanographic and meteorological data, together with high frequency micrometeorological data, were also used here to demonstrate that the local, rather than the large scale forcing of the eddies on the atmosphere above, is, as expected, the principal driver of air-sea interaction when transient atmospheric systems are stable (not actively varying) in the study region. We also make use of the in situ data to show the differences (biases) between bulk heat flux estimates (used on atmospheric reanalysis products) and eddy covariance measurements (taken as “sea truth”) of both sensible and latent heat fluxes. The findings demonstrate the importance of short-term changes (minutes to hours) in both the atmosphere and the ocean in contributing to these biases. We conclude by emphasizing the importance of the mesoscale oceanographic structures in the BMC on impacting local air-sea heat fluxes and the marine atmospheric boundary layer stability, especially under large scale, high-pressure atmospheric conditions.

scholarly journals Ability of a soil–vegetation–atmosphere transfer model and a two-source energy balance model to predict evapotranspiration for several crops and climate conditions

2019 ◽  
Vol 23 (12) ◽  
pp. 5033-5058
Author(s):  
Guillaume Bigeard ◽  
Benoit Coudert ◽  
Jonas Chirouze ◽  
Salah Er-Raki ◽  
Gilles Boulet ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Balance Model ◽  
Transfer Model ◽  
Climate Conditions ◽  
Crop Types ◽  
Svat Model

Abstract. The heterogeneity of Agroecosystems, in terms of hydric conditions, crop types and states, and meteorological forcing, is difficult to characterize precisely at the field scale over an agricultural landscape. This study aims to perform a sensitivity study with respect to the uncertain model inputs of two classical approaches used to map the evapotranspiration of agroecosystems: (1) a surface energy balance (SEB) model, the Two-Source Energy Balance (TSEB) model, forced with thermal infrared (TIR) data as a proxy for the crop hydric conditions, and (2) a soil–vegetation–atmosphere transfer (SVAT) model, the SEtHyS model, where hydric conditions are computed from a soil water budget. To this end, the models' skill was compared using a large and unique in situ database covering different crops and climate conditions, which was acquired over three experimental sites in southern France and Morocco. On average, the models provide 30 min estimations of latent heat flux (LE) with a RMSE of around 55 W m−2 for TSEB and 47 W m−2 for SEtHyS, and estimations of sensible heat flux (H) with a RMSE of around 29 W m−2 for TSEB and 38 W m−2 for SEtHyS. A sensitivity analysis based on realistic errors aimed to estimate the potential decrease in performance induced by the spatialization process. For the SVAT model, the multi-objective calibration iterative procedure (MCIP) is used to determine and test different sets of parameters. TSEB is run with only one set of parameters and provides acceptable performance for all crop stages apart from the early growing season (LAI < 0.2 m2 m−2) and when hydric stress occurs. An in-depth study on the Priestley–Taylor key parameter highlights its marked diurnal cycle and the need to adjust its value to improve flux partitioning between the sensible and latent heat fluxes (1.5 and 1.25 for France and Morocco, respectively). Optimal values of 1.8–2 were highlighted under cloudy conditions, which is of particular interest due to the emergence of low-altitude drone acquisition. Under developed vegetation (LAI > 0.8 m2 m−2) and unstressed conditions, using sets of parameters that only differentiate crop types is a valuable trade-off for SEtHyS. This study provides some scientific elements regarding the joint use of both approaches and TIR imagery, via the development of new data assimilation and calibration strategies.

Multi-Scale Modeling of Wind-Wave Interaction in the Presence of Offshore Structures for Renewable Energy Applications

2010 ◽  
Author(s):  
Yi Liu ◽  
Di Yang ◽  
Xin Guo ◽  
Lian Shen
Keyword(s):  
Immersed Boundary Method ◽  
Large Scale ◽  
Wind Wave ◽  
Offshore Structures ◽  
Local Scale ◽  
Immersed Boundary ◽  
Multi Scale ◽  
Scale Modeling ◽  
Boundary Method ◽  
Multi Scale Modeling

We develop a multi-scale modeling capability for the simulation of wind and wave coupling dynamics, with a focus on providing environmental input for wind and wave loads on offshore structures. For the large-scale wind–wave environment, large-eddy simulation for the wind turbulence and high-order spectral simulation for the nonlinear ocean waves are dynamically coupled. For the local-scale air and water flows past the structure, we use a hybrid interface capturing and immersed boundary method. Coupled level-set/volume-of-fluid/ghost-fluid method is used to capture the wave surface. Immersed boundary method is used to represent the structure. The large-scale wind–wave simulation provides inflow boundary conditions for the local-scale air–water–structure simulation. Our simulation captures the dynamic evolution of ocean nonlinear wavefield under the wind action. The wind field is found to be strongly coupled with the surface waves and the wind load on a surface-piercing object is largely wave-phase dependent.

Idealized Hot Spot Experiments with a General Circulation Model

2007 ◽  
Vol 20 (5) ◽  
pp. 908-925 ◽  
Author(s):  
Eric D. Maloney ◽  
Adam H. Sobel
Keyword(s):  
Latent Heat ◽  
General Circulation ◽  
Large Scale ◽  
Initial Conditions ◽  
Hot Spot ◽  
Heat Content ◽  
Circulation Model ◽  
Heat Fluxes ◽  
External Parameter ◽  
Large Scale Circulation

Abstract Idealized experiments are conducted using a GCM coupled to a 20-m slab ocean model to examine the short-term response to an initial localized positive equatorial SST anomaly, or “hot spot.” A hot spot is imposed upon an aquaplanet with globally uniform 28°C SST, insolation, and trace gas concentrations designed to mimic tropical warm pool conditions. No boundary condition or external parameter other than the Coriolis parameter varies with latitude. A 15-member ensemble is initiated using random atmospheric initial conditions. A 2°C equatorial warm anomaly is switched on, along with ocean coupling (day 0). Enhanced deep convection rapidly develops near the hot spot, forcing an anomalous large-scale circulation that resembles the linear response of a dry atmosphere to a localized heating, as in the Gill model. Enhanced convection, the anomalous large-scale circulation, and enhanced wind speed peak in amplitude at about day 15. Enhanced latent heat fluxes driven primarily by an increase in vector mean wind damp the anomalous heat content of the ocean near the hot spot before day 20. Between day 20 and day 50, suppressed latent heat fluxes due to suppressed synoptic eddy variance cause a warming of the remote Tropics in regions of anomalous low-level easterly flow. This wind-driven evaporative atmosphere–ocean exchange results in a 60–70-day oscillation in tropical mean oceanic heat content, accompanied by a compensating out-of-phase oscillation in vertically integrated atmospheric moist static energy. Beyond day 70 of the simulation, positive SST anomalies are found across much of the tropical belt. These slowly decay toward the 28°C background state.

scholarly journals A Bulk Turbulent Air–Sea Flux Algorithm for High-Wind, Spray Conditions

2008 ◽  
Vol 38 (7) ◽  
pp. 1581-1596 ◽  
Author(s):  
Edgar L. Andreas ◽  
P. Ola G. Persson ◽  
Jeffrey E. Hare
Keyword(s):  
Latent Heat ◽  
Large Scale ◽  
Surface Flux ◽  
Heat Fluxes ◽  
High Wind ◽  
Molecular Processes ◽  
Tropical Ocean ◽  
Wind Speeds ◽  
The Mean ◽  
High Winds

Abstract Sensible and latent heat can cross the air–sea interface by two routes: as interfacial fluxes controlled by molecular processes right at the interface, and as spray fluxes from the surface of sea spray droplets. Once the 10-m wind speed over the ocean reaches approximately 11–13 m s−1, the spray sensible and latent heat fluxes become significant fractions (i.e., 10% or greater) of the corresponding interfacial fluxes. The analysis here establishes that result by combining the Tropical Ocean-Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (COARE) version 2.6 bulk interfacial flux algorithm with a microphysical spray model to partition measured heat fluxes from two good high-wind datasets into spray and interfacial flux contributions. The measurements come from the Humidity Exchange over the Sea (HEXOS) experiment and the Fronts and Atlantic Storm-Tracks Experiment (FASTEX); wind speeds in these two datasets span 5 to 20 m s−1. After the measured heat fluxes are separated into spray and interfacial contributions, the spray fluxes are used to develop a fast spray flux algorithm to combine with the COARE version 2.6 interfacial flux algorithm in a unified turbulent surface flux algorithm for use in large-scale and ocean storm models. A sensitivity analysis of the spray and interfacial components of this unified flux algorithm demonstrates how the two component fluxes scale differently with the mean meteorological variables and why they must therefore be parameterized separately in models intended to treat air–sea fluxes in high winds.

scholarly journals Comparing Simulated and Measured Sensible and Latent Heat Fluxes over Snow under a Pine Canopy to Improve an Energy Balance Snowmelt Model

2008 ◽  
Vol 9 (6) ◽  
pp. 1506-1522 ◽  
Author(s):  
D. Marks ◽  
A. Winstral ◽  
G. Flerchinger ◽  
M. Reba ◽  
J. Pomeroy ◽  
...  
Keyword(s):  
Energy Balance ◽  
Snow Cover ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Energy Content ◽  
Heat Fluxes ◽  
Balance Model ◽  
Mass Fluxes ◽  
Model Efficiency ◽  
Snowmelt Model

Abstract During the second year of the NASA Cold Land Processes Experiment (CLPX), an eddy covariance (EC) system was deployed at the Local Scale Observation Site (LSOS) from mid-February to June 2003. The EC system was located beneath a uniform pine canopy, where the trees are regularly spaced and are of similar age and height. In an effort to evaluate the turbulent flux calculations of an energy balance snowmelt model (SNOBAL), modeled and EC-measured sensible and latent heat fluxes between the snow cover and the atmosphere during this period are presented and compared. Turbulent fluxes comprise a large component of the snow cover energy balance in the premelt and ripening period (March–early May) and therefore control the internal energy content of the snow cover as melt accelerates in late spring. Simulated snow cover depth closely matched measured values (RMS difference 8.3 cm; Nash–Sutcliff model efficiency 0.90), whereas simulated snow cover mass closely matched the few measured values taken during the season. Over the 927-h comparison period using the default model configuration, simulated sensible heat H was within 1 W m−2, latent heat LυE within 4 W m−2, and cumulative sublimation within 3 mm of that measured by the EC system. Differences between EC-measured and simulated fluxes occurred primarily at night. The reduction of the surface layer specification in the model from 25 to 10 cm reduced flux differences between EC-measured and modeled fluxes to 0 W m−2 for H, 2 W m−2 for LυE, and 1 mm for sublimation. When only daytime fluxes were compared, differences were further reduced to 1 W m−2 for LυE and &lt;1 mm for sublimation. This experiment shows that in addition to traditional mass balance methods, EC-measured fluxes can be used to diagnose the performance of a snow cover energy balance model. It also demonstrates the use of eddy covariance methods for measuring heat and mass fluxes from snow covers at a low-wind, below-canopy site.

scholarly journals Role of the Gulf Stream and Kuroshio–Oyashio Systems in Large-Scale Atmosphere–Ocean Interaction: A Review

2010 ◽  
Vol 23 (12) ◽  
pp. 3249-3281 ◽  
Author(s):  
Young-Oh Kwon ◽  
Michael A. Alexander ◽  
Nicholas A. Bond ◽  
Claude Frankignoul ◽  
Hisashi Nakamura ◽  
...  
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Gulf Stream ◽  
Large Scale ◽  
Climate Model ◽  
Low Frequency ◽  
Heat Fluxes ◽  
Western Boundary ◽  
Basin Scale ◽  
Sst Anomalies

Abstract Ocean–atmosphere interaction over the Northern Hemisphere western boundary current (WBC) regions (i.e., the Gulf Stream, Kuroshio, Oyashio, and their extensions) is reviewed with an emphasis on their role in basin-scale climate variability. SST anomalies exhibit considerable variance on interannual to decadal time scales in these regions. Low-frequency SST variability is primarily driven by basin-scale wind stress curl variability via the oceanic Rossby wave adjustment of the gyre-scale circulation that modulates the latitude and strength of the WBC-related oceanic fronts. Rectification of the variability by mesoscale eddies, reemergence of the anomalies from the preceding winter, and tropical remote forcing also play important roles in driving and maintaining the low-frequency variability in these regions. In the Gulf Stream region, interaction with the deep western boundary current also likely influences the low-frequency variability. Surface heat fluxes damp the low-frequency SST anomalies over the WBC regions; thus, heat fluxes originate with heat anomalies in the ocean and have the potential to drive the overlying atmospheric circulation. While recent observational studies demonstrate a local atmospheric boundary layer response to WBC changes, the latter’s influence on the large-scale atmospheric circulation is still unclear. Nevertheless, heat and moisture fluxes from the WBCs into the atmosphere influence the mean state of the atmospheric circulation, including anchoring the latitude of the storm tracks to the WBCs. Furthermore, many climate models suggest that the large-scale atmospheric response to SST anomalies driven by ocean dynamics in WBC regions can be important in generating decadal climate variability. As a step toward bridging climate model results and observations, the degree of realism of the WBC in current climate model simulations is assessed. Finally, outstanding issues concerning ocean–atmosphere interaction in WBC regions and its impact on climate variability are discussed.

scholarly journals Objectively Analyzed Air–Sea Heat Fluxes for the Global Ice-Free Oceans (1981–2005)

2007 ◽  
Vol 88 (4) ◽  
pp. 527-540 ◽  
Author(s):  
Lisan Yu ◽  
Robert A. Weller
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Atmospheric Model ◽  
Initial Study ◽  
Heat Fluxes ◽  
Global Ocean ◽  
Flux Analysis ◽  
Boundary Current ◽  
Basin Scale

A 25-yr (1981–2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air–Sea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset. The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W m−2 between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing.

scholarly journals Analyzing influence of spatial resolution on the estimated evapotranspiration by using remote sensing data over an oasis area in Northwestern China

2009 ◽  
Vol 6 (1) ◽  
pp. 1321-1345
Author(s):  
H. Tian ◽  
J. Wen ◽  
Z. B. Su ◽  
Y. M. Ma ◽  
L. Wang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Spatial Resolution ◽  
Land Surface ◽  
Large Scale ◽  
Northwestern China ◽  
Retrieval Algorithm ◽  
Modis Data ◽  
Relative Errors

Abstract. In this paper, the influence of spatial resolution on the precision of estimates was analyzed through evapotranspiration (ET hereafter) modeling over a typical oasis in northwestern China by using the Landsat-TM and MODIS data. A relatively high consistency was observed between the TM-based latent heat flux and daily ET estimates and in-situ measurements, with relative errors of 9.7% and 8.8%, respectively. Despite lower precision of the relative errors of 22.4% and 17.0%, respectively, the MODIS-based latent heat flux and ET estimates can effectively depict the basic trend of the spatial distribution of the land surface processes. When the visible and near-infrared information of 250 m resolution was syncretized into MODIS LST retrieval algorithm, the precision of latent heat flux prediction was improved evidently. Additionally, the diurnal variation of the reference ET fraction shows that the temporal upscaling method of ET is suitable for the study area. In spite of suffering the influence of the heterogeneity of land surface, the moderate resolution MODIS data, combined with the parameterization model of land surface energy flux applied in this investigation, are suitable for the ET mapping at large scale while high-resolution data can serve as an important supplement.

scholarly journals Inter-seasonal and inter-annual variations of mean and eddy atmospheric energetics over India

MAUSAM ◽  
2021 ◽  
Vol 47 (1) ◽  
pp. 41-46
Author(s):  
M. RAJEEVAN ◽  
K. C. SINHA RAY
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Large Scale ◽  
Monsoon Season ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Mean Flow ◽  
Annual Variations ◽  
Eddy Fluxes

Using daily upper air data from 1000 to 250 hPa of 20 stations during the period 1983-87 , the inter-sasonal and inter-annual variations of vertically intearated mean and eddy sensible and latent heat fluxes over India were examined. Vertically intearated meridional, sensible and latent fluxes (both mean and eddy fluxes) were generally southwards over the country except over northeastern parts. Large seasonal variation of mean sensible heat and latent heat flux values occur in association with the seasonal shifts of Hadley circulation. Maximum sensible heat fluxes were observed during pre-monsoon season over northern parts of India. Maximum latent heat fluxes were observed over central parts of India during monsoon season. Eddy fluxes were two order smaller than fluxes due to mean flow during all seasons. Maximum eddy fluxes occur in winter and are accomplished by large scale transient eddies. The eddy fluxes were practically negligible equatorwards of 15°N. Seasonal variations of fluxes over low latitudes were, however, different from the zonal pattern of annual cycle obtained by Oort (1971).   There were significant differences in meridional mean and eddy flux values between 1983 (a good monsoon year) and 1987 (a bad monsoon year). During 1983 (1987) the sensible heat flux values due to transient eddies were equatorwards (polewards) during the premonsoon as well as monsoon seasons. Similarly during monsoon season of 1983 larger northward mean sensible and latent heat fluxes were observed. In addition there were significant differences in vertical structure of zonal sensible and latent heat fluxes between 1983 and 1987 also.

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