Role of net radiation on energy balance closure in heterogeneous grasslands

Abstract. Low energy balance closure (EBC) at a particular eddy-covariance flux site increased the uncertainties of carbon, water and energy measurements and thus hampered the urgent research of scaling up and modeling analysis through site combinations. A series of manipulative experiments were conducted in this study to explore the role of net radiation (Rn) in the EBC in relation to spatial variability of vegetation characteristics, source area, sensor type, and dome condition in the Inner Mongolian grassland of Northern China. At all three sites, the daytime peak residual fluxes of EBC were consistently about 100 W m−2 regardless of radiometers (i.e., REBS Q7.1 or CNR1). The spatial variability in net radiation was 19 W m−2 (5% of Rn) during the day and 7 W m−2 (16%) at night, with an average of 13 W m−2 (11%) from eight plot measurements across the three sites. Net radiation results were affected more by measurement source area in unclipped heterogeneous system than in clipped homogeneous vegetation. Large area measurement significantly (P<0.0001) increased by 9 W m−2 during the day and decreased by 4 W m−2 at night in unclipped treatments. With an increase in clipping intensity, net radiation decreased by 25 W m−2 (6% of Rn) at midday and 81 MJ m−2 (6%) during a growing season with heavier regular clipping than that in unclipped treatments. Additional effort in EBC between 9:00 and 15:00 LT is needed for future research because of high variation. Using this method, the EBC difference derived from the two types of net radiometers was only 6 W m−2. Results from Q7.1 with new domes were higher during the day but lower at night than those with used domes. Overall, the inclusion of the uncertainty in available energy accounted for 60% of the 100 W m−2 shortfalls in the lack of closure. Clearly, the unclosed energy balance at these three grassland sites remains significant, with unexplored mechanisms for future research.

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Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

Hydrology and Earth System Sciences ◽

10.5194/hess-21-3401-2017 ◽

2017 ◽

Vol 21 (7) ◽

pp. 3401-3415 ◽

Cited By ~ 18

Author(s):

Nobuhle P. Majozi ◽

Chris M. Mannaerts ◽

Abel Ramoelo ◽

Renaud Mathieu ◽

Alecia Nickless ◽

...

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Surface Energy ◽

Latent Heat ◽

Surface Energy Balance ◽

Sensible Heat Flux ◽

Dry Season ◽

Energy Balance Closure ◽

Net Radiation ◽

Wet Season

Abstract. Flux towers provide essential terrestrial climate, water, and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based Earth observation and monitoring efforts, such as assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches. In this paper, 15 years of Skukuza eddy covariance data, i.e. from 2000 to 2014, were analysed for surface energy balance closure (EBC) and partitioning. The surface energy balance closure was evaluated using the ordinary least squares regression (OLS) of turbulent energy fluxes (sensible (H) and latent heat (LE)) against available energy (net radiation (Rn) less soil heat (G)), and the energy balance ratio (EBR). Partitioning of the surface energy during the wet and dry seasons was also investigated, as well as how it is affected by atmospheric vapour pressure deficit (VPD), and net radiation. After filtering years with low-quality data (2004–2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed the wet season with 1.17 and spring (1.02) being closest to unity, with the dry season (0.70) having the highest imbalance. Nocturnal surface energy closure was very low at 0.26, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity. The energy partition analysis showed that sensible heat flux is the dominant portion of net radiation, especially between March and October, followed by latent heat flux, and lastly the soil heat flux, and during the wet season where latent heat flux dominated sensible heat flux. An increase in net radiation was characterized by an increase in both LE and H, with LE showing a higher rate of increase than H in the wet season, and the reverse happening during the dry season. An increase in VPD is correlated with a decrease in LE and increase in H during the wet season, and an increase in both fluxes during the dry season.

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Research Status and Development Trends of Hazardous Materials Transportation

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.361-363.1230 ◽

2011 ◽

Vol 361-363 ◽

pp. 1230-1239

Author(s):

Zong Feng Zou ◽

Bao Quan Zhang

Keyword(s):

Hazardous Materials ◽

Future Research ◽

Joint Control ◽

Large Area ◽

Role Of Government ◽

Hazardous Materials Transportation ◽

Transportation Risk ◽

Hazmat Transportation ◽

Research Situation

The related issues of hazardous materials transportation in recent years are summarized and reviewed from the following aspects: hazardous materials transportation risk evaluation models, road routing models, the application of related technology, early warning for emergency response and joint action mechanism and platform construction, the research situation and development pattern of unified monitoring platform, etc. Analysis shows that it is essential to establish more in-depth and scientific quantitative models based on the attainment of more comprehensive and continuous data as well as the consideration of various constraints. It is a direction for future research to develop comprehensive application of technology and to establish HAZMAT transportation joint control platform in large area, and the leading and facilitating role of government should be paid more attention on joint control platform construction in large area.

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Testing energy balance closure with GOES-retrieved net radiation and in situ measured eddy correlation fluxes in BOREAS

Journal of Geophysical Research Atmospheres ◽

10.1029/1999jd900390 ◽

1999 ◽

Vol 104 (D22) ◽

pp. 27881-27893 ◽

Cited By ~ 48

Author(s):

Jiujing Gu ◽

Eric A. Smith ◽

James D. Merritt

Keyword(s):

Energy Balance ◽

Eddy Correlation ◽

Energy Balance Closure ◽

Net Radiation

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Heat storage in forest biomass improves energy balance closure

Biogeosciences ◽

10.5194/bg-7-301-2010 ◽

2010 ◽

Vol 7 (1) ◽

pp. 301-313 ◽

Cited By ~ 70

Author(s):

A. Lindroth ◽

M. Mölder ◽

F. Lagergren

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Latent Heat ◽

Heat Storage ◽

Soil Heat Flux ◽

Energy Balance Closure ◽

Sensible Heat ◽

Net Radiation ◽

Tree Biomass ◽

Stable Conditions

Abstract. Temperature measurements in trunks and branches in a mature ca. 100 years-old mixed pine and spruce forest in central Sweden were used to estimate the heat storage in the tree biomass. The estimated heat flux in the sample trees and data on biomass distributions were used to scale up to stand level biomass heat fluxes. The rate of change of sensible and latent heat storage in the air layer below the level of the flux measurements was estimated from air temperature and humidity profile measurements and soil heat flux was estimated from heat flux plates and soil temperature measurements. The fluxes of sensible and latent heat from the forest were measured with an eddy covariance system in a tower. The analysis was made for a two-month period in summer of 1995. The tree biomass heat flux was the largest of the estimated storage components and varied between 40 and −35 W m−2 on summer days with nice weather. Averaged over two months the diurnal maximum of total heat storage was 45 W m−2 and the minimum was −35 W m−2. The soil heat flux and the sensible heat storage in air were out of phase with the biomass flux and they reached maximum values that were about 75% of the maximum of the tree biomass heat storage. The energy balance closure improved significantly when the total heat storage was added to the turbulent fluxes. The slope of a regression line with sum of fluxes and storage as independent and net radiation as dependent variable, increased from 0.86 to 0.95 for half-hourly data and the scatter was also reduced. The most significant finding was, however, that during nights with strongly stable conditions when the sensible heat flux dropped to nearly zero, the total storage matched the net radiation very well. Another interesting result was that the mean energy imbalance started to increase when the Richardson number became more negative than ca. −0.1. In fact, the largest energy deficit occurred at maximum instability. Our conclusion is that eddy covariance measurements can function well during stable conditions but that the functioning under strong instabilities might be a so far unforeseen problem.

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Heat storage in forest biomass significantly improves energy balance closure particularly during stable conditions

Biogeosciences Discussions ◽

10.5194/bgd-6-8531-2009 ◽

2009 ◽

Vol 6 (4) ◽

pp. 8531-8567

Author(s):

A. Lindroth ◽

M. Mölder ◽

F. Lagergren

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Latent Heat ◽

Heat Storage ◽

Soil Heat Flux ◽

Energy Balance Closure ◽

Sensible Heat ◽

Net Radiation ◽

Tree Biomass ◽

Stable Conditions

Abstract. Temperature measurements in trunks and branches in a mature ca. 100 years-old mixed pine and spruce forest in central Sweden were used to estimate the heat storage in the tree biomass. The estimated heat flux in the sample trees and data on biomass distributions were used to scale up to stand level biomass heat fluxes. The rate of change of sensible and latent heat storage in the air layer below the level of the flux measurements was estimated from air temperature and humidity profile measurements and soil heat flux was estimated from heat flux plates and soil temperature measurements. The fluxes of sensible and latent heat from the forest were measured with an eddy covariance system in a tower. The analysis was made for a two-month period in summer of 1995. The tree biomass heat flux was the largest of the estimated storage components and varied between 40 and −35 W m−2 on summer days with nice weather. Averaged over two months the diurnal maximum of total heat storage was 45 W m−2 and the minimum was −35 W m−2. The soil heat flux and the sensible heat storage in air were out of phase with the biomass flux and they reached maximum values that were about 75% of the maximum of the tree biomass heat storage. The energy balance closure improved significantly when the total heat storage was added to the turbulent fluxes. The slope of a regression line with sum of fluxes and storage as independent and net radiation as dependent variable, increased from 0.86 to 0.95 for half-hourly data and the scatter was also reduced. The most significant finding was, however, that during nights with strongly stable conditions when the sensible heat flux dropped to nearly zero, the total storage matched the net radiation nearly perfectly. Another interesting result was that the mean energy imbalance started to increase when the Richardson number became more negative than ca. −0.1. In fact, the largest energy deficit occurred at maximum instability. Our conclusion is that eddy covariance measurements can function well during stable conditions but that the functioning under strong instabilities might be a so far unforeseen problem.

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Surface energy balance closure in an arid region: role of soil heat flux

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2003.09.005 ◽

2004 ◽

Vol 122 (1-2) ◽

pp. 21-37 ◽

Cited By ~ 180

Author(s):

B.G Heusinkveld ◽

A.F.G Jacobs ◽

A.A.M Holtslag ◽

S.M Berkowicz

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Surface Energy ◽

Arid Region ◽

Surface Energy Balance ◽

Soil Heat Flux ◽

Energy Balance Closure

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Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

10.5194/hess-2016-685 ◽

2017 ◽

Author(s):

Nobuhle P. Majozi ◽

Chris M. Mannaerts ◽

Abel Ramoelo ◽

Renaud Mathieu ◽

Alecia Nickless ◽

...

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Surface Energy ◽

Latent Heat ◽

Friction Velocity ◽

Surface Energy Balance ◽

Sensible Heat Flux ◽

Energy Balance Closure ◽

Net Radiation ◽

Wet Season

Abstract. Flux towers provide essential terrestrial climate, water and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based earth observation and monitoring efforts, such as assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches. In this paper, 15 years of Skukuza eddy covariance data, i.e. from 2000 to 2014, were analysed for surface energy balance closure (EBC) and partitioning. The surface energy balance closure was evaluated using the ordinary least squares regression (OLS) of turbulent energy fluxes (sensible (H) and latent heat (LE)) against available energy (net radiation (Rn) less soil heat (G)), and the energy balance ratio (EBR). Partitioning of the surface energy during the wet and dry seasons was investigated, as well as how it is affected by atmospheric vapor pressure deficit (VPD), and net radiation. After filtering years with bad data (2004–2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed summer (0.98) and spring (1.02) were closest to unity, with winter (0.70) having the least closure. Nocturnal surface energy closure was very low at 0.11, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity. The surface energy partitioning of this savanna ecosystem showed that sensible heat flux dominated the energy partitioning between March and October, followed by latent heat flux, and lastly the soil heat flux, and during the wet season where latent heat flux dominated the sensible heat flux. An increase in net radiation was characterized by an increase in both LE and H, with LE showing a higher rate of increase than H in the wet season, and the reverse happening during the dry season. An increase in VPD is characterized by a decrease in LE and increase in H during the wet season, and an increase of both fluxes during the dry season.

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On the energy balance closure and net radiation in complex terrain

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2016.05.012 ◽

2016 ◽

Vol 226-227 ◽

pp. 37-49 ◽

Cited By ~ 9

Author(s):

Wohlfahrt Georg ◽

Hammerle Albin ◽

Niedrist Georg ◽

Scholz Katharina ◽

Tomelleri Enrico ◽

...

Keyword(s):

Energy Balance ◽

Complex Terrain ◽

Energy Balance Closure ◽

Net Radiation

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Surface-Energy-Balance Closure over Land: A Review

Boundary-Layer Meteorology ◽

10.1007/s10546-020-00529-6 ◽

2020 ◽

Vol 177 (2-3) ◽

pp. 395-426 ◽

Cited By ~ 6

Author(s):

Matthias Mauder ◽

Thomas Foken ◽

Joan Cuxart

Keyword(s):

Energy Balance ◽

Surface Energy ◽

Surface Energy Balance ◽

Transport Processes ◽

Heat Fluxes ◽

Future Research ◽

Turbulent Heat ◽

Energy Balance Closure ◽

Airborne Measurements ◽

Open Questions

Abstract Quantitative knowledge of the surface energy balance is essential for the prediction of weather and climate. However, a multitude of studies from around the world indicate that the turbulent heat fluxes are generally underestimated using eddy-covariance measurements, and hence, the energy balance is not closed. This energy-balance-closure problem, which has been heavily covered in the literature for more than 25 years, is the topic of the present review, in which we provide an overview of the potential reason for the lack of closure. We demonstrate the effects of the diurnal cycle on the energy balance closure, and address questions with regard to the partitioning of the energy balance residual between the sensible and the latent fluxes, and whether the magnitude of the flux underestimation can be predicted based on other variables typically measured at micrometeorological stations. Remaining open questions are discussed and potential avenues for future research on this topic are laid out. Integrated studies, combining multi-tower experiments and scale-crossing, spatially-resolving lidar and airborne measurements with high-resolution large-eddy simulations, are considered to be of critical importance for enhancing our understanding of the underlying transport processes in the atmospheric boundary layer.

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