Surface energy balance measurements at a tropical site in West Africa during the transition from dry to wet season

Mauder, Matthias; Jegede, Olugbemiro J.; Okogbue, Emmanuel Chilekwu; Wimmer, Florian; Foken, Thomas

doi:10.1007/s00704-006-0252-6

Cited by 84 publications

(70 citation statements)

References 44 publications

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“…It must therefore be assumed that on the local scale of typical energy balance measurements with no internal boundary layers and 'ideal' footprint conditions, the energy balance cannot be closed in a heterogeneous landscape due to deficits of measurement concepts and methodologies. Since energy balance closure could be demonstrated for sites with relatively homogeneous surroundings (Heusinkveld et al 2004;Mauder et al 2007a), it is assumed that terrain heterogeneity causes the transfer of energy by other mechanisms than just non-organised turbulent motions. It has been reported that additional fluxes are generated at forest edges (Klaassen et al 2002).…”

Section: Discussionmentioning

confidence: 99%

Energy balance closure for the LITFASS-2003 experiment

Foken

Mauder

Liebethal

et al. 2009

Theor Appl Climatol

140

108

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In the first part, this paper synthesises the main results from a series of previous studies on the closure of the local energy balance at low-vegetation sites during the LITFASS-2003 experiment. A residual of up to 25% of the available energy has been found which cannot be fully explained either by the measurement uncertainty of the single components of the surface energy balance or by the length of the flux-averaging period. In the second part, secondary circulations due to heterogeneities in the surface characteristics (roughness, thermal and moisture properties) are discussed as a possible cause for the observed energy balance non-closure. This hypothesis seems to be supported from the fluxes derived from area-averaging measurement techniques (scintillometers, aircraft).

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Section: Discussionmentioning

confidence: 99%

Energy balance closure for the LITFASS-2003 experiment

Foken

Mauder

Liebethal

et al. 2009

Theor Appl Climatol

140

108

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“…Smaller imbalances were found in homogenous terrain with little deviation from the 'ideal site requirement' (e.g. Grelle and Lindroth 1996;Heusinkveld et al 2004;Mauder et al 2007a).…”

Section: Introductionmentioning

confidence: 99%

Available energy and energy balance closure at four coniferous forest sites across Europe

Moderow

Aubinet

Feigenwinter

et al. 2009

Theor Appl Climatol

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The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J H , latent heat J E , heat storage of biomass J veg and heat storage due to photosynthesis J C were of minor importance during day but of some importance during night, where J veg turned out to be the most important one. Comparisons of calculated storage terms (J E , J H ) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m −2 (10-11 W m −2 for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m −2 (approximately 6 W m −2 for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone.

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“…net radiation minus soil heat flux, is equal to the sum of the turbulent fluxes (Rn − G = LE + H); however, in most instances, the measured available energy is larger than the sum of the measured turbulent fluxes of sensible heat and latent heat. Extensive research on the issue of surface energy imbalance in EC observations has been done (Barr et al, 2012;Chen et al, 2009;Foken et al, 2010;Franssen et al, 2010;Mauder et al, 2007), and closure error (or imbalance) has been documented to be around 10-30 % (Wilson et al, 2002;von Randow et al, 2004;Sánchez et al, 2010).…”

mentioning

confidence: 99%

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

Majozi

Mannaerts

Ramoelo

et al. 2017

Hydrol. Earth Syst. Sci.

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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)(2005)(2006)(2007)(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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Surface energy balance measurements at a tropical site in West Africa during the transition from dry to wet season

Cited by 84 publications

References 44 publications

Energy balance closure for the LITFASS-2003 experiment

Energy balance closure for the LITFASS-2003 experiment

Available energy and energy balance closure at four coniferous forest sites across Europe

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

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