Dynamics and Diurnal Variations of Surface Radiation Budget over Agricultural Crops Located in Sudanian Climate

Kounouhéwa, Basile; Mamadou, Ossénatou; N’Gobi, Gabin Koto; Awanou, Cossi Norbert

doi:10.4236/acs.2013.31014

Cited by 12 publications

(6 citation statements)

References 15 publications

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“…The daily meteorological conditions of the two sites, located 13 km apart, were expectedly close except for LAI and soil moisture. At both sites, minimum annual values of SW up were observed during the wet seasons mainly due to cloud cover [ Gounou et al ., ; Kounouhéwa et al ., ]. During the dry seasons, SW up was lower than its value during the moistening period (Figure a) due to the aerosols which are brought by the Harmattan winds in the region [ Marticorena et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

et al. 2016

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Natural ecosystems in sub‐Saharan Africa are experiencing intense changes that will probably modify land surface feedbacks and consequently the regional climate. In this study, we have analyzed water vapor (QLE) and sensible heat (QH) fluxes over a woodland (Bellefoungou, BE) and a cultivated area (Nalohou, NA) in the Sudanian climate of Northern Benin, using 2 years (from July 2008 to June 2010) of eddy covariance measurements. The evaporative fraction (EF) response to environmental and surface variables was investigated at seasonal scale. Soil moisture was found to be the main environmental factor controlling energy partitioning. During the wet seasons, EF was rather stable with an average of 0.75 ± 0.07 over the woodland and 0.70 ± 0.025 over the cultivated area. This means that 70–75% of the available energy was changed into actual evapotranspiration during the investigated wet seasons depending on the vegetation type. The cumulative annual actual evapotranspiration (AET) varied between 730 ± 50 mm yr−1 at the NA site and 1040 ± 70 mm yr−1 at the BE site. With similar weather conditions at the two sites, the BE site showed 30% higher AET values than the NA site. The sensible heat flux QH at the cultivated site was always higher than that of the woodland site, but observed differences were much less than those of QLE. In a land surface conversion context, these differences are expected to impact both atmospheric dynamics and the hydrological cycle.

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Section: Resultsmentioning

confidence: 99%

Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

et al. 2016

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“…The four seasons are described in the next section together with four 15-day periods that were chosen to characterize the atmospheric conditions and the surface response characteristics prevailing during each of these stages of the monsoon cycle. In this study, we focused on the net longwave and shortwave radiations, but more details on the four components of the radiative budget can be found in Kounouhéwa et al (2013).…”

Section: A Contrasting Seasonal Cyclementioning

confidence: 99%

Energy fluxes and surface characteristics over a cultivated area in Benin: daily and seasonal dynamics

Mamadou

Cohard

Galle

et al. 2014

Hydrol. Earth Syst. Sci.

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Abstract. Latent and sensible heat surface fluxes are key factors of the western African monsoon dynamics. However, few long-term observations of these land surface fluxes are available; these are needed to increase understanding of the underlying processes and assess their impacts on the energy and water cycles at the surface-atmosphere interface. This study analyzes turbulent fluxes of one full year, measured with the eddy covariance technique, over a cultivated area in northern Benin (western Africa). The study site is part of the long-term AMMA-CATCH (African Monsoon Multidisciplinary Analysis-Coupling of the Tropical Atmosphere and Hydrological Cycle) hydrological observatory. The flux partitioning was investigated through the evaporative fraction (EF) and the Bowen ratio (β) at both seasonal and daily scales. Finally, the surface conductance (G s ) and the decoupling coefficient ( ) were calculated and compared with specific bare soil or canopy models.Four contrasting seasons were identified and characterized by their typical daily energy cycles. The results pointed out the contrasting seasonal variations of sensible and latent heat fluxes due to changing atmospheric and surface conditions. In the dry season, the sensible heat fluxes were largely dominant (β ∼ 10) and a low but significant evapotranspiration was measured (EF = 0.08); this was attributed to a few neighboring bushes, possibly fed by the water table. During the wet season, after the monsoon onset, surface conditions barely affected the evaporative fraction (EF), which remained steady (EF = 0.75); the latent heat flux was dominant and the Bowen ration (β) was about 0.4. During the dry-to-wet and wet-to-dry transition seasons, both EF and β were highly variable, as they depended on the atmospheric forcing or the response to isolated rains. A complete surface-atmosphere decoupling was never observed in 2008 (0 < < 0.6), which suggests a systematic mixing of the air within the canopy with the atmospheric surface layer, irrespective of the atmospheric conditions and the vegetation height.Modeling approaches showed a good agreement of soil resistance with the Sakaguchi bare soil model. Canopy conductance was also well reproduced with the Ball-Berry stomata model. We showed that the skin surface temperature had a large seasonal and daily amplitude, and played a major role in all the surface processes. Consequently, an accurate modeling of the surface temperature is crucial to represent correctly the energy and water budgets for this region.

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“…Net radiation (𝑅 𝑁 ) flux is the total energy flux available at the ground surface, and can either be measured directly or estimated from some other meteorological variables (Amarakoon and Chen 1999;Samani et al 2005Samani et al , 2007Jegede et al 2006;Ayoola et al 2014). Net radiation can be deduced from the earth's energy budget equation i.e., summation of short-wave (incoming and outgoing solar irradiance) and long-wave (terrestrial) radiation parameters (Polavarapu 1970;Kounouhéwa 2013), and is given by…”

Section: Introductionmentioning

confidence: 99%

Analysis of global and net radiation fluxes in relation to surface albedo at DACCIWA site in Ile-Ife, southwest Nigeria

Ajao

Abiye²,

Agboola³

2023

Theor Appl Climatol

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Measurements of global solar and net radiation fluxes were made above a grass-covered surface at DACCIWA site in a tropical location, Ile-Ife, southwest Nigeria for a period of three years (2017 -2019). The radiation data sets were obtained from a four-component net radiometer (model NR01). Observations were made for cases of clear sky and cloudy conditions during the measurement period. The results showed considerable fluctuations of both radiation fluxes occurring during the period of measurements at the location. For clear sky conditions, the magnitudes of global and net radiation fluxes were higher than those observed for cloudy conditions due to attenuation by clouds and aerosols. For the period of observation, the highest radiation flux values occurred in 2018 while the lowest were observed in 2017. The daily surface albedo (𝛼) values ranged from 0.16 to 0.22 at the site. Empirical relationships obtained for global solar and net radiation are 𝑅 𝑁 = 0.754 𝑅 𝐺 -17.4 Wm -2 and 𝑅 𝑁 = 0.657 𝑅 𝐺 -32.7 Wm -2 for wet and dry seasons respectively. Based on the empirical relationships, daily net and global solar radiation can be obtained when measurements like these are not available. Linear relationships between 𝑅 𝑁 and 𝑅 𝐺 show that for all days (cloudy and clear sky conditions), average 𝑅 𝑁 is about 65 % of 𝑅 𝐺 , and about 50 % of 𝑅 𝐺 for clear sky conditions at the location.

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Dynamics and Diurnal Variations of Surface Radiation Budget over Agricultural Crops Located in Sudanian Climate

Cited by 12 publications

References 15 publications

Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

Energy fluxes and surface characteristics over a cultivated area in Benin: daily and seasonal dynamics

Analysis of global and net radiation fluxes in relation to surface albedo at DACCIWA site in Ile-Ife, southwest Nigeria

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