Seasonal and diurnal variations in moisture, heat and  CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes over a typical steppe prairie in Inner Mongolia, China

Gao, Zhiqiu; Lenschow, Donald H.; He, Zhongshi; Zhou, Mengzi

doi:10.5194/hess-13-987-2009

Cited by 24 publications

(16 citation statements)

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“…Table 3 gives an overview of the median land cover specific H and LE over all flight patterns, and their median spatial variability. These results fall well within the range of summertime ensemble average fluxes during solar noon observed by ground-based EC measurements over different land covers in this region (100 W m −2 < H < 310 W m −2 and 100 W m −2 < LE < 480 W m −2 ; Gao et al, 2009;Hao et al, 2007;Hao et al, 2008;Shao et al, 2008). In comparison, the flight-line average heat fluxes are in the range of 71 W m −2 < H < 310 W m −2 and 46 W m −2 < LE < 300 W m −2 (Table B2).…”

Section: Extrapolation and Summarizationsupporting

confidence: 85%

Spatially explicit regionalization of airborne flux measurements using environmental response functions

et al. 2013

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Abstract. The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50–100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decomposition of the turbulence data enables a spatial discretization of 90 m of the flux measurements. For a total of 8446 flux observations during 12 flights, MODIS land surface temperature (LST) and enhanced vegetation index (EVI) in each flux footprint are determined. Boosted regression trees are then used to infer an environmental response function (ERF) between all flux observations (H, LE) and biophysical (LST, EVI) and meteorological drivers. Numerical tests show that ERF predictions covering the entire Xilin River catchment (&approx;3670 km2) are accurate to ≤18% (1 σ). The predictions are then summarized for each land cover type, providing individual estimates of source strength (36 W m−2 < H < 364 W m−2, 46 W m−2 < LE < 425 W m−2) and spatial variability (11 W m−2 < σH < 169 W m−2, 14 W m−2 < σLE < 152 W m−2) to a precision of ≤5%. Lastly, ERF predictions of land cover specific Bowen ratios are compared between subsequent flights at different locations in the Xilin River catchment. Agreement of the land cover specific Bowen ratios to within 12 &pm; 9% emphasizes the robustness of the presented approach. This study indicates the potential of ERFs for (i) extending airborne flux measurements to the catchment scale, (ii) assessing the spatial representativeness of long-term tower flux measurements, and (iii) designing, constraining and evaluating flux algorithms for remote sensing and numerical modelling applications.

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Section: Extrapolation and Summarizationsupporting

confidence: 85%

Spatially explicit regionalization of airborne flux measurements using environmental response functions

et al. 2013

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“…In summer and autumn, the seasonally averaged carbon flux exceeds −5.0 µmol m −2 s −1 (in July and August, the monthly averaged NEE can reach around −6.5 µmol m −2 s −1 , not shown), but the amount of carbon uptake is still much less than those observed in forests and croplands (Niyogi et al, 2004). It is also less than that observed in the semi-arid area in Tongyu (44 • 25 N, 122 • 52 E) and in the typical steppe prairie in Inner Mongolia (44 • 08 31 N, 116 • 18 45 E) both covered by grassland and can reach −18 µmol m −2 s −1 and −14 µmol m −2 s −1 (Gao et al, 2009) in summer, respectively. During the summer (June-August), we observe significant diurnal variation in NEE, with a relatively steady respiration (net carbon output from the vegetation) and a strong photosynthesis that tracks the solar radiation during the daytime from 06:00 to 20:00 LT.…”

Section: Cloudinessmentioning

confidence: 75%

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

et al. 2010

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Abstract. The impacts of clouds and atmospheric aerosols on the terrestrial carbon cycle at semi-arid Loess Plateau in Northwest China are investigated, by using the observation data obtained at the SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) site. Daytime (solar elevation angles of larger than 50 • ) net ecosystem exchange (NEE) of CO 2 obtained during the midgrowing season (July-August) are analyzed with respect to variations in the diffuse radiation, cloud cover and aerosol optical depth (AOD). Results show a significant impact by clouds on the CO 2 uptake by the grassland (with smaller LAI values) located in a semi-arid region, quite different from areas covered by forests and crops. The light saturation levels in the canopy are low, with a value of about 434.8 W m −2 . Thus, under overcast conditions of optically thick clouds, the CO 2 uptake increases with increasing clearness index (the ratio of global solar radiation received at the Earth surface to the extraterrestrial irradiance at a plane parallel to the Earth surface), and a maximum CO 2 uptake and light use efficiency of vegetation occur with the clearness index of about 0.37 and lower air temperature. Under other sky conditions, CO 2 uptake decreases with cloudiness but light use efficiency is enhanced, due to increased diffuse fraction of PAR. Additionally, under cloudy conditions, changes in the NEE of CO 2 also result from the interactions of many environmental factors, especially the air temperature. In contrast to its response to changes in solar radiation, the carbon uptake shows a slightly negative response to increased AOD. The reason for the difference in the response of the semi-arid grassland from that of the forest and crop lands may be due to the difference in the canopy's architectural structure.

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“…Wen et al (2009), using data from the LOPEX05 (Loess Plateau mesa region land surface process field Experiment 2005), showed that the contributions from heat storage in the soil and the atmospherecanopy layer between the Sonic anemometer and land surface were about 11% and 3%, respectively. Gao et al (2009) were also aware of this problem and reported an increase of about 20% in the slope of the linear regression when includ- ing the soil heat storage in a steppe prairie in Inner Mongolia. An average imbalance of about 18% still remained once all the storage terms were considered.…”

Section: Energy Balance Closurementioning

confidence: 99%

“…The eddy-covariance (EC) method has become a standard tool in the study of the surface-atmosphere boundary layer interactions. However, a lack of closure in the surface energy balance of about 10-30% is traditionally reported when using EC techniques to measure the turbulent fluxes (Wilson et al, 2002;Barr et al, 2006;Gao et al, 2009;Ma et al, 2009;Wen et al, 2009;. This imbalance has implications on how energy flux measurements should be interpreted and how these estimates should be compared with model simulations (Twine et al, 2000;Xin et al, 2010;Liu et al, 2010;Were et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

Sánchez

Caselles

Rubio

2010

Hydrol. Earth Syst. Sci.

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Abstract. The imbalance in the surface energy budget, when using eddy-covariance techniques to measure turbulent fluxes, is still an unresolved problem. Important progresses have been reported in recent years identifying potential reasons for this lack of energy balance closure. In this paper we focus on the data collected in a FLUXNET boreal forest site in Sodankylä, Finland. Using one month half-hourly data, an average Energy Balance Ratio (EBR) of 0.72 is obtained. The inclusion of the heat storage terms in the energy budget yields an improvement of about 6% in the total closure. The sensitivity of the energy balance closure to the turbulence intensity is analysed in terms of the friction velocity, and atmospheric stability/instability conditions. Significant better closure is obtained for high values of the friction velocity and unstable conditions. The mismatch in variable footprints for different fluxes is checked by analysing the dependence of the closure on wind direction. The inhomogeneities of the emplacement surrounding the flux tower induce a critical decrease in the EBR of up to 30% for specific wind directions. After filtering all unfavourable conditions, EBR=0.94. This is a reasonable good result for the energy balance closure. However there is still a 6% of the available energy unaccounted. Part of this remaining imbalance could be justified as the impossibility of the 30 min averaging time to capture the low frequency flux contributions, since the closure is improved by a 5% when the averaging time is expanded to 2 h.

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Seasonal and diurnal variations in moisture, heat and CO<sub>2</sub> fluxes over a typical steppe prairie in Inner Mongolia, China

Cited by 24 publications

References 50 publications

Spatially explicit regionalization of airborne flux measurements using environmental response functions

Spatially explicit regionalization of airborne flux measurements using environmental response functions

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

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Seasonal and diurnal variations in moisture, heat and CO&lt;sub&gt;2&lt;/sub&gt; fluxes over a typical steppe prairie in Inner Mongolia, China

Cited by 24 publications

References 50 publications

Spatially explicit regionalization of airborne flux measurements using environmental response functions

Spatially explicit regionalization of airborne flux measurements using environmental response functions

The effects of clouds and aerosols on net ecosystem CO&lt;sub&gt;2&lt;/sub&gt; exchange over semi-arid Loess Plateau of Northwest China

Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

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Resources

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Seasonal and diurnal variations in moisture, heat and CO<sub>2</sub> fluxes over a typical steppe prairie in Inner Mongolia, China

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China