Methane flux measurements on multiple scales in an agricultural landscape: linking tall tower flux measurements with short eddy covariance towers

Agricultural landscapes exhibit spatially and temporally complex methane (CH4) fluxes: emissions originate from strong point sources, such as ruminants and cowsheds, and from fertilisation of fields, which adds short-term peaks in the methane flux to the atmosphere [1]. Furthermore, in some locations, such as the study site, these sources are overlaid on a CH4 flux originating from underlying peaty soils and drainage ditches between the fields [2]. In order to account for all these different sources, the CH4 fluxes need to be monitored continuously with a system that integrates the fluxes over a large area, providing the effective flux of CH4 from the landscape (~1 km2) to the atmosphere. Traditionally eddy covariance (EC) method has been used to obtain the ecosystem scale (~ 1 ha) fluxes of various compounds. However, it is questionable whether EC fluxes at one location can capture the high variability of CH4 fluxes in an agricultural landscape. To test this, methane exchange was measured at three locations with short (6.5 m high) EC towers a few kilometres apart from each other and at two heights (20 m and 60 m) in one tall tower. Additionally, it is assessed whether the short tower fluxes can be upscaled to match the CH4 fluxes measured at the tall tower using footprint modelling. The measurement campaign was held between the 1st and 25th of July 2012 in the vicinity of the Cabauw Experimental Site for Atmospheric Research (CESAR) (51°58’12.00”N, 4°55’34.48”E), which is located in the Netherlands. The landscape is an intensively managed agricultural area, with soil consisting of peat, topped by an approximately 1 meter thick bed of clay. Tentative results show large variability in CH4 fluxes between the three short tower sites: cumulative CH4 fluxes over a 10-day-period range from 188 mg(CH4) m-2 to 306 mg(CH4) m-2. Tall tower CH4 fluxes from the same period summed up to 275 mg(CH4) m-2 (20 m height) and 430 mg(CH4) m-2 (60 m height). High fluxes at 60 m height could be explained by cowsheds within the footprint, whereas systems located closer to the ground did not detect the hotspot emissions from the cowsheds. The presentation will discuss CH4 flux variability in an agricultural landscape, issues related to upscaling flux measurements and the usability of EC CH4 flux measurements at tall towers for estimating landscape scale exchange of methane. [1] P.S. Kroon et al., 2007, Biogeosciences, 4, 715-728. [2] A.P. Schrier-Uijl et al., 2010, Plant Soil, 329, 509-520

Climate control of terrestrial carbon exchange across biomes and continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ∼16 ®C (a threshold value of mean annual temperature), above which no further increase of CO,.2uptake with temperature was observed and dryness influence overrules temperature influence. © 2010 lOP Publishing Ltd

Characterization of Geographical and Meteorological Parameters

[EN]This chapter is devoted to the introduction of some geographical and meteorological information involved in the numerical modeling of wind fields and solar radiation. First, a brief description of the topographical data given by a Digital Elevation Model and Land Cover databases is provided. In particular, the Information System of Land Cover of Spain (SIOSE) is considered. The study is focused on the roughness length and the displacement height parameters that appear in the logarithmic wind profile, as well as in the albedo related to solar radiation computation. An extended literature review and characterization of both parameters are reported. Next, the concept of atmospheric stability is introduced from the Monin–Obukhov similarity theory to the recent revision of Zilitinkevich of the Neutral and Stable Boundary Layers (SBL). The latter considers the effect of the free-flow static stability and baroclinicity on the turbulent transport of momentum and of the Convective Boundary Layers (CBL), more precisely, the scalars in the boundary layer, as well as the model of turbulent entrainment

Climate control of terrestrial carbon exchange across biomes and continents

Peer reviewe

Opportunistic sensing with recreational hot-air balloon flights

We report about a new third-party observation, namely, wind measurements derived from hot-air balloon (HAB) tracks. We first compare the HAB winds with wind measurements from a meteorological tower and a radio acoustic wind profiler, both situated at the topographically flat observatory near Cabauw, the Netherlands. To explore the potential of this new type of wind observation in other topographies, we present an intriguing HAB flight in Austria with a spectacular mountain–valley circulation. Subsequently, we compare the HAB data with a numerical weather prediction (NWP) model during 2011–13 and the standard deviation of the wind speed is 2.3 m s−1. Finally, we show results from a data assimilation feasibility experiment that reveals that HAB wind information can have a positive impact on a hindcasted NWP trajectory

Measuring low-altitude winds with a hot-air balloon and their validation with Cabauw tower observations

A field experiment with a hot-air balloon was conducted in the vicinity of the meteorological observatory of Cabauw in The Netherlands. Recreational hot-air balloon flights contain useful wind information in the atmospheric boundary layer (ABL). On a yearly basis between 8000 and 9000 flights are taking place in The Netherlands, mainly during the morning and evening transition. An application (app) for smartphones has been developed to collect location data. We report about a feasibility study of a hot-air balloon experiment where we investigated the accuracy of the smartphone’s Global Navigation Satellite System (GNSS) receiver using an accurate geodetic GNSS receiver as a reference. Further, we study the dynamic response of the hot-air balloon on variations in the wind by measuring the relative wind with a sonic anemometer, which is mounted below the gondola. The GNSS comparison reveals that smartphones equipped with a GNSS chip have in the horizontal plane an absolute position error standard deviation of 5 m, but their relative position error standard deviation is smaller. Therefore, the horizontal speeds, which are based on relative positions and a time step of 1 s, have standard deviations of σu = 0.8 m s-1 and σv = 0.6 m s-1. The standard deviation in altitude is 12 m. We have validated the hot-air balloon derived wind data with observations from the Cabauw tower and the results are encouraging. We have studied the dynamics of a hot-air balloon. An empirical value of the response length has been found which accounts for the balloon’s inertia after a changing wind, and which compared favorable with the theoretical derived value. We have found a small but systematic movement of the hot-air balloon relative to the surrounding air. The model for the balloon dynamics has been refined to account for this so-called inertial drift

Measuring low-altitude winds with a hot-air balloon and their validation with Cabauw tower observations

A field experiment with a hot-air balloon was conducted in the vicinity of the meteorological observatory of Cabauw in The Netherlands. Recreational hot-air balloon flights contain useful wind information in the atmospheric boundary layer (ABL). On a yearly basis between 8000 and 9000 flights are taking place in The Netherlands, mainly during the morning and evening transition. An application (app) for smartphones has been developed to collect location data. We report about a feasibility study of a hot-air balloon experiment where we investigated the accuracy of the smartphone’s Global Navigation Satellite System (GNSS) receiver using an accurate geodetic GNSS receiver as a reference. Further, we study the dynamic response of the hot-air balloon on variations in the wind by measuring the relative wind with a sonic anemometer, which is mounted below the gondola. The GNSS comparison reveals that smartphones equipped with a GNSS chip have in the horizontal plane an absolute position error standard deviation of 5 m, but their relative position error standard deviation is smaller. Therefore, the horizontal speeds, which are based on relative positions and a time step of 1 s, have standard deviations of σu = 0.8 m s-1 and σv = 0.6 m s-1. The standard deviation in altitude is 12 m. We have validated the hot-air balloon derived wind data with observations from the Cabauw tower and the results are encouraging. We have studied the dynamics of a hot-air balloon. An empirical value of the response length has been found which accounts for the balloon’s inertia after a changing wind, and which compared favorable with the theoretical derived value. We have found a small but systematic movement of the hot-air balloon relative to the surrounding air. The model for the balloon dynamics has been refined to account for this so-called inertial drift.</p