Measurements of Aerodynamic Roughness, Bowen Ratio, and Atmospheric Surface Layer Height by Eddy Covariance and Tethersonde Systems Simultaneously over a Heterogeneous Rice Paddy

Abstract

The aerodynamic roughness, Bowen ratio, and friction velocity were measured over a rice paddy using tethersonde and eddy covariance (EC) systems. In addition, the height ranges of the atmospheric inertial sub-layer (ISL) were derived using the tethersonde data. Comparison of the friction velocity, latent and sensible heat fluxes, and Bowen ratio estimated from these systems show their correlation coefficients to be >0.7. This difference between the observational systems can be associated with their respective footprint areas. The aerodynamic roughness was observed to be about 0.03 m for wind blowing from a paddy-dominated area (PDA) and about 0.37 m from a rice paddy interspersed with buildings (PIB) based on the ISL profile. Results are close to the effective roughness length model of Mason, having the same shear stresses at the blending height. In contrast, both the geometric mean model of Taylor and the arithmetic mean model of Tsai and Tsuang underestimate the effective roughness over the PIB. During daylight hours, the height range of the ISL ranged from a few meters to 25 m above ground level (AGL) for wind blowing from the PDA and 14-42 m for wind blowing from the PIB

Impact of Effective Roughness Length on Mesoscale Meteorological Simulations over Heterogeneous Land Surfaces in Taiwan

“…The z 0eff values were derived based on the research performed by Tsai and Tsuang [12] and Tsai et al [13] following the method of Goode and Belcher [14]. In Goode and Belcher [14], z 0eff was estimated by considering the individual local roughness, z 0i , of the underlying LU types that compose the modeling grid box; moreover, the concept of a blending layer was introduced to obtain the spatially averaged surface stress.…”

“…Two sets of z 0eff values were prepared for this study. The first z 0eff dataset was calculated using the z 0i values supplied from the dominant LU lookup table (the "default" column in Table 1), while the second z 0eff dataset was estimated using the updated z 0i values, for which the observed z 0i values of three LU types (urban, dry cropland and pasture, and irrigated cropland and pasture) were determined based on observed surface fluxes and wind, TA, and humidity profiles at three sites in Taiwan [13,19]. The method used to calculate z 0i was first proposed in Tsuang et al [19] and further applied for different LU types in Tsai et al [12,13].…”

“…The first z 0eff dataset was calculated using the z 0i values supplied from the dominant LU lookup table (the "default" column in Table 1), while the second z 0eff dataset was estimated using the updated z 0i values, for which the observed z 0i values of three LU types (urban, dry cropland and pasture, and irrigated cropland and pasture) were determined based on observed surface fluxes and wind, TA, and humidity profiles at three sites in Taiwan [13,19]. The method used to calculate z 0i was first proposed in Tsuang et al [19] and further applied for different LU types in Tsai et al [12,13]. Assuming that the conditions in the atmospheric inertial sublayer (ISL) are steady and horizontally homogeneous, the z 0i , zero-displacement height, friction velocity, surface SHF, surface LHF, and Monin-Obukhov stability length can all be determined by fitting the integral forms of Businger's equations [20].…”

Surface energy flux measurements in a flooded and an aerobic rice field using a single eddy-covariance system

“…They investigated fast and slow response meteorological variables, determining surface roughness using the Martano (2000) method and analysing the adequacy of the fetch through an accurate footprint analysis described in Harazono et al (1998). Footprint analysis is largely used to quantify the contributing source areas to the scalar flux measurement (Tsai et al 2010). This is especially important when the ecosystems of interest are inhomogeneous (natural ecosystems) or their extensions are limited (agricultural fields).…”

“…In literature, different footprint models were adopted to evaluate the fetch of turbulent fluxes over rice fields. Schuepp et al (1990) analytical footprint model was used in the works of Gao et al (2003Gao et al ( ), (2006 over an homogeneous field of about one hectare, while Hsieh et al (2000) model was implemented in the study of Tsai et al (2010) over an heterogeneous terrain of about 80 hectares. Generally, the range of applicability of these models is based on the stability conditions of the atmosphere (Masseroni et al 2014).…”