Structure Function Analysis of Two-Scale Scalar Ramps. Part II: Ramp Characteristics and Surface Renewal Flux Estimation

2018

The earlier formulation based on surface renewal (SR) analysis for estimating the sensible (or buoyant) heat flux (H) of a surface without requiring calibration involved canopy parameters to simultaneously estimate H and the friction velocity (u * ). A SR-based formulation is derived that allows estimating u * and subsequently H that, at most, involves the zero-plane displacement. Regardless of the measurement height above the canopy and the stability case, u * and H estimates were closed to values measured using the eddy covariance method for either homogeneous or sparse (orchards) canopies. The proposed SR analysis can be potentially considered for gap filling in half-hourly eddy covariance series of u * and H and to estimate parameters useful for land surface modeling, such as the roughness length for momentum, the roughness lengths for momentum, and heat and the turbulent Prandtl number. CASTELLVÍ10,134

Section: Introductionmentioning

confidence: 99%

An Advanced Method Based on Surface Renewal Theory to Estimate the Friction Velocity and the Surface Heat Flux

2018

“…Some experiments have shown that under near neutral conditions α Z is approximately 0.5. In general, and regardless of the ramp model used, α Z depends on the measurement height and the stability conditions [ Paw et al ., ; Katul et al ., ; Snyder et al ., ; Castellví , ; Castellví and Snyder , ; Shapland et al ., ]. Two expressions have been derived to explain the variability of parameter α Z , the first requires as input the horizontal wind speed [ Castellví , ] and the second the temperature gradient [ Castellví , ].…”

Section: Theorymentioning

confidence: 99%

Daytime sensible heat flux estimation over heterogeneous surfaces using multitemporal land‐surface temperature observations

Cammalleri

Ciraolo

et al. 2016

Equations based on surface renewal (SR) analysis to estimate the sensible heat flux (H) require as input the mean ramp amplitude and period observed in the ramp-like pattern of the air temperature measured at high frequency. A SR-based method to estimate sensible heat flux (H SR-LST ) requiring only lowfrequency measurements of the air temperature, horizontal mean wind speed, and land-surface temperature as input was derived and tested under unstable conditions over a heterogeneous canopy (olive grove). H SR-LST assumes that the mean ramp amplitude can be inferred from the difference between land-surface temperature and mean air temperature through a linear relationship and that the ramp frequency is related to a wind shear scale characteristic of the canopy flow. The land-surface temperature was retrieved by integrating in situ sensing measures of thermal infrared energy emitted by the surface. The performance of H SR-LST was analyzed against flux tower measurements collected at two heights (close to and well above the canopy top). Crucial parameters involved in H SR-LST , which define the above mentioned linear relationship, were explained using the canopy height and the land surface temperature observed at sunrise and sunset. Although the olive grove can behave as either an isothermal or anisothermal surface, H SR-LST performed close to H measured using the eddy covariance and the Bowen ratio energy balance methods. Root mean square differences between H SR-LST and measured H were of about 55 W m 22 . Thus, by using multitemporal thermal acquisitions, H SR-LST appears to bypass inconsistency between land surface temperature and the mean aerodynamic temperature. The one-source bulk transfer formulation for estimating H performed reliable after calibration against the eddy covariance method. After calibration, the latter performed similar to the proposed SR-LST method.In LST-based applications, the latent heat flux (kET) is often determined as a residual of a simplified SEB, in which the available energy at the surface, given by the difference between the net radiation (R n ) and the soil heat flux (G), is partitioned between kET and sensible heat flux (H) [e.g., Allen et al., 2005]. Even if LST plays an important role in determining the upwelling long-wave component of R n as well as surface

“…A nonzero mean local vertical gradient,

\frac{\partial T_{(z)}}{\partial z}

, is required to observe ramps in air temperature time series [ Holzer and Siggia , ], and while

A_{(z)}

is related with

\partial T_{(z)}

τ

is mainly dependent on the transfer of momentum to the ground. Thus,

\frac{1}{τ}

is expected to be related with

\frac{u}{z}

\frac{u_{*}}{z}

[ Paw U et al ., ; Chen et al ., ; Castellví et al ., ; Finnigan et al ., ; Shapland et al ., ]. Therefore, for a given measurement height, the parameter

s_{(z)}

mainly depends on the stability conditions.…”

Section: Theorymentioning

confidence: 99%

“…The latter represents an injection of scalar into the bulk of the flow which can be identified by a regular ramp‐like shape observed in the scalar concentration time series (recorded at high frequency) measured above the surface. The SR method has been successfully employed over various canopies to estimate H from the air temperature, which is typically measured at between 8 and 20 Hz in either the roughness or inertial sublayers [ Paw U et al ., ; Snyder et al ., 1996; Castellví , ; Castellví and Snyder , ; Shapland et al ., ; French et al, ]. Using thermal infrared (IR) imagery with a large field of view, spatial trends in

T_{c}

along transects in direction of the wind have been observed.…”

Section: Introductionmentioning

confidence: 99%

Combining the bulk transfer formulation and surface renewal analysis for estimating the sensible heat flux without involving the parameter

Jiménez-Gavilán

González‐Dugo

2014

The single-source bulk transfer formulation (based on the Monin-Obukhov Similarity Theory, MOST) has been used to estimate the sensible heat flux, H, in the framework of remote sensing over homogeneous surfaces (H MOST ). The latter involves the canopy parameter, kB 21 , which is difficult to parameterize. Over short and dense grass at a site influenced by regional advection of sensible heat flux, H MOST with kB 21 5 2 (i.e., the value recommended) correlated strongly with the H measured using the Eddy Covariance, EC, method, H EC . However, it overestimated H EC by 50% under stable conditions for samples showing a local air temperature gradient larger than the measurement error, 0.4 km 21 . Combining MOST and Surface Renewal analysis, three methods of estimating H that avoid kB 21 dependency have been derived. These new expressions explain the variability of H versus u Ã T c 2T ðzÞ À Á , where u Ã is the friction velocity, T c is the radiometric surface temperature, and T ðzÞ is the air temperature at height, z. At two measurement heights, the three methods performed excellently. One of the methods developed required the same readily/commonly available inputs as H MOST due to the fact that the ratio between T c 2T ðzÞ À Á and the ramp amplitude was found fairly constant under stable and unstable cases. Over homogeneous canopies, at a site influenced by regional advection of sensible heat flux, the methods proposed are an alternative to the traditional bulk transfer method because they are reliable, exempt of calibration against the EC method, and are comparable or identical in cost of application. It is suggested that the methodology may be useful over bare soil and sparse vegetation.