Monitoring the Sensible Heat Flux over Urban Areas using Large Aperture Scintillometry: Case Study of Marseille City During the Escompte Experiment

Abstract

Sensible heat flux estimated by Large Aperture Scintillometry (LAS) has been tested against the more traditional eddy covariance technique over Marseille city centre, a reasonably homogeneous surface. Over the 3 week test period fluxes were found to be similar, yet less noisy for the LAS due to the spatial integration. No systematic bias between the estimates was found as a function of wind direction, indicating the homogeneity of the site. Sensitivity analysis of the required aerodynamic parameters shows that careful attention must be paid to the displacement height along the measurement path. Spatial variability of surface sensible heat flux is studied via a second LAS measurement path over the city.

Long-term Turbulent Sensible-Heat-Flux Measurements with a Large-Aperture Scintillometer in the Centre of Łódź, Central Poland

“…This is consistent with other studies (e.g. Lagouarde et al 2006;Ward et al 2014). Since both u * and T * are connected via L, their ultimate values must be solved iteratively using Eqs.…”

“…It seems that for the inflow from the western and northern sectors, the diurnal cycle of Q H in Łódź had features characteristic of city centres (e.g. Christen and Vogt 2004;Lagouarde et al 2006;Kotthaus and Grimmond 2014a, b). For the less dense settlement, the night-time Q H is almost always negative, except for January and February.…”

“…The SAS instrument provides fluxes averaged over relatively short paths (up to 250 m), and to obtain fluxes representative of larger areas, a large-aperture scintillometer (LAS) should be used. The LAS instrument has been used in a number of cities, e.g., Marseille (Lagouarde et al 2006), London (Wood et al 2013a), Helsinki (Wood et al 2013b), Łódź (Zieliński et al 2013), Swindon (Ward et al 2014), and Changzou (Zhang and Zhang 2015), London (Crawford et al 2017). More recently, Ward et al (2015a, b) used a system consisting of a LAS intrument and a microwave scintillometer to measure the sensible and latent heat fluxes simultaneously over the city of Swindon in the UK.…”

Influence of Mean Rooftop-Level Estimation Method on Sensible Heat Flux Retrieved from a Large-Aperture Scintillometer Over a City Centre

“…Scintillometers provide highly reliable heat fluxes and have been successfully applied in turbulent sensible heat-flux measurements in many different environments ranging from natural (e.g., Green et al 1994;De Bruin et al 1995;Beyrich et al 2002Beyrich et al , 2012Meijninger et al 2002;Ezzachar et al 2007;Evans et al 2012) to urban areas (e.g., Kanda et al 2002;Roth et al 2006;Lagouarde et al 2006;Pauscher 2010;Zieliński et al 2013;Wood et al 2013;Ward et al 2014Ward et al , 2015Zhang and Zhang 2015). Large-aperture scintillometers (LAS) allow the estimation of the refractive index structure parameter C 2 n along an optical path of up to several kilometres in length.…”

“…Using auxiliary weather data, the temperature structure parameter C 2 T and consequently the turbulent sensible heat flux, H can be retrieved. Several authors investigated errors in the determination of the sensible heat flux related to uncertainties in the path-averaged friction velocity (Andreas 1992), the Bowen ratio (Solignac et al 2009), or topography Lagouarde et al 2006;Evans and De Bruin 2011;Gruber et al 2014), or uncertainties in the scintillometer measurement itself (e.g., Hill 1988). However, there was no attempt to investigate the sensitivity of the sensible heat flux to the rooftop-level computation method.…”