Articles | Volume 16, issue 14
Atmos. Chem. Phys., 16, 9489–9504, 2016

Special issue: The Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST)...

Atmos. Chem. Phys., 16, 9489–9504, 2016

Research article 29 Jul 2016

Research article | 29 Jul 2016

Estimation of the advection effects induced by surface heterogeneities in the surface energy budget

Joan Cuxart1, Burkhard Wrenger2, Daniel Martínez-Villagrasa1, Joachim Reuder3,4, Marius O. Jonassen3,5, Maria A. Jiménez1, Marie Lothon6, Fabienne Lohou6, Oscar Hartogensis7, Jens Dünnermann2, Laura Conangla8, and Anirban Garai9 Joan Cuxart et al.
  • 1University of the Balearic Islands, Palma, Mallorca, Spain
  • 2Hochschule Ostwestfalen-Lippe, Höxter, North Rhine-Westphalia, Germany
  • 3Geophysical Institute, University of Bergen, Bergen, Norway
  • 4Bjerknes Centre for Climate Research, Bergen, Norway
  • 5The University Centre in Svalbard, Longyearbyen, Norway
  • 6Centre Recherches Atmosphériques, Univ. Toulouse & CNRS, Lannemezan, France
  • 7Wageningen University of Research, Wageningen, the Netherlands
  • 8Universitat Politècnica de Catalunya, Manresa, Catalonia, Spain
  • 9University of California, San Diego, California, USA

Abstract. The effect of terrain heterogeneities in one-point measurements is a continuous subject of discussion. Here we focus on the order of magnitude of the advection term in the equation of the evolution of temperature as generated by documented terrain heterogeneities and we estimate its importance as a term in the surface energy budget (SEB), for which the turbulent fluxes are computed using the eddy-correlation method. The heterogeneities are estimated from satellite and model fields for scales near 1 km or broader, while the smaller scales are estimated through direct measurements with remotely piloted aircraft and thermal cameras and also by high-resolution modelling. The variability of the surface temperature fields is not found to decrease clearly with increasing resolution, and consequently the advection term becomes more important as the scales become finer. The advection term provides non-significant values to the SEB at scales larger than a few kilometres. In contrast, surface heterogeneities at the metre scale yield large values of the advection, which are probably only significant in the first centimetres above the ground. The motions that seem to contribute significantly to the advection term in the SEB equation in our case are roughly those around the hectometre scales.

Short summary
Estimations of the effect of thermal advection in the surface energy budget are provided. Data from the experimental campaign BLLAST, held in Southern France in summer 2011, are used, including airborne data by drones and surface-based instrumentation. Model data outputs and satellite information are also inspected. Surface heterogeneities of the order of the kilometer or larger seem to have little effect on the budget, whereas hectometer-scale structures may contribute significantly to it.
Final-revised paper