The BLLAST field experiment: Boundary-Layer late afternoon and sunset turbulence



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Yagüe Anguis, Carlos and Román Cascón, Carlos and Sastre Marugán, Mariano (2014) The BLLAST field experiment: Boundary-Layer late afternoon and sunset turbulence. Atmospheric chemistry and physics, 14 (20). pp. 10931-10960. ISSN 1680-7316

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Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state. These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere. Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions. Ground-based measurements combined with tethered-balloon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period. Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations.

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© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 License.The BLLAST field experiment was made possible thanks to the contribution of several institutions and supports: INSU-CNRS (Institut National des Sciences de l’Univers, Centre national de la Recherche Scientifique, LEFE-IMAGO program), Météo-France, Observatoire Midi-Pyrénées (University of Toulouse), EUFAR (EUropean Facility for Airborne Research) BLLATE-1&2, COST ES0802 (European Cooperation in the field of Scientific and Technical) and the Spanish MINECO projects CGL2009–08609, CGL2012–37416–C04–03, CGL2012–37416–C04–02 and CGL2011-13477-E. The field experiment would not have occurred without the contribution of all participating European and American research groups, which all have contributed in a significant amount. The Piper Aztec research airplane is operated by SAFIRE, which is a unit supported by INSU-CNRS, Météo-France and the French Spatial Agency (CNES). BLLAST field experiment was hosted by the instrumented site of Centre de Recherches Atmosphériques, Lannemezan, France (Observatoire Midi-Pyrénées, Laboratoire d’Aérologie). Its 60m tower is partly supported by the POCTEFA/FLUXPYR European program. BLLAST data are managed by SEDOO, from Observatoire Midi-Pyrénées. See for all contributions. Since 2013, the French ANR supports BLLAST analysis. Finally, we thank Harm J. J. Jonker, Robert J. Beare and Zbignew Sorbjan for fruitful discussions.

Uncontrolled Keywords:Advection; Atmospheric convection; Convective boundary layer; Diurnal variation; Experimental study; Ground-based measurement; Numerical model; Turbulence
Subjects:Sciences > Physics > Geophysics
Sciences > Physics > Meteorology
ID Code:29087
Deposited On:10 Mar 2015 19:02
Last Modified:05 Jun 2018 17:16

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