Abstract. 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 tetheredballoon 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.
Abstract. The Development of Methodologies for WaterVapour Measurement (DEMEVAP) project aims at assessing and improving humidity sounding techniques and establishing a reference system based on the combination of Raman lidars, ground-based sensors and GPS. Such a system may be used for climate monitoring, radiosonde bias detection and correction, satellite measurement calibration/validation, and mm-level geodetic positioning with Global Navigation Satellite Systems. A field experiment was conducted in September-October 2011 at Observatoire de Haute-Provence (OHP). Two Raman lidars (IGN mobile lidar and OHP NDACC lidar), a stellar spectrometer (SOPHIE), a differential absorption spectrometer (SAOZ), a sun photometer (AERONET), 5 GPS receivers and 4 types of radiosondes (Vaisala RS92, MODEM M2K2-DC and M10, and Meteolabor Snow White) participated in the campaign. A total of 26 balloons with multiple radiosondes were flown during 16 clear nights. This paper presents preliminary findings from the analysis of all these data sets. Several classical Raman lidar calibration methods are evaluated which use either Vaisala RS92 measurements, point capacitive humidity measurements, or GPS integrated water vapour (IWV) measurements. A novel method proposed by Bosser et al. (2010) is also tested. It consists in calibrating the lidar measurements during the GPS data processing. The methods achieve a repeatability of 4-5 %. Changes in the calibration factor of IGN Raman lidar are evidenced which are attributed to frequent optical re-alignments. When modelling and correcting the changes as a linear function of time, the precision of the calibration factors improves to 2-3 %. However, the variations in the calibration factor, and hence the absolute accuracy, between methods and types of reference data remain at the level of 7 %. The intercomparison of radiosonde measurements shows good agreement between RS92 and Snow White measurements up to 12 km. An overall dry bias is found in the measurements from both MODEM radiosondes. Investigation of situations with low RH values (< 10 %RH) in the lower and middle troposphere reveals, on occasion, a lower RH detection limit in the Snow White measurements compared to RS92 due to a saturation of the Peltier device. However, on other occasions, a dry bias is found in RS92, instead. On average, both RS92 and Snow White measurements show a slight moist bias at night-time compared to GPS IWV, while the MODEM measurements show a large dry bias. The IWV measurements from SOPHIE (night-time) and SAOZ (daytime) spectrometers, AERONET photometer (daytime) and calibrated Raman lidar (night-time) showed excellent agreement with the GPS IWV measurements.
?? 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Urbanized valleys are particularly vulnerable to particulate air pollution during the winter, when ground-based stable layers or cold-air pools persist over the valley floor. We examine whether the temporal variability of PM10 concentration in the section of the Arve River Valley between Cluses and Servoz in the French Alps can be explained by the temporal variability of the valley heat deficit, a bulk measure of atmospheric stability within the valley. We do this on the basis of temperature profile and ground-based PM10 concentration data collected during wintertime with a temporal resolution of one hour or finer, as part of the Passy-2015 field campaign conducted around Passy in this section of valley. The valley heat deficit was highly correlated with PM10 concentration on a daily time scale. The hourly variability of PM10 concentrations was more complex and cannot be explained solely by the hourly variability of the valley heat deficit. The interplay of the diurnal cycles of emissions and local dynamics is demonstrated and a drainage mechanism for observed nocturnal dilution of near-surface PM10 concentrations is proposed
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