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

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.publishedVersio

Urban thermodynamic island in a coastal city analyzed from an optimized surface network

Within the framework of ESCOMPTE, a French experiment performed in June and July 2001 in the south-east of France to study the photo-oxidant pollution at the regional scale, the urban boundary layer (UBL) program focused on the study of the urban atmosphere over the coastal city of Marseille. A methodology developed to optimize a network of 20 stations measuring air temperature and moisture over the city is presented. It is based on the analysis of a numerical simulation, performed with the non-hydrostatic, mesoscale Meso-NH model, run with four nested-grids down to a horizontal resolution of 250 m over the city and including a specific parametrization for the urban surface energy balance. A three-day period was modelled and evaluated against data collected during the preparatory phase for the project in summer 2000. The simulated thermodynamic surface fields were analysed using an empirical orthogonal function (EOF) decomposition in order to determine the optimal network configuration designed to capture the dominant characteristics of the fields. It is the first attempt of application of this kind of methodology to the field of urban meteorology. The network, of 20 temperature and moisture sensors, was implemented during the UBL-ESCOMPTE experiment and continuously recorded data from 12 June to 14 July 2001. The measurements were analysed in order to assess the urban thermodynamic island spatio-temporal structure, also using EOF decomposition. During nighttime, the influence of urbanization on temperature is clear the field is characterized by concentric thermo-pleths around the old core of the city, which is the warmest area of the domain. The moisture field is more influenced by proximity to the sea and airflow patterns. During the day, the sea breeze often moves from west or south-west and consequently the spatial pattern for both parameters is characterized by a gradient perpendicular to the shoreline. Finally, in order to assess the methodology adopted, the spatial structures extracted from the simulation of the 2000 preparatory campaign and observations gathered in 2001 have been compared. They are highly correlated, which is a relevant validation of the methodology proposed. The relations between these spatial structures and geographical characteristics of the site have also been studied. High correlations between temperature spatial structure during nighttime and urban cover fraction or street aspect ratio are observed and simulated. For temperature during daytime or moisture during both daytime and nighttime these geographical factors are not correlated with thermodynamic fields spatial structures

High-frequency boundary layer profiling with reusable radiosondes

International audienceA new system for high-frequency boundary layer profiling based upon radiosondes and free balloons was tested during the field phases of the Boundary Layer Late Afternoon and Sunset Turbulence experiment (BLLAST 2011, Lannemezan, France) and of the Hydrological cycle in the Mediterranean Experiment (HyMeX, 2012). The system consists of a conventional Vaisala receiver and a GPS radiosonde (pressure, wind, humidity and temperature), that is tied to a couple of inflated balloons. The principle of the sounding system is to permit the first balloon to detach from the rawinsonde at a predetermined altitude, allowing for the rawinsonde to slowly descend with the second balloon to perform a second, new sounding. The instrumentation is then eventually recovered. The expecting landing area is anticipated before the flight by estimating the trajectory of the probe from a forecasted wind profile and by specifying both the balloon release altitude and the mean ascent and descent rates of the system. The real landing point is determined by the last transmission of the radiosonde GPS and the visual landmark provided by the second balloon. Seventy-two soundings were performed during BLLAST (62) and HyMeX (10), with a recovery rate of more than 80% during the BLLAST field campaign. Recovered radiosondes were generally reused several times, often immediately after recovery, which definitely demonstrates the high potential of this system

L’effet rafraichissant des parcs à Paris pendant PANAME 2023

International audienceEn juillet 2023, une grande campagne expérimentale de recherche (PANAME2023), a eu lieu pour étudier la météorologie de l'agglomération parisienne, en particulier l'îlot de chaleur urbain. Cette campagne, regroupant plusieurs laboratoires de recherches, est copilotée par le Centre National de Recherches Météorologiques (CNRM). Ceci permettra à terme de mieux prévoir la météo au sein même des villes. En effet, les agglomérations françaises, et Paris en particulier, subissent des canicules de plus en plus fréquentes et intenses sous l'effet du changement climatique. Celles-ci sont aggravées localement par des îlots de chaleur dus à l'effet de l'urbanisation, qui accroissent la dangerosité des conditions auxquelles sont exposés habitants, visiteurs et infrastructures. L'approfondissement des connaissances du rôle joué par les parcs et l'infrastructure urbaine est un point essentiel pour adapter la ville aux fortes chaleurs.Dans ce cadre, le CNRM a réalisé plus de 300 profils météorologiques à l'aide de drones légers sur neuf sites parcs et urbains dans Paris Métropole pour mieux connaître les paramètres thermodynamiques (température, humidité, pression, force et direction du vent) de l'atmosphère entre le sol et 120m d'altitude à la fin de la journée. Des profils par drone au sein des sites urbains en proximité des parcs vont servir à établir un point de référence, permettant d'évaluer l'effet rafraîchissant des parcs

Absolute Calibration or Validation of the Altimeters on the Sentinel-3A and the Jason-3 over Lake Issykkul (Kyrgyzstan)

International audienc

The development of the Atmospheric Measurements by Ultra-Light Spectrometer (AMULSE) greenhouse gas profiling system and application for satellite retrieval validation

International audienceWe report in this paper the development of an embedded ultralight spectrometer (<3 kg) based on tuneable diode laser absorption spectroscopy (with a sampling rate of 24 Hz) in the mid-infrared spectral region. This instrument is dedicated to in situ measurements of the vertical profile concentrations of three main greenhouse gases – carbon dioxide (CO2), methane (CH4) and water vapour (H2O) – via standard weather and tethered balloons. The plug and play instrument is compact, robust, cost-effective, and autonomous. The instrument also has low power consumption and is non-intrusive.It was first calibrated during an in situ experiment on an ICOS (Integrated Carbon Observation System) site for several days, then used in two experiments with several balloon flights of up to 30 km altitude in the Reims region of France in 2017–2018 in collaboration with Météo-France CNRM (Centre National de Recherches Météorologiques).This paper shows the valuable interest of the data measured by the AMULSE (Atmospheric Measurements by Ultra-Light Spectrometer) instrument during the APOGEE (Atmospheric Profiles of Greenhouse Gases) measurement experiment, specifically for the vertical profiles of CO2 and CH4, measurements of which remain very sparse. We have carried out several experiments showing that the measured profiles have several applications: the validation of simulations of infrared satellite observations, evaluating the quality of chemical profiles from chemistry transport models (CTMs) and evaluating the quality of retrieved chemical profiles from the assimilation of infrared satellite observations. The results show that the simulations of infrared satellite observations from IASI (Infrared Atmospheric Sounding Interferometer) and CrIS (Cross-track Infrared Sounder) instruments performed in operational mode for numerical weather prediction (NWP) by the radiative transfer model (RTM) RTTOV (Radiative Transfer for the TIROS Operational Vertical Sounder) are of good quality. We also show that the MOCAGE (Modèle de Chimie Atmosphérique de Grande Echelle) and CAMS (Copernicus Atmospheric Monitoring Service) CTMs modelled ozone profiles fairly accurately and that the CAMS CTM represents the methane in the troposphere well compared to MOCAGE. Finally, the measured in situ ozone profiles allowed us to show the good quality of the retrieved ozone profiles by assimilating ozone-sensitive infrared spectral radiances from the IASI and CrIS

SMOSREX : A Long Term Field Campaign Experiment for Soil Moisture and Land Surface Processes Remote Sensing

International audienceThe primary goal of the SMOS mission is to deliver global fields of sea surface salinity and surface soil moisture using L-band (1.4 GHz) radiometry. Within the context of the preparation of SMOS activities over land, a field campaign, SMOSREX (Surface Monitoring Of the Soil Reservoir EXperiment), has been in operation since January 2001 in Mauzac, near Toulouse in France. Continuous ground measurements of meteorological variables, soil moisture and temperature profiles have been taken over bare soil and a grass plot left fallow. Since January 2003, SMOSREX has been providing accurate field measurements of dual polarized L-band brightness temperature up-welling from both bare soil and fallow plots, together with multi-spectral (from visible to infrared frequencies) remote sensing surface data. The scientific objectives are presented in this paper and the corresponding experimental design is described. The experimental concept is totally new since (i) SMOSREX combines land–surface–atmosphere observations, passive microwave measurements and VIS to NIR remote sensing, (ii) SMOSREX is based on highly accurate L-band measurements carried out by a radiometer specifically designed for the experiment, and (iii) SMOSREX provides a unique continuous data set of L-band measurements over several years. The characteristics of the L-band emission are presented at diurnal, seasonal and annual temporal scales, and the emissions are compared over bare soil and natural grass. The surface emissions over bare soil and fallow area are shown to be counter-phased at the diurnal scale due to small variations in vegetation water content and bare soil surface moisture. Innovative long term results using L-band measurements for both bare soil and natural grass are presented in this paper, and the relationship between the surface emission at L-band and surface bare soil moisture is shown to be suitable for a long term period (19 months). Soil freezing is shown to be drastically different for bare soil and vegetation covered plots, with a large threshold effect on microwave surface emission

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

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

La campagne Passy-2015 : dynamique atmosphérique et qualité de l’air dans la vallée de l’Arve

International audienceWintertime anticyclonic conditions, associated with clear sky and cold nights, trigger the formation of persistent layers of stable air over the ground. In an urban area, these persistent layers lead to poor air quality, especially when the terrain is mountainous. This is particularly the case in the Arve River Valley near the city of Passy, located 20 km downstream of Chamonix-Mont-Blanc, where air quality stands among the poorest ones in France.Beyond the monitoring of air quality, as performed by the Auvergne-Rhône-Alpes air quality agency or within the scientific project DECOMBIO led by the Institute for Geosciences and the Environment (IGE), knowledge of the atmospheric dynamics at the valley scale should be gained to understand how pollutants are dispersed. This is the motivation of the Passy project, which started in 2014. It relies on the Passy-2015 field experiment, whereof presentation, along with the discussion of a few results, is the purpose of the present paper. The objective of this field experiment is to document the atmospheric dynamics in the Arve River Valley during wintertime pollution episodes.The work conducted during the Passy project and the analysis of the Passy-2015 field experiment will benefit from a several-year long collaboration among the different partners. The knowledge thus gained will contribute to refine weather forecast and air quality prediction in the Arve River Valley and, more generally, in mountain urban areas under stable conditions. From an operational perspective, our goal is to improve our ability to forecast critical events such as low temperatures, ice and fog formation, pollution events or locations subject to high pollutant concentration.Les conditions anticycloniques hivernales (ciel clair, nuits froides) conduisent à la formation de couches stables persistantes qui favorisent les épisodes de pollution, particulièrement en terrain montagneux. La vallée de l’Arve est très sensible à ce phénomène, en particulier près de la ville de Passy (Haute-Savoie), située à 20 kilomètres en aval de Chamonix-Mont-Blanc, où la qualité de l’air est l’une des moins bonnes de France.Au-delà du suivi de la qualité de l’air, tel que réalisé par Atmo Auvergne-Rhône-Alpes ou par le projet DECOMBIO piloté par l’Institut des Géosciences et de l’Environnement (IGE), il est primordial d’améliorer la connaissance de la dynamique atmosphérique à l’échelle de la vallée en conditions stables pour mieux comprendre comment, couplée au cycle et à la géographie des émissions, elle pilote la dispersion des polluants. C’est la motivation du projet Passy, initié en 2014. Ce projet s’appuie sur les observations de la campagne Passy-2015, présentées dans cet article avec quelques premiers résultats. L’objectif général de cette campagne est de documenter la dynamique atmosphérique au sein de la vallée de l’Arve lors des épisodes de pollution hivernale.Les travaux menés dans le cadre du projet et de l’analyse des données de la campagne s’inscrivent au sein d’une collaboration sur plusieurs années entre les différents partenaires. Ils contribueront à affiner la prévision du temps et de la qualité de l’air dans ce type de vallée, et plus généralement en conditions stables. Il s’agit en particulier d’améliorer la capacité à prévoir des phénomènes critiques, comme les températures minimales, le verglas, le brouillard, les évènements de pollution ou encore les zones de pollution intense