Etude de la couche limite atmosphérique côtière durant ESCOMPTE 2001. Evaluation et amélioration des performances d'un radar UHF.

Forecasting of pollution events was the main objective of the ESCOMPTE-2001 campaign, which took place in the Marseille/Fos/Berre heterogeneous area (southeastern France) in the early summer 2001. This goal requires good understanding and taking into account, by physico-chemical numerical models, of the physical processes in the Atmospheric Boundary Layer (ABL), in which pollutants are emitted, transported and diffused.In the ESCOMPTE-2001 campaign context, this work was devoted to study the low troposphere during sea breeze events, related to meteorological conditions responsible for poor air quality of coastal areas. It presents notably an oscillation of the sea breeze intensity and competitions of locals and regional sea breeze, which change the advected time of the marine air above the continental surface and thus influence the ABL development and its pollutants concentration. This study is based principally on the network of four UHF wind profilers radars set up on the coastal area of Marseille/Fos/Berre, allowing a continuous three-dimensional description of the sea breeze flow and the ABL.For the needs of this phenomenological work, methodological developments was realized to improve the measurement of ABL turbulent properties with UHF radars (terms of turbulent kinetic energy budget) and the use of wind profilers network for the study of pollutants plumes trajectography.La prévision des phénomènes de pollution atmosphérique est l'objectif central de la campagne ESCOMPTE-2001, qui s'est déroulée durant l'été 2001 dans la région très hétérogène de Marseille/Fos/Berre. Cet objectif nécessite une bonne compréhension et prise en compte, par les modèles numériques de physico-chimie, des processus physiques intervenant dans la Couche Limite Atmosphérique (CLA), au sein de laquelle s'effectuent le transport et la diffusion des polluants émis en surface.Dans le cadre de la campagne ESCOMPTE-2001, ce travail de thèse est consacré à l'étude de la basse troposphère en période de brise de mer, situation météorologique défavorable à la qualité de l'air des zones côtières. Il a permis notamment de mettre en évidence une oscillation de l'intensité de la brise de mer et des compétitions de brises de mer locales et régionales, qui modifient le temps d'advection de l'air marin sur la surface terrestre et ont donc des répercussions importantes sur le développement de la CLA et sa concentration en polluants. Ces travaux s'appuient principalement sur le réseau de quatre radars profileurs de vent UHF mis en place sur la zone côtière de Marseille/Fos/Berre, permettant une description en trois dimensions et en continu dans le temps des écoulements de brises de mer et de la CLA.Pour les besoins de cette étude phénoménologique, des développements méthodologiques sont apportés sur la mesure des propriétés turbulentes de la CLA par les radars UHF (termes du bilan de l'énergie cinétique turbulente) et sur leur utilisation en réseau pour l'étude de la trajectographie de panaches de polluants

Etude de la couche limite atmosphérique côtière durant ESCOMPTE 2001 (évaluation et amélioration des performances d'un radar UHF)

TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Comparison of pollution events during the ESCOMPTE 2001 campaign: sea-breeze and synoptic wind conditions

(août 2004)The ESCOMPTE experiment was dedicated to the study of pollution events. A brief description of this program is presented in the companion paper (Moppert et al.) which is devoted to the description of the thermodynamic environment including the vertical structure of the low troposphere, during an intensive observation period (IOP2). A few results are first recalled here. This latter paper focuses on the difference between the first two days (2001 June 22 and 23: IOP2a) when the Mistral mesoscale wind is blowing and the three following days (2001 June 24 to 26 : IOP2b) when sea-breeze conditions and a weak wind are encountered. The boundary layer (BL) development is typical of a sunny summer day on June 22 only, reaching heights (zi) of 1900m in the early afternoon. The advection of colder air from sea limits the BL development that hardly reaches 1000m during IOP2b. A mesoscale effect due to the high pressure situation induces downward mesoscale vertical velocities that stem the BL growth. On June 23, a negative mesoscale velocity, not explained yet, also prevents the BL from growing until 15 UTC. One location in the ESCOMPTE area does not follow these general features : it is the entrance of the Durance valley, to the North-East of the domain, where the valley wind added to the Ventury effect enhances high development of BL (up to 2500m). To study the possibilities of transfers of pollution between the BL and the staggered layers capping the BL, a preliminary analysis is made using June 24 ozone profiles, as tracers of the various air masses. Except for the case of the Durance valley, the transfers are, most of the time, limited to a few number of cases and to a small depth in the low troposphere, due to the weakness of the BL developments

Study of the boundary layer: the 23th of june 2001 (IOP 2a) comparisons between data from model-aircraft-profilers network. The methodology

(janvier)

Contribution of a profiler network in the monitoring of a polluted area

(2-4 février 2005

Stratification of the lower troposphere during the ESCOMPTE campaign

Implementation of adapted air quality policies and prediction of pollution events require the improvement of our understanding of combined chemical and dynamical processes which lead to high pollutants concentration in the atmospheric boundary layer. The ESCOMPTE program was devoted to establish a detailed 3-D database of primary pollutant emissions together with the dynamics and chemical composition of the atmosphere in order to validate and improve chemistry transport models. The ESCOMPTE experiment took place in the early summer of 2001, in the south-eastern part of France where the combination of high urbanization and industrialization with hot and sunny weather enhances photochemical pollution events. Due to the complex terrain of this region (both coastal and moderately mountainous area, channeling effects of the Rhône and Durance valleys,…), a preliminary effort is necessary to study the atmospheric dynamics in this heterogeneous region in relation with larger scales processes. The main objectives of this paper is to present the vertical structure of the ESCOMPTE area during different meteorological conditions of the second intensive observation period (IOP2) which lasted from June 22 to June 26

Photochemical pollution episodes during ESCOMPTE 2001 under sea-breeze or synoptic wind conditions

(2-4 février 2005

Determination of turbulent parameters in the atmospheric boundary layer with an UHF wind profiler. Comparison with in situ measurements

(Août 2004)This study presents methods to determine turbulent parameters in the ABL with UHF wind profilers. These methods are compared with aircraft data measured during TRAC-98 campaign. The results of this comparison show that : (i) the turbulent kinetic energy dissipation rate measured by both instruments are well correlated with a slightly overestimation and underestimation of the UHF radar below and above 0.7Zi respectively ; (ii) the momentum fluxes measured by the UHF profiler is the same order of magnitude than the aircraft ones but is globally underestimated in the ABL, which can be the consequence of the larger turbulent scales not took into account by this instrument (keeping out the levels inferior to 0.3Zi where ground echoes perturb UHF profiler measurements) ; (iii) the sensible heat fluxes measured by both instruments are well correlated with a slightly overestimation of the UHF radar mainly caused by the overestimation of the dissipation rate and losses of mechanical production below and above 0.7Zi respectively

Lower troposphere stratification during sea-breeze event and impact on ozone over Marseille during IOP2B of the ESCOMPTE campaign

(2-4 février 2005)