Abstract
Surface and remote-sensing instruments deployed during ESCOMPTE experiment over the Marseille area, along the Mediterranean coast, were used to investigate the fine structure of the atmospheric boundary layer (ABL) during sea-breeze circulation in relation to pollutant transport and diffusion. Six sea-breeze events are analyzed with a particular focus on 25 June 2001. Advection of cool and humid marine air over land has a profound influence on the daytime ABL characteristics. This impact decreases rapidly with the inland distance from the sea. Nearby the coast (3 km inland), the mixing height Zi rises up to 750 m and falls down after 15:00 (UT) when the breeze flow reaches its maximum intensity. A more classical evolution of the ABL is observed at only 11-km inland where Zi culminates in the morning and stabilizes in the afternoon at about 1000 m height. Fine inspection of the data revealed an oscillation of the sea-breeze with a period about 2 h 47 min. This feature, clearly discernable for 3 days at least, is present in several atmospheric variables such as wind, temperature, not only at the ground but also aloft in the ABL as observed by sodar/RASS and UHF wind profilers. In particular, the mixing height Zi deduced from UHF profilers observations is affected also by the same periodicity. This pulsated sea-breeze is observed principally above Marseille and, at the northern and eastern shores of the Berre pond. In summary, the periodic intrusion over land of cool marine air modifies the structure of the ABL in the vicinity of the coast from the point of view of stability, turbulent motions and pollutants concentration. An explanation of the source of this pulsated sea-breeze is suggested.
Highlights
For evident reasons of commercial exchanges, the most important industrial complexes and megalopolis are located along maritime coastal region
The present paper describes and analyses the pulsated nature of the seabreeze observed during the ESCOMPTE experiment
The ratio between fluxes measured at the two levels was nearly equal to one, suggesting that both are in the inertial sublayer
Summary
For evident reasons of commercial exchanges, the most important industrial complexes and megalopolis are located along maritime coastal region. The work presented here is an experimental study focusing on breeze circulation observed during ESCOMPTE and its influence on the dynamics and pollution of the atmospheric boundary layer (ABL). Finkele et al (1995) observed such a sea-breeze circulation cell with an instrumented aircraft They pointed out that days without a return flow in upper levels can occur. The last part discusses on the impact of a pulsated sea-breeze on the coastal low atmosphere of Marseille from the stability, ABL depth and pollution point of view.
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