HR: 0800h
AN: A31C-0079    [Abstracts]
TI: Three Years of Raman Lidar Observations of Saharan Dust Intrusion Over Potenza
AU: * Mona, L
EM: mona@imaa.cnr.it
AF: Istituto di Metodologie per l'Analisi Ambientale IMAA-CNR, Contrada S. Loja, Tito Scalo, PZ I-85050 Italy
AU: Amodeo, A
EM: amodeo@imaa.cnr.it
AF: Istituto di Metodologie per l'Analisi Ambientale IMAA-CNR, Contrada S. Loja, Tito Scalo, PZ I-85050 Italy
AU: Pandolfi, M
EM: pandolfi@imaa.cnr.it
AF: Istituto di Metodologie per l'Analisi Ambientale IMAA-CNR, Contrada S. Loja, Tito Scalo, PZ I-85050 Italy
AU: Pappalardo, G
EM: pappalardo@imaa.cnr.it
AF: Istituto di Metodologie per l'Analisi Ambientale IMAA-CNR, Contrada S. Loja, Tito Scalo, PZ I-85050 Italy
AB: The Sahara desert is the most prominent localized source of atmospheric aerosol with a total amount of emitted dust of about 600 Mt per year. Because of the short distance, intrusions of Saharan dust in the Mediterranean basin are very common. Dust occurrences in the Mediterranean region were investigated by means of satellite measurements, but at the present time, there is a serious lack of knowledge of the vertical structure and of the optical properties of dust injected from Sahara over the Mediterranean area. In the framework of EARLINET (European Aerosol Research LIdar NETwork), the first aerosol lidar network on continental scale, since May 2000 until April 2003, we collected more than 100 cases of Saharan dust intrusions in the center of the Mediterranean area, by means of the IMAA Raman-elastic lidar system located in Potenza, Southern Italy. For each case, the observed aerosol layers have been characterized in terms of aerosol extinction and backscatter coefficients at 355 nm, retrieved from combined Raman elastic-backscatter lidar independent measurements, and thus of the lidar ratio. Moreover, aerosol backscatter coefficient at 532 nm is retrieved from elastic lidar signal with an iterative approach. For this 3-years climatological analysis, the 4-days backtrajectories analysis provided by German Weather Service have been used to identify the origin of the observed aerosol layers as the Sahara region. In particular, we find that typically dust observed in Potenza comes from the Central and Western part of the Sahara, while we observed Saharan dust coming from the East part of the Sahara only in 4 cases. Saharan dust layers have been found to typically extend between 2.5 and 6 km above sea level (a.s.l.), reaching a maximum altitude of about 8 km a.s.l. and with frequent intrusions in the Planetary Boundary Layer. The aerosol layer center of mass, calculated starting from the aerosol backscatter coefficient, has a mean altitude of about 3.5 km a.s.l., extending between 2.3 and 6.6 km a.s.l.. The desert dust strongly contributes to the aerosol load within a mean optical depth of about 0.12. An high variability has been observed for the mean aerosol backscatter and extinction coefficient within the layer as well as of the optical parameters integrated over the whole dust layer, reflecting the large natural variability of Saharan dust emission phenomenon. However, there is a strong seasonal behavior for all considered optical properties: a large amount of dust has been observed during spring and summer, when most of Saharan dust intrusions occur and the mean optical depth of the layer reaches its maximum, instead a lower desert aerosol load is observed during autumn. The lidar ratio mean values calculated along the aerosol dust layer range between 6 and 78 sr, with a mean value of 38 sr. No significant difference has been observed between winter and summer values of lidar ratio, but summer values distribution is wider than the winter one and also the variability along the dust layer is higher than during the winter. A detailed analysis of the lidar ratio values collected within the observed Saharan dust layers shows a trimodal gaussian distribution. A mode centered around 22 sr is related to few cases with high aerosol load in a situation of contamination with the Planetary Boundary Layer. A wider mode at 57 sr is correlated to the tails of the aerosol layer. Finally the most populated mode, centered around 37 sr, results from the central part of the aerosol layer. ACKNOWLEDGMENTS The support of this work by the European Commission under grant EVRI-CT1999-40003 is gratefully acknowledged.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting