Modeling of Saharan dust outbreaks over the Mediterranean by RegCM3: case studies

Abstract. The regional climate model RegCM3 coupled with a radiatively active aerosol model with online feedback is used to investigate direct and semi-direct radiative aerosol effects over the Sahara and Europe in a test case of July 2003. The aerosol model includes dust particles in addition to sulfates, hydrophobic and hydrophilic black carbon and organic carbon. The role of the aerosol online feedback on the radiation budget and the direct radiative forcing (short-wave and long-wave) by dust particles are investigated by intercomparing results from three experiments: REF, including all interactive aerosol components, Exp1, not accounting for the aerosol radiative feedback, and Exp2 not accounting for desert dust particles. The comparison of results in the REF experiment with satellite observations, sun/sky radiometer measurements, and lidar profiles at selected Central Mediterranean sites reveals that the spatio-temporal evolution of the aerosol optical depth is reasonably well reproduced by the model during the entire month of July. Results for the dust outbreaks of 17 and 24 July, averaged over the simulation domain, show that the daily-mean SW direct radiative forcing by all particles is −24 Wm−2 and −3.4 Wm−2 on 17 July and −25 Wm−2 and −3.5 Wm−2 on 24 July at the surface and top of the atmosphere, respectively. This is partially offset by the LW direct radiative forcing, which is 7.6 Wm−2 and 1.9 Wm−2 on 17 July and 8.4 Wm−2 and 1.9 Wm−2 on 24 July at the surface and top of the atmosphere, respectively. Hence, the daily-mean SW forcing is offset by the LW forcing of ~30% at the surface and of ~50% at the ToA. It is also shown that atmospheric dynamics and hence dust production and advection processes are dependent on the simulation assumptions and may significantly change within few tens of kilometers. The comparison of REF and Exp1 shows that the aerosol online feedback on the radiation budget decreases the domain-average daily-mean value of the 2 m-temperature, aerosol column burden (CB), and short-wave (SW) atmospheric forcing by −0.52 °C, 14%, and 0.9%, respectively on 17 July and by −0.39 °C, 12% and 12%, respectively on 24 July. The comparison of REF and Exp2 reveals that on 17 July, radiatively-active dust particles decrease the daily-mean 2 m-temperature averaged over the whole simulation domain by 0.4% even if are responsible for 99.8% and 97% of the daily-mean aerosol column burden and SW atmospheric forcing, respectively

In Situ Samplings and Remote Sensing Measurements to Characterize Aerosol Properties over Southeast Italy

Abstract Ground-based particulate matter (PM) samplers, an XeF Raman lidar operating in the framework of the European Aerosol Research Lidar Network (EARLINET), and a sun/sky radiometer operating in the framework of the Aerosol Robotic Network (AERONET) have been used to characterize vertical profiles, optical and microphysical properties, and chemical composition of aerosols during the 29 June–1 July 2005 dust outbreak that occurred over the central-eastern Mediterranean. Aerosol backscatter coefficient, total depolarization, and lidar ratio vertical profiles revealed that a well-mixed dust layer extending from ∼0.5 to 6 km was present over southeastern Italy on 30 June. Sun/sky radiometer measurements revealed a bimodal lognormal size distribution during all measurement days. The particle volume distribution was found to be well correlated either to the PM mass distribution measured at ground by a seven-stage cascade impactor and to the fine to total suspended PM mass ratio measured by ground-based PM samplers. Scanning electron microscopy and ion chromatography analyses on PM samples revealed that coarse-mode aerosols were mainly made of carbonate, aluminum-silicate, and sea salt particles. Carbon, sulfate, and nitrate particles were the main components of fine-mode aerosols representing more than 50% of the total aerosol load; the significant role of fine-mode anthropogenic particles during a dust event is highlighted. Finally, the potential capabilities of complementary measurements by passive and active remote sensing techniques and in situ observations to retrieve the vertical distribution of the particle number and mass concentration are analyzed and discussed

Modeling of Saharan dust outbreaks over the Mediterranean by RegCM3: case studies

International audienc

Advection patterns and aerosol optical and microphysical properties by AERONET over south-east Italy in the central Mediterranean

International audienceAerosol products by AERONET sun-sky radiometer measurements combined with air-mass backtrajectories were analyzed to identify source regions and pathways of air masses carrying aerosols to south-east Italy, and to determine the dependence of aerosol mean optical properties on advection patterns. Aerosol optical depth (AOD), fine mode fraction (?), single scattering albedo (SSA), asymmetry factor (g), and lidar ratio (Lr) at 440 nm were used to characterize aerosol properties. The analysis of 5-day-backtrajectories ending in Lecce on south-east Italy and referring to 240 measurement days of the 2003?2004 years revealed that 32% of the measurement days were characterized by air masses coming from Sector A, which includes all continental European sources with the exception of Spain. 3% of the measurement days were characterized by air masses coming from both the Sector B, which includes the Southern Mediterranean Sea and the Africa continent, and the Sector C, which includes the Western Mediterranean, the Iberian Peninsula, and the Atlantic Ocean. 62% of the measurement days were characterized by mixed advection patterns (Sector M). We found that AOD, SSA and g average values were not significantly dependent on air mass source Sector. In contrast, ? and Lr average values were quite affected by the air mass source Sector. AOD, ?, SSA, g, and Lr average values, which were equal to 0.29±0.15, 0.93±0.03, 0.93±0.03, 0.67±0.03, and 72±20 sr, respectively indicated that the Sector A aerosol could be considered representative of "continental average aerosol", mostly made of water soluble and a small amount of soot and insoluble components. Polluted-desert dust particles characterized by AOD=0.29±0.05, ?=0.72±0.05, SSA=0.94±0.03, g=0.69±0.02, Lr=56±13 sr, were advected over south-east Italy from Sector B. Sector C was instead responsible for the advection of maritime-polluted particles, which were characterized by AOD=0.3±0.2, ?=0.8±0.1, SSA=0.94±0.03, g=0.67±0.03, Lr=60±20 sr. Hence, we found that the aerosol load over south-east Italy was dominated by moderately-absorbing, fine-mode particles even if it was also affected by the minor contribution of desert and maritime type aerosol. The application of an aerosol mask to the Sector M data points supported last commen

© Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics Advection patterns and aerosol optical and microphysical properties by AERONET over south-east Italy in the central Mediterran

Abstract. Aerosol products by AERONET sun-sky radiometer measurements combined with air-mass backtrajectories were analyzed to identify source regions and pathways of air masses carrying aerosols to south-east Italy, and to determine the dependence of aerosol mean optical properties on advection patterns. Aerosol optical depth (AOD), fine mode fraction (η), single scattering albedo (SSA), asymmetry factor (g), and lidar ratio (Lr) at 440 nm were used to characterize aerosol properties. The analysis of 5-day-backtrajectories ending in Lecce on south-east Italy and referring to 240 measurement days of the 2003–2004 years revealed that 32% of the measurement days were characterized by air masses coming from all continental European sources with the exception of Spain. 3 % of the measurement days were characterized by air masses coming from both the Souther