In this work, we have studied the seasonal and inter-annual variability of the aerosol vertical distribution over Sahelian Africa for the years 2006, 2007 and 2008, characterizing the different kind of aerosols present in the atmosphere in terms of their optical properties observed by ground-based and satellite instruments, and their sources searched for by using trajectory analysis. This study combines data acquired by three ground-based micro lidar systems located in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analysis (AMMA), by the AEROsol RObotic NETwork (AERONET) sun-photometers and by the space-based Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the CALIPSO satellite (Cloud-Aerosol Lidar and Infrared Pathfinder Observations). <br><br> During winter, the lower levels air masses arriving in the Sahelian region come mainly from North, North-West and from the Atlantic area, while in the upper troposphere air flow generally originates from West Africa, crossing a region characterized by the presence of large biomass burning sources. The sites of Cinzana, Banizoumbou and M'Bour, along a transect of aerosol transport from East to West, are in fact under the influence of tropical biomass burning aerosol emission during the dry season, as revealed by the seasonal pattern of the aerosol optical properties, and by back-trajectory studies. <br><br> Aerosol produced by biomass burning are observed mainly during the dry season and are confined in the upper layers of the atmosphere. This is particularly evident for 2006, which was characterized by a large presence of biomass burning aerosols in all the three sites. <br><br> Biomass burning aerosol is also observed during spring when air masses originating from North and East Africa pass over sparse biomass burning sources, and during summer when biomass burning aerosol is transported from the southern part of the continent by the monsoon flow. <br><br> During summer months, the entire Sahelian region is under the influence of Saharan dust aerosols: the air masses in low levels arrive from West Africa crossing the Sahara desert or from the Southern Hemisphere crossing the Guinea Gulf while in the upper layers air masses still originate from North, North-East. The maximum of the desert dust activity is observed in this period which is characterized by large AOD (above 0.2) and backscattering values. It also corresponds to a maximum in the extension of the aerosol vertical distribution (up to 6 km of altitude). In correspondence, a progressive cleaning up of the lowermost layers of the atmosphere is occurring, especially evident in the Banizoumbou and Cinzana sites. <br><br> Summer is in fact characterized by extensive and fast convective phenomena. <br><br> Lidar profiles show at times large dust events loading the atmosphere with aerosol from the ground up to 6 km of altitude. These events are characterized by l...

[1] Coupled Pattern Reconstruction (CPR) and multivariate Empirical Orthogonal Function Reconstruction (mEOF-R) techniques have been applied to infer the vertical structure of the sea from surface/integrated measurements in the Sicily Channel (Mediterranean Sea). The data used to train the methods are the CTD casts present in the MEDAR/MEDATLAS climatology. The independent test and validation data set consisted of Topex/Poseidon sea level measurements and CTD profiles collected during the SYnoptic Mesoscale PLankton EXperiment (SYMPLEX) 1996 and 1998 cruises. mEOF-R was found to give the more accurate and promising results, being able to discriminate and reconstruct the main processes that drive the variability inside the channel. In particular, the analysis of the covariance of steric heights, temperature and salinity profiles confirmed that mesoscale processes are predominant. In fact, the first mEOF steric height pattern closely resembles the first baroclinic normal mode estimated from the mean stratification profile. A critical discussion on the signals contributing to the sea level variability has been done before applying the mEOF-R to altimetric data. The steric contribution of the upper 300 dbar has then been estimated from Topex/Poseidon measurements. The effects of the adjustment of altimeter data with a synthetic mean dynamic topography have also been quantified.

¶ Institute des Researches pour le Developpement, Niger SUBMITTED TO THE INTERNATIONAL JOURNAL OF REMOTE SENSING-MAY 2009 Three ground based portable low power consumption microlidars (MULID) have been built and deployed at three remote sites in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analyses (AMMA) project for the characterization of aerosols optical properties. A description of the instrument and a discussion of the data inversion method , including a careful analysis of measurement uncertainties (systematic and statistical errors) are presented. Some case studies of typical lidar profiles observed over the Banizoumbou site during 2006 are shown and discussed with respect to the AERONET 7-day back-trajectories and the biomass burning emissions from the Combustion Emission database for the AMMA campaign.

We present and discuss ground-based and satellite observations of aerosol optical properties over Sahelian Africa for the years 2006, 2007 and 2008. <br><br> This study combines data acquired by three ground-based micro lidar systems located in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analysis (AMMA), by the AEROsol RObotic NETwork (AERONET) sun-photometers and by the space-based Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). <br><br> The 2006 seasonal pattern of the aerosols vertical distribution is presented. It shows the presence of aerosol mainly confined in the lower levels of the atmosphere during the dry season, with the aerosol layer increasing in vertical extension and absolute values in spring, reaching the largest values in summer in correspondence with a progressive clearing up of the atmosphere at the lowermost levels. <br><br> Aerosol produced by biomass burning are observed mainly during the dry season, when north-easterly air masses pass over large biomass burning areas before recirculating over the measurement sites. This kind of aerosol is present mainly in layers between 2 and 6 km of altitude, although episodically it may show also below 2 km, as observed in Banizoumbou (Niger) in 2006. Biomass burning aerosol is also observed during spring when air masses originating from North and East Africa pass over sparse biomass burning sources, and during summer when biomass burning aerosol is transported from the southern part of the continent by the monsoon flow. <br><br> The summer season on the whole is characterized by a large presence of desert dust along the entire Sahelian region, widespread in altitude with Aerosol Optical Depths above 0.2. <br><br> The interannual variability in the three year monitoring period is not very significant. An analysis of the aerosol transport pathways, aiming at detecting the main source regions, revealed that air originated from the Saharan desert is present all year long and it is observed in the lower levels of the atmosphere at the beginning and at the end of the year. In the central part of the year it extends upward and the lower levels are less affected by air masses from Saharan desert when the monsoon flow carries inland air from the Guinea Gulf and Southern Hemisphere. Biomass burning is mainly confined in the higher layers and observable in winter and in autumn

Different methods for the extrapolation of vertical profiles from sea surface measurements are presented. The techniques, called Coupled Pattern Reconstruction (CPR) and multivariate EOF Reconstruction (mEOF-R) base on the multivariate analysis of the variability of vertical profiles from hydrographic data and on the hypothesis that only few modes are needed to explain most of the variance/covariance of the fields. The CPR and mEOF-R methods have been applied and tested on the data collected during SYMPLEX survey in a selected area of the Mediterranean sea (the Channel of Sicily), also using simultaneous altimeter measurements as surface input.