Abstract
Abstract. In this study we use a new dust product developed using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) observations and EARLINET (European Aerosol Research Lidar Network) measurements and methods to provide a 3-D multiyear analysis on the evolution of Saharan dust over North Africa and Europe. The product uses a CALIPSO L2 backscatter product corrected with a depolarization-based method to separate pure dust in external aerosol mixtures and a Saharan dust lidar ratio (LR) based on long-term EARLINET measurements to calculate the dust extinction profiles. The methodology is applied on a 9-year CALIPSO dataset (2007–2015) and the results are analyzed here to reveal for the first time the 3-D dust evolution and the seasonal patterns of dust over its transportation paths from the Sahara towards the Mediterranean and Continental Europe. During spring, the spatial distribution of dust shows a uniform pattern over the Sahara desert. The dust transport over the Mediterranean Sea results in mean dust optical depth (DOD) values up to 0.1. During summer, the dust activity is mostly shifted to the western part of the desert where mean DOD near the source is up to 0.6. Elevated dust plumes with mean extinction values between 10 and 75 Mm−1 are observed throughout the year at various heights between 2 and 6 km, extending up to latitudes of 40° N. Dust advection is identified even at latitudes of about 60° N, but this is due to rare events of episodic nature. Dust plumes of high DOD are also observed above the Balkans during the winter period and above northwest Europe during autumn at heights between 2 and 4 km, reaching mean extinction values up to 50 Mm−1. The dataset is considered unique with respect to its potential applications, including the evaluation of dust transport models and the estimation of cloud condensation nuclei (CCN) and ice nuclei (IN) concentration profiles. Finally, the product can be used to study dust dynamics during transportation, since it is capable of revealing even fine dynamical features such as the particle uplifting and deposition on European mountainous ridges such as the Alps and Carpathian Mountains.
Highlights
Mineral dust is ubiquitous in the atmosphere and one of the main contributors to the global aerosol load (Zender et al, 2004; Textor et al, 2006), with almost half of the global dust emissions generated in Africa (Huneuus et al, 2011)
The results showed an absolute bias on the AOD of the order of −0.03, improving on the statistically significant biases of the order of −0.10 reported in the literature for the original Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) product
In comparison with studies relevant to the time period considered in this work, the dust optical depth (DOD) decrease of 0.001 yr−1 over the northern coast of Africa is in agreement with Floutsi et al (2016), who based their analysis on 12 years of Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua observations (2002– 2014), reporting an average decrease of 0.003 yr−1 for the coarse mode fraction of the AOD over the broader Mediterranean Sea
Summary
Mineral dust is ubiquitous in the atmosphere and one of the main contributors to the global aerosol load (Zender et al, 2004; Textor et al, 2006), with almost half of the global dust emissions generated in Africa (Huneuus et al, 2011). It has been shown that the EARLINET-optimized CALIPSO dust product presented in Amiridis et al (2013) is in better agreement with Aerosol Robotic Network (AERONET) collocated measurements over the Sahara and Europe and with Moderate Resolution Imaging Spectroradiometer (MODIS) measurements over the Mediterranean for collocated cells with low cloudiness This product is considered as the first accurate dust retrieval from space, since dust discrimination methods applied on passive sensors are based on the separation of the fine from coarse particle mode (e.g., Kaufman et al, 2005), delivering mostly biased DODs (dust optical depths) over the oceans due to the contamination of the coarse mode by sea salt particles (Su et al, 2013).
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