Find in Library

<p>Remote sensing measurements of aerosols using depolarization Raman lidar systems from four EARLINET (European Aerosol Research Lidar Network) stations are used for a comprehensive analysis of Saharan dust events over the Mediterranean basin in the period 2014–2017. In this period, 51 dust events regarding the geometrical, optical and microphysical properties of dust were selected, classified and assessed according to their radiative forcing effect on the atmosphere. From west to east, the stations of Granada, Potenza, Athens and Limassol were selected as representative Mediterranean cities regularly affected by Saharan dust intrusions. Emphasis was given on lidar measurements in the visible (532&thinsp;nm) and specifically on the consistency of the particle linear depolarization ratio (<span class="inline-formula"><i>δ</i>_p532</span>), the extinction-to-backscatter lidar ratio (<span class="inline-formula">LR₅₃₂</span>) and the aerosol optical thickness (<span class="inline-formula">AOT₅₃₂</span>) within the observed dust layers. We found mean <span class="inline-formula"><i>δ</i>_p532</span> values of <span class="inline-formula">0.24±0.05</span>, <span class="inline-formula">0.26±0.06</span>, <span class="inline-formula">0.28±0.05</span> and <span class="inline-formula">0.28±0.04</span>, mean <span class="inline-formula">LR₅₃₂</span> values of <span class="inline-formula">52±8</span>, <span class="inline-formula">51±9</span>, <span class="inline-formula">52±9</span> and <span class="inline-formula">49±6</span>&thinsp;sr and mean <span class="inline-formula">AOT₅₃₂</span> values of <span class="inline-formula">0.40±0.31</span>, <span class="inline-formula">0.11±0.07</span>, <span class="inline-formula">0.12±0.10</span> and <span class="inline-formula">0.32±0.17</span>, for Granada, Potenza, Athens and Limassol, respectively. The mean layer thickness values were found to range from <span class="inline-formula">∼</span>&thinsp;1700 to <span class="inline-formula">∼</span>&thinsp;3400&thinsp;m&thinsp;a.s.l. Additionally, based also on a previous aerosol type classification scheme provided by airborne High Spectral Resolution Lidar (HSRL) observations and on air mass backward trajectory analysis, a clustering analysis was performed in order to identify the mixing state of the dusty layers over the studied area. Furthermore, a synergy of lidar measurements and modeling was used to analyze the solar and thermal radiative forcing of airborne dust in detail. In total, a cooling behavior in the solar range and a significantly lower heating behavior in the thermal range was estimated. Depending on the dust optical and geometrical properties, the load intensity and the solar zenith angle (SZA), the estimated solar radiative forcing values range from <span class="inline-formula">−59</span> to <span class="inline-formula">−22</span>&thinsp;W&thinsp;m<span class="inline-formula">⁻²</span> at the surface and from <span class="inline-formula">−24</span> to <span class="inline-formula">−1</span>&thinsp;W&thinsp;m<span class="inline-formula">⁻²</span> at the top of the<span id="page15148"/> atmosphere (TOA). Similarly, in the thermal spectral range these values range from <span class="inline-formula">+</span>2 to <span class="inline-formula">+</span>4&thinsp;W&thinsp;m<span class="inline-formula">⁻²</span> for the surface and from <span class="inline-formula">+</span>1 to <span class="inline-formula">+</span>3&thinsp;W&thinsp;m<span class="inline-formula">⁻²</span> for the TOA. Finally, the radiative forcing seems to be inversely proportional to the dust mixing ratio, since higher absolute values are estimated for less mixed dust layers.</p>