Lidar ratios of stratospheric volcanic ash and sulfate aerosols retrieved from CALIOP measurements

Andrew T. Prata, Stuart A. Young, Steven T. Siems, Michael J. Manton
2017 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> We apply a two-way transmittance constraint to nighttime CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) observations of volcanic aerosol layers to retrieve estimates of the particulate lidar ratio (<i>S</i><sub>p</sub>) at 532<span class="thinspace"></span>nm. This technique is applied to three volcanic eruption case studies that were found to have injected aerosols directly into the stratosphere. Numerous lidar observations permitted characterization of
more » ... characterization of the optical and geometric properties of the volcanic aerosol layers over a time period of 1–2 weeks. For the volcanic ash-rich layers produced by the Puyehue-Cordón Caulle eruption (June 2011), we obtain mean and median particulate lidar ratios of 69<span class="thinspace"></span>±<span class="thinspace"></span>13<span class="thinspace"></span>sr and 67<span class="thinspace"></span>sr, respectively. For the sulfate-rich aerosol layers produced by Kasatochi (August 2008) and Sarychev Peak (June 2009), the means of the retrieved lidar ratios were 66<span class="thinspace"></span>±<span class="thinspace"></span>19<span class="thinspace"></span>sr (median 60<span class="thinspace"></span>sr) and 63 ± 14<span class="thinspace"></span>sr (median 59<span class="thinspace"></span>sr), respectively. The 532<span class="thinspace"></span>nm layer-integrated particulate depolarization ratios (<i>δ</i><sub>p</sub>) observed for the Puyehue layers (<i>δ</i><sub>p</sub> = 0.33<span class="thinspace"></span>±<span class="thinspace"></span>0.03) were much larger than those found for the volcanic aerosol layers produced by the Kasatochi (<i>δ</i><sub>p</sub> = 0.09<span class="thinspace"></span>±<span class="thinspace"></span>0.03) and Sarychev (<i>δ</i><sub>p</sub> = 0.05 ± 0.04) eruptions. However, for the Sarychev layers we observe an exponential decay (<i>e</i>-folding time of 3.6 days) in <i>δ</i><sub>p</sub> with time from 0.27 to 0.03. Similar decreases in the layer-integrated attenuated colour ratios with time were observed for the Sarychev case. In general, the Puyehue layers exhibited larger colour ratios (<i>χ</i>′ = 0.53<span class="thinspace"></span>±<span class="thinspace"></span>0.07) than what was observed for the Kasatochi (<i>χ</i>′ = 0.35<span class="thinspace"></span>±<span class="thinspace"></span>0.07) and Sarychev (<i>χ</i>′ = 0.32<span class="thinspace"></span>±<span class="thinspace"></span>0.07) layers, indicating that the Puyehue layers were generally composed of larger particles. These observations are particularly relevant to the new stratospheric aerosol subtyping classification scheme, which has been incorporated into version 4 of the level 2 CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data products.</p>
doi:10.5194/acp-17-8599-2017 fatcat:syy2qyb4qzeadhhtzauqv4uohm