Nabro Aerosol Evolution Observed Jointly By Lidars At A Mid-latitude Site And CALIPSO

Volcano eruption is an important source of aerosols. A large volcano outbreak can even yield powerful plumes reaching or penetrating the tropopause. The volcano induced aerosol particles remain in the stratosphere for a long period from months to years and spread over a very wide area. The sustained stratospheric aerosol layer has important impacts on regional and global climate.Mount Nabro erupted violently in June 2011 and released large amounts of sulfur dioxide and water vapor into lower stratosphere which led to a significant rise in the stratospheric aerosol loading. The characteristics of Nabro aerosol particles were jointly observed by ground-based lidars at Wuhan (30.5°N,114.4°E), China and CALIPSO.Evolution of the Nabro volcanic aerosols from initially-localized plumes to a decaying hemispherically-covered layer was jointly observed by Wuhan University 532-nm polarization lidar and CALIPSO. During the aerosol plume formation period, from the Nabro eruption to early July 2011, the lidar backscatter ratio related to the Nabro aerosols above Wuhan varied strongly both in vertical structure and intensity, suggesting that the Nabro aerosol distribution was horizontally inhomogeneous. The stratospheric aerosol optical depth (AOD) from CALIPSO shows that the Nabro plume first circled around the Asian monsoon anticyclone and then gradually fulfilled the whole anticyclone area with a net aerosol enhancement, which may reflect a gas-particle conversion (from sulfur dioxide gas) and/or particle injection from the upper troposphere. During the horizontal dispersion period, from early July to mid-August 2011, the stratospheric AOD over Wuhan declined rapidly since the Nabro particles were transported throughout the northern hemisphere. A nearly horizontally-uniform volcanic aerosol layer was formed. During the local cleansing period, from mid-August to the end of 2011, the Nabro aerosol layer over Wuhan had a single-peak structure and decayed uniformly. The corresponding e-folding decay time for the layer AOD is-130 days.Nabro aerosols were detected jointly by Wuhan University 532-nm depolarization liadr and 355-nm multi-channel lidar on 8 July 2011. The lidar measurements at Wuhan gave a small depolarization ratio and large backscatter-related Angstrom exponent for the Nabro aerosols on 8 July, suggesting that the majority of these aerosols were spherical and small. Physical parameters were derived from optical parameters of Nabro particles. Results show that the effective radius and total mass for the Nabro aerosol particles were ?0.26 ?m and-0.32 Tg respectively.Properties of cirrus over Wuhan were also investigated based on 532-nm polarization lidar measurements during October 2010 to March 2014, to assess whether Nabro induced aerosols affected nighttime cirrus clouds above Wuhan. Results show that no significant effect was found on cirrus optical property (backscatter coefficient), but Nabro particles may increase cirrus occurrence frequencies in fall.