Variations of Dust Extinction Coefficient Estimated by Lidar Observations over Japan, 2007-2016

Dust extinction coefficients, a fundamental product of the Asian Dust and Aerosol Lidar Observation Network, were analyzed to evaluate climatological variations of Asian dust in Japan. Dust optical depth (vertically integrated dust extinction coefficients) from the network displayed peaks similar to those in the official Japan Meteorological Agency reports in spring, and in other seasons they were more responsive signals of moderate dust events. Between 2007 and 2016, dust optical depth decreased by 2.5% per year in Japan, and by 0.7% per year in Mongolia, a major source region of Asian dust. Relative to Mongolia, then, Japan has displayed a stronger negative trend in dust extinction coefficients, which is attributed to the meteorological field between continental Asia and Japan, including wind and rainfall during transportation. This negative trend of Asian dust in Japan was stronger in the middle troposphere (5-6 km altitude) than in the planetary boundary layer.