2025 Volume 44 Issue 4 Pages 335-348
Lidar observations at 532 nm were made in conjunction with Total Carbon Column Observing Network (TCCON) observations in Burgos, Philippines (18.52˚N, 120.65˚E) in Southeast Asia to investigate the effects of aerosols and thin cirrus clouds on column-averaged dry air mole fractions of greenhouse gases such as carbon dioxide (XCO2) estimated from the Greenhouse gases Observing SATellite (GOSAT) and its successor GOSAT-2. Here, we report on stratospheric aerosol events observed from January 2017 to March 2020, and from January to March 2023. Non-spherical smoke particles originating from the Canadian forest fires in August 2017 were observed on 25 September 2017. The backscattering ratio (BSR) and the particle depolarization ratio (PDR) of these smoke particles were 1.20 and 0.15 at an altitude of 18.24 km. Furthermore, smoke particles were still detected around 20 km altitude on 2 April 2018, exhibiting a PDR of 0.07.
Three aerosol layers were observed on 2 October 2019, with respective BSR peaks of 1.40 (18.09 km), 1.57 (20.79 km), and 2.07 (25.14 km). The narrow aerosol layer at an altitude of 25 km was observed on 8 out of 12 nights from 11 September to 24 October 2019. These increases in stratospheric aerosols could be the result of the eruption of Mt. Raikoke (48.29˚N, 153.25˚E) in June 2019 and the eruption of Mt. Ulawun (5.05˚S, 151.33˚E) in August 2019.
During the whole lidar observation period, the maximum value of the integrated backscattering coefficient (IBC) of stratospheric aerosols from the tropopause to 33 km altitude was 4.45×10−4 sr−1 on 29 September 2017, and the minimum IBC was 4.53×10−5 sr−1 on 2 October 2017. Assuming a lidar ratio of 50 sr, we estimated the maximum value of the stratospheric aerosol optical depth (SAOD) to be 0.022 on 29 September 2017 and the minimum SAOD to be 0.0023 on 2 October 2017.
