Optical Characteristics of Forest-Fire Smoke Observed with Two-Wavelength Mie-Scattering Lidars and a High-Spectral-Resolution Lidar over Japan

Abstract

Smoke plumes originating from a forest fire in northern Mongolia were observed with a two-wavelength (1064 nm, 532 nm) polarization (532 nm) lidar in Nagasaki at altitudes of 12 to 14 km and 3 to 10 km on June 10, 2007. Smoke from the same region was also observed in Tsukuba with a 532 nm high-spectral-resolution lidar (HSRL) at altitudes of 15 to 15.5 km on June 12, 2007. A two-wavelength data analysis method was applied to the Nagasaki data, and the extinction-to-backscatter ratio (the lidar ratio) at 532 nm was estimated to be 65 ± 5 sr (50 ± 5 sr) for the smoke at 12 to 14 km (3.5 to 4.5 km) altitudes. The particle depolarization ratio (PDR) was 0.14 ± 0.03 (0.12 ± 0.03), and the backscatter-related Angstrom exponent (BAE) between 532 nm and 1064 nm was 1.1 ± 0.2 (0.9 ± 0.1) for the high (low) altitude smoke. The optical thickness of the high (low) altitude plume was approximately 1.0 (0.03). The lidar ratio of the smoke in Tsukuba measured with the HSRL at 15 to 15.5 km was 75 ± 5 sr, and the PDR was 0.15 ± 0.04. The optical thickness was 0.03. The lidar ratio was comparable to those reported previously for forest-fire smoke in the lower troposphere. However, the PDR in the present case was two times higher, and the BAE was slightly lower. A possible explanation of the results involves mixing with solid particles such as those of ash and/or mineral dust in the strong convection found with pyrocumulonimbus. A discussion on lidar methods for characterizing smoke aerosols is also provided.