Volcanic Aerosol Layer Observed by Shipboard Lidar over the Tropical Western Pacific

Volcanic aerosol layer just above the tropopause was observed by a shipboard lidar over the tropical western Pacific in February 2005. The aerosol layer with vertical thickness less than 1 km was observed at the altitudes of about 19 km in the regions of 0-2 degrees N and 7-9 degrees N along about 156 degrees E. The optical properties derived from the lidar data show the thin layer had optical thickness less than 0.01, small scattering ratio, moderate particle depolarization ratio, and large backscatter-related Angstrom exponent compared to cirrus clouds below the tropopause. From the report on the volcanic eruptions and the wind profiles of the sonde data, it was concluded that the aerosol source was the 27-28 January large eruptions of Manam volcano in Papua New Guinea (4.10 degrees S, 145.06 degrees E). The volcanic emissions injected into the lower stratosphere were transported by tropical westerly and deposited at the altitudes of weak wind which is interpreted as the phase change of the Quasi-Biennial Oscillation (QBO).