Takuya Tajiri

Balloon-borne and Raman lidar observations of Asian dust and cirrus cloud properties over Tsukuba, Japan

The vertical distributions of the microphysical and optical properties of tropospheric aerosols and cirrus cloud were measured using an instrumented balloon and a ground-based Raman lidar over Tsukuba, Japan (36°N, 140°E), during the Asian dust events on 9 and 21 May 2007 to investigate the influence of Asian mineral dust on ice cloud formation in the upper troposphere. The instrumented balloon measured the particle size distribution, ice crystal images, dew/frost point, relative humidity, and temperature. The Raman lidar measured the particle backscattering and extinction coefficients and the depolarization ratio at a wavelength of 532 nm. The results of the balloon measurements showed that supermicrometer (0.7 to 2.8 µm in optical-equivalent radius) dust particles and ice crystals (10 to 400 µm in maximum dimension) were present in the upper troposphere (8 to 12 km in altitude), with number concentrations varying from 5 × 10−3 to 0.6 cm−3 for dust and from 5 × 10−3 to 0.15 cm−3 for ice crystals. The Raman lidar measurement indicated that the particle depolarization ratios were 15 to 35% in the altitude range of 6 to 12 km, indicating the predominance of nonspherical particles in the region. The temperature ranged from −33 to −63°C, and the relative humidity with respect to ice (RHi), estimated from the total (vapor plus condensate) water content obtained with the Snow White hygrometer in the cloud, was 130% at maximum on 9 May, which was close to the activation point of Asian mineral dust as ice nuclei to form ice crystals.

CCN and IN parameter of Arizona test dust derived from laboratory experiments to simulate ice crystal formation by condensation freezing

The hygroscopicity parameter and ice nucleation rate of Arizona Test Dust (ATD) particles were derived from laboratory experiments. The mean hygroscopicity of ATD particles was 0.017. The calculated activation energy and contact angle using the nucleation rate obtained from the cloud chamber experiment was 1.4×10−19 J and 37.0 degree, respectively. A new parcel model implemented with κ-Kohler theory and classical ice nucleation theory for freezing has been developed. Using the parcel model and the parameters derived from laboratory experiments for ATD, the condensation freezing induced by ATD particles was preliminarily tested. The model simulation for adiabatic ascent at 5 ms−1 from −20°C presents physically reasonable results.