资源环境科技发展态势分析平台

Two years of continuous in situ measurements of Arctic low-level clouds have been made at the Mount Zeppelin Observatory (78 degrees 56N, 11 degrees 53E), in Ny-angstrom lesund, Spitsbergen. The monthly median value of the cloud particle number concentration (N-c) showed a clear seasonal variation: Its maximum appeared in May-July (658cm(-3)), and it remained low between October and March (87cm(-3)). At temperatures warmer than 0 degrees C, a clear correlation was found between the hourly N-c values and the number concentrations of aerosols with dry diameters larger than 70nm (N-70), which are proxies for cloud condensation nuclei (CCN). When clouds were detected at temperatures colder than 0 degrees C, some of the data followed the summertime N-c to N-70 relationship, while other data showed systematically lower N-c values. The lidar-derived depolarization ratios suggested that the former (CCN-controlled) and latter (CCN-uncontrolled) data generally corresponded to clouds consisting of supercooled water droplets and those containing ice particles, respectively. The CCN-controlled data persistently appeared throughout the year at Zeppelin. The aerosol-cloud interaction index (ACI=dlnN(c)/(3dlnN(70))) for the CCN-controlled data showed high sensitivities to aerosols both in the summer (clean air) and winter-spring (Arctic haze) seasons (0.220.03 and 0.250.02, respectively). The air parcel model calculations generally reproduced these values. The threshold diameters of aerosol activation (D-act), which account for the N-c of the CCN-controlled data, were as low as 30-50nm when N-70 was less than 30cm(-3), suggesting that new particle formation can affect Arctic cloud microphysics.