Characteristics of Aeolian Dust Observed by Sky-Radiometer in the Intensive Observation Period 1 (IOP1)

Abstract

A sky-radiometer network was developed in order to investigate the characteristics of aeolian dust on the way of transportation from the source region to the Japan area. From the analysis of the sky-radiometer data, optical thickness in the visible to near infrared regions and size spectrum from radius 0.0l to 5 μm can be obtained. Five observation sites are set at Aksu, Qira, Shapotou, Qingdao, and Beijing in China, and four observation sites at Naha, Fukuoka, Nagoya and Tsukuba in Japan. The data of six observation sites (Qira, Shapotou, Naha, Fukuoka, Nagoya and Tsukuba) are automatically transferred to Meteorological Research Institute (MRI) through telephone lines.The following results were obtained from the data analysis of intensive observation period (IOP) in Apri1, 2002. (1) The data with Angstrom exponent between 0.0 and 0.5 corresponds to the dust event day data. (2) The contribution of the particles with radius greater than 0.5 μm, which correspond to coarse dust particles, to the total optical thickness frequently exceeds more than ∼70% in the source region, and exceeds in Qingdao and sites in Japan on the dust event day. (3) The contribution of particles with radius greater than 0.5 μm to the total volume is more than ∼80% on the dust event day. (4) The retrieved volume spectrum in the source region, Aksu and Qira, is not dependent on the optical thickness. This means that the floating aerosols mainly consist of dust particles in the source region. (5) The total volume observed in Japan sites is one third of that in the source region. (6) When the size distribution for the coarse mode (r > 0.5 μm) is approximated by log-normal size distribution, effective radius reff is 2.1 to 2.3 μm in China sites and 1.6 to 1.8 μm in Japan sites. rg is about 0.7 μm at Aksu, Qira, and Shapotou and about 0.5 μm at other sites (ln rg is the center of log-normal size distribution). The width of size distribution (σg) is scattered between O.67 and O.87. These difference of size distribution among the observation sites are caused by the modification of air mass including aeolian dust; coarser dust particles are partially removed during the transportation, and the air mass including aeolian dust as a main component are partially contaminated by the aerosol into the atmosphere from anthropogenic activities. The observation network of ADEC caught this change clearly.