Features of Individual Asian Dust-storm Particles Collected at Nagoya, Japan

Abstract

Measurements of aerosol particles and light scattering coefficient were carried out at Nagoya in

Aerosol Optical Characteristics in the Yellow Sand Events Observed in May, 1982 at Nagasaki-Part II Models

“…Morphological analysis of scanning electron microscope images of yellow sand particles showed that the distribution of the ratio of the minor radius to the major one had a mode around 0.6, which is equivalent to r=1.03. Okada et al (1987) also got a similar value. Larger values of x0 and G compared with the cases studied by Pollack and Cuzzi show that the nonsphericity of and backscattering phase function (Pb) in the normal condition (Table 3a) and the yellow sand event (Table 3b).…”

“…As for a strong perturbation of the radiation regime by dust storms, however, such an assumption seems to be too simplified, because dust particles have irregular shapes Okada et al, 1987) and are large enough to affect the light scat- tering property. Welch et al (1981) showed that it is possible to overestimate the particle concentration by several tens of percent if we neglect the nonsphericity in the analysis of flux measurements.…”

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

“…Sulfate-coated mineral particles have been found in the free troposphere ($4 km in altitude) over Japan [Iwasaka et al, 1988] and over the North Pacific Ocean [Ikegami et al, 1993]. Okada et al [1987Okada et al [ , 1990 have reported that these coated mineral particles are frequently present in the surface atmosphere in Japan during Asian dust events. Niimura et al [1998] suggested that the minerals could mix with sea salts during transportation over the Sea of Japan, based on the individual particle analyses of the Asian dust particles collected in eastern China (Beijing, 40°N, 116°E) and in the west end of Japan (Nagasaki, 33°N, 130°E).…”

“…It should be noted that these assumptions are crucial for b a,coarse rather than b a,fine . For example, if we assume an aspect ratio of 1.4 [Okada et al, 1987] for the coarse particles, b a,coarse become larger by a factor of 1.6-2.0. If we assume a refractive index of n = 1.55+0.01i, b a,coarse becomes smaller by a factor of 0.7 -0.8 for spheres.…”

“…Using this technique, Kwon et al [1997] and Sakai et al [2000] have shown that the depolarization ratio in the free troposphere is generally high (>10%) over a wide range of relative humidities in the spring over Nagoya in Japan, probably due to the transport of mineral dust particles from the Asian arid regions. Because the depolarization ratio is a measure of particle nonsphericity [e.g., Bohren and Huffman, 1983], it can be utilized to detect mineral dust particles since they are mostly nonspherical [e.g., Okada et al, 1987Okada et al, , 2001. The lidar depolarization measurement technique has been widely used for cloud studies and has provided much useful information about the microphysical properties of clouds and precipitation [Sassen, 1991[Sassen, , 2000.…”