Mass Transport of Background Asian Dust Revealed by Balloon-Borne Measurement: Dust Particles Transported during Calm Periods by Westerly from Taklamakan Desert

The dust storm which is caused by low pressure activities in China and Mongolia has been investigated by many investigators, but very thin dust clouds, which can be frequently detected in every season (we call it background Asian dust here) by lidar in Japan, Korea, and China but not by satellite, have attracted very few investigators since detection of the cloud is not easy. It, however, has been suggested that the background Asian dust also plays an important role in the biogeochemical cycle of dust in east Asia and west Pacific regions through long range transport of dust particles by westerly winds, and information of outflow rate of background dust particles over the dust source areas is strongly desired since previous investigations were made mostly in the down wind regions (Iwasaka et al. 1988; Matsuki et al. 2002; Trochkine et al. 2002). According to the balloon-borne measurements made under the calm weather condition in 2001–2004 at Dunhuang (40°00′N, 94°30′E), China, mass flux of background Asian dust due to westerly wind was about 50 ton/km

2

/day over the Taklamakan desert (about 4 to 6 km altitudes) and total mass of mineral dust transported by westerly from the Taklamakan desert to downwind will be about 1.4 × 10

7

ton/year. From those values it is suggested that background Asian dust transported from the Taklamakan desert is very important and more investigations are desired to clarify the effect of the background Asian dust to environment and climate in east Asia and west Pacific regions.

Keywords

: Background Asian dust, background KOSA, balloon-borne measurement, mass flux of Asian dust particle