ABSTRACT |
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The quality of simulations of the Yellow Sand phenomena that are frequently occurring in the East Asian region during spring depends upon the meteorological fields properly resolved in space and time, the source informations including the location, time of occurrence, duration period and amount of dust emission, and
the advection and diffusion model that can take into account the transport, diffusion and deposition processes.
Dust whirl reports at the synoptic weather code in East Asia were analyzed to identify the location, occurrence frequency, initiating time and duration of the Yellow Sand event for three sequent spring seasons from 1993 to 1995. The results indicated that the source regions could be subdivided into three distinctive regions according to soil types of loess, sand and gobi to simulate more properly the Yellow Sand events occurring in China. The loess region was characterized by relatively weak threshold wind speed and high variabilities of occurrence frequencies of the dust rise due to high relative humidity in association with frequent rainfall. The gobi region was characterized by the relatively high threshold wind speed and a relatively cold region due to its location of high elevation and high latitude. Consequently this region had a relatively low occurrence frequency of Yellow Sand. However, the sand region had the most favorable conditions for the occurrence of yellow sand due to its dryness. The optimum threshold velocities in the loess, sand and gobi regions were respectively 36 cm/s, 50 cm/s, and 67 cm/s with the assumed surface roughness of 0.5 cm, 1 cm, and 3 cm. The long range transport model of Meteorological Research Institute of Japan (MRI-LTM) that produced the meteorological variables every hour was used to simulate two cases of Yellow Sand events that observed at Seoul on 1-4 April and 6-7 April 1993. The simulation with a hypothetical single source located at the most frequent occurrence station during three sequent spring seasons from 1993 to 1995 yielded a similar particle distribution pattern to the simulation with multiple sources identified from the reports of synoptic weather code. These two simulations could successfully simulate both cases of Yellow Sand events observed in Seoul. But multiple sources could provide the various source region of Yellow Sand. However, the simulation with the threshold friction velocity of 60 cm/s used for the Sahara desert dust could not simulate the first case of the Yellow Sand events. But the model using the three different threshold friction velocities according to soil types could simulate both cases of the Yellow Sand events observed in Korea. The simulated starting time of Yellow Sand in Korea well coincided with that of observation. |