The Relationship between Occurrence of Dust Events and Synoptic Climatological Condition in East Asia, 1999-2003

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Regional differences in occurrence frequency of dust events (dust storms, sand storms and blowing dust) observed in spring (March, April, and May) in 1999-2003 in the northern half of China (north of 35°N), and Mongolia are studied from the viewpoint of the relationship with strong wind and precipitation occurrence. In order to categorize the weather conditions, World Surface Data were used. Dust events are frequently observed in the regions of (I) West Tarim Basin, (II) East Tarim Basin and East Xinjiang, (III) the Hexi Corridor, (IV) southern Mongolia to Inner Mongolia, (V) a part of southern Dongbei Plain (Northeast China Plain), and (VI) the Loess Plateau. However, dust event occurrence frequency under strong wind condition, is not the same among regions and these 6 areas are divided into 2 groups as follows. In areas (I), (II), (III), and (VI), dust event frequency under strong wind conditions is high, even though the number of strong wind occurrences is small. In contrast, in areas (IV) and (V), the number of dust event occurrences is large, but the dust event frequency under strong wind conditions is low. Dust events were observed not only in arid, or semi arid region. At almost all of observatories in the study area, dust events were reported at least once in 1999-2003. However, there are areas where both the number of dust events, and dust event frequency under strong wind conditions are low, even close to arid/semi-arid land, such as Dzungaria Basin. It is attributed to high frequency of precipitation events under strong wind and land surface characteristics. We made composite maps of sea level pressure, surface air temperature, and surface wind for 10 severest "Widespread Dust Event Cluster" (WDE Clusters) by using NCEP/NCAR reanalysis data for the above 6 areas respectively. It is found that severe dust events are observed in these 6 areas on the condition that anti-cyclones develop over Kazakhstan to the Altai Mountains and western Mongolia, associated with strong cold wind over each area. In areas (I), (II), (III), and (VI), dust events occurred only under the influence of these anti-cyclones. On the other hand, in areas (IV) and (V), a clean contrast was found between these anti-cyclones and cyclones located around 47.5°N, 120°E, and the role of these cyclones seems to be important. Only in area (V), surface air temperature tends to increase at the time of the 10 strongest WDE Clusters. This is caused by southerly wind associated with the cyclone. It is suggested that the possible causes of low dust event frequencies, under strong wind condition in areas (IV) and (V), are precipitations and land surface characteristics (e.g., snow cover) caused by the cyclone development.
2007-04-25

The Relationship between Occurrence of Dust Events and Synoptic Climatological Condition in East Asia, 1999-2003

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