Comparative Study Of Cold Front Type And Mongolia Cyclone Type Sandstorm Process

By an integrated utilization of aerial observation data, surface observation data, ground truth data, satellite remote sensing data and NCEP reanalysis data, this thesis comparatively analyzed certain characteristics, such as frequency, coverage, effect region and intensity, of the cold-front sandstorms and Mongolia cyclone sandstorms occurred during 2001-2010 years, based on the general sandstorm processes investigation data in North China in the same time period. Then, we conducted the synoptic comparative analysis and diagnostic analysis of the dynamic-thermal structures and mechanisms of both the cold-front sandstorm and Mongolia cyclone sandstorm, happened in March 19-20,2010 and March 9-10,2006 respectively. The results shown:(1) The occurrences of sandstorms in northern China was decreasing in a fluctuating way and having its maximum value happened in year 2001. (2) Cold-front sandstorm happened more often than the Mongolia cyclone sandstorm, taking 60% and 40% of the total occurrence, respectively; and the dust weather occurred most frequently in April and then in March. (3) The average duration of cold-front sandstorm and Mongolia cyclone sandstorm are 1.54 and 1.68 days, respectively; both of their maximum duration is less than 3 days. For the cold-front sandstorm, the occurrences of 1-day and 2-day lasting sandstorms are nearly the same, each taking 48.5% of the total occurrences. While for the Mongolia cyclone sandstorm, the 2-day lasting sandstorm occurred most frequently, taking 54% of the total occurrence. (4)The coverage of cold-front sandstorm is larger than that of Mongolia cyclone sandstorm. Most of the cold-front sandstorms moved to east and southeast; and the main direction was from northwest to southeast; while for Mongolia cyclone sandstorm, most of them moved to east, southeast and northeast; and the main direction was west-east. The regions under the influence of cold-front sandstorm usually include Xinjiang, northwest, northeast and east parts of China, meanwhile Mongolia cyclone sandstorm often affected the northwest, north and northeast parts of China; (5) The average maximum speed of the two kinds of sandstorm is between 15-18 m·s-1; and both kinds of the sandstorm gains maximum speed in April,32 m·s-1 and 28 m·s-1, respectively. (6) The average intensity of Mongolia cyclone sandstorm is larger than that of cold-front sandstorm; averagely, each cold-front sandstorm and each Mongolia cyclone sandstorm can be observed respectively by 14 and 22.5 stations in China.The typical cases analysis of the cold-front sandstorm and Mongolia cyclone sandstorm cases happened in March 19-20,2010 and March 9-10,2006 respectively had the following results:(1) the cold-front large-scale circulation had two trough a ridge form while that of Mongolia cyclone has a trough-ridge form. There was apparent barocline forcing in both kinds of the sandstorm. For the cold-front sandstorm, the high-level trough became deeper as its height decreased; for Mongolia cyclone sandstorm, there were breaking low pressure formed at low layer (850hPa) and middle layer(500hPa). (2) The difference between the highest and the lowest ground pressure value was larger in cold-front sandstorm than in Mongolia cyclone sandstorm. (3) The anticorrelation between wind speed and visibility in cold-front sandstorm is higher than in Mongolia cyclone sandstorm; and the post-frontal temperature in cold-front sandstorm decreased more apparently than in Mongolia cyclone sandstorm. (4) With the development of cold-front sandstorm system, momentum-downlink of cold front firstly appeared between 300 and 700hPa, then from 700hPa to ground surface as mixture layer forming at low layer of troposphere. For the Mongolia cyclone sandstorm, the main momentum-downlink happened between 300 and 700hPa; the development of the weather system and the increasing gradient in low layer accounted majorly for the increment of wind speed at the low layer of troposphere and above ground. (5) The stratification in both kind of the sandstorm has apparent daily variations. When dust weather existed, the mixture layer is higher than not, and the formation of which further helps the occurrence of sandstorm. (6) The pre-frontal upward motion center and post-frontal downward motion center in cold-front sandstorm was at 700hPa and 600hPa, respectively. At the center of Mongolia cyclone and its nearby region below 300hPa, there existed strong upward motion. The frontal passage in cold-front process usually led to a dramatic decrease of relative humidity. The air is relatively dry in the south side of the cyclone in Mongolia cyclone process which usually results in server sandstorm. In the cold-front process, the positive vorticity near the front was increasing with its height, reaching its maximum at 300hPa. In the Mongolia cyclone process, the positive vorticity was located at the cyclone center and its nearby regions, reaching its maximum at 700hPa. (7) The weather conceptual models of cold-front sandstorm and Mongolia cyclone sandstorm were summarized.