Analysis Of Dust Transport In Typical Synoptic System In China

Dust weather (DW) always occurred with specific synoptic system, so the study of the transport characteristics of dust in different synoptic systems is important for forecasting the occurrence, development and the affected area of the DW.Three DW episodes were selected for representing three different types of DW (Cyclonic Cold Front DW, Dry Cold Front DW and High Bottom DW) episodes respectively. According to the MICAPS meteorology data, the horizontal distributions of the three DW episodes were analyzed. Then, absorbing aerosol index (AAI) of OMI/Aura satellite data was used for analyzing the daily distribution of dust semi-quantitatively, and the dust sources were determined combined with MICAPS meteorology data. After that, based on CALIOP/CALIPSO satellite data, including Total Attenuated Backscatter (TAB), Volume Depolarization Ratio (VDR) and Backscatter Color Ratio (BCR), the features of the particle size and the irregularity varying with altitude, as well as the vertical distribution of dust aerosol were studied. Finally, Weather Research and Forecasting (WRF) model was used for studying the mechanism of dust transport. The following results are obtained:(1) As a type of the Cyclonic Cold Front DW, a process occurred in 25-29 May 2008, taking place in central and southern Mongolia was selected. Affected by the Mongolian cyclone and the cold front, large area of central and eastern Inner Mongolia was covered by sand-dust storm. The area of AAI with large values showed a cyclone-like shape, and its value reached the maximum 8 in the center of "cyclone". The transport height is generally between 2km and 4km above sea level, the maximum height that the recognizable dust aerosol could reach was about 5km. At the deposition area, it mainly stayed at 1km below. At the front of the cyclone, the dust particle size was so large that the maximum VDR and BCR reached 0.38 and 1.64, at the deposition area, they were 0.32 and 1.57, respectively.(2) The Dry Cold Front DW occurred in Taklimakan desert in 7-11 May 2007. Most part of northern China suffered from dust storm as a result of the cold front before the anticyclone. The daily AAI value ranged from 1.5 to 3.5, its maximum was about 5. Near the source region, the dust aerosol rose to 5.5km, a transport layer at 3km was found. The height of the dust layer increased with latitude, and the maximums of VDR and BCR reached 0.4 and 1.3, respectively.(3) The High Bottom DW occurred in Taklimakan Desert from 28 to 31 March 2008. Under the influence of the cold anticyclone and the weak cyclone, blowing dust weather occurred in Northwest China. At the source area, the AAI ranged from 2 to 5, in northern Gansu province and western Inner Mongolia, the maximum is about 4, which was the second largest value. Dust was found mainly below 3km, the particle size and irregularity decreased with altitude.(4) The source regions of Cyclonic Cold Front DW were otindag sandy land in Inner Mongolia and Gobi desert in central and southern Mongolia, while the source regions of the other two dust weathers were Taklimakan desert in Tarim basin in Xinjiang and desertification area in western Inner Mongolia, northern Gansu and Ningxia.(5) The VDR and the BCR of the dust aerosol firstly increased and then decreased with altitude in the dust area, and the rate of increase was larger than that of the decrease generally, the result agreed with the fact that big and irregular dust particles were located in the middle and lower level. And the analysis of the CALIOP data in the areas without dust, they were both confirmed that determining dust aerosol with VDR>0.1, BCR> 0.3 and low relative humidity was viable.(6) DW was always accompanied with a high jet. In Cyclonic Cold Front DW process, the high jet went from northwest to southeast, and the dust was mainly located on the left of the high jet. In Dry Cold Front DW process, the high jet showed an inverse "V" like, and the dust was on the right rear of the high jet. In High Bottom DW process, the high jet went from west to east, and the dust was on the left rear of the high jet.(7) Both in Cyclonic Cold Front and Dry Cold Front DW processes, the development of the surface synoptic systems were strengthened by the spreaded downward momentum that was caused by the high jet. The distribution and the intensity of the DW were closely related to the surface synoptic systems. Floating dust and blowing sand mainly occurred at the front of the cold front, and the dust storm was mainly occurred in the strong northwest wind behind the cold front. Additionally, in Cyclonic Cold Front process, the intensity of DW was in agreement with that of the cyclonic.(8) In High Bottom DW process, the DW was caused by the surface synoptic system initially, and then was strengthened by the momentum spreaded downward from the high jet, then the strong east wind at the bottom of the anticyclone near the surface was weakened by the high west jet, so the High Bottom DW was the weakest of all the episodes.