Wednesday, 17 January 2007: 10:30 AM
Desert dust storms in Northern China: a trajectory analysis for the last 25 years
214C (Henry B. Gonzalez Convention Center)
Dust-sand storms are phenomena characterizing desert area and affecting human activities, agriculture, territories and local climate. Wind speed, atmospheric stability, and source region surface characteristics are the main environmental factors that influence the probability of occurrence, intensity, impact and vertical depth of such phenomena. In order to describe the variability of dust-sand storms affecting Beijing and its surroundings during the last years, an analysis of wind field, and its ability to initiate the erosion process over the main Chinese dust sources has been conducted using the NCEP-NCAR Reanalysis data for the latest 25 years. In fact wind intensity and direction regulate the dust/sand raising and transport, and determine the DSS pathways. In order to perform this analysis with this kind of data, it was necessary to consider the desert zones from which the dust could be transported by wind. To do this we have considered the Bare Soil Textural Classes, obtained from the projection of the Global Land Cover 2000 data on the FAO Textural Map. This analysis was devoted to the identification of the potential dust/sand originating areas and, among them, the areas with a great potential of generating DSS affecting Beijing surroundings, furthermore this analysis relates the change in wind conditions to the different origin, development and transport of dust over the target area. For each days of the year, the forward trajectories from Alashan desert were computed in order to evaluate the possibility of dust transport over Beijing. The daily and monthly numbers of trajectories starting from each spot and the mean time occurred to reach various locations are been evaluated in order to make some consideration about how climate variations through years affect the spring dust phenomena, and the different development through years of the direction and the occurrence of the dust trajectories. Diagrams of span vs. duration of dust event originated by Alashan desert are been evaluated to understand the dynamical behavior and changing in dust-storms.