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Title: Flow analysis and Lagrangian stochastic modelling of dust particle motion over the Taklamakan Desert
Other Titles: Takelamagan Shamo liu chang fen xi ji Lagelangri sha chen yun dong mo ni
Authors: Cheung, Man Sze (張敏思)
Department: Dept. of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Dust storms -- China -- Xinjiang Uygur Zizhiqu
Takla Makan Desert (China)
Notes: CityU Call Number: QC959.C6 C44 2006
Includes bibliographical references (leaves 99-106)
Thesis (M.Phil.)--City University of Hong Kong, 2006
xviii, 106 leaves : ill. (some col.) ; 30 cm.
Type: Thesis
Abstract: The Taklamakan Desert in the Tarim Basin has the highest frequency of dust events on the planet and is claimed to be one of the largest dust sources to the global atmosphere. The physical processes for dust entrainment and transport in the Taklamakan are quite unique, as dust events there are mostly observed in light-wind conditions. Flow in the Tarim Basin is strongly affected by the surrounding topography, which generates complex patterns of dust distribution. The main objective of this study is to investigate dust motion in the Tarim Basin through data analysis and numerical modeling. The prevailing flow patterns in the Tarim Basin are first studied by calculating the joint probability density functions of wind speed and direction. The surface data for the June 1998 - August 2003 period at 21 weather stations are used for the purpose. The data are provided by the China Meteorological Administration in MICAPS (Meteorological Information Comprehensive Analysis and Processing System) format. A Lagrangian stochastic model is proposed, which combines the equation of particle motion and a stochastic differential equation for turbulent fluid motion. The Lagrangian stochastic model is then applied in conjunction with a regional atmospheric model to the prediction of dust particles in the Tarim Basin. The regional model used in this study is the Computational Environmental Modelling System 5 (CEMSYS5). Finally, an analysis of dust budget for the Tarim Basin is carried out. The synoptic analysis reveals an interesting flow pattern frequently occurring in the Tarim Basin, i.e., a flow converging from the northeast to the southwest of the basin superposed by a local mountain-desert circulation. This flow pattern is responsible for the frequent dust suspension over the southern part of the Taklamakan. Although wind in the Tarim Basin is influenced by both synoptic systems and local radiative effects, it is found that the former play a determining role during dust episodes. Four scenarios have been tested with using the Lagrangian model with dust particles released from different sectors of the basin. It is found that dust particles are mostly transported to the southwestern part of the basin. As the streams flowing from the northern and northeastern parts of the basin converge in the Hetian and Minfeng area, dust particles are then transported upward and eastward by the westerly in the upper atmosphere. As a result, dust-in-suspension events occur frequently in the southwest of the Tarim Basin. This conclusion is supported by the synoptic records of dust events. Flow pattern and dust budget analysis suggest that much of the dust emitted from the basin is deposited back to it, indicating that the net dust provision from the Taklamakan may be not as strong as previously thought.
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