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《Journal of Applied Meteorological Science》 2014-05
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Fine Spatial and Temporal Characteristics of Humidity and Wind in Beijing Urban Area

Dou Jingjing;Wang Yingchun;Miao Shiguang;Chinese Academy of Meteorological Sciences;Institute of Urban Meteorology,CMA;Beijing Meteorological Service;  
The temporal and spatial characteristics of specific humidity,wind speed and direction in Beijing urban area and urban effects are investigated in terms of hourly automatic weather station data during 2008 —2012.Results show that values of specific humidity(q) in urban areas are lower than those in rural area during summer daytime and early night in Beijing,which is known as "urban dry island"(UDI).Values show a multi-center distribution,due to the non-uniform distribution of non-evaporating urban impervioussurfaces,which decrease evapotrans-piration,increase run-off,and thus lower urban specific humidity levels.In winter,urban values of q are bigger than rural ones at most hours which are affected by anthropogenic emissions.Studies on 10-m wind directions show that they are affected by seasonal prevailing winds,topography and urban effects.During summer valley-breeze time,southerlies bypass Beijing urban area because of buildings,while air flows converge into city during summer mountain-breeze time due to combined effects of topography,urban effects and seasonal prevailing wind.During winter breeze-time,a convergence line is formed in northwest-southeast direction in urban area.Wind speeds are reduced by the large Beijing surface-roughness.A low-speed region is observed in more urbanized areas between Second Ring Road and Third Ring Road due to its high surface-roughess.It shows that humidity and air flow are strongly affected by urban effects besides the much studied "urban heat island" in Beijing.The local urban effects have to be taken into account in fine weather forecasting.In addition,the result will contibute to the discussion of urban atmospheric environmental governance and city planning and construction.
【Fund】: 北京市科委绿色通道项目(Z111100074211010);; 国家自然科学基金项目(41175015)
【CateGory Index】: P426.1;P425
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