中文摘要：

临界起沙阈值可表征地表土壤的可蚀性,是风蚀起沙研究中非常重要的物理量之一。基于微气象学方法,将沙尘浓度和垂直沙尘通量均开始增加且至少持续0.5 h所对应的摩擦速度（或风速）确定为临界起沙摩擦速度u_（＊t）（或临界起沙风速U_t）。利用内蒙古科尔沁沙地地区2010—2013年春季大气环境综合观测资料,分析了不同沙尘天气过程（扬沙、沙尘暴和强沙尘暴）起沙阶段沙尘浓度和垂直沙尘通量随摩擦速度的演变特征,精细确定了该地区临界起沙摩擦速度（u_（＊t））和临界起沙风速（U_t）的范围分别为0.45±0.20和6.5±3.0m/s,同时讨论了不同起沙判据对确定临界起沙阈值产生的影响。相比而言,采用的起沙判据尽可能地排除了沙尘输送和沉降过程的影响,适用于不同的沙尘天气类型,使沙尘粒子进入大气的起沙结果更趋于合理,其结果可为建立统一、合理的起沙判据提供参考。

英文摘要：

Threshold for dust emission represents soil erodibility and becomes one of the important parameters in wind-erosion research.From the view of micrometeorology,the dust emission threshold friction velocity（u_（＊t））and dust emission threshold wind speed（U_t）are defined as the value of friction velocity and wind speed when both of dust concentration and vertical dust flux begin to increase with friction velocity and last for half an hour at least.Using the observational data of sand-dust events in2010-2013 spring over the Horqin Sandy Land area in Inner Mongolia,the evolution of dust concentration and vertical dust emission flux with friction velocity during the different dust emission period of sand-dust events（e.g.blowing dust events,sand-dust storm events,and severe sand-dust storm events）is analyzed.According to the definition,the values u_（＊t）and Utover the Horqin Sandy Land area are determined to be 0.45±0.20 and 6.5±3.0m/s,respectively.Meanwhile,the effects of different dust-emission criteria to the determination of dust emission thresholds are discussed.Comparing with the previous dustemission criteria,the one used in this study can effectively exclude the influence of dust advection and deposition and reduce the simplicity and subjectivity of the criteria.This study can provide references to set up uniform dust-emission criteria in the future.