The impact of sandwich foehn on air pollution in Urumqi, a gap town located on the northern leeside of the Tianshan Mountains of China, is analyzed. The results show that during days with high pollution, the boundary ...
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The impact of sandwich foehn on air pollution in Urumqi, a gap town located on the northern leeside of the Tianshan Mountains of China, is analyzed. The results show that during days with high pollution, the boundary layer over the city and the down-valley area can be divided into a three-layer structure, with the southeasterly foehn sandwiched between the northwesterly winds on top and the cold-air surface pool beneath. The southeasterly foehn at heights between 480 and 2,100 m results in a very stable boundary layer structure. In combination with the decoupling between the foehn flow and cold air pool, such boundary layer structure prevents vertical mixing of atmospheric *** the up-valley area from the northern leeside flank to the southern urban area, the ground-based foehn confronts the thermally driven valley breeze and forms a "mini-front," which moves northwards in the morning and retreats southwards in the afternoon. Although the mini-front disappears in the early evening, the wind shear of the mountain breeze between the southern suburb and downtown areas is still remarkable, which is favorable for a convergence line to persist around the city all day long. In this case, air pollutants emitted from the up-valley and down-valley areas are transported toward the urban area. Therefore, the air pollutants accumulate daily, leading to the frequent occurrence of heavy pollution events in Urumqi. This indicates that the sandwich foehn plays a critical role in the formation of heavy air pollution events in Urumqi.
利用TIGGE(THORPEX Interactive Grand Global Ensemble)单中心集合预报系统(CMA,ECMWF,JMA和NCEP)以及由此所构成的多中心模式超级集合预报系统2010年与2011年台风路径与强度(中心气压)资料,采用集合平均、超级集合与卡尔曼滤波技术对2...
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利用TIGGE(THORPEX Interactive Grand Global Ensemble)单中心集合预报系统(CMA,ECMWF,JMA和NCEP)以及由此所构成的多中心模式超级集合预报系统2010年与2011年台风路径与强度(中心气压)资料,采用集合平均、超级集合与卡尔曼滤波技术对2011年6月之后(包括6月)的台风进行24-48小时的短期顺序预报,并比较与评估了上述三种方法的结果。结果表明,卡尔曼滤波技术比集合平均、超级集合与单中心集合预报要好:单中心的台风路径与强度预报属ECMWF最好,超级集合预报比ECMWF略优,提升了集成的预报准确度。24-48小时预报,卡尔曼滤波预报误差比最佳单模式(ECMWF)分别降低了约36%与41%,提升了多模式集成的台风路径预报技巧。卡尔曼滤波对强度的预报也有较明显提升,24与48小时的预报误差均降低了约4-6hPa,且该技术较准确地预测了台风中心气压的变化趋势,优于其他集成方法。
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