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Air Flow and Transport Patterns over Baoding-Xiong’an Area
LI Hange, CAI Xuhui, KANG Ling, SONG Yu
Acta Scientiarum Naturalium Universitatis Pekinensis    2021, 57 (2): 215-224.   DOI: 10.13209/j.0479-8023.2021.001
Abstract805)   HTML    PDF(pc) (9130KB)(276)       Save
Hourly wind fields were obtained in the period of 2016 to 2017, using the diagnostic model CALMET over the Baoding-Xiong’an area, Hebei province. Data from 22 meteorological observatories and the NCEP-fnl dataset were used in the procedure, and daily trajectories were derived. According to characteristics of the wind fields and trajectories, local air flows were classified into three types: systematic flow, local circulation, and weak synoptic winds. The analysis results depict that the proportion of the three type of flows are approximately 10%, 50% and 40%. The frequency of systematic flow is quite low, with a little more occurrence in spring and summer than that in autumn and winter. The local circulation appears more in autumn and winter than that in spring and summer. The frequency of weak synoptic winds changes little over the whole year, but slightly lower in autumn and winter. The air flow is characterized by the mountains in the northwest of the region, mountain and plain breeze circulations influence the range of about 100 km in front of the mountain, covering Baoding city and a major part of Xiong’an area. The transfer of mountain and plain breeze causes light winds in this area timely. The major transport pathways in this region are southwesterly and northeasterly, corresponding to large-scale background flows. Lateral transports caused by mountain and plain breeze circulations are relatively short in northwest and southeast directions. Occasionally, under conditions of systematic flow and weak synoptic winds in winter and spring, transport trajectories can also extend to southeast.
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Study of Turbulence Transfer at Different Levels during Fog Periods in Tianjin
YE Xinxin, WEI Wei, LI Hang, ZHANG Hongsheng
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (5): 809-818.   DOI: 10.13209/j.0479-8023.2015.141
Abstract1406)   HTML    PDF(pc) (917KB)(877)       Save

Based on the observational atmospheric turbulent data obtained from 255-m tower in Tianjin, the characteristics of different atmospheric variables and turbulent transfer during the fog periods were studied. The results show that before the fog, there exists high humidity, and the height of inversion reaches to 100 m. The inversion of radiation fog is stronger than that of the advection fog. During the fog, the inversion continues strengthening. With the lifting of inversion, the neutral and unstable stratification occurres which means the dissipation of fogs. Meanwhile, the development of inversion in the radiation fog is more obvious than that in advection fogs, the height of radiation fogs is lower than that of advection fogs, and the main reasons for the dissipation of radiation and advection fogs are temperature and wind speed, respectively. The stratification is changed by the fog period, resulting in an unstable nocturnal atmosphere. The vertical transfer is weak and the horizontal transfer strengthened in the later stage. The increasing in the ratio of mean kinetic energy to turbulent kinetic energy before the fog can be treated as the signal of the occurrence of fog and the decreasing marks the dissipation of fog.

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