Observed Characteristics of Boundary Layer Low-Level Jet over Beijing Area
Based on two-year routine sounding data and intensive radiosonde data collected at multiple stations from August 28 to September 2,2016,over the Beijing area,this study investigated the relationship between boundary layer low-level jet(BLLJ)and meteorological elements,analyzed the differences in BLLJ characteristics between urban and suburban areas,and briefly explored its formation mechanism.The results show that:(1)The BLLJ in autumn and winter was more frequent,higher,and stronger,and the main jet direction was southerly.In spring and summer,it became less frequent,lower in height,and weaker,and the jet was primarily northerly.(2)The jet was closely related to the vertical structure of the atmospheric boundary layer.In most cases,an elevated inversion layer was observed above the jet.The height of inversion exhibited good consistency with the minimum wind speed above jet height and the wind direction change height.(3)The diurnal variation of potential temperature was similar to the cycle of the BLLJ from its formation to dissipation.The main driver of the nocturnal BLLJ in Beijing was inertial oscillations under clear weather conditions.(4)The difference in BLLJ characteristics between urban and suburban areas was significant.Urban jets were usually abrupt and not coherent,short-lived,and rarely observed.By contrast,suburban jets were frequent and long-lived.In a typical urban jet case,the jet core height was 150 m higher,and the jet intensity was 1.6 m s-1 smaller than those of a suburban jet at the same time.
boundary layer low-level jetseasonal characteristicselevated inversion layerdiurnal variationdifferences between urban and suburban areas
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