北京地区边界层低空急流的时空发展特征分析

Temporal and spatial characteristics of the low-level boundary layer jet over Beijing

利用2018—2019年多普勒激光雷达资料及Micaps数据,探讨了北京地区边界层低空急流的季节变化、日变化及发展演变特征,统计分析了不同天气系统下,边界层低空急流出现的频次。结果表明:(1)北京地区边界层低空急流表现出明显的季节性差异特征。急流在春、夏、冬季每日发生的频率分别为56.2%、52.3%、54.8%,而秋季最高,为79.4%,且四季都存在单日多急流过程的现象;急流轴高度表现为单峰状态,春、冬两季急流发生频率与高度呈反比,秋、冬两季的急流多发生于200~400 m低层峰值内;北京地区全年急流强度多以弱急流为主,主要集中于5~9 m·s^(-1),春、秋及冬季急流强度较弱,夏季急流较强。(2)北京地区边界层低空急流具有明显的日变化特征,近89.5%的急流发生于夜间,日间发生的急流主要集中于上午,发生频率为7.6%,统计发现这部分急流主要为夜间急流的延续。(3)北京地区边界层低空急流按其发展特征可分为5种类型:经典型、抬升型、下沉型、间歇型及弱风速带型。(4)急流多发的天气形势可分为高压控制、高压前部、高压后部、高压底部、高压顶部及均压场6种类型,急流发生频率分别为11.1%、9.5%、7.9%、6.3%、15.9%及38.1%。

In this study,based on the 2018-2019 Doppler Lidar data and Micaps data,the seasonal variation,diurnal variation and evolution characteristics of the Low-Level Jet(LLJ)in Beijing area were discussed.In addition,the frequency of LLJ in the boundary layer under different weather systems was analyzed statistically.Results show that:(1)the LLJ in the boundary layer over Beijing shows obvious seasonal differences.The daily occurrence frequency of LLJ in spring,summer and winter was 56.2%,52.3%and 54.8%,respectively,and in autumn,it was the highest,which was 79.4%.And the phenomenon of multi-LLJ process in a single day exists in all seasons.The height of LLJ axis shows a single peak state.The frequency of the LLJ in spring and winter is inversely proportional to the height,while the LLJ in autumn and winter mostly occurs within the 200-400 m peak.The intensity of the LLJ in Beijing is mainly weak jet,mainly concentrated around 5-9 m·s^(-1).The LLJ is weak in spring,autumn and winter,but is stronger in summer.(2)The LLJ in the boundary layer in Beijing shows obvious diurnal variation.Nearly 89.5%of the LLJ occurred at night,and the LLJ occurred during the day mainly concentrated in the morning,with a frequency of 7.6%.Statistics show that this part of the LLJ is mainly the continuation of the night jet.(3)According to its development characteristics,the boundary layer LLJ over Beijing can be divided into five types:meridian type,uplift type,subsidence type,intermittent type and weak wind speed zone type.(4)The weather conditions with multiple jet streams can be divided into six types:high pressure control,high pressure front,high pressure back,high pressure bottom,high pressure top and uniform pressure field,and the LLJ frequency was 11.1%,9.5%,7.9%,6.3%,15.9%and 38.1%.