Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II
Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II
复制标题
DOI：
10.5194/acp-11-2111-2011
复制
发表时间：
2011-01-01
影响因子：
6.3
通讯作者：
Harrison, R. M.
中科院分区：
文献类型：
--
作者：
Barlow, J. F.;Dunbar, T. M.;Harrison, R. M.
城市边界层（UBLs）可以是高度复杂的，由于不均匀的粗糙度和加热的表面，特别是在夜间。由于普遍缺乏观测，尚不清楚边界层混合的规范模型是否适合模拟城市地区的空气质量。本文报道了多普勒激光雷达观测的湍流廓线在伦敦，英国的中心，作为第二REPARTEE运动的一部分，在2007年秋季。激光雷达测量的垂直速度的标准偏差平均超过30分钟的时间间隔一般比较以及在现场声波风速计测量在190米的BT电信塔。在平静的夜间，激光雷达低估了湍流混合，主要是由于有限的采样率。由湍流得到的混合高度和由后向散射剖面得到的气溶胶层高度显示出相似的日变化，变化范围从c。300到800米，增加到C。在晴朗的天空下200到850米。气溶胶层的高度有时显着不同的混合高度，特别是在晴朗的天空下，在夜间。对于对流和中性的情况下，缩放的湍流廓线类似于规范的结果，这是不太清楚的稳定的情况下。激光雷达观测清楚地表明，层积云下的混合增强，有时达到约一半的白天边界层深度。有一次，夜间湍流结构与夜间急流一致，表明存在稳定层。考虑到观测结果与规范湍流廓线之间的一般一致性，使用现有的湍流混合模型计算了在街道水平释放的被动标量到达BT塔的混合时间尺度。据估计，C。10分钟扩散到190米，夜间上升到20至50分钟，取决于稳定性。混合时间尺度的确定是很重要的，当比较的物理化学过程中同时测量的污染物种类在地面和BT塔在运动。从3周的秋季数据集有证据表明，偶尔稳定层在伦敦中心，有效地解耦地面排放从空中。
Urban boundary layers (UBLs) can be highly complex due to the heterogeneous roughness and heating of the surface, particularly at night. Due to a general lack of observations, it is not clear whether canonical models of boundary layer mixing are appropriate in modelling air quality in urban areas. This paper reports Doppler lidar observations of turbulence profiles in the centre of London, UK, as part of the second REPARTEE campaign in autumn 2007. Lidar-measured standard deviation of vertical velocity averaged over 30 min intervals generally compared well with in situ sonic anemometer measurements at 190 m on the BT telecommunications Tower. During calm, nocturnal periods, the lidar underestimated turbulent mixing due mainly to limited sampling rate. Mixing height derived from the turbulence, and aerosol layer height from the backscatter profiles, showed similar diurnal cycles ranging from c. 300 to 800 m, increasing to c. 200 to 850m under clear skies. The aerosol layer height was sometimes significantly different to the mixing height, particularly at night under clear skies. For convective and neutral cases, the scaled turbulence profiles resembled canonical results; this was less clear for the stable case. Lidar observations clearly showed enhanced mixing beneath stratocumulus clouds reaching down on occasion to approximately half daytime boundary layer depth. On one occasion the nocturnal turbulent structure was consistent with a nocturnal jet, suggesting a stable layer. Given the general agreement between observations and canonical turbulence profiles, mixing timescales were calculated for passive scalars released at street level to reach the BT Tower using existing models of turbulent mixing. It was estimated to take c. 10 min to diffuse up to 190 m, rising to between 20 and 50 min at night, depending on stability. Determination of mixing timescales is important when comparing to physicochemical processes acting on pollutant species measured simultaneously at both the ground and at the BT Tower during the campaign. From the 3 week autumnal data-set there is evidence for occasional stable layers in central London, effectively decoupling surface emissions from air aloft.