English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Urban boundary layers (UBLs) can be highly complex due to the heterogeneousroughness and heating of the surface, particularly at night. Due to ageneral lack of observations, it is not clear whether canonical models ofboundary layer mixing are appropriate in modelling air quality in urbanareas. This paper reports Doppler lidar observations of turbulence profilesin the centre of London, UK, as part of the second REPARTEE campaign inautumn 2007. Lidar-measured standard deviation of vertical velocity averagedover 30 min intervals generally compared well with in situ sonicanemometer measurements at 190 m on the BT telecommunications Tower. Duringcalm, nocturnal periods, the lidar underestimated turbulent mixing duemainly to limited sampling rate. Mixing height derived from the turbulence,and aerosol layer height from the backscatter profiles, showed similardiurnal cycles ranging from c. 300 to 800 m, increasing to c. 200 to 850 munder clear skies. The aerosol layer height was sometimes significantlydifferent to the mixing height, particularly at night under clear skies. Forconvective and neutral cases, the scaled turbulence profiles resembledcanonical results; this was less clear for the stable case. Lidarobservations clearly showed enhanced mixing beneath stratocumulus cloudsreaching down on occasion to approximately half daytime boundary layerdepth. On one occasion the nocturnal turbulent structure was consistent witha nocturnal jet, suggesting a stable layer. Given the general agreementbetween observations and canonical turbulence profiles, mixing timescaleswere calculated for passive scalars released at street level to reach the BTTower 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 atnight, depending on stability. Determination of mixing timescales isimportant when comparing to physico-chemical processes acting on pollutantspecies measured simultaneously at both the ground and at the BT Towerduring the campaign. From the 3 week autumnal data-set there is evidence foroccasional stable layers in central London, effectively decoupling surfaceemissions from air aloft

Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II