Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II
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. T...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2011-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/11/2111/2011/acp-11-2111-2011.pdf |
| _version_ | 1811342721649999872 |
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| author | J. F. Barlow T. M. Dunbar E. G. Nemitz C. R. Wood M. W. Gallagher F. Davies E. O'Connor R. M. Harrison |
| author_facet | J. F. Barlow T. M. Dunbar E. G. Nemitz C. R. Wood M. W. Gallagher F. Davies E. O'Connor R. M. Harrison |
| author_sort | J. F. Barlow |
| collection | DOAJ |
| description | 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 850 m
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 physico-chemical 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. |
| first_indexed | 2024-04-13T19:15:45Z |
| format | Article |
| id | doaj.art-9aac385c0699463fb41ca9c286c1d222 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-13T19:15:45Z |
| publishDate | 2011-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-9aac385c0699463fb41ca9c286c1d2222022-12-22T02:33:41ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242011-03-011152111212510.5194/acp-11-2111-2011Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-IIJ. F. Barlow0T. M. Dunbar1E. G. Nemitz2C. R. Wood3M. W. Gallagher4F. Davies5E. O'Connor6R. M. Harrison7Department of Meteorology, University of Reading, P.O. Box 243, Reading, RG6 6BB, UKDepartment of Meteorology, University of Reading, P.O. Box 243, Reading, RG6 6BB, UKCentre for Ecology and Hydrology (Edinburgh), Bush Estate, Penicuik, EH26 0QB, UKDepartment of Meteorology, University of Reading, P.O. Box 243, Reading, RG6 6BB, UKSchool of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UKRoom 315 Peel Building, University of Salford, The Crescent, Greater Manchester, M5 4WT, UKDepartment of Meteorology, University of Reading, P.O. Box 243, Reading, RG6 6BB, UKSchool of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UKUrban 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 850 m 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 physico-chemical 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.http://www.atmos-chem-phys.net/11/2111/2011/acp-11-2111-2011.pdf |
| spellingShingle | J. F. Barlow T. M. Dunbar E. G. Nemitz C. R. Wood M. W. Gallagher F. Davies E. O'Connor R. M. Harrison Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II Atmospheric Chemistry and Physics |
| title | Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II |
| title_full | Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II |
| title_fullStr | Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II |
| title_full_unstemmed | Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II |
| title_short | Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II |
| title_sort | boundary layer dynamics over london uk as observed using doppler lidar during repartee ii |
| url | http://www.atmos-chem-phys.net/11/2111/2011/acp-11-2111-2011.pdf |
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