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Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project

The study of the boundary layer can be most difficult when it is in transition and forced by a complex surface, such as an urban area. Here, a novel combination of ground-based remote sensing and in situ instrumentation in central London, UK, is deployed, aiming to capture the full evolution of the...

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Autores principales: Halios, Christos H., Barlow, Janet F.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Springer Netherlands 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6952043/
https://www.ncbi.nlm.nih.gov/pubmed/31983757
http://dx.doi.org/10.1007/s10546-017-0300-z
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author Halios, Christos H.
Barlow, Janet F.
author_facet Halios, Christos H.
Barlow, Janet F.
author_sort Halios, Christos H.
collection PubMed
description The study of the boundary layer can be most difficult when it is in transition and forced by a complex surface, such as an urban area. Here, a novel combination of ground-based remote sensing and in situ instrumentation in central London, UK, is deployed, aiming to capture the full evolution of the urban boundary layer (UBL) from night-time until the fully-developed convective phase. In contrast with the night-time stable boundary layer observed over rural areas, the night-time UBL is weakly convective. Therefore, a new approach for the detection of the morning-transition and rapid-growth phases is introduced, based on the sharp, quasi-linear increase of the mixing height. The urban morning-transition phase varied in duration between 0.5 and 4 h and the growth rate of the mixing layer during the rapid-growth phase had a strong positive relationship with the convective velocity scale, and a weaker, negative relationship with wind speed. Wind shear was found to be higher during the night-time and morning-transition phases than the rapid-growth phase and the shear production of turbulent kinetic energy near the mixing-layer top was around six times larger than surface shear production in summer, and around 1.5 times larger in winter. In summer under low winds, low-level jets dominated the UBL, and shear production was greater than buoyant production during the night-time and the morning-transition phase near the mixing-layer top. Within the rapid-growth phase, buoyant production dominated at the surface, but shear production dominated in the upper half of the UBL. These results imply that regional flows such as low-level jets play an important role alongside surface forcing in determining UBL structure and growth.
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spelling pubmed-69520432020-01-23 Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project Halios, Christos H. Barlow, Janet F. Boundary Layer Meteorol Research Article The study of the boundary layer can be most difficult when it is in transition and forced by a complex surface, such as an urban area. Here, a novel combination of ground-based remote sensing and in situ instrumentation in central London, UK, is deployed, aiming to capture the full evolution of the urban boundary layer (UBL) from night-time until the fully-developed convective phase. In contrast with the night-time stable boundary layer observed over rural areas, the night-time UBL is weakly convective. Therefore, a new approach for the detection of the morning-transition and rapid-growth phases is introduced, based on the sharp, quasi-linear increase of the mixing height. The urban morning-transition phase varied in duration between 0.5 and 4 h and the growth rate of the mixing layer during the rapid-growth phase had a strong positive relationship with the convective velocity scale, and a weaker, negative relationship with wind speed. Wind shear was found to be higher during the night-time and morning-transition phases than the rapid-growth phase and the shear production of turbulent kinetic energy near the mixing-layer top was around six times larger than surface shear production in summer, and around 1.5 times larger in winter. In summer under low winds, low-level jets dominated the UBL, and shear production was greater than buoyant production during the night-time and the morning-transition phase near the mixing-layer top. Within the rapid-growth phase, buoyant production dominated at the surface, but shear production dominated in the upper half of the UBL. These results imply that regional flows such as low-level jets play an important role alongside surface forcing in determining UBL structure and growth. Springer Netherlands 2017-10-29 2018 /pmc/articles/PMC6952043/ /pubmed/31983757 http://dx.doi.org/10.1007/s10546-017-0300-z Text en © The Author(s) 2017 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
spellingShingle Research Article
Halios, Christos H.
Barlow, Janet F.
Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project
title Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project
title_full Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project
title_fullStr Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project
title_full_unstemmed Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project
title_short Observations of the Morning Development of the Urban Boundary Layer Over London, UK, Taken During the ACTUAL Project
title_sort observations of the morning development of the urban boundary layer over london, uk, taken during the actual project
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6952043/
https://www.ncbi.nlm.nih.gov/pubmed/31983757
http://dx.doi.org/10.1007/s10546-017-0300-z
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