EGU21-15472, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-15472
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Distributed urban drag parameterization in the sub-kilometre scale London Model

Birgit Sützl1, Gabriel Rooney2, Anke Finnenkoetter2, Sylvia Bohnenstengel3, Sue Grimmond4, and Maarten van Reeuwijk1
Birgit Sützl et al.
  • 1Imperial College London, Department of Civil and Environmental Engineering, London, United Kingdom of Great Britain – England, Scotland, Wales (b.sutzl@imperial.ac.uk)
  • 2Met Office, Exeter, United Kingdom of Great Britain – England, Scotland, Wales
  • 3MetOffice@Reading, Reading, United Kingdom of Great Britain – England, Scotland, Wales
  • 4University of Reading, United Kingdom of Great Britain – England, Scotland, Wales

Urban environments in numerical weather prediction models are currently parameterised as part of the atmosphere-surface exchange at ground-level. The vertical structure of buildings is represented by the average height, which does not account for heterogeneous building forms at the subgrid-level. The use of city-scale models with sub-kilometre resolutions and growing number of high-rise buildings in cities call for a better vertical representation of urban environments.

We present the use of a newly developed, height-distributed urban drag parameterization with the London Model, a high-resolution version of the Met Office Unified Model over Greater London and surroundings at approximately 333 m resolution. The distributed drag parameterization requires vertical morphology profiles in form of height-distributed frontal area functions, which capture the full extent and variability of building-heights. These morphology profiles were calculated for Greater London and parameterised by an exponential distribution with the ratio of maximum to mean building-height as parameter.

A case study with the high-resolution London Model and the new drag parameterization appears to capture more realistic features of the urban boundary layer compared to the standard parameterization. The simulation showed increased horizontal spatial variability in total surface stress, identifying a broad range of morphology features (densely built-up areas, high-rise building clusters, parks and the river). Vertical effects include heterogeneous wind profiles, extended building wakes, and indicate the formation of internal boundary layers. This study demonstrates the potential of height-distributed urban parameterizations to improve urban weather forecasting, albeit research into distribution of heat- and moisture-exchange is necessary for a fully distributed parameterization of urban areas.

How to cite: Sützl, B., Rooney, G., Finnenkoetter, A., Bohnenstengel, S., Grimmond, S., and van Reeuwijk, M.: Distributed urban drag parameterization in the sub-kilometre scale London Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15472, https://doi.org/10.5194/egusphere-egu21-15472, 2021.

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