Details
| Original language | English |
|---|---|
| Pages (from-to) | 191-217 |
| Number of pages | 27 |
| Journal | Boundary-Layer Meteorology |
| Volume | 157 |
| Issue number | 2 |
| Early online date | 18 Jul 2015 |
| Publication status | Published - 29 Nov 2015 |
Abstract
A footprint algorithm, based on a Lagrangian stochastic (LS) model embedded into a parallelized large-eddy simulation (LES) model, is used for the evaluation of flux and concentration footprints of passive scalars in flow in and above an urban-like canopy layer of a neutrally stratified 440 m deep boundary layer. The urban-like canopy layer is realized by an aligned array of cuboids whose height H is 40 m. The canopy flow involves strong small-scale inhomogeneities although it is homogeneous at the large scale. The source height is 1m (0.025H) above the ground in the street canyons, roughly mimicking traffic emissions. Footprints are evaluated for four heights from 0.25H to 2.5H, and for up to eight different horizontal sensor positions per measurement height, comprising sensor positions inside as well as outside of the street canyon that extend perpendicular to the mean wind direction. The LES-LS footprints are compared with footprints estimated by a conventional model (Kormann and Meixner, in Boundary-Layer Meteorol 99:207–224, 2001). It becomes evident that the local heterogeneity of the flow has a considerable impact on flux and concentration footprints. As expected, footprints for measurements within and right above the canopy layer show complex and completely different footprint shapes compared to the ellipsoidal shape obtained from conventional footprint models that assume horizontal homogeneity of the turbulent flow as well as the sources of passive scalars. Our results show the importance of street-canyon flow and turbulence for the vertical mixing of scalar concentration.
Keywords
- Concentration footprint, Flux footprint, Lagrangian stochastic model, Large-eddy simulation, Urban canopy
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Atmospheric Science
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In: Boundary-Layer Meteorology, Vol. 157, No. 2, 29.11.2015, p. 191-217.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Footprint Evaluation for Flux and Concentration Measurements for an Urban-Like Canopy with Coupled Lagrangian Stochastic and Large-Eddy Simulation Models
AU - Hellsten, Antti
AU - Luukkonen, Sofia M.
AU - Steinfeld, Gerald
AU - Kanani-Sühring, Farah
AU - Markkanen, Tiina
AU - Järvi, Leena
AU - Lento, Juha
AU - Vesala, Timo
AU - Raasch, Siegfried
PY - 2015/11/29
Y1 - 2015/11/29
N2 - A footprint algorithm, based on a Lagrangian stochastic (LS) model embedded into a parallelized large-eddy simulation (LES) model, is used for the evaluation of flux and concentration footprints of passive scalars in flow in and above an urban-like canopy layer of a neutrally stratified 440 m deep boundary layer. The urban-like canopy layer is realized by an aligned array of cuboids whose height H is 40 m. The canopy flow involves strong small-scale inhomogeneities although it is homogeneous at the large scale. The source height is 1m (0.025H) above the ground in the street canyons, roughly mimicking traffic emissions. Footprints are evaluated for four heights from 0.25H to 2.5H, and for up to eight different horizontal sensor positions per measurement height, comprising sensor positions inside as well as outside of the street canyon that extend perpendicular to the mean wind direction. The LES-LS footprints are compared with footprints estimated by a conventional model (Kormann and Meixner, in Boundary-Layer Meteorol 99:207–224, 2001). It becomes evident that the local heterogeneity of the flow has a considerable impact on flux and concentration footprints. As expected, footprints for measurements within and right above the canopy layer show complex and completely different footprint shapes compared to the ellipsoidal shape obtained from conventional footprint models that assume horizontal homogeneity of the turbulent flow as well as the sources of passive scalars. Our results show the importance of street-canyon flow and turbulence for the vertical mixing of scalar concentration.
AB - A footprint algorithm, based on a Lagrangian stochastic (LS) model embedded into a parallelized large-eddy simulation (LES) model, is used for the evaluation of flux and concentration footprints of passive scalars in flow in and above an urban-like canopy layer of a neutrally stratified 440 m deep boundary layer. The urban-like canopy layer is realized by an aligned array of cuboids whose height H is 40 m. The canopy flow involves strong small-scale inhomogeneities although it is homogeneous at the large scale. The source height is 1m (0.025H) above the ground in the street canyons, roughly mimicking traffic emissions. Footprints are evaluated for four heights from 0.25H to 2.5H, and for up to eight different horizontal sensor positions per measurement height, comprising sensor positions inside as well as outside of the street canyon that extend perpendicular to the mean wind direction. The LES-LS footprints are compared with footprints estimated by a conventional model (Kormann and Meixner, in Boundary-Layer Meteorol 99:207–224, 2001). It becomes evident that the local heterogeneity of the flow has a considerable impact on flux and concentration footprints. As expected, footprints for measurements within and right above the canopy layer show complex and completely different footprint shapes compared to the ellipsoidal shape obtained from conventional footprint models that assume horizontal homogeneity of the turbulent flow as well as the sources of passive scalars. Our results show the importance of street-canyon flow and turbulence for the vertical mixing of scalar concentration.
KW - Concentration footprint
KW - Flux footprint
KW - Lagrangian stochastic model
KW - Large-eddy simulation
KW - Urban canopy
UR - http://www.scopus.com/inward/record.url?scp=84942500219&partnerID=8YFLogxK
U2 - 10.1007/s10546-015-0062-4
DO - 10.1007/s10546-015-0062-4
M3 - Article
AN - SCOPUS:84942500219
VL - 157
SP - 191
EP - 217
JO - Boundary-Layer Meteorology
JF - Boundary-Layer Meteorology
SN - 0006-8314
IS - 2
ER -