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bubble
tracer experiments During
the BUBBLE IOP in Summer 2002 a series of SF 6
tracer experiments were carried over the urban surface of the City of
Basel by Risø National Laboratory,
ETH Zurich, the
Bulgarian National Insitute of Meteorology and Hydrology and the University
of Basel. The tracer experiments were performed
with near roof-level sources. Samplers were distributed close to
roof level in a down-wind area stretching out to about 2 km.
The tracer
experiments were carried out in the city part called "Kleinbasel"
where most of the near-surface measurements were focused during the IOP. The main urban
station "Basel-Sperrstrasse" was
centered in the tracer area (Sampling point 3 on the map). The city structure
in this area is fairly homogeneous with a mean building height of approx. 15 m and a
mean plan area density of 40%. For this city part a digital
3d building model is available. During the
IOP four successful tracer experiments were carried out on 26 June, 4, 7 and 8
July. All experiments lasted 3 hours with 6 integral
30 min samples at 12 different locations. The
tracer units (samplers) were typically positioned 1.5 metres above the
roofs. At the micrometeorological tower "Basel-Sperrstrasse"
a tracer concentration profile was made within the street canyon. At
"Basel-Messe" (Site 9 on the map)
Tethered baloon profiles were measured during Experiments 1, 4 and 5. It was the aim to perform the tracer
experiments under a thermally driven wind system called "Clarawind"
that in the afternoon on
cloud free summer days develops over Basel and is characterised by a
persistent north-westerly direction of the wind. During experiment
1,4 and 5 (26 June, 7 and 8 July) the Clarawind developed. Therefore
the release point "R1"
in the North of the area was chosen. The release
took place 3.8 metres above a roof of a parking deck at "Basel-Horburg".
Experiment
3 (July 4) was carried out under mechanically driven west winds.
The tracer was released form a mobile hydraulic platform (R2 on the map). The release was
21 metres above the street.
Further, in the wind
tunnel the tracer dispersion experiments will be remodeled. A comprehensive data set of
tracer gas concentrations at various locations in the wind tunnel, including the full scale
sampling locations, is expected to provide further insights in the turbulent
dispersion during these experiments.
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The
standard release point in the North of the Area ("R1", at station "Basel-Horburg")
on the roof of a parking building. |
Release
form the basket of a mobile hydraulic platform at the release point "R2" during
experiment 3 (4.7.2002). |
The
samplers mounted at the micrometeorological tower at "Basel-Sperrstrasse"
at 3 different heights from z/h=1.30, 0.75 and 0.23 down into the canyon. |
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Standard
sampler at site 08. Most of the samplers are attached on tripods
1.5m above rooftop. |
Each
sampler sucks air through a metal tube into sampling bags that are
inside the white basket. After 30 min the bags are changed. |
Panorama views
from selected sampler sites
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360° Panorama
from the roof at the release point R1 ("Basel-Horburg"). |
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180° Panorama
from the roof at sampler site 02. |
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360° Panorama
from the tower at sampler site 3 ("Basel-Sperrstrasse"). |
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360° Panorama
from the roof at sampler site 6. |
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180° Panorama
from the roof at sampler site 8. |
Photos by
Andreas Christen, Jan Eitel, Eva van Gorsel, Irene Lehner, Mathias Müller
and Gergely Rigo,
University of Basel. |
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Report
A detailed
experiment experiment report is currently in work. Contact Mathias
Rotach for additional information.
Sven-Erik Gryning, Ekaterina Batchvarova, Mathias W. Rotach, Andreas
Christen and Roland Vogt : "Roof-level SF6 tracer experiments in the
city of Basel" |
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Maps
of the Experiment Layout

Map
of all sampler locations during experiments 1 to 5
Map of tracer experiment 1
(June 26)
Map of tracer experiment 3
(July 4)
Map of tracer experiment 4
(July 7)
Map of tracer experiment 5
(July 8)
Digital
3d building model
Important notice:
These digital maps (i.e. the base map) may not be reproduced or published
without permission by the Grundbuch-
und Vermessungsamt Basel-Stadt. Base maps: © Copyright GVA BS,
25.10.2002.
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Meteorological
Conditions during the Experiment Days

Windfields
over the city
June
26 (Animation, 4.3 MB)
July
4
(Animation, 4.3 MB)
July
7
(Animation, 4.3 MB)
July
8
(Animation, 4.3 MB)
(Key to station numbers)
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TV-Report
on BUBBLE-tracer experiments (22.08.2002, © SFDRS "MTW",
in german, 8min, real audio needed)
Wind
tunnel modeling of the tracer experiments.
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