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Vertical profiles of the variance of the vertical wind component and

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Presentation on theme: "Vertical profiles of the variance of the vertical wind component and"— Presentation transcript:

1 Vertical profiles of the variance of the vertical wind component and
turbulence intensities from sodar soundings in urban measurement campaigns Stefan Emeis Institute for Meteorology and Climate Research, Dept. Atmospheric Environmental Research (IMK-IFU) Forschungszentrum Karlsruhe GmbH Garmisch-Partenkirchen, Germany

2 Large SODAR of IMK-IFU (METEK DSDR3x7) frequency: Hz range: m resolution: m lowest range gate: ca. 60 m size of instrument: height: m width: ,50 m length: m weight: t

3 30 m Measurements from an urban boundary-layer Hannover, Germany
overall roughness length: about 1 m large SODAR on industrial grounds near a railway station typical range: 500 to 700 m temporal resolution: 30 min 30 m

4 Measurements from an urban boundary-layer
Budapest (Hungary) on the western side hills, 100 – 200 m above the Danube river, in the western outskirts of the town large SODAR typical range: 500 to 700 m temporal resolution: 30 min

5 Measurements from rural boundary-layers
flat terrain (Fürstenfeldbruck (FFB), alpine foreland) complex terrain (Black Forest, at a sattle point on a crest line) roughness length: FFB: a few cm, Black Forest about 1 m large SODAR typical range: 500 to 700 m temporal resolution: 30 min nearly flat terrain in Northern Bavaria MiniSODAR 100 to 150 m 10 min

6 mean wind speed

7 Monthly mean vertical profiles of wind speed

8 Monthly mean vertical profiles of wind speed

9 Monthly mean diurnal variation of wind speed

10

11 Monthly mean diurnal variation of wind speed

12 sigma w

13 Monthly mean vertical profiles of sigma w

14 Monthly mean diurnal variation of sigma w

15

16 Monthly mean diurnal variation of sigma w

17 turbulence intensity

18 Monthly mean diurnal variation of turbulence intensity

19 Monthly mean vertical profiles of turbulence intensity

20

21 Monthly mean vertical profiles of turbulence intensity

22 Conclusions for the urban boundary layer
The variances of the vertical velocity component are about 30% higher than over rural terrain. In the afternoon the variance is increasing considerably with height, in summer up to about 350 m above ground, in winter up to about 200 m. This feature is not found over rural terrain. In summer and autumn the variance is increasing with height even at night-time, which it does not over rural terrain. The turbulence intensity at night-time is double as high as over rural terrain. The daytime increase in turbulence intensity is larger than over rural terrain. This indicates a stronger heating of the urban surface. The turbulence intensity is highest at 60 m agl, at night-time it is up to 50% larger than the turbulence intensity at 210 m agl. The nocturnal decrease of the turbulence intensity with height is much stronger than over rural terrain. Also, we find that the wind speed at 60 m agl is nearly constant all the day, whereas over flat rural terrain it shows an increase around noon.

23 Vertical structure of the UBL over Hannover m
500 400 Ekman-layer 300 200 Prandtl-layer 100 Wake-layer urban roughness-layer Canopy-layer

24 measurements over an airport

25 Paris airport Ch. de Gaulle June/July 2005 The sodar was situated at no. 6

26 S2 S4 vertical profiles of wind speed u CDG June/July 2005
S2: influenced by the airport (lower wind speed over rough surface) S4: rural profiles (higher wind smooth surface) S2 S4

27 S4 S2 vertical profiles of sw (variance of vertical
wind speed, a measure for turbulence) S2: influenced by the airport (higher turbu- lence over rough surface) S4: rural profiles (lower turbu- smooth surface) S4 S2

28 S4 S2 vertical profiles of turbulence intensity (u / sw) CDG
S2: influenced by the airport (higher turbu- lence over rough surface) S4: rural profiles (lower turbu- smooth surface) S4 S2

29 mixing-layer height

30 Algorithms to detect MLH from SODAR data criterion 1: upper edge
height height Algorithms to detect MLH from SODAR data criterion 1: upper edge of high turbulence criterion 2: surface and lifted inversions MLH = Min (C1, C2) acoustic backscatter intensity acoustic backscatter intensity

31 from Ceilometer-Daten criterion minimal vertical gradient
height height Algorithms to detect MLH from Ceilometer-Daten criterion minimal vertical gradient of backscatter intensity (the most negative gradient) optical backscatter intensity vertical gradient of optical backscatter intensity

32 comparison of both algorithms height height height
acoustic backscatter intensity optical backscatter intensity vertical gradient of optical backscatter intensity

33 acoustic backscatter intensity
optical backscatter intensity vertical gradient of optical backscatter intensity

34 RL RL RL RL CBL CBL SBL SBL SBL SBL RL RL RL RL CBL CBL SBL SBL SBL
Simultaneous operation SODAR-Ceilometer: examples for summer days RL RL RL RL CBL CBL SBL SBL SBL SBL RL RL RL RL CBL CBL SBL SBL SBL SBL Emeis, S., K. Schäfer, 2006: Remote sensing methods to investigate boundary-layer structures relevant to air pollution in cities. Bound.-Lay Meteorol., 121, ,

35 frequency distribution of MLH
Hannover, Germany, February 2002 nocturnal inver- sions dominate days with strong winds without diurnal variations CBL tops dominate

36 Monthly mean diurnal courses of mixing-layer height
Hannover, Germany 2002/03 Emeis, S., M. Türk, 2004: Frequency distributions of the mixing height over an urban area from SODAR data. Meteorol. Z., 13,

37 attempt to derive turbulence exchange coefficients
from sodar data

38 The efficiency of vertical transport by turbulent motion is
described by the turbulent viscosity t of the flow. In numerical flow models this turbulent viscosity is called turbulent exchange coefficient. t = or approximated by sodar data  a(z) = 1.6 (0-200 m), 2.0 (200 – 600 m), 2.5 (600 – 1000 m)

39

40 Available papers wind profiles mixing layer height
Emeis, S., 2001: Vertical variation of frequency distributions of wind speed in and above the surface layer observed by sodar. Meteorol. Z., 10, DOI: / /2001/ Emeis, S., 2004: Vertical wind profiles over an urban area. Meteorol. Z., 13, DOI: / /2004/ mixing layer height Emeis, S., M. Türk, 2004: Frequency distributions of the mixing height over an urban area from SODAR data. Meteorol. Z., 13, DOI: / /2004/ Emeis, S. and K. Schäfer, 2006: Remote sensing methods to investigate boundary-layer structures relevant to air pollution in cities. Bound-Lay. Meteorol., 121, DOI: /s Schäfer, K., S. Emeis, H. Hoffmann, C. Jahn, 2006: Influence of mixing layer height upon air pollution in urban and sub-urban areas. Meteorol. Z., 15, DOI: / /2006/0164 Piringer, M., S. Joffre, A. Baklanov, A. Christen, M. Deserti, K. De Ridder, S. Emeis, P. Mestayer, M. Tombrou, D. Middleton, K. Baumann-Stanzer, A. Dandou, A. Karppinen, J. Burzynski, 2007: The surface energy balance and the mixing height in urban areas – activities and recommendations of COST-Action 715. Published online in Bound.-Lay. Meteorol. DOI: /s parameterization of turbulent exchange coefficients Emeis, S., 2004: Parameterization of turbulent viscosity over orography. Meteorol. Z., 13, DOI: / /2004/


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