Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft IMK-IFU, Stefan Emeis...

Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

IMK-IFU, Stefan Emeis [email protected]

Vertical profiles of the variance of the vertical wind component and

turbulence intensitiesfrom 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

[email protected]



Large SODARof IMK-IFU(METEK DSDR3x7)

frequency: 1500 Hzrange: 1300 mresolution: 20 mlowestrange gate: ca. 60 m

size of instrument:

height: 4 mwidth: 1,50 mlength: 10 mweight: 8 t



Measurements from an urban boundary-layer

Hannover, Germanyoverall roughness length: about 1 mlarge SODAR on industrial grounds near a railway stationtypical range: 500 to 700 mtemporal resolution: 30 min

30 m



Measurements from an urban boundary-layer

Budapest (Hungary) on the western side hills,100 – 200 m above the Danube river, in thewestern outskirts of the town

large SODAR

typical range: 500 to 700 mtemporal resolution: 30 min



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 mtemporal resolution: 30 min

nearly flat terrain in Northern Bavaria

MiniSODAR

100 to 150 m10 min



mean wind speed



Monthly mean vertical profiles of wind speed



Monthly mean vertical profilesof wind speed



Monthly mean diurnal variation of wind speed



Monthly mean diurnal variationof wind speed



sigma w



Monthly mean vertical profiles of sigma w



Monthly mean diurnal variation of sigma w



Monthly mean diurnal variationof sigma w



turbulence intensity



Monthly mean diurnal variation of turbulence intensity



Monthly mean vertical profiles of turbulence intensity



Monthly mean vertical profilesof turbulenceintensity



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.



0

100

200

300

400

500

Vertical structure of the UBL over Hannover

Ekman-layer

Prandtl-layer

Canopy-layer

Wake-layerurban roughness-layer

m



measurements over an airport



June/July 2005

The sodar wassituated at no. 6

Paris airportCh. de Gaulle



vertical profilesof wind speed u

CDG

June/July 2005

S2: influenced by the airport (lower wind speed over rough surface)

S4: rural profiles (higher wind speed over smooth surface)

S2S4



vertical profilesof w

(variance of vertical wind speed, a measure for turbulence)

S2: influenced by the airport (higher turbulence over rough surface)

S4: rural profiles (lower turbulence over smooth surface)

S4S2



vertical profilesof turbulenceintensity (u / w)

CDG

S2: influenced by the airport (higher turbulence over rough surface)

S4: rural profiles (lower turbulence over smooth surface)

S4 S2



mixing-layer height



Algorithms todetect MLHfrom SODAR data

criterion 1:upper edge

of highturbulence

criterion 2:surface andliftedinversions

MLH = Min (C1, C2)

acoustic backscatter intensity acoustic backscatter intensity

height height



Algorithms todetect MLHfrom Ceilometer-Daten

criterion

minimal vertical gradientof backscatterintensity (the mostnegative gradient)

optical backscatter intensity vertical gradient ofoptical backscatter intensity

height height



comparison of both algorithms

acoustic backscatter intensity

optical backscatter intensity

vertical gradient ofoptical backscatter intensity

heightheightheight



optical backscatter intensity

acoustic backscatter intensity

vertical gradient of optical backscatter intensity



Simultaneous operation SODAR-Ceilometer: examples for summer days

CBLCBL

CBLCBL

SBLSBL

SBLSBL

RLRL

RLRL

RL

RL RL

RL

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, 377-385,



nocturnal inver-sions dominate

CBL tops dominate days with strong winds withoutdiurnal variations

frequency distribution of MLHHannover, Germany, February 2002


IMK-IFU, Stefan Emeis [email protected]@imk.fzk.de

Monthly mean diurnal courses of mixing-layer heightHannover, Germany 2002/03

Emeis, S., M. Türk, 2004: Frequency distributions of the mixing height over an urban area from SODAR data. Meteorol. Z., 13, 361-367.



attempt to derive turbulence exchange coefficientsfrom sodar data



The efficiency of vertical transport by turbulent motion isdescribed by the turbulent viscosity t of the flow.

In numerical flow models this turbulent viscosity is calledturbulent 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)

zu

wu

''

zu

za

w

)(

2



Available papers1) wind profiles

Emeis, S., 2001: Vertical variation of frequency distributions of wind speed in and above the surface layer observed by sodar. Meteorol. Z., 10, 141-149. DOI: 10.1127/0941-2948/2001/0010-0141

Emeis, S., 2004: Vertical wind profiles over an urban area. Meteorol. Z., 13, 353-359. DOI: 10.1127/0941-2948/2004/0013-0353

2) mixing layer height

Emeis, S., M. Türk, 2004: Frequency distributions of the mixing height over an urban area from SODAR data. Meteorol. Z., 13, 361-367.DOI: 10.1127/0941-2948/2004/0013-0361

Emeis, S. and K. Schäfer, 2006: Remote sensing methods to investigate boundary-layer structures relevant to air pollution in cities. Bound-Lay. Meteorol., 121, 377-385. DOI: 10.1007/s10546-006-9068-2

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, 647-658. DOI: 10.1127/0941-2948/2006/0164

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: 10.1007/s10546-007-9170-0

3) parameterization of turbulent exchange coefficients

Emeis, S., 2004: Parameterization of turbulent viscosity over orography. Meteorol. Z., 13, 33-38. DOI: 10.1127/0941-2948/2004/0013-0033

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