Funded by CRTI Project # 02-0093RD

The current meteorological models can be run at high resolutions reaching a few hundreds of meters. Since the cities cover several grid points of the integration domain at such a scale, the impact of the urban radiative, energetic and dynamical processes must be taken into account in the computation of surface exchanges. Thus, the Meteorological Research Branch (MRB) of the Meteorological Service of Canada launched a large program in order to improve the representation of cities in the Canadian meteorological models including four main components:

The implementation of a new urban parameterization requires to provide land-use classifications including specific urban covers in order to describe the spatial distribution and the diversity of urban areas. A methodology based on the joint analysis of satellite imagery (Landsat-7, Aster) and digital elevation models (SRTM-DEM, NED, CDED1) has been developed to produce 60-m resolution urban-cover classifications in a semi-automatic way for the main North American cities.

The anthropogenic heat and humidity releases can be of major importance, more specifically during wintertime. The current version of TEB includes constant forcing of sensible and latent fluxes due to traffic and industrial activities. A methodology is under development to quantify in a more realistic way the anthropogenic sources asso-ciated to North American cities. Based on Sailor and Lu (2004), this method enables the estimation of the diurnal and seasonal cycles of releases due to metabolisms, traffic, and energy consumption.

60-m Montreal land-cover classification produced from the joint analysis of Landsat-7 and SRTM-DEM minus CDED1

High buildings

Mid-high buildings

Low buildings

Very low buildings

Sparse buildings

Industrial areas

Roads and parkings

Road mix

Dense residential

Mid-density residential

Low-density residential

Mix of nature and built

Deciduous broadleaf trees

Short grass and forbs

Long grass

Crops

Mixed wood forest

Water

Excluded

Hourly fraction profiles for vehicular traffic in the United States (Sailor and Lu, 2004)

Databases

The Montreal Urban Snow Experiment (MUSE) 2005 aimed to document the evolution of surface characteristics and energy budgets in a dense urban area during the winter-spring transition: Evolution of snow cover from ~100% to 0% in an urban environment Impact of snow on surface energy and water budgets Quantification of anthropogenic fluxes in late winter and spring conditions Evaluation of TEB in reproducing the surface characteristics and budgets in these conditions

From March 17th to April 14th, continuous measurements were conducted to document:

- Incoming and outgoing radiation- Turbulent fluxes by eddy-correlation- Radiative surface temperatures

by thermal camera and infrared thermometers - Air temperature and humidity inside street and alley

Observations and Measurements

Dense urban district of Montreal instrumented

during MUSE

During four intensive observational periods, manual measurements complemented the database:

- Snow properties (depth, density albedo, surface temperature)- Radiative surface temperatures on various sites and urban

elements- Photographs of street condition

JD77

JD79

JD81

JD83

JD85

Short-wave radiation budget and manual albedo measurements Thermal camera imagery – JD78

Roof with snow

Roof without snow

StreetSidewalk

Modelling

- Radiative trapping and shadow effect- Heat storage- Mean wind, temperature and humidity inside the street- Water and snow on roofs and roads

- Mean urban canyon composed of 1 roof, 2 identical walls, 1 road- Isotropy of the street orientations- No crossing streets

The Town Energy Balance (TEB) (Masson, 2000) has been recently implemented in the physics package of the Canadian meteorological models GEM and MC2.

Urban canopy model, dedicated to built-up covers, parameterizing water and energy exchanges between canopy and atmosphere Three-dimensional geometry of the urban canopy for:

Idealized urban geometry i.e.

Representation of the principal TEB scheme variables

QH topQE top

QH trafficQE traffic

QH industryQE industry

QH roofQE roof

Water Snow

Ti bld

Troof1Troof2Troof3

Twall1Twall2Twall3

Troad1Troad2Troad3

SnowWater

QH roadQE road

Tcanyonqcanyon

QH wallQE wall

Rroof

Rwall

Rroof Snow

Rroad Rroad Snow

Rtop

Atmospheric level

Input dataPrognostic variablesDiagnostic variablesUa , Ta , qa

Meso-γ and offline

Regional NWP MUSE II

MUSETEB urban scheme

3d-turbulence

Surface fields

Anthropogenic heat sources

Modelling Databases Transfer Observations

A. Lemonsu1, S. Bélair1, J. Mailhot1, N. Benbouta2, M. Benjamin3, F. Chagnon2 , M. Jean2 , A. Leroux2 , G. Morneau3, C. Pelletier1, L. Tong4, S. Trudel2

Environment Canada; 1MSC, Meteorological Research Branch; 2MSC, Environmental Emergency Response Division; 3Quebec Region; 4MSC, Development Branch

RMetS Conference 2005Poster 940

Environment Canada

Environnement Canada

For high resolution modelling application (less than 1 km), the Reynolds time-averaged form of the compressible Navier-Stokes equations and the generalized 3D budget TKE equation have been introduced in MC2. This implementation will also be done in GEM soon.

Extensive evaluation of the “urbanized” version of the model against observations is currently performed within the framework of the Joint Urban 2003 experiment (Oklahoma City, OKC, US). The first results are encouraging giving the fact that TEB has never been tested over North American city centers.

2-m air temperature modelled by the 1-km offline version of GEM

including TEB

299

300

301

302

303

304

07 13 19 01 07Time (Hour LST)

ObservationsModel without TEBModel with TEB

20

25

30

35

40

45

Tem

pera

ture

(oC

)

Air temperature inside the streets observed during Joint Urban 2003 and modelled by the 200-m offline version

of GEM with and without TEB

July 17th 0000LST