Overview and First Results of the Montreal Urban Snow Experiment 2005

• Published in: Journal of applied meteorology and climatology Vol. 47; no. 1; pp. 59 - 75
• Main Authors: Lemonsu, A., Bélair, S., Mailhot, J., Benjamin, M., Chagnon, F., Morneau, G., Harvey, B., Voogt, J., Jean, M.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01-01-2008
• Subjects: Air temperature; Alleys; Atmospheric models; Computational fluid dynamics; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Earth Sciences; Earth, ocean, space; Energy balance; Exact sciences and technology; External geophysics; Fluctuations; Fluxes; Footprints; Influence; Latent heat; Meteorology; Metropolitan areas; Muses; Net radiation; Partitioning; Radiometers; Sciences of the Universe; Sensible heat; Sensors; Snow; Snow cover; Snowmelt; Studies; Surface temperature; Turbulence; Urban areas; Urban environments; Urban structures; Canada; Quebec; Eastern Canada; Montreal Quebec Canada; Canada, Quebec, Montreal; radiative transfer; Air ground interaction; energy balance; Measurement campaign; urban areas; North America; Urban atmosphere; Winter; Micrometeorology; Automatic measurement; Spring(season); Observation data; Continuous measurement; Snow cover; heat transfer
• ISSN: 1558-8424; 1558-8432
• DOI: 10.1175/2007jamc1639.1

Within the framework of a large urban meteorology program recently launched in Canada, the Montreal Urban Snow Experiment (MUSE) campaign has been conducted in order to document the thermoradiative exchanges in a densely built-up area of Montreal in late winter and spring conditions. The targeted period is of particular scientific interest because it covers the transition period from a mainly snow-covered urban environment to a mainly snow-free environment. The campaign is based on four weeks of observations from 17 March to 14 April 2005. It couples automatic and continuous measurements of radiation and turbulent fluxes, radiative surface temperatures, and air temperature and humidity with manual observations performed during intensive observation periods to supplement the surface temperature observations and to characterize the snow properties. The footprints of radiation and turbulent flux measurements are computed using the surface–sensor–sun urban model and the flux-source area model, respectively. The analysis of the radiometer footprint underscores the difficulty of correctly locating this type of instrument in urban environments, so that the sensor sees a representative combination of the urban and nonurban surfaces. Here, the alley contribution to the upward radiation tends to be overestimated to the detriment of the road contribution. The turbulent footprints cover homogeneous zones in terms of surface characteristics, whatever the wind direction. The initial analysis of the energy balance displays the predominance of the residual term (Q
Res=Q* −QH
−QE
) in comparison with the turbulent sensible (QH
) and latent (QE
) heat fluxes, since its daytime contribution exceeds 50% of the net radiation (Q*). The investigation of energy balances observed at the beginning and at the end of the experiment (i.e., with and without snow) also indicates that the snow plays a significant role in the flux partitioning and the daily pattern of fluxes. Without snow, the energy balance is characteristic of energy balances that have been already observed in densely built-up areas, notably because of the hysteresis observed forQ
ResandQH
in relation toQ* and because of the high contribution ofQ
Res, which includes the effect of heat storage inside the urban structures. With snow, the flux partitioning is modified by the snowmelt process leading to contributions of the residual term and latent heat flux, which are larger than in the case without snow to the detriment of the sensible heat flux.