Micrometeorological conditions observed during the experimental campaigns of the MCity Project

Abstract

The rapid growth of urban areas in tropical and subtropical regions has imposed new challenges to local governments of countries located at theses latitudes. Among all changes, the substitution of natural land use by built ones and the anthropogenic gas emissions in urban areas have modified the physical processes in the surface-atmosphere interface and the energy balance components, altering the local climate and contributing to the green gas emssions significantly. The MCity Brazil project is a recent scientific iniciative from Micrometeorology Groups of University of São Paulo (LabMICRO) and Federal University of Rio de Janeiro (LabMIM) to obtain a full picture of the Urban Boundary Layer. This project combines the monitoring of the budget energy components at the surface, radiosonde and remote sensing measurements in the two major urban areas of Brazil, São Paulo and Rio de Janeiro.\ud This work describes observational activiies of MCity Brazil project carried out In the Metropolitan Area of Rio de Janeiro in 2013. There a Micrometeorological Platform (PM IGEO) was set up at the top of Geosciences Institute 3-store building, located in the Federal University of Rio de Janeiro campus at the Fundão Island in February 2013. In this plataform hourly values of energy balance components (Sensible and latent energy fluxes, net radiation and soil heat flux) and carbon dioxide turbulent flux were estimated at 22 m above using a sonic anomemeter and gas analyser in a 10m micrometeorological tower. During 10 days in March (summer) and 10 days in July (winter) of 2013 two intensive field campaigns were carried out where surface measurements were complemented with thermodynamic and dynamic profiels vertical profiles obtained by the realease of 160 radiosondes (every each 3 hours) at the Galeão Airport. During these two field campaings UBL height was simultaneous ly monitored with a LIDAR.\ud The landuse within circle of 1 km radius in the experimental site area show a suburban pattern, with 50 % of bulit area (University, residential and comercial buildings, 35 % vegetation and 15 % of water. in the neighborhood of the Baia de Guanabara.\ud In the Summer campaing, the maximum amplitude of the mean diurnal evolution for net radiation was 600 Wm-2 (March), about 200 Wm-2 higher than the observed during the Winter. The sensible and latent heat fluxes are equivalent in both periods. The Bowen ratio is approximately equal to 1 under diurnal conditions. During the night, the latent heat flux is small and positive, probably because of the high water vapor concentration in the experimental site. The behavior of the carbon dioxide turbulent flux presents a similar pattern to the observed in suburban areas, with negative values between 9 and 15 local time. In the rush hour traffic (early morning and later afternoon), the carbon dioxide turbulent flux shows a slight increase and becomes positive. The UBL height reached 1500 m in the Summer and about 1200 m in the Winter. During the nigthtime the surface inverstion layer reached as much as 300 m. The low level jet of 10 m/s and from NE direction was systematicaly observed during the nighttime.FAPESPFAPERJCNP