This work presents the use of two elastic lidar systems to assess the horizontal variation of the PBL height (PBLH) and aerosol layer aloft in the São Paulo Megacity. These two lidars performed simultaneous measurements 10.7 km apart in a highly urbanized and relatively flat area of São Paulo for two winter months of 2019. The results showed that the PBLH differences display diurnal variation that depends on the PBL during daytime growth phases. Cloud and sea breeze effects control most of PBLH variation. In the absence of cloud and sea breeze, the maximum difference (~300 m) occurs in the rapid development stage and is due to topographic effects. When the PBL approaches its maximum daily value, it tends to level off with respect to the topography. In addition, it was presented a method that combines elastic lidar (to detect an aerosol layer) and satellite data (to classify such a layer from Aerosol Optical Depth (AOD) and Aerosol Index (AI) information) for the detection of biomass burning events. This methodology demonstrated that the variations caused by Biomass Burning in AOD and AI enable both the detection of aerosol plumes originating from biomass burning and the identification of their origin.

This study evaluates nine Planetary Boundary Layer (PBL) turbulence parameterization schemes from the Weather Research and Forecasting (WRF) mesoscale meteorological model, comparing hourly values of meteorological variables observed and simulated at the surface of the Metropolitan Region of São Paulo (MRSP). The numerical results were objectively compared with high-quality observations carried out on three micrometeorological platforms representing typical urban, suburban, and rural land use areas of the MRSP, during the 2013 summer and winter field campaigns as part of the MCITY BRAZIL project. The main objective is to identify which PBL scheme best represents the diurnal evolution of conventional meteorological variables (temperature, relative and specific humidity, wind speed, and direction) and unconventional (sensible and latent heat fluxes, net radiation, and incoming downward solar radiation) on the surface. During the summer field campaign and over the suburban area of the MRSP, most PBL scheme simulations exhibited a cold and dry bias and overestimated wind speed. They also overestimated sensible heat flux, with high agreement index and correlation values. In general, the PBL scheme simulations performed well for latent heat flux, displaying low mean bias error and root square mean error values. Both incoming downward solar radiation and net radiation were also accurately simulated by most of them. The comparison of the nine PBL schemes indicated the local Mellor-Yamada-Janjic (MYJ) scheme performed best during the summer period, particularly for conventional meteorological variables for the land use suburban in the MRSP. During the winter field campaign, simulation outcomes varied significantly based on the site’s land use and the meteorological variable analyzed. The MYJ, Bougeault-Lacarrère (BouLac), and Mellor-Yamada Nakanishi-Niino (MYNN) schemes effectively simulated temperature and humidity, especially in the urban land use area. The MYNN scheme also simulated net radiation accurately. There was a tendency to overestimate sensible and latent heat fluxes, except for the rural land use area where they were consistently underestimated. However, the rural area exhibited superior correlations compared to the urban area. Overall, the MYJ scheme was deemed the most suitable for representing the convectional and nonconventional meteorological variables on the surface in all urban, suburban, and rural land use areas of the MRSP.

Main properties of the Low-Level Jet (LLJ) in the metropolitan region of São Paulo (MRSP) are numerically simulated with the WRF (Weather Research Forecasting) model for two 10-day field campaigns of the MCITY BRAZIL Project, carried out in February 19-28 (Summer) and August 6-15 (winter) 2013. The WRF model was able to simulate 66.6% of the observed LLJ events, displaying a high degree of agreement with the observed main properties. These modeling results confirmed that the presence of an Upper Tropospheric Cyclonic Vortex northeast MRSP during summer and South Atlantic Subtropical High circulation in the MRSP during winter favor the LLJ formation. On average, the simulated LLJ is 2.9 m s-1 more intense in the rural area and 189 m higher in the urban area. The direction of the LLJ does not vary much between the urban and rural areas. These differences can be attributed to the urban- rural contrast in the roughness and thermal properties at the surface, which together influence the intensity of turbulence in the urban boundary layer. The simulations indicated that LLJ is part of a shallow flow reminiscent of the daytime sea-breeze circulation produced by shallow baroclinicity associated by the daytime land-ocean thermal contrast. The WRF-model simulation indicates that the LLJ observed in the MRSP spreads westward for more than 300 km over the interior of the State of São Paulo, becoming more intense. The behavior of the rural LLJ can be explained in terms of the mechanical blocking effect produced by the Serra de Cantareira high hills to the easterly flow from ocean caused by a combination of sea breeze and large-scale circulations in the MRSP.