Observational Investigation of the Low‐Level Jets in the Metropolitan Region of São Paulo, Brazil

Abstract

The main features of low‐level jet (LLJ) in the metropolitan region of São Paulo (MRSP), Brazil, are assessed using rawinsondes carried out: (a) every 3‐hr during 10‐consecutive days in summer and winter field campaigns of the MCITY BRAZIL Project in 2013, (b) at 0900 and 2100 local time, from September 2009 to August 2013. These observations indicate that the LLJ is a typical feature of the MRSP, observed in 85% of the 20 days of the field‐campaigns and 77.6% of the 1,446 days of regular rawinsonde period. The fine temporal and spatial resolution soundings indicate that most of the LLJs occur during nighttime and early in the morning, with mean intensity of 8.5 ± 0.3 m s−1, height of 539 ± 26 m, and mostly (52.5%) from east and north. The coarse resolution soundings indicate the LLJ display a seasonal variation with maximum intensity in October (8.6 ± 0.3 m s−1) and a minimum in February (7.1 ± 0.2 m s−1), a maximum height in March (703 ± 151 m) and a minimum in June (577 ± 151 m). During MCITY campaigns about 76.4% of LLJ events show inertial oscillation and 35.3% of them are combined with sea breeze. Only 17.6% of LLJ events are associated with cold fronts and post‐frontal high pressure system. The urban heat island intensity, surface inversion layer strength, particulate matter 2.5 and carbon monoxide concentrations are negatively correlated with the LLJ intensity, suggesting the jet‐induced turbulent mixing may contribute to reduce them.

Low-level jets and their implications on air pollution: A review

“…Low-level jets (LLJs) are a common phenomenon in the atmospheric boundary layer (ABL) and have been widely observed worldwide, including in North America (Smith et al, 2019), South America (Sánchez et al, 2022), East Asia (Wei et al, 2014;Miao et al, 2018), Europe (Tuononen et al, 2017), and Africa (King et al, 2021). However, there is no universal consensus on the definition of the LLJs (Fiedler et al, 2013).…”

Caracterização observacional da turbulência na superfície da Região Metropolitana de São Paulo

“…Uma propriedade típica da RMSP são Jatos de Baixos Níveis (JBN), que ocorrem comumente à noite e no início da manhã, frequentemente de N e E, com intensidades médias variando de 7,1 m s −1 em fevereiro a 8,6 m s −1 em outubro e alturas de 577 m em junho a 703 em março (Sánchez et al, 2022) Este método de detecção e remoção de picos espúrios é baseado em Vickers e Mahrt (1997). A remoção de picos foi aplicada aos dados brutos de u, v, w, T, ρH2O e ρCO2.…”