Atmospheric thermodynamics and dynamics during convective, stratiform and nonprecipitating clouds over the metropolitan area of Rio de Janeiro – Brazil

Abstract

Physical mechanisms involved in the development and forecast of clouds and precipitation are both quite complex and dependent on the local atmospheric environment, especially when severe weather conditions are imminent. Research aimed at understanding the environmental mechanisms favorable to the different atmospheric scenarios can help operational weather forecasters to issue warnings. This paper provides qualitative and quantitative contributions from radiosondes, radar, and numerical simulations to evaluate the formation of convective, stratiform, and nonprecipitating clouds over the metropolitan area of Rio de Janeiro, Brazil. The convective available potential energy (CAPE) and lifted index (LI), showed higher values on convective days (CAPE = 2600 J.Kg^–1 and LI = –4 ºC), followed by nonprecipitating (CAPE = 1500 J.Kg^–1 and LI = –2 ºC) and stratiform cloud days (CAPE = 1400 J.Kg^–1 and LI = –1.5 ºC). High wind convergence was observed at low- (1000–850 hPa) and mid- (850–700 hPa) levels on convective days (^–16.5 s^–1 and –9.6 s^–1, respectively). In contrast, wind divergence at the same levels was observed on stratiform (6.4 s^–1 and 6.9 s^–1) and nonprecipitating (9.7 s^–1 and 7.3 s^–1) days. Higher wind divergence (8.3 s^–1) was observed on convective days at upper levels (300–200 hPa) compared with stratiform (3.2 s^–1) and nonprecipitating (2.8 s^–1) days. Results show a coupling of wind convergence, moisture and energy in the lower troposphere and divergence at upper levels on convective days. Despite moisture availability on stratiform days and thermodynamic energy on nonprecipitating days, the respective coupling between these conditions and dynamic triggers was not observed.