15 May 2023
 | 15 May 2023

Day-night differences in δ18O and d-excess of convective rainfall in the Rio Claro station, inland tropics of Brazil

Vinicius dos Santos, Didier Gastmans, Ana María Durán-Quesada, Ricardo Sánchez-Murillo, Kazimierz Rozanski, Oliver Kracht, and Demilson de Assis Quintão

Abstract. The tropical central-southern part of Brazil (CSB) is characterized by strong convective systems bringing generous water supply for agro-industrial activities but also pose flood risks for large cities. Here, we present high-frequency (5–10 minutes) rainfall isotopic compositions to better understand those systems, with a total of 90 intra-event samples collected during the period 2019–2021. Convective activity and moisture transport modulate the seasonal rainwater isotopic composition with low δ18O values during summer and high during autumn and spring. In summer, both regional and local factors contribute to the observed depletion in heavy isotope contents of rainfall, with strong, continuous rainout along the trajectories of moisture-laden air masses arriving at the rainfall collection site from the Amazon basin, and diurnal convective activity of the local atmosphere, respectively. This activity generates convective clouds with distinct features (cloud depth and cloud base height) and induces differences in atmospheric conditions below the cloud base level (relative humidity and rainfall rates) modifying isotopic characteristics of rainfall and revealing novel perspective on day-night contrast in δ18O and d-excess values. During daytime, enhanced sub-cloud effects lead to high δ18O and low d-excess while continuous regional rainout during night-time results in low δ18O and high d-excess values of local rainfall. Our results offer a new framework of key drivers controlling the isotopic variability of rainfall in tropical South America that must be considered in future studies of convective systems across the tropics.

Vinicius dos Santos et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-710', Anonymous Referee #1, 23 May 2023
  • RC2: 'Comment on egusphere-2023-710', Anonymous Referee #2, 29 Jun 2023
  • AC1: 'Comment on egusphere-2023-710', Didier Gastmans, 25 Aug 2023

Vinicius dos Santos et al.

Vinicius dos Santos et al.


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Short summary
We present novel about convective rainfall, the summer rain in the late afternoon, coupling water stable isotopes, micro rain radar and satellite data. We found tallest clouds in the afternoon and much smaller cloud at night, resulting in differences in day-night ratios in water stable isotopes. Our sampling scheme, rain and meteorological variables every 5–10 minutes, allowing to evaluate the development of convective rainfall, contributing for understanding rainfall related to extreme events.