Dissertation Defense
Antonio Quispe Rivera
Program: Meteorology
Title: "Microfísica das nuvens de tempestades com e sem raios na América do Sul inferidas pelo GPM-DPR e GLM"
Advisor: Prof. Dr. Carlos Augusto Morales Rodriguez - IAG/USP
Judging Committee:
- Prof. Dr. Carlos Augusto Morales Rodriguez – Presidente e Orientador - IAG/USP
- Prof. Dr. Jorge Alberto Martins – UTFPR
- Prof. Dr. Evandro Moimaz Anselmo – FUNCEME
Alternate Members:
- Profa. Dra. Rachel Ifanger Albrecht - IAG/USP
- Prof. Dr. Micael Amore Checchini - IAG/USP
- Prof. Dr. Gerson Paiva Almeida – UECE
- Prof. Dr. Moacir Lacerda - EPL & YANSA SCIENCE
- Prof. Dr. Enrique Viera Mattos – UNIFEI
- Prof. Dr. Thiago Souza Biscaro - INPE
Abstract: This study conducted a microphysical analysis of storm clouds with and without lightning in South America with the objective of understanding how different hydrometeor growth mechanisms contribute to cloud electrification. To comprehend the microphysical processes that lead to the electrification of thunderstorms (clouds with lightning), this study analyzed the observed differences in the vertical profiles of the radar reflectivity factor (Z), mass-weighted mean diameter (Dm), and the normalized intercept parameter (Nw). These were inferred by the dual-frequency radar of the Global Precipitation Measurement (GPM) satellite during 2020 in the South American region (90ºW-30ºW and 50ºS-20ºN) for precipitating clouds that had lightning and those that did not. The clouds were identified based on Z fields (2ADPR) greater than 20 dBZ. To identify thunderstorms, lightning data detected by the Geostationary Lightning Mapper (GLM) were used, which served to classify precipitating systems that have lightning (LPS) and those that do not (NLPS). Based on this methodology, 146 033 precipitating clouds were identified, of which 3 887 (approximately 4%) had more than 10 flashes and were classified as LPS. The mean vertical profiles of storms with and without lightning showed that: (i) Z was higher in LPS, by 2 to 6 dBZ at all temperature levels, which implies the presence of supercooled water and the predominance of the accretion process in the mixed-phase region (0ºC to -20ºC), whereas in NLPS, the predominance of the aggregation process was observed; (ii) the Dm of hydrometeors in LPS is larger (up to 0.4 mm) and suggests the presence of graupel and hail particles; (iii) NLPS presented higher values of Nw, indicating a greater concentration of smaller hydrometeors. Statistical analyses (Student's t-test) confirmed that the differences between the mean values of Z, Dm, and Nw for LPS and NLPS are significant with a 95% confidence level at all temperature levels. Statistically significant differences were also observed in thunderstorms based on their electrical activity and extent. Storms with high electrical activity (more than 268 flashes) have a greater amount of supercooled water in the cold region (between 0ºC and -40ºC) and hydrometeors with a larger Dm and in greater quantity, compared to storms with low electrical activity (10 to 22 flashes). Regarding horizontal extent, large storms (more than 126 pixels) presented a low flash rate (0.05 flashes/km²) and more stratiform characteristics, while small storms (4 to 12 pixels) showed a higher flash rate (0.1-0.4 flashes/km²), and were therefore more convective. This characteristic is associated with higher values of Z (up to 3 dBZ) and Dm (up to 0.3 mm). Finally, the comparison between weak thunderstorms (fewer than 10 flashes) and NLPS showed that weak storms have: (i) higher Z (by 3 to 5 dBZ) at all temperature levels; (ii) a larger Dm by about 0.15 mm in the mixed-phase region and 0.25 mm in the warm region; (iii) and a lower concentration of large hydrometeors. These results demonstrated that even for storms with few flashes, the presence of larger hydrometeors, such as graupel and hail, and supercooled water droplets in the cloud's mixed-phase region is necessary. In conclusion, this study showed that the efficiency of the electrification process depends on the presence of supercooled water droplets and the activation of the ice crystal accretion process in the mixed-phase zone of the cloud.
Keywords: thunderstorms, hydrometeor growth processes, lightning, weather radar