A comparison of Indian and South American monsoon variability and likely causes

The main goal of the present work is to compare and contrast the characteristics of distinct monsoon systems like the Indian monsoon system (IMS) and South American monsoon system (SAMS) for the period (1979–2022). In addition, we discuss in some detail the theoretical aspects of the two monsoon systems by examining the energetics and the applicability of “convective quasi-equilibrium, (CQE).” We have also analyzed the precipitation interannual variability of SAMS and IMS considering neutral, El Niño, and La Niña years. Then, a discussion of the applicability of CQE along with the recent changes in surface entropy is presented. In our analysis, we found that interannual variability in the case of SAMS is less than that of IMS, and rainfall of SAMS is not drastically affected by ENSO when compared to IMS. We observed that rainfall characteristics over IMS are more complex than SAMS. The annual cycle of the vertically integrated total kinetic energy (KE) over SAMS is maximum in Austral spring, while the precipitation is higher in Austral summer. This is in sharp contrast to the IMS, where the maximum KE and rainfall coincide, both occurring in July and August. Further analysis showed that the conversion from the mean available potential energy PZ to the eddy available potential energy PE and conversion from PE to KE are important over SAMS. This shows that in South America, baroclinic conversions associated with baroclinic instability are important in austral summer, while over IMS, baroclinic conversions are not important in boreal summer. Our results support CQE for the IMS, but in the case of El Niño, we found that CQE is invalid. For SAMS, the applicability of CQE is climatologically doubtful, but during El Niño, the applicability of CQE is robustly visible.