The impact of the Madden-Julian oscillation on spring and autumn afternoon diurnal convection in Sri Lanka

Abstract

This study examines the impact of strong Madden-Julian Oscillation (MJO) phases (P1–P8) on diurnal rainfall patterns focusing on Afternoon Diurnal Convection (ADC) events in Sri Lanka during 2001–2020 spring and autumn. Daily mean rainfall increases (decreases) during the P2-to-P3 (P6-to-P7) MJO phases in both seasons, while the diurnal rainfall amplitude peaks during the P2-to-P3 (P8-to-P1) MJO phases in spring (autumn). ADC events also occur more frequently and intensely during MJO P2-to-P3 (P8-to-P1) in spring (autumn). The MJO’s modulation of diurnal rainfall amplitude and ADC events is more apparent in autumn than in spring. Active MJO phases enhance the westward propagation of diurnal rainfall associated with ADC events, sustained by moisture flux convergence and enhanced upward motion. The prevailing mid-to-upper level easterly wind, combined with deep convection over Sri Lanka, contributes to a more pronounced westward propagation during the P2-to-P3 (P8-to-P1) phases for ADC events in spring (autumn).

Enhanced Influence of Indian Ocean Dipole on Sri Lanka Rainfall in Recent Decades

“…Given the importance of canonical IOD seasonality (e.g., Zhang et al 2020), we have examined the effect of IOD on the Sri Lanka rainfall during the IOD peak season rather than the rainy season timescale. Recent studies suggest that due to the global warming, severe drought and flood conditions would be expected (Roudier et al 2016;Ma and Yuan 2024) and, the Madden-Julian Oscillation (MJO) has also been identified as a potential driver of variability in the Indian Ocean climate during autumn (Huang et al 2024). Furthermore, it is noted that there is a strong anomalous rising (sinking) motion over Sri Lanka during the positive (negative) IOD (Jayawardena et al 2024).…”