Temporal characteristics of northeast monsoon rainfall and its teleconnection with the large-scale circulation indices

This study investigates the temporal variability of the northeast monsoon rainfall (NEMR) in India and its relationship with El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) using wavelet analysis. The results show that NEMR is highly variable, with a coefficient of variation of about 25%, which is due to its dependence on dynamic systems with a wide range of spatial and temporal scales. The temporal variability of NEMR is at different time scales ranging from intra-annual to interannual to decadal time scales. The large-scale circulation features, ENSO and IOD, also exhibit variability at different time scales. El Niño events have a typical frequency range of 2 to 7 years, with a prolonged impact that can last for several months, spreading across the globe. Wavelet transforms of SOI and Nino 3.4 have revealed variability at the time scale of 2–8 years, which is in line with the observed ENSO cycle. The wavelet transform of DMI displays significant variability in short time scales, typically less than 2–4 years. The study also finds a strong negative relationship between NEMR and SOI, recorded in September, especially over Tamil Nadu, Kerala, and Coastal Andhra Pradesh during the periods 1900–1920 and 1980–2000. This correlation is strong at time scales of 2–4 years and 4–8 years during the periods 1880–1920, possibly related to the ENSO cycle and the oscillation of anomalous SST over the Indian Ocean. The study highlights the need for further studies to understand the physical processes that contribute to the observed variability in El Niño and other ocean–atmosphere interactions.