Recent changes in the spatio-temporal characteristics of monsoon intraseasonal oscillations

Monsoon intraseasonal oscillations (MISOs) define a significant proportion of intraseasonal variability of the Indian summer monsoon. In the backdrop of increasing temperatures related to global warming, it is expected that MISOs would exhibit more spatio-temporal variability, prompting an increased frequency of extreme events. Hence, the present study investigates the observed changes in the characteristics of long (≥ 7 days) and short (< 7 days) active and break spells in the early twenty-first century (2001–2019) in comparison with the late twentieth century (1982–2000). In the recent period, a decreased (increased) frequency of the short (long) active/break spells along with a strengthening of short spells has been noticed. An east–west asymmetry in the spatial distribution of rainfall is further noted with western India experiencing intensified (weakened) active (break) spells. Contrariwise, the central and eastern parts of the country witness weakening (intensification) of active (break) spell in the early twenty-first century. A comprehensive composite investigation of various dynamical and thermodynamical parameters reveals an increase in the strength of low-level winds in the Arabian Sea, thereby increasing the moisture convergence and instability over the western Indian region and the nearby oceanic regions, resulting in the observed east–west asymmetry in the rainfall spatial distribution. Increased intensity of the equatorial Madden–Julian oscillation and its coupling with the northward propagating MISO spells seem to play a pivotal role in lengthening the active/break spells. It is speculated that such changes are triggered by the amplified temperatures over the global oceans in the recent period.