The Indian monsoon is the main source of irrigation in the northern Indian plains and a vital source of water for more than a billion people. Therefore, research investigating the mechanisms driving its onset and progression can have a substantial positive impact on society. The INCOMPASS project has been designed to tackle these key challenges, through an observational field campaign supplemented by high-resolution convection-permitting numerical simulations.

The analysis of these simulations shows that the progression of the Indian monsoon in June 2016 over the plains of NW India is modulated by the interaction between the moist SW-ly flow from the Arabian Sea and the NW-ly intrusion of dry air from neighbouring arid regions. Lagrangian trajectories have been used to highlight the path of these airstreams and the processes driving their evolution, complementing a Eulerian analysis of the state of the troposphere throughout the monsoon progression.

These analyses confirm that the aforementioned airstreams are primary drivers of the general moistening of the troposphere associated with the monsoon progression in the region but also highlight that this process is far from steady. In fact, processes at several scales, from synoptic-scale transient weather features to local diabatic processes, influence the location, direction and extension of these dry and moist airstreams, which in turn drive the overall evolution.