The Indian summer monsoon rainfall varies on a 10-60 day cycle, with periods of high and low rainfall. By studying moisture movement from oceans and land to India, researchers found that the western and central Indian Oceans provide moisture for north-south rainfall patterns, while the Ganga basin contributes to east-west patterns. During active periods, the monsoon trough over the Indo-Gangetic plain brings moisture from the Bay of Bengal and Ganga basin to the Core Monsoon Zone. It's important for models to accurately represent both oceanic and terrestrial moisture sources to simulate monsoon variability.