The South Asian Monsoon System Response to AMOC Perturbations

The response the South Indian monsoon to changes in the global ocean circulation are investigated using a set of freshwater hosing experiments in the NCAR Community Earth System Model version 1 (CESM1). Results show that a collapsed AMOC weakens the South Asian monsoonal circulation, especially during the boreal summer. Both branches of the double ITCZ exhibited in the Indian Ocean shift southward; the northward branch weakens, brining less precipitation to the Indian subcontinent. We hypothesize that this is due to a weakening of the extratropical ocean heat transport and land-sea gradient changes. Results also suggest that there is uniquely strengthening response over the Bay of Bengal, as changes in the circulation bring increased moisture to the region. We further examine the linearity of these responses in two freshwater hosing experiments of varying strengths. Finally, we also investigate the response of the South Indian monsoon in additional experiments with a collapsed AMOC but an active PMOC. Our results shed additional insights onto the relationships between the South Asian monsoon and the AMOC across timescales.