Observed trends in South Asian monsoon low-pressure systems and rainfall extremes since the late 1970s
The core Indian monsoon region receives more than half of the rainfall extremes from low-pressure systems (LPSs), which typically form over the Bay of Bengal and propagate upstream against the time-mean low-level westerlies. Yet, the relationship between the trends of LPSs and rainfall extremes remains uncertain. Using two tracking algorithms and reanalyses-derived LPSs, we find that LPS activity and extreme rainfall exhibit coherent trends during the post-1979 satellite era. Over time, the LPSs propagate preferentially into south-central India rather than north-central India, imparting a corresponding dipole footprint in rainfall extremes. Consistent with existing theories that the diabatic heating is instrumental in shifting the LPSs west-southwestward, the LPSs traveling through south-central India have stronger updrafts on their west-southwestern flank than those passing through north-central India. The increased frequency of LPSs propagating into south-central India is likely due to a strengthened cross-equatorial moisture transport, which favors stronger storm ascents.
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Also Published In
- Geophysical Research Letters