A new insight into monsoon intraseasonal variability as revealed from distinct wind-precipitation regimes over the southwest coast of India

This study evaluates the observed non-linearity in the wind-precipitation relationship over India’s southwest coast and maps this non-linearity to monsoon intraseasonal oscillations. The wind-precipitation data is subjected to clustering, and five distinct regimes are identified. The large-scale dynamical and thermodynamical condition that leads to wind-precipitation clustering is explored. It uses novel observations from the Stratosphere–Troposphere wind profiler radar placed over Cochin (10.04° N; 76.33° E) for the period 2019–2021 to derive characteristics of monsoon low-level jets. Out of five wind-precipitation clusters, low wind low precipitation (LWLP) and low wind high precipitation clusters (LWHP) bear signatures of monsoon break conditions over central India. The occurrence of Madden Julian events or monsoon lows in LWHP generates heavy rainfall over the southwest coast. The high wind low precipitation (HWLP) cluster occurs during the weak phase of northward propagating monsoon intraseasonal oscillation (MISO) over the southwest coast, while the high wind high precipitation (HWHP) cluster lies within the strong phase of MISO. The fifth cluster, the high wind extreme precipitation cluster (HWEP), although technically lying within the strong phase of MISO, however has more apparent signatures of northwestward propagating monsoon depressions. The Lagrangian trajectories launched from 500 hPa level for each cluster reveal some intriguing aspects. The dry air intrusion from adjacent regions near the west coast makes the mid-troposphere dry over the southwest coast in LWLP and HWLP clusters. In HWHP and HWEP, strong moisture sources confined over the west coast create mid-troposphere moistening owing to the moisture supply from below 500 hPa. This study highlights that wind-precipitation clustering effectively defines sub-seasonal variability during the monsoon.