Cloud regime evolution in the Indian monsoon intraseasonal oscillation: Connection to large‐scale dynamical conditions and the atmospheric water budget

Abstract

AbstractWe examine the intraseasonal oscillation (ISO) of the Indian summer monsoon to establish the connections of cloud regimes to large‐scale dynamical states defined by dynamical convergence and moisture advection. Over the Indian subcontinent, the developing phase toward ISO peaks (rainfall maximum) is associated with positive anomalies of moisture advection leading in 4–6 days to positive anomalies of dynamical convergence, triggering abrupt transitions from shallow cumulus to deep convections in 1–2 days. The decaying phase toward ISO troughs (rainfall minima) is associated with negative anomalies of moisture advection and decreasing dynamical convergence, accompanying opposite transitions in cloud regimes. Due to northward propagation of anomalies, processes over the Indian Ocean are similar but lead those over the subcontinent by ~10 days. During the transitions cirrus clouds always accompany but lag deep convective clouds by ~10 days. Over the equatorial Indian Ocean cirrus clouds are modulated by equatorial waves.