Exacerbation of Indian Summer Monsoon Breaks by the Indirect Effect of Regional Dust Aerosols

Evaluation of century‐long simulations of the Community Earth System Model (CESM) reveals model fidelity in capturing characteristics of aerosols, clouds, convection, rainfall and circulation over India associated with the active/break phase with wetter/drier than average rainfall within the summer monsoon season. During the breaks, aerosols build up over central India due to desert dust transported from the west by anomalous circulation, the trapping of dust emissions from the Thar‐desert and the increased aerosol lifetime in dry conditions. Break spells exhibit reduced cloud effective radius and enhanced lower atmospheric warming over central India as potential evidence for the indirect effect induced by dust aerosols. Consistently, break spells intensify in CESM simulation with increased loading of dust aerosols. The indirect effect of dust aerosols in warming the atmosphere and exacerbating the severity of breaks is conspicuous in simulations forced with the indirect effect of aerosols alone, both for present‐day and pre‐industrial periods. Plain Language Summary Century‐long climate simulation experiments using the state‐of‐the‐art climate model, Community Earth System Model (CESM), reveal the model fidelity in capturing the characteristics of aerosols, cloud, convection, rainfall and circulation over India associated with the active and break spells having excess and deficit rainfall over central India within the summer monsoon season. During break spells, the aerosols build up over India due to the transport of desert dust from the west to central India by lower‐level atmospheric winds, the abundance of desert dust emitted from the Thar desert and the increased lifetime of aerosols in dry conditions. With the accumulation of dust aerosols which absorb solar radiation and cause warming of the clouds, break spells exhibit reduced cloud effective radius and increased lower atmospheric warming as potential evidence for the indirect effect of dust aerosols. Consistently, the severity of break spells is exacerbated with enhanced loading of dust aerosols over central India in CESM simulation. Key Points Dust builds up over India during break spells due to the dust transport by anomalous winds and the trapping of dust emitted from Thar‐desert The breaks exhibit reduced cloud effective radius and enhanced lower atmospheric warming as evidence for the dust‐induced indirect effect Indirect effect of dust in warming atmosphere and exacerbating severity of break