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Priyanka Banerjee and S. Prasanna Kumar

Abstract

Mineral dust is known to affect many aspects of the climate of the north Indian Ocean (IO). However, what controls its interannual variability over this region is largely unknown. The authors study the mechanism controlling the interannual variability of dust aerosols in the principal dust belts bordering the northwest IO. It is shown that annual dust activity to the north of the Persian Gulf has an inverse relation with preceding precipitation during October–December and soil moisture during current dust season (April–August). These are in turn remotely controlled by El Niño–Southern Oscillation (ENSO) through the modification of the intensity of convection over the Indo-Pacific warm pool region, which affects moisture flux to the dust sources. While La Niña leads to a negative precipitation anomaly and more dust generation during the following summer, El Niño is responsible for the opposite. During the summer following La Niña, the air–sea interaction leads to a lowering of geopotential height over the Indo-Iranian region, resulting in an increased gradient between the Indo-Iranian region and the surrounding regions. This intensifies the dust-transporting northwesterly and northeasterly winds over the Arabian Peninsula. The dust transport by the intensified low-level southwesterlies and upper-level westerlies is the main factor responsible for enhanced dust over the open northwest IO during the years following La Niña. The Indian Ocean dipole potentially impacts the variability of dust over the northwest IO by modifying the moisture associated with El Niño.

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Priyanka Banerjee, S. K. Satheesh, K. Krishna Moorthy, Ravi S. Nanjundiah, and Vijayakumar S. Nair

Abstract

Synergizing satellite remote sensing data with vertical profiles of atmospheric thermodynamics and regional climate model simulations, we investigate the relative importance, transport pathways, and seasonality of contribution of dust from regional (Thar Desert and adjoining arid regions) and remote (southwest Asia and northeast Africa) sources over the northeast Indian Ocean [i.e., the Bay of Bengal (BOB)]. We show that while over the northern BOB dust from the regional sources contribute more than 50% to the total dust load during the southwest monsoon period (June–September), interestingly; the remote dust sources dominate rest of the year. On the other hand, over the southern BOB, dust transported from the remote-source regions dominate throughout the year. During June, the dry elevated layer (at altitudes between 850 and 700 hPa) of dust, transported across the Indo-Gangetic Plain to the northern BOB, arises primarily from the Thar Desert. Dust from remote sources in the far west reaches the southern BOB after traversing over and around the southern Indian Peninsula. Since dust from these distinct source regions have different mineral composition (hence optical properties) and undergo distinct changes during atmospheric transport, it is important to understand source-specific dust contribution and transport pathways to address dust–climate feedback.

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