The atmospheric aerosol spatial distribution and tropical intra-seasonal oscillations over the South Asian region

Abstract

Intra-seasonal oscillations (ISO) are well known to modulate the weather phenomena which in turn are known to influence the atmospheric aerosol loading. This study investigates how aerosol loading is modulated in ISO spatio-temporal scales over the Indian region using long-term satellite aerosol optical depth data from Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, onboard Terra Satellite. It is shown that Madden-Julian Oscillation (MJO) and Equatorial Rossby waves (ER) have the highest effect (15–20% of the mean) followed by Mixed-Rossby-gravity and Tropical depressions (MT), and Kelvin wave (KE) (5–15%). Further, a dipolar pattern in aerosol loading was observed, with poles over the Arabian Sea and the Bay of Bengal. These variabilities were found to be mainly driven by anomalous winds associated with the ISOs. Similar to aerosol, dipolar signatures in the atmospheric aerosol radiative forcing (ARF) were also observed with clearer patterns. However, the forcing poles are not centered exactly where aerosol poles were observed, indicating the effect of differential properties of aerosols on the aerosol radiative forcing. Quantitatively, at the surface level, modulation in ARF is up to 3 Wm-2 (15%) for MJO and ER, and up to 2 Wm-2 (5%) for KE and MT; in the atmosphere and at the top of the atmosphere, modulation is up to 2 Wm-2 (15%) for MJO and ER, and up to 1 Wm-2 (5%) for KE and MT.