Short wave versus long wave radiative forcing by Indian Ocean aerosols: role of sea-surface winds

Abstract

Recent observations over the Indian Ocean have demonstrated aerosol short wave absorption as high as 20 to 25 W m⁻². The aerosol net radiative forcing reduces substantially while considering the broad spectrum including the long wave region (due to large infrared forcing which is opposite in sign). At high winds, presence of large amounts of sea-salt aerosols (absorbing in infrared) enhances the infrared forcing; hence reduces the net radiative forcing. In this paper, we examine the role of sea-surface winds (which enhance sea-salt aerosols) on long wave aerosol forcing. Even at moderate winds (6–10 m s⁻¹), the short wave forcing reduces by ∼45% due to the dominance of sea-salt aerosols. At high winds (>10 m s⁻¹), a major fraction of the long wave forcing is contributed by sea-salt (more than 70%). Our studies show that neglecting aerosol long wave radiative forcing can cause large errors in climate models.