CALIPSO observations of changes in dust properties during transport: Statistics for Saharan dust

The vertical distribution of dust shape and size is highly important for understanding and accurately estimating dust radiative forcing. This study uses CALIPSO nighttime datasets to examine the vertical structure and evolution of Saharan dust during transport. The results show that most Saharan dust is lifted to high altitude and descends after traveling thousands of km-s. Initially, the depolarization ratio and color ratio of Saharan dust are uniformly distributed along altitude, suggesting vertically constant particle size and shape distributions. During transport, the depolarization ratio of Saharan dust drops (increases) at lower (higher) altitudes, suggesting that particle shapes become less (more) irregular; while at relatively high altitudes, the depolarization ratio of dust increases during transport. The changes observed during transport likely come from the effects of gravitational sorting caused by variations in particle shape and size.