When rain amounts in the Sahel are higher, the volume of dust is lower.The higher rainfall could make more vegetation grow in the Sahel, leaving less sand exposed to winds to blow away.States or departments in four nations contain "Amazonas" in their names.The Amazon represents over half of the planet's remaining rainforests, The rainforest likely formed during the Eocene era.Climate fluctuations during the last 34 million years have allowed savanna regions to expand into the tropics.During the Oligocene, for example, the rainforest spanned a relatively narrow band.It appeared following a global reduction of tropical temperatures when the Atlantic Ocean had widened sufficiently to provide a warm, moist climate to the Amazon basin.
During the mid-Eocene, it is believed that the drainage basin of the Amazon was split along the middle of the continent by the Purus Arch.
Analyses of sediment deposits from Amazon basin paleolakes and from the Amazon Fan indicate that rainfall in the basin during the LGM was lower than for the present, and this was almost certainly associated with reduced moist tropical vegetation cover in the basin.
This debate has proved difficult to resolve because the practical limitations of working in the rainforest mean that data sampling is biased away from the center of the Amazon basin, and both explanations are reasonably well supported by the available data.
CALIPSO uses a laser range finder to scan the Earth's atmosphere for the vertical distribution of dust and other aerosols.
CALIPSO regularly tracks the Sahara-Amazon dust plume.