Thread: Sahara sand storms in So. Florida

Saharan dust has been blowing across the Atlantic since the desert was born during the Ice Age. (It was savannah-type grassland prior to that.) It is a major source of nutrients in the open ocean where sedimentation rates are otherwise excedingly low. It also carries spores and living organisms which find habitat on the reefs and islands in the Caribbean. Locusts and spiders have been known to survive the trip.

Dust has interesting properties. It absorbs infrared radiation from the sun and from the surface, so tends to warm the layer in which it resides. It also scatters visible light so it tends to shade the surface. These two effects -- cooling below and warming aloft -- tend to stabilize the column so that we see fewer cumulus clouds within the dust plume than in surrounding dust-free areas.

However, dust also acts as a nucleating agent and can enhance cloud development if the concentration drops below a critical threshold: too high and cooling plus competition reduces drop-size; we want some sun to get through and just the right number of particles per liter.

In the 30's, dust from the American Dust Bowl was blowing out into the Atlantic on the westerlies. It arrived in London. So we see that this is a two-way street, and that the continents have been "talking"down the centuries, sending gifts to one another.

Dave