During hurricane season meteorologists often for waves moving off the coast of Africa that can develop into strong hurricanes near the Cape Verde Islands. These Cape Verde storms can be long lived and become quite large as they track from east to west across the Atlantic towards the Caribbean. Tropical waves are not the only things satellites keep watch for in this region. Dry air that contains millions of dust particles known as the Saharan Air Layer can also extend from the desert where it originates over parts of the Atlantic Ocean. Like tropical waves it can be tracked however instead of initiating tropical development it work to inhibit development and potentially weaken existing storms.
Infrared satellite detects clouds by measuring the heat radiated from the clouds itself. Different temperatures for different cloud types. By comparing different wavelengths an infrared satellite can actually tell the difference between clouds and dust. This imagery shown above highlights the dry dusty Saharan Air Layer moving from east to west off the coast of Africa. A visible picture courtesy of NASA can also be used to verify and track the dust but it only works if you can see it.
So what can these images be used for? Like we mentioned earlier the dry dusty air can work against the formation or intensification of tropical systems. Hot dry air over a cooler ocean creates what is known as an inversion and will limit, or even prevent, storms from forming. Dry air surrounding an existing storm can be drawn in thus limiting moisture and preventing further intensification or even weakening it altogether. The stronger wind that carries the dust over the ocean can also be an indication of increasing wind shear which can work to prevent tropical cyclone development. Tracking this feature over the open ocean can lead to better initial forecasts when it is impossible or impractical to investigate with aircraft.
In certain cases this Saharan dust has been tracked across the Atlantic Ocean and been observed in parts of the Caribbean and United States. Hazy skies and a drop in air quality were observed in parts of Texas and the Caribbean.