The ‘So What’ Of The Phoenix Haboob And Trans-Atlantic Saharan Dust
“Cool” weather picture are typically everywhere on social media: sunsets, shelf clouds, waterspouts, tornadoes, or interesting clouds. However, I could not help but notice that during the first week of August 2018 dust dominated weather headlines and social media. There was a jaw-dropping haboob in Phoenix, and African dust was moving across the Atlantic Ocean. Here’s why you should care.
As a scientist, I am usually aware of the significance of an event but many in the public are thinking, “why do I care that dust is moving across the Atlantic?” or “ummm, a haboob looks cools and sounds funny but so what?” Let’s start with the impressive haboob that affected Phoenix, Arizona.
The National Weather Service (NWS)-Phoenix preliminary report on the meteorological conditions that led to this social media-dominating event said,
As the storms progressed, the strong outflow winds caused a large dust storm to develop and move south-to-north across the two counties. Numerous reports of near zero visibility were reported early in the storm, though the intensity of the dust storm waned as it moved northward into the Phoenix area (primarily due to a lack of new dust to ingest and decreasing intensity as the flow fanned out)
My colleague Trevor Nace has written a very good explainer in Forbes on how haboobs form. In a bizarre twist, there has been some recent “nationalization” of the weather term but as Jason Samenow wrote in a Capital Weather Gang article from a previous event,
the Weather Service’s use of ‘haboob’ was entirely appropriate….Haboobs are common in the desert Southwest and the Middle East, where the term originated. It’s also true that many weather and Earth science terms we use are derived from other languages — hurricane, tornado and derecho are all Spanish in origin, not to mention El Niño and La Niña.
Haboobs are an underrated weather hazard. According to a 2016 National Weather Service report, blowing dust is the 3rd deadliest weather phenomenon in Arizona behind extreme heat and flooding. It is also the leading cause of weather-related injuries. Blowing dust is a significant respiratory hazard and creates challenges for all modes of transportation. It may also be linked to the spread of Valley Fever. The report also points out,
There are two types of blowing dust phenomena that are common across Arizona…..A haboob is a wall of dust that extends several hundred meters to up to a couple thousand meters into the atmosphere. In the United States, the word haboob was first used by Idso et al. (1972) in a paper entitled “An American Haboob.” Since the early 2000’s the usage of the word haboob has become more common with increased usage by meteorologists, media and the public……The second type of blowing dust is much more localized and occurs when large scale weather systems produce gusty winds, mainly in the fall, winter and spring with dust becoming airborne by more single point sources such as degraded desert, abandoned farmland and dirt roads
The other dust story is captured perfectly by Logan Vicknair’s tweet on August 4th, “dust clouds from Africa and Galveston’s (Texas) been clear multiple times. What a wild summer.” Headlines in Portugal and Spain wrote of unbelievable heat and yellow skies caused by an influx of Saharan dust. The University of Athens SKIRON model (below) illustrates how winds from the south transported dust into the Iberian Peninsula. The model also reveals that African dust takes a “fork in the road” and aheads west across the Atlantic Ocean. From a meteorological perspective, Saharan dust rides the easterly trade winds to the west. In the United States, weather basically moves west to east, but in the tropics it is reversed. This is related to complex fluid dynamics associated with general circulation of the planet.
Dust has been apparent in the Caribbean islands and as far west as Texas this summer. According to the BoDEx study,
most atmospheric dust comes from a very few places. By far the dustiest is the Bodélé depression (in the Djourab of northern Chad). At the Bodélé, strong winds, funnelled round the eastern slopes of the Tibesti Mountains, pick up fine diatomites and clays from the bed of a now-dry lake. Some 5000 years ago, when it was full, the lake was “Mega-Chad”, then the size of the Caspian Sea. Today, the Bodélé contributes well over half of the c. 400-700M tonnes of dust that leave West Africa each year. Much ends in the Atlantic, but some reaches South America. The process is year-long, but it is most intense in spring and early summer, when the Harmattan cloaks West Africa in dust.
Matt Lanza is managing editor of Space City Weather. During an earlier July event in which Saharan dust was apparent in Texas, Lanza told the Houston Chronicle, “It’s not so much out of the ordinary……It only happens a couple times per summer.” The dust palls coming from African can take roughly one week to traverse the Atlantic Ocean. The “so what” is that Saharan dust has been found to cause allergic reactions in humans, coral disease, aviation hazards, and red tides. Published studies are starting to close in on Saharan dust as a cause of increasing respiratory disease in Puerto Rico.
It will be important going forward to understand this mega-dust generating region because the dust plays a role in the Earth’s climate and even meteorological processes. For example, the NASA image (below) shows significant Saharan dust activity during the 2017 hurricane season. Dust can impede the development of hurricanes because it brings dry air into the hurricane “heat engine.” The Saharan dust plumes also bring hurricane-suppressing wind shear, and the dust particles may reduce the formation of cloud droplets.