Friday 23 August, 2019

From showers to Saharan dust: Met Office warns of another surge

The country seems to be see-sawing between periods of rainfall and Saharan dust, as another rise in dusty conditions is set to take place over the next four days.

The Met Office said in an update Monday that the highest concentration of dust will take place on Tuesday.

"An increased presence of Saharan dust is expected over the next four days, but the highest concentrations are likely tomorrow. Please be advised accordingly."

"A break is likely on Thursday 25th, as some moisture and showers should be moving through the area, but a brief return is expected on Friday 26th. The weekend is likely to be generally dust free as a rainfall event is possible," the Met Office said. 

Citizens also also experienced a surge in Saharan dust last Friday into the weekend, however the Met Office said that conditions should decrease toward the end of July.

People with dust-related health conditions are advised to limit their exposure and to have their medication handy. 

Have you experienced dust-related health issues? Share your comments below.

 

About the Saharan Air Layer (SAL)

Saharan dust is a mixture of sand and dust from the Sahara, the vast desert area that covers most of North Africa. 

In the case of Africa, winds blow twenty percent of dust from a Saharan storm out over the Atlantic Ocean, and twenty percent of that, or four percent of a single storm's dust, reaches all the way to the western Atlantic.

The remainder settles out into the ocean or washes out of the air with rainfall. Scientists think that the July 2000 measurements made in Puerto Rico, nearly 8 million tonnes, equalled about one-fifth of the total year's dust deposits.

The SAL passes over the Canary Islands where the phenomenon is named "Calima" and manifests as a fog that reduces visibility and deposits a layer of dust over everything.

These clouds of dust are visible in satellite photos as a milky white to grey shade, similar to haze.

Findings to date indicate that the iron-rich dust particles that often occur within the SAL reflect solar radiation, thus cooling the atmosphere. The particles also reduce the amount of sunlight reaching the ocean, thus reducing the amount of heating of the ocean.

They also tend to increase condensation as they drift into the marine layer below, but not precipitation as the drops formed are too small to fall and tend not to readily coalesce.

These tiny drops are subsequently more easily evaporated as they move into drier air laterally or dry air mixes down from the SAL aloft. Research on aerosols also shows that the presence of small particles in air tends to suppress winds.

The SAL has also been observed to suppress the development and intensifying of tropical cyclones, which may be related directly to these factors.

The SAL is a subject of ongoing study and research.

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