Polar jet circulation changes bring Sahara dust to Arctic, increasing temperatures, melting ice

Summary points

A new atmospheric mechanism by which dust travels from the Sahara Desert across the eastern side of the North Atlantic Ocean towards the Arctic has been discovered

The dust emission was generated by a Saharan cyclone that was triggered by the intrusion of a trough emanating from the polar jet

The poleward transport of warm dust was caused by a meandering polar jet stream

Approximately half of the warming in the Arctic is being attributed to increased moisture and heat fluxes transported to the region from lower latitudes

Abu Dhabi, October 10, 2018: Research scientists at NYU Abu Dhabi, along with other global researchers, have identified a new mechanism by which warm dust travels from the Sahara Desert to the Arctic Circle, which has been proven to affect rising temperatures and ice melt in Greenland.

Their findings highlight the role that the polar jet and associated atmospheric circulation plays in the transport of mineral dust from the Sahara desert to the Arctic across eastern side of the North Atlantic Ocean.

A meandering polar jet was discovered as responsible for both the emission and transport of dust from Northwest Africa to the Arctic. The emission has been linked to an intense Saharan cyclone that formed in early April 2011, which was caused by the intrusion of an upper-level trough emanating from the polar jet.

The study has found that atmospheric circulation of this nature enables the transport of dust, warm and moist air masses from subtropics and mid-latitudes to the Arctic, where approximately half of the warming is now being attributed to increased moisture and heat fluxes transported to the region.

The warm and moist air masses accompanying the Saharan dust caused a rise in surface temperature of 10C for more than three consecutive days upon reaching southeastern Greenland. Subsequent temperature observations detected increased melting within the ice across this same area.

“The polar jet stream has been identified as the main driver for such events leading to the transport of large amount of dust to high-latitudes,” said Diana Francis, atmospheric scientist at NYU Abu Dhabi and lead research scientist in this study. “If the polar jet is set to slow more frequently due to the changes in the Arctic climate system and to the Arctic Amplification, such events are expected to become more frequent,” Francis added.

The newly discovered poleward route is considered the most substantial in terms of dust load import into the Arctic, due to the minimal geographical distance between the origin point and the destination.

‘The impact of dust deposition on ice in Greenland, such as darkening ice and formation of algae on ice or cryoconite, as well as the link between Saharan dust transport and the Arctic heat dome must be investigated further in collaboration with scientists in UK and Germany’ Francis emphasized.

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The study: (open access)

Polar jet associated circulation triggered a Saharan cyclone and derived the poleward

transport of the African dust generated by the cyclone.

Abstract:

In this study, we identify a new mechanism by which dust aerosols travel over long distances across the eastern side of the North Atlantic Ocean toward the Arctic. The meandering polar jet was at the origin of both dust emission through cyclogenesis over Northwest Africa and poleward transport of the uplifted dust towards the Arctic, through cut-off circulation. The dust emission was associated with an intense Saharan cyclone that formed over Northwest Africa in early April 2011. The formation of the cyclone was caused by the intrusion into subtropics, of a high-latitude-upper-level trough, linked to the meandering polar jet. The trough initiated cyclogenesis over Northwest Africa after orographic blocking by the Anti-Atlas Mountains. The still meandering polar jet led to the formation of a cut-off low further south with which the Saharan dust-cyclone merged 2 days later and moved northward with the main stream. Beside satellite observations, a simulation at high resolution was performed using the prognostic-dust permitting model MesoNH.

The total dust load carried during this event to areas located north of 40 N was estimated by the model to be 38 Tg and dust deposition was estimated to be 1.3 Tg.

The Saharan dust reaching Greenland was accompanied by warm and moist air masses that caused a rise in surface temperature of about 10C for more than 3 consecutive days over the southeastern Greenland. Ice melt over this area of Greenland was detected in the brightness temperature observations.

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