Discernible rhythm in the spatio/temporal distributions of transatlantic dust 1Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, Rehovot, Israel
01 Mar 2012
2Department of Physics, Michigan Technological University, Houghton, Michigan, USA
3Department of Geophysics and Planetary Sciences, Tel Aviv University, Tel Aviv, Israel
Received: 27 July 2011 – Published in Atmos. Chem. Phys. Discuss.: 19 August 2011 Abstract. The differences in North African dust emission regions and transport routes,
between the boreal winter and summer, are thoroughly documented. Here we
re-examine the spatial and temporal characteristics of dust transport over
the tropical and subtropical North Atlantic Ocean, using 10 yr of
satellite data, in order to better characterize the different dust transport
periods. We see a robust annual triplet: a discernible rhythm of
"transatlantic dust weather".
Revised: 05 January 2012 – Accepted: 09 January 2012 – Published: 01 March 2012
The proposed annual partition is composed of two heavy loading periods,
associated here with a northern-route period and southern-route period, and
one light-loading period, accompanied by unusually low average optical depth
of dust. The two dusty periods are quite different in character: their
duration, transport routes, characteristic aerosol loading and frequency of
pronounced dust episodes.
The southern-route period lasts ~4 months. It is characterized by a
relatively steady southern positioning, low frequency of dust events, low
background values and high variance in dust loading. The northern-route
period lasts ~6.5 months and is associated with a steady drift
northward of ~0.1 latitude day−1, reaching ~1500 km north
of the southern-route. The northern period is characterized by higher
frequency of dust events, higher (and variable) background and smaller
variance in dust loading. It is less episodic than the southern period.
Transitions between the periods are brief. Separation between the southern
and northern periods is marked by northward latitudinal shift in dust
transport and by moderate reduction in the overall dust loading. The second
transition, between the northern and southern periods, commences with an
abrupt reduction in dust loading and rapid shift southward of ~0.2
latitude day−1, and ~1300 km in total.
Based on cross-correlation analyses, we attribute the observed rhythm to the
contrast between the northwestern and southern Saharan dust source spatial
distributions. Despite the vast difference in areas, the Bodélé
Depression, located in Chad, appears to modulate transatlantic dust patterns
about half the time.
Citation: Ben-Ami, Y., Koren, I., Altaratz, O., Kostinski, A., and Lehahn, Y.: Discernible rhythm in the spatio/temporal distributions of transatlantic dust, Atmos. Chem. Phys., 12, 2253-2262, doi:10.5194/acp-12-2253-2012, 2012.