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| Titel |
Modulation of Saharan dust export by the North African dipole |
| VerfasserIn |
S. Rodríguez, E. Cuevas, J. M. Prospero, A. Alastuey, X. Querol, J. López-Solano, M. I. García, S. Alonso-Pérez |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 13 ; Nr. 15, no. 13 (2015-07-10), S.7471-7486 |
| Datensatznummer |
250119882
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| Publikation (Nr.) |
 copernicus.org/acp-15-7471-2015.pdf |
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| Zusammenfassung |
| We have studied the relationship between the long-term interannual
variability in large-scale meteorology in western North Africa – the largest
and most active dust source worldwide – and Saharan dust export in summer, when enhanced dust mobilization
in the hyper-arid Sahara results in maximum dust impacts throughout the North
Atlantic. We address this issue by analyzing 28 years (1987–2014) of summer
averaged dust concentrations at the high-altitude Izaña observatory
(~ 2400 m a.s.l.) on Tenerife, and satellite and meteorological
reanalysis data. The summer meteorological scenario in North Africa (aloft
850 hPa) is characterized by a high over the the subtropical Sahara and a
low over the tropics linked to the monsoon. We measured the variability of
this high–low dipole-like pattern in terms of the North African dipole
intensity (NAFDI): the difference of geopotential height anomalies averaged
over the subtropics (30–32° N, Morocco) and the tropics
(10–13° N, Bamako region) close to the Atlantic coast (at
5–8° W). We focused on the 700 hPa standard level due to
dust export off the coast of North Africa tending to occur between 1 and
5 km a.s.l. Variability in the NAFDI is associated with displacements of
the North African anticyclone over the Sahara and this has implications for
wind and dust export. The correlations we found between the 1987–2014 summer
mean of NAFDI with dust at Izaña, satellite dust observations and
meteorological re-analysis data indicate that increases in the NAFDI (i)
result in higher wind speeds at the north of the Inter-Tropical Convergence
Zone that are associated with enhanced dust export over the subtropical North
Atlantic, (ii) influence the long-term variability of the size distribution
of exported dust particles (increasing the load of coarse dust) and (iii) are
associated with enhanced rains in the tropical and northern shifts of the
tropical rain band that may affect the southern Sahel. Interannual
variability in NAFDI is also connected to spatial distribution of dust over
the North Atlantic; high NAFDI summers are associated with major dust export
(linked to winds) in the subtropics and minor dust loads in the tropics
(linked to higher rainfall), and vice versa. The evolution of the summer
NAFDI values since 1950 to the present day shows connections to climatic
variability (through the Sahelian drought, ENSO (El Niño–Southern
Oscillation) and winds) that have implications for dust export paths. Efforts
to anticipate how dust export may evolve in future decades will require a
better understanding of how the large-scale meteorological systems
represented by the NAFD will evolve. |
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