African dust outbreaks over the western Mediterranean Basin: 11-year characterization of atmospheric circulation patterns and dust source areas

摘要

The occurrence of African dust outbreaks over different areas of the westernMediterranean Basin were identified on an 11-year period (2001–2011). Themain atmospheric circulation patterns causing the transport of African airmasses were characterized by means of an objective classification methodologyof atmospheric variable fields. Next, the potential source areas of mineraldust, associated to each circulation pattern were identified by trajectorystatistical methods. Finally, an impact index was calculated to estimate theincidence of the African dust outbreaks produced during each circulationpattern, in the areas of study.Four circulation types were obtained (I–IV) and three main potentialsource areas of African dust were identified (Western Sahara and Morocco;Algeria; northeastern Algeria and Tunisia). The circulation pattern I(24% of the total number of episodic days) produced the transport of dustmainly in summer from Western Sahara, southern Morocco and Tunisia. Thecirculation pattern IV (33%) brings dust mainly from areas of northernand southern Algeria in summer and autumn, respectively. The circulationpattern II (31%) favored the transport of dust predominantly fromnorthern Algeria, both in spring and summer. Finally, the circulation type III was the less frequently observed (12%). It occurred mainly in springand with less intensity in winter, carrying dust from Western Sahara andsouthern Morocco.Our findings point out that the most intense episodes over the westernMediterranean Basin were produced in the summer period by the circulationtype I (over the western side of the Iberian Peninsula) and the circulationtype IV (over the central and eastern sides of the Iberian Peninsula and theBalearic Islands).