Objective identification of synoptic meteorological patterns favouring African dust intrusions into the marine boundary layer of the subtropical eastern north Atlantic region

Abstract

Synoptic geopotential height anomalies patterns favouring African dust outbreaks into the marine boundary layer (MBL) of the subtropical Eastern North Atlantic Region (SENAR) were objectively identified. The proportion of the total variance explained by each of these patterns was also calculated. Dust intrusions into the MBL of the SENAR were identified using total suspended particles (TSP) data at a rural background station in Tenerife Island (El Rio station, ER). Geopotential height anomalies at 1,000, 850, 700 and 500 hPa, respectively, in days of African dust intrusion in the period 1998–2003 were grouped in monthly sets. Two different but complementary methods (K-means and Principal Components) were applied to daily geopotential height anomalies for each month and for each pressure level in case of African dust intrusion. Three principal geopotential height anomalies patterns were found. Type I consist on a high-pressure system over Europe that affects North Africa, occasionally giving rise to a ridge. The Canary Islands are in the south-west flank of this high-pressure system. This pattern is dominant throughout the whole year. Type II and type III patterns consist on a low located to the northeast and southeast of the Canary Islands, respectively, coupled with a high over the Mediterranean basin and/or North Africa. Two case analyses are presented, as well as a systematic validation of the meteorological pattern classification for all dust intrusions detected at ER station within the period 2004–2007.