Introduction

Wind‐blown (or aeolian) dust emissions of arid/semi‐arid areas contribute about 1–3 billion tons to the global atmospheric mineral dust load (Mahowald et al., 1999; 2006; Ginoux et al., 2001). Several hundred million tons of dust are transported every year from Saharan source areas in the direction of the European continent (Stuut et al., 2009; Barkan and Alpert, 2010). The accumulated particles contribute to soil forming processes, while the atmospheric mineral dust has an impact on the radiation budget, cloud forming processes, the pH of precipitation, and biogeochemical cycles of marine ecosystems (Harrison et al., 2001; Maher et al., 2010).

Research studies have confirmed that Saharan dust events (SDEs) in Central Europe are not particularly uncommon (Borbély‐Kiss et al., 2004; Koltay et al., 2006; Szoboszlai et al., 2009; Varga et al., 2013). North African desert dust has been identified on 130 occasions in the atmosphere of the Central European Carpathian Basin between 1979 and 2012, primarily based on data from NASA's Total Ozone Mapping Spectrometer (TOMS) and Aerosol Index (AI) measurements from the Ozone Monitoring Instrument (OMI). SDEs in the Carpathian Basin typically occur in spring, with a ‐secondary maximum in summer; about three‐quarters of the identified episodes occur between March and August.

Three different, major types of synoptic background responsible for particulate matter transport have been distinguished by Varga et al. (2013). In the case of Type‐1 events, the dust transport is connected to the steep pressure gradient between a southward moving trough (along the Atlantic coast of Africa) and the eastern cell of the divided subtropical high. During Type‐2 events Saharan dust is transported by the warm sector winds on the foreside of eastward moving low‐pressure systems (Mediterranean and Sharav cyclones), while Type‐3 events are connected to the longest transport route from western parts of the Sahara, along the western fringe of an anticyclone and thence by westerly winds.

In 2013 and early 2014, four different Saharan dust events generated significant general interest, with a prolonged reduction in atmospheric transparency, spectacular optical phenomena (e.g. Bishop's Ring) and significant wet and dry deposition of dust particles, including red ‘blood’ rain (Figure 1).

Figure 1 Open in figure viewerPowerPoint (a) Reduced transparency of the atmosphere on 30 April 2013 in Hungary. (Photograph: Hungarian Meteorological Service (HMS) automatic webcam service ‐– reproduced with the kind permission of HMS.) (b) Bishop's Ring on 1 May 2013. (Photograph: Mónika Landy‐Gyebnár.) (c) Wet deposition of dust after ‘blood rain’ on 29 May 2013. (Photograph: Márta Goda.)

In this article, the synoptic meteorological conditions, air mass transport routes and possible source areas of four unusual Saharan dust events are discussed. An explanation for the peculiar nature of these dusty episodes in the Carpathian Basin is also offered.