The main objects of study in this paper are the synoptic scale atmospheric circulation systems associated with the rather frequent phenomenon of coloured rain and the very rare phenomenon of dust or sand deposits from a Saharan sandstorm triggered by a developing strong depression. Analysis of two such cases revealed that two days before the occurrence of the coloured rain or the dust deposits over Greece a sand storm appeared over the north-western Sahara desert. The flow in the entire troposphere is southerly/south-westerly with an upward vertical motion regime. If the atmospheric conditions over Greece favour rain then this rain contains a part of the dust cloud while the rest is drawn away downstream adopting a light yellow colour. In cases where the atmospheric circulation on the route of the dust cloud trajectories is not intensively anticyclonic dust deposits can occur on the surface long far from the region of the dust origin. Such was the case on 4th April, 1988, when significant synoptic-scale subsidence occurred over Italy and towards Greece. The upper air data, in the form of synoptic maps, illustrate in detail the synoptic-scale atmospheric circulations associated with the emission-transport-deposition and confirm the transportation of dust particles. 1. Introduction The phenomenon of coloured rain over the South Balkans and, in particular, over Greece occurs rather frequently, being associated with the appearance of Sahara or Atlas Mountains depressions [1–3]. On the other hand a significant easily visible, dust deposit upon Greece, coming from North Africa, is a very rare phenomenon occurring only once within the last twenty years on 4 April 1988 in north Greece. Also on 17 April 2005 the city of Athens was enveloped in a thick dust cloud. The dust cloud was not a localised event over Athens, but it was part of a synoptic-scale dust transport from Africa [4]. This event over Athens seems to be a little bit different from the other one, on 4th April 1988 in Thessalonica, studied here, because the dust was concentrated in the boundary layer with very little dry deposit on surface reducing dramatically the visibility. Of course coloured rain and/or dust deposits occur also in other European countries which are further north than Greece, for example, United Kingdom [5, 6], Spain [7], and generally Europe [8]. Also the transport and deposition of African dust is known to affect distant regions in the North Atlantic as far away as the Caribbean Islands [9, 10]. Something similar occurs for the East Asian dust that is transported and deposited
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