Saharan dust in the Carpathian Basin

(more details see in Varga, Gy. et al. 2013. Analysis of Saharan dust intrusions into the Carpathian Basin (Central Europe) over the period of 1979–2011. Global and Planetary Change 100. pp. 333–342.) 

The global annual input of mineral dust deflated from arid-semiarid areas can be set in the range between 1 and 3 billion of tons. Most important sources are situated in Saharan and Sahel regions, which are responsible for 50–70% of the global emission. Four main pathways of Saharan dust transport can be distinguished: (1) southward to Gulf of Guinea; (2) westward over the North Atlantic Ocean; (3) eastward to Middle East; and (4) northward to Europe.
Fine-grained particles lift to higher levels of the atmosphere and have a long atmospheric residence time up to a few weeks. Aeolian dust from North Africa can often be detected in Europe’s high-latitude areas e.g. in British Isles, in Germany, in Scandinavia and even in our study area, the Carpathian Basin (CB) (Central Europe). Nowadays the CB is generally not regarded as a dusty place, except for episodic dust storms related to cold fronts invading the region at the beginning of the vegetation period in the early spring. However, dust activity of the region was much more significant during the Plio–Pleistocene periods, as it is shown by thick aeolian dust deposits covering more than half of the area. It has been recognized that mineral dust particles of these aeolian sediments originate mainly from local sources (e.g. alluvial plains), and only the clay and fine-silt fractions may be linked to Saharan sources.

During the investigation period of 1979–2011 130 Saharan dust episodes could be identified in the CB atmosphere. The time series of annual number of SDEs are characterized by high amplitude annual variations. Outstanding values of 1984, 1985, 1992, 2000, 2001 and 2008 with 8 or more SDEs are in contrast with the years of 1981, 1991, 2003, 2004, 2006 and 2009, when the number of identified events was far below the average. The causal relationships among the changing annual frequency of SDEs, Saharan and Sahel droughts, climate teleconnections and atmospheric circulation patterns are not yet fully understood. In some cases, the increased number of identified SDEs over the CB is coincident with Saharan drought periods (e.g. in 1983–84), but in other cases this relationship become increasingly uncertain (e.g. in 2008 and 2009). 
Monthly values of dust events demonstrate that the main period of dust transportation is in the spring, with a secondary maximum in the summer (in July and August), and dust activities in February and October are also fairly high. This seasonality pattern of our observations fairly agrees with reports of several previous studies on Saharan dust events.

A multi-year record of various data sources including TOMS Aerosol Index, satellite images, HYSPLIT backward trajectory counting and synoptical meteorology were used to identify and analyse Saharan dust events in the CB atmosphere over the period of 1979–2011. In this period, 130 SDEs were detected altogether, primarily during spring and summer. Based on the daily geopotential height, wind flow and meridional wind vector maps of dusty days, the SDEs were classified into three main types. In the case of Type-1, a trough emanates from the direction of Bay of Biscay to the Atlantic coast of Africa. The eastern cell of the divided subtropical high and the cyclonic stream of a low-pressure system cause the strong SW flow. During Type-2 events, dust transportation can be connected to the warm sector winds on the foreside of an eastern moving Mediterranean cyclone. The relatively seldom Type-3 events are responsible for the longest dust transportation from the western parts of the Sahara along the western fringe of an anticyclone and by the westerlies. 
Our results nicely demonstrate that Saharan dust could often be detected in the CB atmosphere. SDEs, during the dustier periods of the Pliocene and Pleistocene could have served as significant source of clay and fine silt particles which then may have contributed to the widely distributed aeolian dust deposits in the basin.

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