319Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.DOI: 10.15201/hungeobull.72.4.1 Hungarian Geographical Bulletin 72 2023 (4) 319–337. Introduction The changing climate has increased the im- portance of atmospheric research in recent decades. The combined study of the many in- terconnected components of the Earth system is necessary to gain a deeper understanding of the scale and rate of change in the atmosphere, and to unravel the interconnections between them, on a scale and at a rate not previously known in human history (Easterling, D.R. et al. 2000; Shepherd, T.G. 2014; IPCC, 2022). A key part of this is the study of atmospheric components traveling with the major circula- tions and the winds driven by these airflow systems over long distances (Harrison, S.P. et al. 2001; Kohfeld, K.E. and Tegen, I. 2007; Maher, B.A. et al. 2010; Pósfai, M. and Buseck, P.R. 2010). Over the past decades, atmospheric mineral dust has been in the focus of climate and environmental research. The emission, transport and deposition of particulate matter has an impact on our environment 1 Geographical Institute, HUN-REN Research Centre for Astronomy and Earth Sciences, Budaörsi út 45. H-1112 Budapest, Hungary. Corresponding author’s e-mail: varga.gyorgy@csfk.org 2 Research Institute of Biomolecular and Chemical Engineering, University of Pannonia, Veszprém, Hungary. 3 ELTE Department of Meteorology, Institute of Geography and Earth Sciences, ELTE Eötvös Loránd Univer- sity, Budapest, Hungary. 4 Air Chemistry Research Group, Research Institute of Biomolecular and Chemical Engineering, University of Pannonia, Veszprém, Hungary. 5 Faculty of Environmental and Forest Sciences, Agricultural University of Iceland, Reykjavik, Iceland. 6 Department of Water Resources and Environmental Modelling, Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic. Increasing frequency and changing nature of Saharan dust storm events in the Carpathian Basin (2019–2023) – the new normal? György VARGA 1,2,3, Ágnes ROSTÁSI 2,4, Aida MEIRAMOVA 2,4, Pavla DAGSSON-WALDHAUSEROVÁ5,6 and Fruzsina GRESINA 1,3 Abstract The number and intensity of Saharan dust storm events identified in Europe has been increasing over the last decade. This can be explained by the role of ongoing climate change. An extension of previous studies covering a 40-year period is presented in this paper, with new data on the frequency, synoptic meteorological background, source areas, grain size, grain shape and general mineralogy of deposited dust for the period 2019–2023 in the Carpathian Basin. A total of 55 dust storm episodes have been identified in the region over the five-year period, which is significantly higher than the long-term average. The classification based on synoptic meteorological background clearly showed that the frequency of circulation types with a more pronounced meridional component increased and dust material reached further north more frequently than before. In sev- eral cases, large amounts of dust were deposited, from which samples were collected and subjected to detailed granulometric analysis. The varied grain size data showed that coarse silt (20–62.5 µm) and sand (62.5 < µm) fractions were also present in large quantities in the transported dust material. Keywords: Saharan dust, climate change, Carpathian Basin, grain size Received October 2023, accepted December 2023. Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.320 locally, regionally and globally (Monteiro, A. et al. 2022). Mineral particles with a wide variety of material properties are released into the atmosphere and scatter, reflect and absorb radiation from the sun, directly modifying the irradiance patterns (Arimoto, R. 2001). The role of particulate matter in cloud formation is considered as an indirect radiative effect (Nickovic, S. et al. 2016; Rieger, D. et al. 2017; Weger, M. et al. 2018; Adebiyi, A.A. et al. 2023). For a given water vapour content, the increased atmospheric particle number also increases the number of condensation nuclei required for cloud and ice formation, thus contributing to the formation of more but smaller cloud elements (Hoose, C. et al. 2008; Nickovic, S. et al. 2016; Ginoux, P. 2017; Kok, J.F. et al. 2017; Ansmann, A. et al. 2019). This will result in the formation of lighter but longer-lived clouds due to the dust-loaded air masses. Other environmental effects of long-range mineral particles at the point of deposition are also significant: in soil formation (see e.g., Terra rossa soils of the Mediterranean – MacLeod, D.A. [1980]; Jackson, M.L. et al. [1982]; Jahn, R. et al. [1991]; Atalay, I. [1997]; Muhs, D.R. et al. [2010]); in the carbon cycle through the iron and phosphorus supply to ocean and marine ecosystems (Ridgwell, A.J. 2002); in the modification of precipitation pH (Rodá, F. et al. 1993; Rogora, M. et al. 2004; Čanić, K.Š. et al. 2009) and in many other processes (for details, see e.g., Meinander, O. et al. 2022; Monteiro, A. et al. 2022). Every year, billions of tons of mineral dust are picked up by the winds from arid semi- arid regions and transported, sometimes thousands of kilometres (Tegen, I. and Lacis, A.A. 1996; Mahowald, N.M. et al. 1999, 2006; Ginoux, P. et al. 2001). The main source areas are in the Sahara, from where the dust is transported to the Atlantic (as far as the Americas); northwards to Europe; and eastwards to the Middle East. The frequency of dust transport to Europe has changed in recent years (Varga, Gy. 2020; Hrabcak, P. 2022; Salvador, P. et al. 2022; Cuevas-Agulló, E. et al. 2023; Kok, J.F. et al. 2023). In Spain, France, Central Europe, the Carpathian Basin and even at higher latitudes such as Greenland (Francis, D. et al. 2018), Iceland (Varga, Gy. et al. 2021), and Finland (Varga, Gy. et al. 2023), the changing flow patterns and the occurrence of African dust have been noticed. The general picture of the Saharan dust masses and dust storm events reaching the Carpathian Basin over the last 40 years has been described in great detail in previous publications (Varga, Gy. et al. 2013; Varga, Gy. 2020). In this paper, we present the frequency and intensity variations observed in the last few years, including the characteristics of the grain size and particle size distribution of the transported dust. Material and methods Study area We investigate Saharan dust events reaching the Carpathian Basin (45°–48.5° N, 16°–23° E). This closed basin in central Europe is bound- ed by the Alps, Carpathians and Dinarides mountain ranges. The climate and weather are determined by three meteorological re- gimes: Atlantic, Continental and Mediter- ranean. Previous research by Varga, Gy. (2020) on dust storm events from the Sahara has shown that air masses of African origin typically transport desert dust into the region in spring and summer. Winter dust storm events have also increased in the last decade, sometimes accompanied by significant depo- sition and muddy rain. From 1979 to 2018, 218 Saharan dust storm events have reached the Carpathian Basin, with a clear increasing trend in the time series. Identification of dust storm events For reasons of consistency with previous research, the same methodology was used as before. Potential dust storm events were identified using standardised values from 321Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. daily TOMS, EP and OMI Aerosol Index data available since 1979. Verification of the potential events was based on a multi-step procedure using satellite imagery, modelling of the air trajectory propagation by HYSPLIT back-trajectory (HYbrid Single-Particle La- grangian Integrated Trajectory – Stein, A.F. et al. 2015), CALIPSO aerosol v4.10 subtype vertical profiles (https://www-calipso.larc. nasa.gov/) to verify the presence of mineral dust in the air column, and the MERRA-2 Dust Column Mass Density dataset avail- able since 1980 (Area-Averaged of Dust Col- umn Mass Density [M2T1NXAER v5.12.4] – Gelaro, R. et al. [2017] – data were obtained from Giovanni application for visualisation and access Earth science remote sensing data platform [https://giovanni.gsfc.nasa.gov/gio- vanni/]). Also from the MERRA-2 database are the wet and dry dust deposition data (Dust Dry Deposition Bin-all: M2TMNXADG v5.12.4; Dust Wet Deposition Bin-all: M2TM- NXADG v5.12.4; Dust Dry+Wet Deposition Bin-all: M2TMNXADG v5.12.4). In addition to the areal averages of the MERRA-2 datasets, we also used spatial flux data of dust dispersion and the Barcelona Supercomputing Center NMMB/BSC model (Pérez, C. et al. 2011; Klose, M. et al. 2021), where dust load, dry and wet deposition values were estimated using the SDS-WAS (Sand and Dust Storm Warning Advisory and Assessment System) interface. Synoptic meteorology Synoptic meteorology-based typing of indi- vidual events was based on the Daily Mean Composite application of NOAA Earth Sys- tem Research Laboratory (http://www.esrl. noaa.gov/psd/) using the NCEP/NCAR (Na- tional Centers for Environmental Protection / National Center for Atmospheric Research) Reanalysis Project dataset (Kalnay, E. et al. 1996) 700 hPa potential level, meridional and zonal wind components, and wind vectors. The use of the 700 hPa level as a vertical level, also considered as a typical transport altitude, has been shown to be characteristic in previous studies (Alpert, P. et al. 2004; Barkan, J. et al. 2005; Varga, Gy. et al. 2013). To analyse the possible role of high-altitude eddy-driven polar jet stream flow and its changing patterns, data for the 250 hPa level were also examined. Granulometric analyses Mineral dust samples collected during dust storm events coinciding with intense depo- sition were analysed using automated static image processing technology with a Malvern Morphologi G3-IDSE. During the study, the size and shape parameters of tens of thou- sands (typically 50,000) of individual grains are automatically recorded during scanning with a 40 pixel per µm2 resolution objective. Among the available parameters, we used the circle-equivalent diameter, high-sensitiv- ity circularity, convexity, aspect ratio, solid- ity and grayscale intensity determined as a function of transmittance. Circle-equivalent diameter is calculated as the diameter of a circle with the same area as the projected two-dimensional particle image. The shape parameters are highly depend- ent on the size of the grain (partly for meas- urement-technical reasons), so the 5–40 µm range was investigated for shape-analyses. An accurate indicator of the circularity prop- erty is the high sensitivity (HS) circularity, which is calculated by the instrument as the ratio of the projected area of the grain to the square of its circumference. Solidity value is given by the ratio of the area of the investi- gated object to the area enclosed by the con- vex hull, while aspect ratio is the ratio of the width to the length of a given particle. The value of convexity is determined by dividing the circumference of the convex hull by the circumference of the grain. The perimeter of the convex hull is the smallest convex poly- gon containing the area of the grain. In addition to automated image pro- cessing, mineral composition studies were also performed using a Raman spectrom- Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.322 eter (Kaiser Optical Systems Raman Rxn1 Spectrometer, 785 nm, < 500 mW) as part of the instrument, after correlating the recorded spectra of selected grains with a reference database (BioRad-KnowItAll Informatics System 2017, Raman ID Expert). Results Saharan dust storm events in the Carpathian Basin The identified dust storm events were clas- sified into three main groups based on their synoptic meteorological background and closely related air mass trajectories. A de- tailed description of the classification can be found in Varga, Gy. (2020). The most fre- quent events (about two thirds of all events) are associated with the southward flow of the high-altitude atmospheric trough over the Eastern Atlantic basin, and mainly Saharan dust storm events transported over the West- ern Mediterranean basin are placed in this cluster. African air masses arriving into the Carpathian Basin over the Central Mediterra- nean basin with the frontal flow of the Medi- terranean cyclones were classified as Type-2, accounting for a quarter of all episodes. The relatively rare Type-3 events, under which conditions dust material was drifting over the Atlantic Ocean and then became long-range dust transport episodes with westerly winds, accounted for 8 percent of all events over the last four and a half decades (Figure 1). The previously published database has been extended to November 2023, and now contains 273 identified Saharan dust storm events from 1979 onwards. The time series and seasonality distributions, completed with MERRA-2 deposition data, are shown in Figure 2 and Table 1. The data clearly demonstrate that the number of dust storm events in the region has increased over the last decade and a half. During the first three decades of the period under study, an average of 3–5 episodes per year hit the Carpathian Basin. This number increased to Fi g. 1 . S yn op tic m et eo ro lo gi ca l b ac kg ro un d (m ea n ge op ot en tia l h ei gh t m ap a nd w in d ve ct or s at 7 00 h Pa ) o f d iff er en t t yp es o f S ah ar an d us t e ve nt s. So ur ce : V ar ga , G y. 2 02 0. 323Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. an average of 9 in the 2010s, and to 11 in the 2019–2023 period, which is examined below in detail. According to surface observations and European reports (e.g., Salvador, P. et al. 2022; Cuevas-Agulló, E. et al. 2023), the intensity of each event (the amount of trans- ported and deposited dust) also increased during this period. This is confirmed by the increasing frequency of local muddy rain events, which regularly receive considerable media coverage. A detailed analysis of the dust storm events of the fifth (half)decade of the 45-year database has been undertaken in this article. This included the identification of 55 new ep- isodes between 2019 and 2023. In addition to the increased number of events, it was strik- ing that the occurrence of Type-3 episodes increased significantly, especially in 2022 and 2023. During the five-year period, 10 such episodes were recorded, compared to a to- tal of 17 in the previous 40 years. However, based on surface observations, MERRA-2 Dust Column Mass Density data and dust load data from the BSC operational forecast, there have been changes in intensity in recent years (Figures 3 and 4). Characteristics of some selected events To illustrate the changing intensity of dust transport and increasing frequency of Type-3 episodes, 11 events were selected (Figure 5), the main characteristics of which are present- ed in the following: SDE #1: 23 April 2019. The most intense and widespread Saharan dust storm event in decades hit Europe in April 2019. By 19 April, atmospheric dust forecast models were already predicting large amounts of dust over the Iberian Pen- insula, with a steady supply from the African continent. The cut-off low of 20 April 2019 (a closed circulation system formed from an upper-level trough in the preceding days) de- termined the synoptic situation of North Af- rica, and the cyclonic flow lifted a huge mass of desert dust into the atmosphere. The dust- loaded air masses drifted north and northeast (to the western Mediterranean, Spain, south- ern France and Italy, then towards the Bal- kans, central and western Europe, the British Isles), and on 23–24 April atmospheric dust was observed over the continent from almost Table 1. Decadal, seasonal and type-specific frequencies of Saharan dust storm events in the Carpathian Basin between 1979 and 2023 Types and seasons Decades 1998–2008 1989–1998 1999–2008 2009–2018 2019–2023* Total Type-1 Seasons spring summer autumn winter 14 14 2 2 10 4 2 – 15 15 3 2 17 24 9 13 10 10 10 5 66 67 26 22 T1 total 32 16 35 63 35 181 Type-2 Seasons spring summer autumn winter 7 – 3 4 6 – 1 – 8 2 2 2 7 2 4 7 6 2 1 1 34 6 11 14 T2 total 14 7 14 20 10 65 Type-3 Seasons spring summer autumn winter – 1 1 – 2 1 – – 3 4 – – 3 1 4 2 5 – – 7 – 6 2 2 10 3 12 6 6 27T3 total Total 48 27 53 90 55 273 *Refers to a half-decade period. Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.324 Fi g. 2 . F re qu en cy o f S ah ar an d us t s to rm e ve nt s by ty pe a nd te m po ra l c ha ng es in m od el le d va lu es o f d ep os iti on in th e C ar pa th ia n Ba si n be tw ee n 19 79 a nd 2 02 3. S ou rc e: A ut ho rs ’ o w n el ab or at io n. 325Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. Fig. 3. MERRA-2 daily Dust Column Mass Density and monthly deposition data, and identified Saharan dust storm events by type, 2019 to 2023. Source: Authors’ own elaboration. Fig. 4. Dust transport pathways of Saharan dust storm events reaching the Carpathian Basin by year between 2019 and 2023. (Numbered and bolded trajectories of selected episodes are described in the text). Source: Authors’ own elaboration. Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.326 Fig. 5. Synoptic meteorological background (700 hPa geopotential height); backward trajectories of dust-loaded air masses; modelled dust load and wet dust deposition. Data source: WMO Barcelona Dust Regional Center and the partners of the Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS) for Northern Africa, the Middle East and Europe. 327Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. Fig. 5. – Continued. Iceland to southern Turkey. The meteorologi- cal background to the event is a cut-off low resulting from the southward movement of a high-altitude atmospheric trough over the eastern Atlantic basin. The intense souther- ly flow formed on the foreward side of the eastward moving low pressure plume, which then spread from NW Europe to the eastern Mediterranean Sea due to the blocking effect of the anticyclone over the continent. SDE #2: 27 May 2019. The strong southerly flow (meridional wind component above 20 < m/s at the typical dust transport height of 700 hPa) of the foreward side of the cyclone that formed over the west- ern Mediterranean Sea and then deepened over the central sub-basin drifted the Saha- ran dust over the Carpathian Basin in late May 2019. During the precipitation events associated with the Mediterranean cyclone, Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.328 large amounts of dust were washed out over central Europe. An extensive cirrus canopy was observed in satellite imagery and in cloud subtype analyses of CALIPSO vertical profiles, the formation of which is assumed to be driven by increased dust concentration and condensation nuclei number. SDE #3: 9 February 2020. The transport path of the Saharan dust storm event identified in February 2020 is the long- est trajectory identified in recent decades, with desert dust reaching the Carpathian Basin atmosphere after a transport of about 7,500 km. The episode associated with the Western Sahara dust plume initially headed towards the Atlantic Ocean, driven by the clockwise flow regime of a large-scale anti- cyclone over the southern Iberian Peninsula and the north-western Sahara. Dust drifting over the ocean was carried northwestward by the circulation system of the high-pres- sure atmospheric object and then moved towards Europe in the westerly wind belt. During this period, the unusually southerly position of the polar jet stream contributed to the formation of several Atlantic depres- sions and their associated storms, violent cyclones and synoptic situations dominated by meridional wind components. The former Iberian anticyclone led to the formation of a western European omega block, which was of fundamental importance in controlling the direction of dust transport. It should be mentioned that the present episode is also included in the catastrophe of Saharan dust storm events reaching Iceland, as well as the April 2019 episode (Varga, Gy. et al. 2021). SDE #4: 15 May 2020. Intense dust storms developed in the south- ern foothills of the Atlas Mountains during the powerful wind gusts of a cold drop from the high amplitude southerly wave of the polar jet stream. African air masses, driven by a southwesterly flow driven by a pressure gradient generated by a frontal trough cross- ing Europe in a southwesterly-northeasterly direction and a pressure gradient between a southeastern European high-pressure block- age, reached the Carpathian Basin in mid- May 2020. The huge amounts of particulate matter were transported from the southern Atlas foothills, from unconsolidated sedi- ments of its mountain foothills, from the deposits of its intermittent water flows and from the sediments of its salt lakes, which also have a hectic water flow, so from rela- tively nearby Saharan source areas. Dust deposition has been reported from many countries (Garofalide, S. et al. 2022), and the deposited dust was clearly observed on car windscreens, roof windows and other outdoor surfaces. The particle size of the samples collected from the deposited particulate matter var- ied over a wide range, with both the finest (fine silt) and sand fractions appearing on the distribution curve, with a mode of 32.6 µm. SDE #5: 24 February 2021. The large-scale circulation conditions of the event were determined by a central European atmospheric ridge and the omega blocking situation formed by the troughs on either side. The western trough appeared more prominent on the pressure maps than the eastern one and extended as far northwest as Africa, where a cut-off low was also formed. This meteoro- logical situation persisted for days and in this stationary state the Saharan dust transport over the western Mediterranean basin flowed directly northwards towards higher latitudes. In the atmospheric trough flow regime, the transport of dust at latitudes N50° deviated from the meridional direction and followed the isohips towards the Carpathian Basin. Both the enhanced, above-average meridionality and the extreme amount of dust transport associ- ated with this event have been discussed in detail by Francis, D. et al. (2023). Intense dust deposition from southwestern Europe to Fin- land has created opportunities for citizen sci- ence campaigns in many places (e.g., Mein- ander, O. et al. 2023). The results of a highly successful project to collect the dust deposited in the French Alps in connection with the event were published in Dumont, M. et al. (2023). 329Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. The particle size of the samples deposited in the Carpathian Basin was found to be par- ticularly coarse-grained, with a mode size of 98.2 µm in the distribution curve during our measurements, and smaller particles barely appearing in the sample. SDE #6: 13 July 2021. On 9 July 2021, intense dust storms devel- oped in the Tidikelt depression (surrounded by plateaus (Tanezrouft, Plateau du Tade- mait) and mountains (Ahaggar, Tassili-n-Ajj- er), with dust material drifting northwards due to the flow system of a low-pressure at- mospheric formation moving eastwards from the Canary Islands. The Saharan dust-loaded air masses were transported eastwards from western Europe by a cyclonic cold front into the central European atmosphere, where an intense washout episode was again observed. SDE #7: 16 March 2022. Another Saharan dust storm event affecting almost all of Europe hit our region in March 2022. Images of orange-coloured snowfields in the Pyrenees and the Alps attracted a lot of press coverage, but even in Finland there was significant washout (Meinander, O. et al. 2023; Varga, Gy. et al. 2023). The synoptic meteoro- logical background of the event was similar to that of the previous ones: the cut-off low from the high-altitude trough, generated by an unusually high-amplitude southern wave of the polar jet stream, caused violent dust storm to pass through the Atlas, with dust material drifting along the northward branch towards the higher latitudes of Europe. The deposited fine-grained dust samples had a mode size of 12.1 µm, which is the smallest of our Saharan dust samples collected so far. SDE #8: 22 April 2022. A powerful cyclone over the Iberian Peninsula advected large amounts of particulate matter into the Mediterranean Sea from the Atlas fore- lands on 20 April 2022. Two days later, as the low-pressure formation drifted eastwards, its frontal meridional flow brought dust-loaded air masses to the atmosphere of central Europe. Precipitation-washed particulate matter once again appeared as muddy rain in the Carpathian Basin, with the mode of the sam- ples occurring at 26 µm on the volume-based size distribution curve. SDE #9: 19 June 2022. The steep pressure gradient between the cut-off low from the high-latitude trough along the Atlantic coast of the Iberian Penin- sula and northwest Africa and the extensive anticyclone that dominates the weather of southwestern Europe was responsible for the atmospheric transport of Saharan dust, which flowed northward in association with the circulation system. The Saharan dust reached the Carpathian Basin along the northern edge of the dissipating anticyclone, with its clockwise flow passing the British Isles, northern Germany and Poland. SDE #10: 21 June 2023.. The weather of the European continent was dominated by an omega-block low-high-low pressure system with an anticyclonic centre over the central Mediterranean basin. The southerly flow of the western low-pressure system transported particulate matter from the intermountain basins of the Atlas north- wards, where the circulation of the northern edge of the anticyclonic system carried air masses towards the Carpathian Basin. SDE #11: 9 October 2023. The weather in western Europe and north- west Africa was dominated by a powerful anticyclone in early October 2023. Large amounts of dust were released from the At- lantic coastal West African source areas as a result of localised heavy dust storms, which drifted over the ocean and then northwards. In the North Atlantic region, a series of cy- clones deepened and the steep pressure gra- dient between the prevailing atmospheric pressure regimes allowed the further long- range transport of air masses containing large amounts of dust. Dust also reached the Irish region and then flowed towards Central Europe via northwesterly currents. Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.330 Temperature changes during dust storm events The intrusion of African air masses into the temperate zone necessarily leads to warm- ing. The variability in seasonality, synoptic background, intensity, transport path and frequency of Saharan dust storm events by type all play a role in the observed tempera- ture changes during episodes over time. During Type-1 SDEs, the major warming effect is mainly observed in autumn and winter, but the average temperature increase is above 1.5 °C in about all seasons (Table 2). Type-2 events associated with Mediterranean cyclones also typically cause above-average warming in autumn and winter, but over the whole period there has been an increase in the spring warming effect on decadal averages. However, just in the last few years, this effect has again been reduced. In the last five-year period examined in detail, the number of Type-3 events has increased, but the low number of cases means that average effects are not worth talking about for earlier periods. Due to the longest transport path, the warm advection influence of this type could be the weakest, but due to the synoptic meteorological background, i.e., the need for anticyclonic effects in the study area prior to the arrival of dust, a relatively large average temperature increase has been observed in the recent past for summer events. Granulometric and mineral characteristics Granulometric analyses of dust samples col- lected during intense deposition events reveal a high degree of heterogeneity (Figure 6). The particle size of the dust material varies widely, Table 2. Average surface temperature increase in the Carpathian Basin during the Saharan dust events by decades and synoptic type Decades Types Seasons Annual meanspring summer autumn winter 1979–1988 Type-1 Type-2 Type-3 Decadal mean 2.7 -0.6 – 1.6 1.7 – -2.2 1.4 6.6 2.2 2.9 3.8 3.6 2.0 – 2.5 2.6 0.8 0.3 2.0 1989–1998 Type-1 Type-2 Type-3 Decadal mean 3.7 1.0 9.6 3.1 3.6 – – 3.6 4.4 3.3 – 4.1 – – 2.4 2.4 3.8 1.3 4.2 3.2 1999–2008 Type-1 Type-2 Type-3 Decadal mean 3.3 2.0 – 2.8 3.7 4.4 – 3.8 6.6 5.4 5.7 6.0 0.0 7.4 4.1 3.8 3.6 3.6 5.3 3.7 2009–2018 Type-1 Type-2 Type-3 Decadal mean 2.6 4.4 2.3 3.0 3.6 1.6 4.0 3.6 4.8 5.9 – 5.1 4.1 4.6 – 4.3 3.6 4.5 3.6 3.8 2019–2023* Type-1 Type-2 Type-3 Decadal mean 1.4 0.4 – 1.0 4.0 1.9 3.3 3.6 5.4 3.1 0.3 4.5 6.9 1.6 1.1 4.8 4.1 1.0 2.3 3.2 Total Type-1 Type-2 Type-3 Mean 2.7 1.5 4.7 2.4 3.3 2.8 3.2 3.2 5.4 4.3 3.4 4.8 4.3 4.0 2.3 3.9 3.5 2.6 3.2 3.3 *Refers to a half-decade period. 331Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. with relatively coarse particles often observed, exceeding 20–30 µm. For the samples studied, the modes of the volume distribution curves varied from 12.1 µm to 98.2 µm. In some events, the size distributions spanned a wide range. This variability was less observed in the shape parameters. Although we have limited the size dependence of the parameters by ana- lysing only the 5–40 µm range, it is still evi- dent that the largest grain size sample of the 24 February 2021 event shows a different character (with significantly smaller convexity and HS circularity values). It is also observed that the dimensionless Intensity mean values, which are also closely related to size and depend on the light transmittance, also vary in a large range (73.4–117.0). Nevertheless, the shape character- istics of the other samples showed very small differences (Table 3). The high convexity (0.97– 0.98) and solidity (0.94–0.98) parameters clearly support the eolian origin. Our Raman spectroscopy measurements, which do not provide enough data for de- tailed mineralogical analysis, identified quartz, feldspar, calcite, dolomite and gyp- sum in the samples. In addition, other min- erals are obviously present in the deposited material, but the technology used is currently not suitable for their detection (Table 4). However, from the information available, it is clear that quartz and feldspars make up the largest proportion of the samples. The number of quartz grains is closely related to the average grain size, with the samples con- taining the coarsest grains showing the high- est number of quartz. In general, it was also observed that gypsum was mainly observed in samples from the Tunisian chotts and the southeastern foreland of the Atlas. However, it is also clear that these mineralogical data do not allow the possible sources to be precisely determined. It is also notable that the sample associated with the strong dust storm event of March 2022, which affected the largest area, was heterogeneous in mineralogical terms, presumably due to the combined emission of several dust sources that were acive at the same time and the mixing of dust material. Discussion Changing dust transport mechanisms – the new normal? We have highlighted in our previous studies that the number and intensity of Saharan dust storm events in Central Europe (Varga, Gy. Fig. 6. Grain size distributions of Saharan dust material deposited in Hungary. Source: Authors’ own elaboration. Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.332 et al. 2013; Varga, Gy. 2020; Rostási, Á. et al. 2022) has increased in the last 10–15 years. These findings have been confirmed by sev- eral other studies across Europe, which also report more frequent (Salvador, P. et al. 2022; Cuevas-Agulló, E. et al. 2023; Kok, J.F. et al. 2023) and intense Saharan dust storm events. It was also striking that North Afri- can dust is not only reaching the southern regions of the European continent, but is also becoming more frequent in more northerly regions (e.g., Greenland – Francis, D. et al. 2018; Iceland – Varga, Gy. et al. 2021; Fin- land – Meinander, O. et al. 2023; Varga, Gy. et al. 2023). This is supported by data from the last five years, which are presented in this ar- ticle. Both the significantly higher number of events than long-term averages and the changing synoptic background fit well into the context of the previously raised idea that climate change is driving significant changes in atmospheric transport processes. One manifestation of this is the increased warming of the Arctic, i.e. the jet stream pat- tern modifying effect of Arctic amplification (Francis, J.A. and Vavrus, S.J. 2012). This spatially differentiated warming results in a decreasing temperature contrast between higher and lower latitudes, which difference drives the jet stream, and thus determines its trajectory to deviate more from the west-east flow direction, which is clearly characterized by zonal components, and to become wavier (the role of meridional wind components is increased). In general, a meridional pattern of wind vectors was observed at high alti- tudes during the intense episodes. The low- pressure atmospheric systems that blew through the Atlas Mountains (driven by the jet), causing severe dust storms there, turned northwards under the influence of the domi- nant flow and reached central and northern Europe. Similar synoptic situations have been described by Francis, D. et al. (2023) for Saharan dust storm events associated with atmospheric river situations in the Alps, which can coexist with severe melting. In another publication (Francis, D. et al. 2018), they reported on this meteorological situa- tion in the context of the transport of African dust-loaded air masses reaching Greenland. Table 3. Shape properties of mineral particles sampled during dust deposition events in Hungary (D[4,3] – Volume Moment Mean – De Brouckere Mean) Sample name SDE #4 15 May 2020 SDE #5 24 February 2021 SDE #7 16 March 2022 SDE #8 22 April 2022 SDE 19 August 2022 Aspect Ratio D[4,3] Convexity D[4,3] Elongation D[4,3] HS Circularity D[4,3] Solidity D[4,3] Mean Intensity D[4,3] Intensity STDV D[4,3] 0.78 0.97 0.45 0.81 0.96 77.56 26.85 0.77 0.86 0.45 0.63 0.94 117.00 25.52 0.77 0.98 0.46 0.82 0.96 78.19 23.21 0.77 0.97 0.45 0.82 0.96 73.39 22.40 0.78 0.98 0.54 0.86 0.98 93.47 19.12 Table 4. General mineralogical properties of the Saharan dust samples collected in Hungary SDE Quartz Feldspar Calcite Dolomite Gypsum % SDE #4 – 15 May 2020 SDE #5 – 24 February 2021 SDE #7 – 16 March 2022 SDE #8 – 22 April 2022 SDE – 19 August 2022 Mean 74.7 85.6 68.1 74.1 75.7 75.9 15.2 4.1 10.1 17.9 14.3 13.0 6.3 1.0 7.2 5.6 1.4 4.4 1.3 9.3 5.8 0.6 4.3 3.8 2.5 0.0 8.7 1.9 4.3 2.9 333Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337. This type of increased meridional flow due to climate change will lead to extreme weather events. Atmospheric flows driven by the wavy jet stream cross zones with fun- damentally different climatic parameters in their general characteristics, sometimes caus- ing cold spells from the Arctic and, as shown in this paper, warm advection from the hot subtropical climatic zones. Effects of giant dust transport on mineral dust- related interpretations The particle size data reported in our observations and measurements also fit well into the range of recent papers on particle size of particulate matter. Previous observations and concepts suggest that the typical grain size of particulate matter reaching Europe (and regions generally further away from source areas) should not be larger than 10–20 µm. As is well illustrated by the Eu- ropean measurement datasets collected by Goudie, A.S. and Middleton, N.J. (2001): Crete: 8–30 µm (mode; Mattson, J.O. and Nihlén, T. 1996), 4–16 µm (median); Spain: 4–30 µm (mean; Sala, J.Q. et al. 1996); Germany: 2.2–16 µm (median); Italy: 16.8 µm (modal), 14.6 µm (median; Ozer, P. et al. 1998); South France: 4–12.7 µm (median; Bücher, A. and Lucas, G. 1984), 8–11 µm (median; Coudé-Gaussen, G. 1991); France (Paris Basin): 8 µm (Coudé-Gaussen, G. et al. 1988); Swiss Alps: 4.5 ± 1.5 µm (median; Wagenbach, D. and Geis, K. 1989); and Central Mediterranean: 2–8 µm (mode; Tomadin, L. and Lenaz, R. 1989). These values are also used as upper bounds in the dust dispersion models (GEOS-5; MACC_II; MASINGAR; MetUM; NGAC; NMMB/BSC-Dust; CHIMERE; CMAQ-KOSA; COAMPS; CUACE/Dust; BSC- DREAM8b; DREAM8-NMME-MACC; TAQM_ KOSA – Benedetti, A. et al. 2014). In recent years, the number of papers on long-range transport of large particulate matter has increased significantly, and they report that sometimes 200–300 µm particles can be trans- ported up to thousands of kilometres (Ryder, C.L. et al. 2018; Van der Does, M. et al. 2018; Adebiyi, A.A. et al. 2023). Our reported data also significantly exceed the particle size that was previously considered typical. This also has a major impact on, for exam- ple, the highly underestimated dust deposi- tion data in the models, where the mass of the deposited particulate is related to the third power of the particle size, so a slight upward shift in the size range has a signifi- cant impact on the dust flux data (Adebiyi, A.A. and Kok, J.F. 2020). The (paleo)environ- mental interpretation of the deposition data is thus greatly modified. The importance of eolian dust deposits in climate reconstruc- tions is of particular importance in some regions (e.g., in regions covered by loess). In these data sets, there has so far been no marked inclusion of long-range dust. Conclusions In the paper, we completed our previous long-term (1979–2018) analysis of Saharan dust storm events in the Carpathian Basin with an analysis of the period 2019–2023. The 218 dust storm events previously identified for a 40-year period have been complement- ed by 55 additional events. The number of events over the five-year period was signifi- cantly higher than the long-term average, and this fits well with the picture already in- dicated by the 2010 studies, i.e. that both the number and intensity of dust storm events have increased significantly. Classification based on the analysis of the synoptic background of dust storm events revealed that the typical meteorological background of these events has been modi- fied. Among the atmospheric flow conditions defined by the wavy jet stream, circulation patterns with a more pronounced meridion- al wind component were dominant during the more intense dust storm events. It was clearly observed that the dust material was moving further north within the European domain and was also regularly observed in Germany, Poland and Finland. Circulation patterns across climatic belts are also as- Varga, Gy. et al. Hungarian Geographical Bulletin 72 (2023) (4) 319–337.334 sociated with marked weather changes, so that extreme weather events are regularly observed; warm spells, muddy rain and wet washouts during Saharan dust storm events. Detailed grain size and particle shape anal- yses of samples of the deposited particulate matter showed that the atmospheric dust material is very diverse. A large amount of coarse-grained fraction was observed in the samples analysed. Among the mineral grains, in some samples, coarse rock flour and sand fractions were dominant. Our knowledge of the long-range transport of this coarse fraction is significantly incomplete, as the range above 20 µm is not even parameterised in climate and dust transport models, i.e. calculations of the amount of transported and deposited dust significantly underestimate the actual values. The data on the long-range transport of large particles also point to the need for revision of (paleo)environmental reconstructions and the role of particulate matter of Saharan origin in sediment and soil formation. Acknowledgement: The research was supported by the NRDI projects FK138692. This work has been imple- mented by the National Multidisciplinary Laboratory for Climate Change (RRF-2.3.1-21-2022-00014) project within the framework of Hungary’s National Recovery and Resilience Plan supported by the Recovery and Resilience Facility of the European Union. 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