Saharan dust storms traveling as far as Iceland have been identified in an international collaboration led by Hungarian researchers from the Geographical Institute of the ELKH Research Centre for Astronomy and Earth Sciences (CSFK FTI). Due to changing atmospheric transport mechanisms associated with climate change, similar events are increasingly being observed at higher latitudes. Of particular significance is the fact the Hungarian researchers also found large quantities of giant mineral dust particles (more than a tenth of a millimetre in diameter), which play the opposite role in the Earth's energy balance to the cooling effect of fine-grained dust, causing net warming of the atmosphere. The results of the research on long-distance transport of Saharan dust were published in the journal Scientific Reports a member of the Nature family of journals.
In the recently published paper "Saharan dust and giant quartz particle transport towards Iceland", György Varga, Senior Research Fellow at CSFK FTI, Fruzsina Holman-Gresina (Research Assistant at CSFK; ELTE PhD student) and their Czech and Icelandic co-authors describe Saharan dust storm events identified in the Icelandic region over the past decade and a half, their meteorological background, dust transport routes, possible source areas and general characteristics of the dust particles. The 15 dust storm events identified by remote sensing methods and computer models clearly show that fine-grained mineral dust can travel thousands of kilometres from the Saharan source areas. In fact, particle size and shape analyses of dust collected during two intense events in the Reykjavík area showed that it is not just fine-grained dust of, up to a few tens of microns in diameter that can reach such distances as previously thought, but also large numbers of very large mineral particles of up to 100 microns in size. The researchers carried out the tests using a granulometric characterization instrument based on automated image processing in the Laboratory for Sediment and Soil Analysis of the CSFK FTI .
Climate change: more dust?
The research addresses several aspects of the ongoing climate change issue. Through this study, the researchers have provided new results on the relationship between increased atmospheric meridionality – i.e. the increased dominance of south-north flow systems – and the increased warming of the Arctic, as well as the resulting decrease in the temperature difference between higher and lower latitudes and changing atmospheric flow systems. Reliable instrumental measurements have been available since the 1880s. Since then, the global average temperature has risen by almost 1 degree Celsius. The vast majority of this warming has occurred in the last 10-15 years and its spatial distribution is not uniform: warming in polar regions is several times greater than the temperature change at lower latitudes (a process known as Arctic amplification). The evolution of Rossby waves, which are responsible for cyclonic activity in the temperate zone, varies with the meridional temperature difference: the smaller the difference, the slower the formation of high atmospheric waves with larger amplitudes. Because of these large-amplitude swings, choppy flows from the desert areas of North Africa can carry large amounts of dust northwards (like blowing the dust off a table with a strong wave motion of the tablecloth). This can sometimes be seen across Europe, and a link has been found in Hungary between the meandering jet stream and the increasing amounts of Saharan dust being transported into the Carpathian Basin. What is particularly interesting, however, is that Saharan dust can travel as far as Iceland on so many occasions.
Giant Saharan dust particles in the Arctic atmosphere
The significance of the research is further enhanced by the fact that the analysis of hundreds of thousands of individual mineral particle sizes and fractions has shown that many more large particles are being released into the atmosphere than previously thought. Because of their size, these dust particles – unlike fine-grained dust – absorb rather than reflect radiation from the Sun, so they have a heating rather than a cooling effect. For this reason, the parameterization of their role in the Earth's energy balance in global climate models needs to be modified. As Iceland is itself the largest dust-emitting region in Europe, with 44,000 km2 of desert area and an average of 135 dust storm days per year, samples collected from the Icelandic source areas were analyzed in the laboratory to separate Saharan and local dust and to exclude possible local 'contamination' of the samples thought to be from the Sahara. Like the samples from settled particulate matter, these were analyzed using automated static image processing. This method allows researchers to obtain direct particle size and shape data from small samples. The granulometric data from hundreds of thousands of individual particles are complemented by data from the Malvern Morphologi G3-IDSE Raman spectroscope, which also provides mineral phase information. The researchers found that the size and shape properties of the dust material from local source areas can be effectively distinguished from each other using this method. Particles of similar size had different shapes and particles of similar shape had different sizes. These tests could not have been carried out with any other instrument. For recurrent dust storm events, this method is used only by the CSFK FTI research team worldwide.
The research was carried out with the support of CSFK, project No. KH130337 ("Granulometric analysis of recent Saharan dust"), project No. K120620 ("Paleoenvironmental reconstruction based on particle size and shape of aeolian dust deposits ") of the National Research, Development and Innovation Office (NKFIH), and the Excellence Cooperation Program (KEP-08/2018) of the Hungarian Academy of Sciences, and in cooperation with the COST Action in Dust program with the participation of Hungarian, Czech and Icelandic researchers.
Varga, Gy.; Dagsson-Walhauserová; Gresina, F.; Helgadottir, A. (2021). Saharan dust and giant quartz particle transport towards Iceland. Scientific Reports
Air masses loaded with Saharan dust heading towards Iceland in February 2008 (source: https://worldview.earthdata.nasa.gov/)
The flow system of the jet stream as it becomes undulating (source: NOAA https://www.climate.gov/)
Malvern Morphologi G3-ID granulometric characterization instrument at the CSFK FTI Rock and Soil Laboratory
Close-up on particle size and shape analysis based on automatic image processing