Vegetation gap patterns in arid grasslands, such as the "fairy circles" of Namibia, are one of nature's greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomasswater feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil-water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass-water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known.drylands | spatial pattern | Triodia grass | Turing instability | vegetation gap P attern-formation theory (1) and the influence of Alan Turing's work on understanding biological morphogenesis (2) are increasingly recognized in environmental sciences (3). Vegetation patterns resulting from self-organization occur frequently in waterlimited ecosystems and, similar to Turing patterns, show pattern morphologies that change from gaps to stripes (labyrinths) to spots with decreasing plant-available moisture (4-6). The patterns may emerge on completely flat and homogeneous substrate and are induced by positive feedbacks between local vegetation growth and water transport toward the growth location.

Aeolian ripples are common in sandy environments on Earth and Mars. On Earth, ripples in sorted dune sands typically are <1 cm high and are erased in high winds. On Mars in similar sands, ripple wavelengths commonly exceed 2 m, with much smaller ripples superimposed. Large Martian ripple sizes and juxtaposition of multiple wavelengths have raised questions about origins and the applicability of terrestrial aeolian physics to different planetary environments. Here, two hypotheses are evaluated for large Martian ripples: (1) fluid/wind drag, analogous to ripples formed under water on Earth, as proposed previously for Martian large ripples; and (2) saltation impact splash, the mechanism creating aeolian ripples of much smaller size on Earth. This study evaluates these hypotheses with numerical experiments and Mars rover observations, and concludes that large Martian ripples develop through the saltation impact splash mechanism. The low-density Martian atmosphere enables aeolian impact ripples to grow much higher into the boundary layer before reaching maximum heights constrained by wind dynamic pressure effects at crests. In this concept, boundary layer conditions influence mature ripple heights more directly than wavelengths. On Mars, low wind dynamic pressures, combined with the impact splash mechanism, also help to explain other distinctively Martian aeolian bedforms, including large longitudinal ripples observed by rovers and orbiters, and transverse aeolian ridges (TARs) distributed widely across the Martian surface. Compared with Earth, low wind dynamic pressures on Mars permit a wider range of ripple sizes, relative ages, morphologies, and orientations in close proximity, as displayed in rover observations. Plain Language Summary On Earth, winds drive sand grains downwind in bouncing motions (called "saltation"). Each high-energy bounce also splashes other surface grains shorter distances, and this impact splash process creates small,~10 cm wavelength ripples with heights <1 cm in typical dune sands. On Mars, sands with similar grain sizes form much larger ripples with wavelengths exceeding 2 m, and their origins have been debated. In this study, numerical simulations and Mars rover observations indicate that aeolian impact ripples can grow much larger on Mars than on Earth because the thin Martian atmosphere does not interfere with the upward growth of ripple crests until ripples are much higher (which in turn constrains minimum, but not maximum, ripple wavelengths). In this concept, wind conditions influence mature aeolian ripple heights more directly than ripple wavelengths. This concept also helps explain other, distinctively Martian aeolian features including large longitudinal ripples, and large transverse aeolian ridges (TARs) observed widely across the Martian surface.

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Dust storms include particulate matter that is transported over land and sea with biota that could impact downwind ecosystems. In addition to the physico-chemical compositions, organismal diversities of dust from two storm events in southern Israel, December 2012 (Ev12) and January 2013 (Ev13), were determined by pyro-sequencing using primers universal to 16S and 18S rRNA genes and compared. The bio-assemblages in the collected dust samples were affiliated with scores of different taxa. Distinct patterns of richness and diversity of the two events were influenced by the origins of the air masses: Ev13 was rich with reads affiliated to Betaproteobacteria and Embryophyta, consistent with a European origin. Ev12, originated in north-Africa, contained significantly more of the Actinobacteria and fungi, without conifers. The abundance of bacterial and eukaryotic reads demonstrates dissemination of biological material in dust that may impose health hazards of pathogens and allergens, and influence vegetation migration throughout the world.

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Quantitative information on the contribution of dust storms to atmospheric PM 10 (particulate matter with an aerodynamic diameter 10 µm) levels is still lacking, especially in urban environments with close proximity to dust sources. The main objective of this study was to quantify the contribution of dust storms to PM 10 concentrations in a desert urban center, the city of Beer-Sheva, Negev, Israel, during the period of [2001][2002][2003][2004][2005][2006][2007][2008][2009][2010][2011][2012]. Toward this end, a background value based on the "dust-free" season was used as a threshold value to identify potentially "dust days. " Subsequently, the net contribution of dust storms to PM 10 was assessed. During the study period, daily PM 10 concentrations ranged from 6 to over 2000 µg/m 3 . In each year, over 10% of the daily concentrations exceeded the calculated threshold (BV t ) of 71 µg/m3 . An average daily net contribution of dust to PM 10 of 122 µg/m 3 was calculated for the entire study period based on this background value. Furthermore, a dust storm intensity parameter (Ai) was used to analyze several storms with very high PM 10 contributions (hourly averages of 1000-5197 mg/m 3 ). This analysis revealed that the strongest storms occurred mainly in the last 3 yr of the study. Finally, these findings indicate that this arid urban environment experiences high PM 10 levels whose origin lies in both local and regional dust events.Implications: The findings indicate that over time, the urban arid environment experiences high PM 10 levels whose origin lies in local and regional dust events. It was noticed that the strongest storms have occurred mainly in the last 3 yr. It is believed that environmental changes such as global warming and desertification may lead to an increased air pollution and risk exposure to human health. IntroductionNumerous studies have reported high concentrations of ambient particulate matter (PM) during dust events in different parts of the world (e.g., Dayan et al., 1991;Gertler et al., 1995;Rodriguez et al., 2001;Kallos et al., 2006;Escudero et al., 2007; Koçak et al., 2007a; Mitsakou et al., 2008; Contini et al., 2010;Alolayan et al., 2013). More importantly, several studies have found excess in mortality and morbidity during dust storm episodes (e.g., Chen et al., 2004;Gyan et al., 2005; Perez et al., 2008;Neophytou et al., 2013).Due to the proximity of Israel to the global dust belt, which extends from West Africa to the Arabian Desert, dust events can increase daily PM 10 (PM with an aerodynamic diameter 10 mm) levels in the center of Israel (Tel Aviv) to as high as 2100 mg/m 3 (Ganor et al., 2009;Kalderon-Asael et al., 2009), which is significantly above all air quality standards. The Negev region in southern Israel is frequently impacted by dust storms (Dayan et al., 1991;Erell and Tsoar, 1999;Offer et al., 2008;Ganor et al., 2010). Hourly average PM 10 concentrations can reach 4200 mg/m 3 during storms in the northern Negev (Offer and Azmon, 1994). The intense dust storms in the N...