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Martian gullies are alcove-channel-fan systems which have been hypothesized to be formed by the action of liquid water and brines, the effects of sublimating CO2 ice or a combination of these processes. Recent activity and new flow deposits in these systems have shifted the leading hypothesis from water-based flows to CO2-driven flows. This shift in thinking is supported by the low availability of atmospheric water under present Martian conditions and the observation that gully activity occurs at times when CO2 ice is present. We recently performed novel experiments that have shown that this hypothesis holds; sediment can be mobilized and fluidized by sublimating CO2 ice under Martian atmospheric pressure. However, if these flows are able to erode the underlying surface and can explain the formation of Martian gully systems over the long term remains unknown. Therefore, we present an additional series of experiments that test the capacity of CO2-driven granular flows under Martian atmospheric conditions to erode sediment. These experiments were conducted in a 4 m long flume in the Aarhus Mars Simulation Wind Tunnel. Our experiments show that CO2-driven granular flows can erode loose sediment under a range of different slopes and CO2-ice fractions. The results also show that incorporation of warmer sediment increases fluidization of the mixture, reflected by an increase in gas pore pressure in the flow. These results thus prove that morphological evolution in the gully systems on Mars can be explained by CO2-driven granular flows.

Activities at a European Planetary Simulation Facility J. P. Merrison, J.J. Iversen, K.R. Rasmussen, A. Waza 1Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark (merrison@phys.au.dk/ Fax: +45-86120740) AbstractThis unique and now improved planetary simulation facility is capable of re-creating extreme terrestrial, Martian and other planetary environments. It is supported by EU activities including Europlanet 2024 RI here the latest research and networking activities will be presented. This facility is also used as a test facility by ESA and NASA Mars missions. Specifically it is capable of recreating the key physical parameters such as temperature, pressure (gas composition), wind flow and importantly the suspension/transport of dust, sand or ice particulates. This facility is available both to the scientific and Industrial communities. Europlanet Transnational Access This environmental simulator facility is utilized for a broad range of research programs including; the study of other planets (such as Mars), for recreating extreme terrestrial environments, or in specific investigations involving aerosols and other forms of Aeolian particulate transport. The facility is also involved in the Europlanet 2024 Research Infrastructure through which a trans-national access program is allowing numerous research groups access to this facility. Some selected recent and upcoming projects are listed below;Polar CO2 ice on Mars (USA) [5] LIBS system on Mars2020 (ISAE France) [3] Sand transport and ripples on Mars (P. Claudin, B. Andreotti, et al. 2019) Dust aerosols at low pressure. INGV, I [6] Flow Testing of a Sonic Anemometer for the Martian Environment (USA) [4] In-situ utilization on Mars2020 and dust loading. Imperial College UK [7] Other activities include the development, testing and calibration of sensor and planetary lander systems, both for ESA and NASA. Testing for missions ExoMars 2020 and Mars Perseverance were carried out. Figure 1 The main Planetary Simulation Facility 2022 carrying out a Europlanet2022RI funded experiments involving sand transport under Marian conditions and guests; Design and operation The simulator consists of a 38m3 environmental (thermal-vacuum) chamber within which a re-circulating wind tunnel is housed [1]. The wind is generated by a set of two fans which draw flow down the 2m×1m tunnel section and return it above and below. Wind speeds in the range 1-40 m/s have been demonstrated. Cooling is achieved by a novel liquid nitrogen flow system which has achieved temperatures below -160ºC. The inner chamber is thermally isolated from the vacuum chamber. An atmospheric cooling system allowing independent control of the air temperature (tested to -50°C) and a range of particle imaging, microscopy and laser based techniques allow study of aerosols [2].Improved functionalities of this facility (funded by Europlanet 2024RI) include the implementation of; improved pumping capabilities to lower pressure ( Figure 2 studying resuspended dust using a Laser Doppler Velocimeter and a light transmission (opacity) system. Sand, dust and ices on Mars With control of wind flow at low pressure and temperature this facility is well suited for recreating the environment at the surfaces of terrestrial type planets such as Mars, Earth and Titan. The interaction of wind and the planetary surface, specifically the transport of sand and dust is fundamental to understanding the evolution of the planets’ surface and atmosphere. Laboratory studies of the entrainment, flow, deposition and erosion are scarce and empirical in nature. The effects of low atmospheric pressure, composition, temperature can now be studied in detail.This laboratory is part of an EU supported European collaboration called ROADMAP including groups from BIRA in Belgium, CSIC in Spain and UDE in Germany, to study dust aerosols on Mars [Home (aeronomie.be)]Recently Martian Aeolian ripples have been recreated in experiments to investigate the behaviour of wind-driven sand transport under decreasing pressures, from the ambient (1 bar) towards Martian atmospheric conditions, and even to lower pressures than on Mars (2 mbar). In comparison to terrestrial conditions, sand transport at Martian pressures is significantly modified by viscous effects. However, centimeter-scale ripples nevertheless emerge (fig. 2), which match observations made by NASA’s rover Opportunity on the surface of Martian dunes. Fig. 3 Ripples created at low pressure (P. Claudin, B. Andreotti, et al.). Conclusion This planetary simulation facility has many unique and recently improved features which make it well suited for both planetary research applications and the development/testing of instrumentation. Details of some of the most recent and upcoming collaborative research activities will be summarized. For information on access to this facility please contact the author.AcknowledgementsThis laboratory is a member of Europlanet 2024 RI which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871149.The laboratory is also a member of the ROADMAP project which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004052.References[1] C. Holstein-Rathlou, et al., American Meteorological Society, 31, 447 (2014)[2] S. Alois et al., J. Aerosol Science 106, 1, (2017)[3] Murdoch, N., et al., Planet and Space Sci, 165 (2019) 260-271[4] White, R. D. et al. AIAA Scitech 2020. AIAA2020-0712[5] G. Portyankina et al., Icarus 322, 210–220 (2019)[6] E. del Bello, et al., Scientific Reports, 8, 14509 (2018)[7] Andreotti and Claudin et al.. PNAS 5, 118 (2021)

The European Commission (EC) is currently formulating their vision for future research infrastructures (RIs) and how they should deliver improved transnational access (TNA) for the broad scientific and industrial community. There is a major emphasis on ensuring RIs are self-governing and sustainable. Many of the larger, often government supported, RIs will operate as European Research Infrastructure Consortia (ERICs). ERICs are generally established around large national research facilities. The Europlanet Society has instead chosen to be a AISBL (International Non-Profit Organization) based in Belgium ensuring control by the scientific community. Upon granting of the AISBL status, expected later in 2022, the Europlanet Society will be in position to lead or co-operate in any future RI initiatives. Based on a series of briefings by the EC, it is predicted that existing established RIs such as Europlanet will be expected to collaborate within and across disciplines to offer a wider range of transnational access. For Europlanet this will mean collaboration within the Astronomy-AstroChemistry communities Opticon, RadioNet, ChETEC, etc. In addition, future TNA programmes will be expected to involve: more diverse facilities; greater interaction with participation by industry; greater globalisation with an emphasis on Africa and Asia; more active participation from the under-represented European states. reduced environmental impact; We believe that Europlanet is in a strong position to achieve many of these requirements. The next call for modified RIs that provide transnational access is expected to be launched in astronomy-space realm at the end of 2022, for calls in 2023 and 2024. It is therefore necessary to start to formulate ideas for a future TNA programme. The presentation at EPSC will give a brief review of the current status of the Europlanet 2024 RI, and is designed to initiate and stimulate discussion within the planetary community as to their wishes for future TNA facilities, specifically in light of ESA goals to return to the Moon and an increased focus on Exoplanetary science.

This work applies a previously suggested model of gravitational field propagation to various planetary bodies within the solar system. Primarily the goal has been to critically test the validity of this model by identifying observations which are in direct conflict with it. Specifically this model predicts a Doppler shift in gravitational acceleration (gD). Applying the model to the planets and the Sun gD acts to increase planetary spin, opposing various sources of drag. The model is seen not to be in conflict with a wide variety of observed parameters which have been treated here and is shown to quantitatively account for several observed phenomena previously thought to be unrelated and which have been di˚cult to explain conventionally. These phenomena include the internal heat generation and magnetospheric generation within the gas giants as well as super rotation which seen in most planetary atmospheres as well as the Sun as differential rotation. This model for the first time provides a quantitative prediction of the low internal heat generation seen in Uranus compared to Neptune. It also provides a novel mechanism for solar coronal heating, thermospheric heating in the gas giants and the correlation between climate and magnetosphere observed on Earth.

The Optical Particle Counter 'MicroMED' will be part of the ExoMars 2022 mission and aims to provide the first ever direct measurement of airborne Martian dust. The instrument has been tested at the INAF - OAC premises, where a Martian chamber is present, simulating the Martian environment in terms of pressure, instrument temperature, atmosphere composition and the presence of dust. However, tests in the presence of wind are also needed for the instrument characterization. To this purpose, a test campaign at the AWTS II simulator at the Aarhus University (Denmark) was performed, testing the instrument in the presence of winds up to 15 m/s. Such tests are important since wind is the main agent of landscape modification on Mars. The present work describes the results of such tests, showing the variation of the instrument detecting ability with the wind speed, as well as the influence of temperature on performances.

Located on top of the mast of the Mars 2020 Perseverance rover, the SuperCam instrument suite includes a microphone to record audible sounds from 100 Hz to 10 kHz on the surface of Mars. It will support SuperCam’s Laser-Induced Breakdown Spectroscopy investigation by recording laser-induced shock-waves but it will also record aeroacoustic noise generated by wind flowing past the microphone. This experimental study was conducted in the Aarhus planetary wind-tunnel under low CO 2 pressure with wind generated at several velocities. It focused on understanding the wind-induced acoustic signal measured by microphones instrumented in a real scale model of the rover mast as a function of the wind speed and wind orientation. Acoustic spectra recorded under a wind flow show that the low-frequency range of the microphone signal is mainly influenced by the wind velocity. In contrast, the higher frequency range is seen to depend on the wind direction relative to the microphone. On the one hand, for the wind conditions tested inside the tunnel, it is shown that the Root Mean Square of the pressure, computed over the 100 Hz to 500 Hz frequency range, is proportional to the dynamic pressure. Therefore, the SuperCam microphone will be able to estimate the wind speed, considering an in situ cross-calibration with the Mars Environmental Dynamic Analyzer. On the other hand, for a given wind speed, it is observed that the root mean square of the pressure, computed over the 500 Hz to 2000 Hz frequency range, is at its minimum when the microphone is facing the wind whereas it is at its maximum when the microphone is pointing downwind. Hence, a full 360 ∘ rotation of the mast in azimuth in parallel with sound recording can be used to retrieve the wind direction. We demonstrate that the SuperCam Microphone has a priori the potential to determine both the speed and the direction of the wind on Mars, thus contributing to atmospheric science investigations.

Aeolian sediment transport is observed to occur on Mars as well as other extraterrestrial environments, generating ripples and dunes as on Earth. The search for terrestrial analogues of planetary bedforms, as well as environmental simulation experiments able to reproduce their formation in planetary conditions, are powerful ways to question our understanding of geomorphological processes towards unusual environmental conditions. Here, we perform sediment transport laboratory experiments in a closed-circuit wind tunnel placed in a vacuum chamber and operated at extremely low pressures to show that Martian conditions belong to a previously unexplored saltation regime. The threshold wind speed required to initiate saltation is only quantitatively predicted by state-of-the art models up to a density ratio between grain and air of $4 \times 10^5$, but unexpectedly falls to much lower values for higher density ratios. In contrast, impact ripples, whose emergence is continuously observed on the granular bed over the whole pressure range investigated, display a characteristic wavelength and propagation velocity essentially independent of pressure. A comparison of these findings with existing models suggests that sediment transport at low Reynolds number but high grain-to-fluid density ratio may be dominated by collective effects associated with grain inertia in the granular collisional layer., Comment: 38 pages, 21 figures

The resuspension of volcanic ash by wind is a significant source of hazard during and after volcanic eruptions. Parameterizing and modeling ash resuspension requires direct measurement of the minimum wind shear stress required to move particles, usually expressed as the threshold friction velocity U ⁎ th, a parameter that, for volcanic ash, has been measured only scarcely and always in the laboratory. Here, we report the first field measurements of U ⁎ th for volcanic ash, with a portable wind tunnel specifically developed, calibrated, and tested. Field measurements, performed on natural reworked ash deposits from Sakurajima (Japan) and Cordón Caulle (Chile) volcanoes, agree well with our laboratory determinations on ash from the same deposits, with values of U ⁎ th ranging from 0.13 to 0.38 m/s. Our results show that the median grain size of the deposit and particle shape have a stronger control on U ⁎ th than the local substratum nature and deposit texture.

Introduction: The transport of ice by wind plays a major role in the surface mass balance of polar caps [1, 2]. Ice can be redistributed by wind due to (1) transport of ice particles and/or (2) transport of water vapour associated with sublimation/condensation. On Mars, although the low atmospheric density is less favourable for the transport of particles than on Earth, both dust and sand have been observed to be transported by wind [3,4]. Despite ice aeolian landforms have been observed at the surface of the North Polar Cap of Mars [2, 5, 6], ice particle transport has not been directly observed on the Martian surface. Similarly, no laboratory studies of snow/ice particle transport under Martian-like conditions have been attempted thus far due to the complexity of the material. In this study we performed experiments of ice particle transport in a wind-flow under low temperatures and low pressures. From the experiments, threshold shear velocity of water ice particle transport is retrieved for different pressures and sizes in order to evaluate the plausibility of ice particle wind-driven transportation at the surface of Mars. The North Polar Cap of Mars: The Martian atmosphere is thin (7 mbar), cold (220 K) and dry (< 80 μm-pr) [7]. These conditions favoured ice sublimation/condensation processes. Spectral analyses [8, 9] suggested the optical ice grain sizes to vary between 10 μm to about 2000 μm for the seasonal frost and surface of the perennial North polar cap. But, the mechanisms of ice deposition are not well established. It can potentially come from vapour condensation directly onto the surface [9] or from snow fall [10]. This will affect the shape and size of ice particles and degree of ice sintering, which all influence the shear velocity threshold. The North polar cap experiences a permanent katabatic wind regime [11] with a typical friction shear velocity u* about 0.2 m.s-1. The complex interaction between the cryosphere and the wind leads to the formation of aeolian features at different scales [2, 5, 6]. Wind tunnel experiments: We performed experiments using the environmental wind tunnel AWTSII at Aarhus University. It is a cylindrical vacuum chamber, housing a recirculating wind tunnel about 8 m long, 2 m wide and 1 m high [12]. The facility can achieve a turbulent boundary layer flow at both low temperature and low pressure. The ice samples were produced by using the Setup for production of Icy Planetary Analogues [13]. The ice samples were sieved (125 - 250 μm, 250 - 500 μm, 500 - 2000 μm) as a monolayer on a plate covered with volcanic regolith (125 μm). The fan speed was increased by steps (shear velocity u* = 0 to 2 m.s-1) and the wind flow characterized by laser Doppler anemometry. The removal of ice particles was monitored by webcam. We performed the experiments for the different particle shapes and sizes for 4 different air pressures; 40, 100, 500 and 1000 mbar. The air temperature was maintained low (~-25°C) close to the sample plate to prevent the ice melting, sublimating and sintering. Threshold shear velocity calculation: The threshold shear velocity was determined from analysis of acquired images. When bright ice particles are removed from the dark volcanic regolith plate, the reflectance of the surface decreases. Black and white reference targets are placed close to the sample plate in the field of view of the webcam. The reflectance evolution of a region of interest (ROI) on the sample plate is calculated as follow: reflectance = (ROI – black target)/(white target – black target) The reflectance serves as a proxy for ice mass removal. For each image the reflectance is linked to the corresponding shear velocity. In most of the cases performed, the reflectance is constant until a certain wind speed and then decreases. To determine the threshold shear velocity uth, we set the threshold reflectance at 10% decrease from the first image at u* = 0 m.s-1. Results and conclusion: We have performed for the 1st time experiments of ice particles transportation at low pressure in a planetary wind tunnel. The averaged threshold shear velocity obtained at 1000 mbar, uth = 0.4 m.s-1, is consistent with theoretical and experimental calculation of ice/snow at terrestrial condition [14, 15], from 0.3 m.s-1 to 0.6 m.s-1 for range of ice particles sizes selected, supporting our set-up reliability. The shear velocity increases significantly as the pressure decreases. The influence of the ice grain sizes is not clear and more experiments are required. The results should then be scaled to Martian gravity in order to compare the results to wind speed simulations and conclude about the likeliness of transport of ice particles by wind at the surface of Mars. References: [1] Das I. et al. (2013) Nature Geoscience, 6, 367-371. [2] Howard A. D. (2000) Icarus, 144, 267-288. [3] Cantor B. A. et al. (2010) Icarus, 208, 61-81. [4] Bridges B. A. et al. (2012) Geology, 40, 31-34. [5] Smith I. B. and Holt J. (2010) Nature, 465, 450-453. [6] Herny C. et al. (2014) EPSL, 403, 56-66. [7] Pankine A. A. et al. (2010) Icarus, 210, 5871. [8] Langevin Y. et al. (2005) Science, 307, 1584-6. [9] Appéré T. et al. (2011) JGR : Planets, 116, E05001. [10] Spiga A. et al. (2017) Nature Geoscience, 10, 652-657. [11] Spiga A. et al. (2011) PSS, 59, 915-922. [12] Holstein-Rathlou C. et al. (2014) Am. Met. Society, 31, 447-457. [13] Pommerol A. et al. (2019) Space Sci. Rev., 215. [14] Shao Y. and Lu H. (2000) JGR, 105, 437-443. [15] Clifton A. et al. (2006) JoG, 52, 585-596. [16] Herny C. et al. (2016) 6th MPSC, Abstract #6075. [17] Bordiec M. et al. (2018) ICAR X. Acknowledgements: This work has been fund by Europlanet (Europlanet 2020 RI has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 654208). This work has been supported by the University of Bern. This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation.

The resuspension of volcanic ash deposits by wind is a well-known source of hazard following explosive eruptions. Besides the mail control exerted by the local wind field, ash resuspension is also influenced by: 1) atmospheric humidity; 2) features of the deposit (grain size distribution, sedimentary structures, etc.), and 3) features of the substrate (i.e. moisture, roughness). Ash resuspension is modeled using numerical simulations, which however require physical characterization and identification of the critical parameters controlling ash resuspension. Wind tunnel studies on volcanic particles are very limited and restricted to laboratory parameterizations, with in-situ effects not been parameterized. We tested field experiments of volcanic ash resuspension developing a portable wind tunnel and deploying on proximal (3 km) ash deposits from the semi-sustained activity of Sakurajima volcano (Japan) and from distal (250 km ca.) ash deposits from the 2011 Cordon Caulle eruption (Chile). The wind tunnel is calibrated with both LDA and pitot tubes measurements. The device allows generating a controlled wind profile within a 110x12x12 cm test section, which is placed directly on an untouched test bed of naturally deposited ash. Two types of experiments were performed: 1) ramp up speed experiments, where the wind speed is increased until reaching the threshold friction speed on four different substrates; 2) constant speed experiments, where three wind speed values where kept for 20 minutes using the same substrate. The threshold friction speed is measured with a hot wire anemometer, and the movement of resuspended ash is detected by means of multiple high speed and high definition digital camcorders. In-situ measured threshold friction speeds are compared to 1) in situ observed episodes of resuspension driven by local winds and 2) laboratory determination of threshold friction speed in controlled environmental conditions, and using the same ash deposited homogeneously.

International audience; The SuperCam instrument suite onboard the Mars 2020 rover will include the Mars Microphone, an experiment designed to record the sounds of the SuperCam laser strikes on rocks and also aeolian noise. In order to record shock waves produced by the laser blasts, the Mars Microphone must be able to record audio signals from 100 Hz to 10 kHz on the surface of Mars, with a sensitivity sufficient to monitor a laser impact at distances up to 4 m. The Aarhus planetary simulator facility has been used to test the Mars 2020 rover microphone in a controlled Martian environment. The end-to-end tests performed in a 6 mbar CO2 atmosphere, with wind, and also with the microphone at −80° C have demonstrated that the SuperCam/Mars Microphone requirements are satisfied. Tests were also performed on Martian soil simulant targets showing that the variation of the acoustic energy of the shock wave depends on the level of compaction of the target.

We have experimentally investigated CO2 ice condensation under conditions similar to those expected in the Martian polar areas using the Environmental Wind Tunnel of Aarhus University in the framework of Trans-National Access opportunities within the EuroPlanet Research Infrastructure. Our goal was to condense CO2 directly from the chamber's atmosphere onto a specially designed cooling plate. We investigated ranges of temperatures and pressures similar to those in Martian polar areas, observed the texture of the created CO2 ice layer, and measured its optical properties. Most importantly, we find that under conditions usual for Martian polar areas in fall and winter, CO2 ice always deposits as a translucent slab. The maximum thickness of the ice that we have achieved approached 2 cm and this CO2 slab ice layer was either transparent or highly translucent. Under significantly lower temperatures or in states away from equilibrium (for example, when CO2 gas input into the chamber was fast and created over-pressure) CO2 deposited as different crystalline structures. In this case, when a thick layer was created, it was not visually transparent. However, even in those cases it still retains some level of translucency. Our results will advance the analysis of remote-sensing data related to CO2 ice, Mars’ seasonal cycles, and various models considering CO2 ice condensation-sublimation related processes.

As a method to experimentally study aerodynamic drag the terminal settling velocities of aerosolized silica and glass microspheres (with sizes of 1–44 μm) have been measured at various gas pressures in the range 0.6–10 mbar and using various gas compositions including He, Ar, Xe, Air, CO 2 , and water vapour. Within the molecular scattering regime, i.e. where the Knudsen number Kn > 10 and up to 500, reasonable agreement has been found with the model of Epstein (1924). Values of the scattering parameter δ were observed to be within the expected range of 1–1.44 for respectively specular/evaporative - diffuse molecular scattering processes. However, δ was seen to depend upon gas composition, specifically for H 2 O; δ = 0.96 ± 0.07, CO 2 ; δ = 1.16 ± 0.07, noble gasses; δ = 1.25–1.44 and in the case of Air δ = 1.18 ± 0.07 which is not in agreement with that conventionally used of around 1.3–1.4. These observations imply disagreement with the concept of a general or universal model of drag for all particle surfaces and atmospheres. Similarly, for Kn < 10 these results were not well described by conventional models such as the semi-empirical expression of Knudsen-Weber (1911) or the general law of fall proposed by Millikan (1923b).

The increasing number of missions to Mars also increases the risk of forward contamination. Consequently there is a need for effective protocols to ensure efficient protection of the Martian environment against terrestrial microbiota. Despite the fact of constructing sophisticated clean rooms for spacecraft assembly a 100 % avoidance of contamination appears to be impossible. Recent surveys of these facilities have identified a significant number of microbes belonging to a variety of taxonomic groups that survive the harsh conditions of clean rooms. These microbes may have a strong contamination potential, which needs to be investigate to apply efficient decontamination treatments. In this study we propose a series of tests to evaluate the potential of clean room contaminants to survive the different steps involved in forward contamination. We used Staphylococcus xylosus as model organism to illustrate the different types of stress that potential contaminants will be subjected to on their way from the spacecraft onto the surface of Mars. Staphylococcus xylosus is associated with human skin and commonly found in clean rooms and could therefore contaminate the spacecraft as a result of human activity during the assembling process. The path the cell will take from the surface of the spacecraft onto the surface of Mars was split into steps representing different stresses that include desiccation, freezing, aeolian transport in a Martian-like atmosphere at Martian atmospheric pressure, and UV radiation climate. We assessed the surviving fraction of the cellular population after each step by determining the integrated metabolic activity of the survivor population by measuring their oxygen consumption rate. The largest fraction of the starting culture (around 70 %) was killed during desiccation, while freezing, Martian vacuum and short-term UV radiation only had a minor additional effect on the survivability of Staphylococcus xylosus. The study also included a simulation of atmospheric transport on Martian dust, which did not significantly alter the metabolic potential of the cells. The high survival potential of skin microbes, which are not among the most robust isolates, clearly underlines the necessity for efficient decontamination protocols and of adequate planetary protection measures. Thus we propose a series of tests to be included into the description of isolates from spacecraft assembly clean rooms in order to assess the forward contamination potential of the specific isolate and to categorize the risk level according to the organisms survival potential. We are aware that the tests that we propose do not exhaust the types of challenges that the microbes would meet on their way and therefore the series of tests is open to being extended.

Dunes in the northern lowlands on planet Mars are composed of volcanic sands with high contents of volcanic glass and these deposits are mobilised and transported by winds in the present-day surface environment. In this experimental study we measured fluid thresholds for detachment of Mars-analogue volcanic glass particles using a low-fluid density wind tunnel under wind shear stresses in the range of 0.1–0.6 N m−2. Measured thresholds for larger particle diameters (>150 µm) were best-explained using a semi-empirical model of detachment which incorporates the effects of drag-induced rolling. Fitting of this semi-empirical model to obtained experimental data, combined with a residual analysis of the model fit with quantified particle properties made it possible to assess the sensitivity and validity of the model for predicting this type of particle detachment. This new model was used to predict the threshold shear stress for detachment of particles on Mars and indicated that larger particle diameters can detach by drag-induced rolling when subjected to present-day surface wind shears. A large morphological and granulometric variety of particles is therefore susceptible to this form of detachment, which provides a possible mechanism for the initial mobilisation of particles at lower wind speeds than required for detachment by saltation. Recent sand mobility may therefore have benefited from rolling as a contributing or as a saltation triggering process.

The results of the Labeled Release and the Gas Exchange experiments conducted on Mars by the Viking Landers show that compounds in the Martian soil can cause oxidation of organics and a release of oxygen in the presence of water. Several sources have been proposed for the oxidizing compounds, but none has been validated in situ and the cause of the observed oxidation has not been resolved. In this study, laboratory simulations of saltation were conducted to examine if and under which conditions wind abrasion of silicates, a process that is common on the Martian surface, can give rise to oxidants in the form of hydrogen peroxide ( H 2 O 2 ) and hydroxyl radicals (⋅OH). We found that silicate samples abraded in simulated Martian atmospheres gave rise to a significant production of H 2 O 2 and ⋅OH upon contact with water. Our experiments demonstrated that abraded silicates could lead to a production of H 2 O 2 facilitated by atmospheric O 2 and inhibited by carbon dioxide. Furthermore, during simulated saltation the silicate particles became triboelectrically charged and at pressures similar to the Martian surface pressure we observed glow discharges. Electrical discharges can cause dissociation of CO 2 and through subsequent reactions lead to a production of H 2 O 2 . These results indicate that the reactions linked to electrical discharges are the dominant source of H 2 O 2 during saltation of silicates in a simulated Martian atmosphere, given the low pressure and the relatively high concentration of CO 2 . Our experiments provide evidence that wind driven abrasion could enhance the reactivity of the Martian soil and thereby could have contributed to the oxidation of organic compounds and the O 2 release observed in the Labeled Release and the Gas Exchange experiments. Furthermore, the release of H 2 O 2 and ⋅OH from abraded silicates could have a negative effect on the persistence of organic compounds in the Martian soil and the habitability of the Martian surface.

Numerical modeling of ash plume dispersal is an important tool for forecasting and mitigating potential hazards from volcanic ash erupted during explosive volcanism. Recent tephra dispersal models have been expanded to account for dynamic ash aggregation processes. However, there are very few studies on rates of disaggregation during transport. It follows that current models regard ash aggregation as irrevocable and may therefore overestimate aggregation-enhanced sedimentation. In this experimental study, we use industrial granulation techniques to artificially produce aggregates. We subject these to impact tests and evaluate their resistance to break-up processes. We find a dependence of aggregate stability on primary particle size distribution and solid particle binder concentration. We posit that our findings could be combined with eruption source parameters and implemented in future tephra dispersal models.

The contact electrification of aerosolized micro particles has been studied using a novel technique involving laser velocimetry. This has allowed the simultaneous determination of size and electrical charge of individual silica microspheres (in the range 1 – 8 µm). Interestingly the particles interacting with the injector tube have been seen to become electrified with a relatively narrow range of surface charge concentration of around Q/4πr 2 ~ −100 e - /µm 2 (~ −0.02 mC/m 2 ) for all particle sizes. Several combinations of aerosol particle and injector tube composition were also investigated, some of which led to positive particle electrification and all of which resulted in similar values of measured surface charge concentration. The electrification was not seen to be strongly affected by gas composition and is in reasonable agreement with the expected maximum surface charge observed in previous experiments ( 2 ). Possible explanations for this effect are discussed, including the possibility of field emission at the contact site. In the future this technique is intended also to be applied to particle-particle induced contact electrification and its material dependence.

Mossbauer spectra of samples from the 2010 Fimmvorðuhals/Eyjafjallajokull eruption are presented with determinations of the Fe3 + /FeTot ratios. Mossbauer spectra of time series of samples from the Eyjafjallajokull eruption show a change in the characteristics of the erupted material mid-way in the eruption, suggesting changing access of water to the eruption.

International audience; Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kV m−1 to 100 kV m−1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m−1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)—MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ electrical measurements.

Purpose This work describes the production and application of an aerosolised formulation of chitosan nanoparticles for improved pulmonary siRNA delivery and gene silencing in mice. Methods Aerosolised chitosan/siRNA nanoparticles were pneumatically formed using a nebulising catheter and sized by laser diffraction. In vitro silencing of aerosolised and non-aerosolised formulations was evaluated in an EGFP endogenous-expressing H1299 cell line by flow cytometry. Non-invasive intratracheal insertion of the catheter was used to study nanoparticle deposition by histological detection of Cy3-labeled siRNA and gene silencing in transgenic EGFP mouse lungs using a flow cytometric method. Results Flow cytometric analysis demonstrated minimal alteration in gene silencing efficiency before (68%) and after (62%) aerosolisation in EGFP-expressing H1299 cells. Intratracheal catheter administration in mice resulted in nanoparticle deposition throughout the entire lung in both alveoli and bronchiolar regions using low amounts of siRNA. Transgenic EGFP mice dosed with the aerosolised nanoparticle formulation showed significant EGFP gene silencing (68% reduction compared to mismatch group). Conclusions This work provides a technology platform for effective pulmonary delivery and gene silencing of RNAi therapeutics with potential use in preclinical studies of respiratory disease treatment.

Aeolian grain transport is a powerful erosion mechanism and a significant factor affecting atmospheric dynamics by the creation of particulate aerosols. Electric fields, both natural and man-made, occur widely at the Earths surface in environments where granular material is found. Such electric fields may induce electrification of granular material and affect the transport dynamics of the grains. In this laboratory study we show that the influence of such electric fields is significant at field strengths well below that at which breakdown occurs and present a simple semi-empirical expression which allows this mechanism to be quantified.

A fine grained magnetic iron oxide precipitate found in Denmark has been studied with regard to grain size, magnetic properties, aerosol transport, grain electrification, aggregation and optical reflectance. It has shown itself to be a good Martian dust analogue. The fraction of the Salten Skov I soil sample

Mossbauer spectroscopy of surface rocks, soil, and dust on Mars from the Mars Exploration Rovers (MER) suggests that the mineral olivine is widespread on the surface. Detection of the mineral by near-IR optical spectroscopy from Martian orbit indicates that it is found in relatively small isolated outcrops concentrated in the floors and rims of craters distributed around the ancient cratered highlands of Mars. To shed light on this apparent paradox, we have performed a detailed Mossbauer and visible-near-IR (VNIR) investigation of dust generated from Icelandic olivine basalt, which is a good Mossbauer analogue to the igneous rocks at Gusev crater on Mars. The results show that the amount of olivine relative to pyroxene can be underestimated by almost an order of a magnitude in VNIR reflectance spectra, most probably because of the longer effective optical path length in pyroxene compared to olivine.

International audience; We review selected experimental saltation studies performed in laboratory wind tunnels and collision experiments performed in (splash-) laboratory facilities that allow detailed observations between impinging particles on a stationary bed.We also discuss progress in understanding aeolian transport in nonterrestrial environments. Saltation studies in terrestrial wind tunnels can be divided into two groups. The first group comprises studies using a short test bed, typically 1–4m long, and focuses on the transitional behavior near the upwind roughness discontinuity where saltation starts. The other group focuses on studies using long test beds — typically 6 m or more — where the saturated saltation takes place under equilibrium conditions between wind flow and the underlying rough bed. Splash studies using upscaled model experiments allow collision simulations with large spherical particles to be recorded with a high speed video camera. The findings indicate that the number of ejected particles per impact scales linearlywith the impact velocity of the saltating particles. Studies of saturated saltation in several facilities using predominantly Particle Tracking Velocimetry or Laser Doppler Velocimetry indicate that the velocity of the (few) particles having high trajectories increases with increasing friction velocity. However, the speed of the majority of particles that do not reachmuch higher than Bagnold's focal point is virtually independent of Shields parameter—at least for lowor intermediate u⁎-values. In this case mass flux depends on friction velocity squared and not cubed as originally suggested by Bagnold. Over short beds particle velocity shows stronger dependence on friction velocity and profiles of particle velocity deviate from those obtained over long beds. Measurements using horizontally segmented traps give average saltation jump-lengths near 60–70 mm and appear to be only weakly dependent on friction velocity, which is in agreement with some, but not all, older or recent wind tunnel observations. Similarly some measurements performed with uniform sand samples having grain diameters of the order of 0.25–0.40mmindicate that ripple spacing depends on friction velocity in a similar way as particle jump length. The observations are thus in agreementwith a recent ripple model that link the typical jump length to ripple spacing. A possible explanation for contradictory observations in some experiments may be that long observation sequences are required in order to assure that equilibrium exists between ripple geometry and wind flow.Quantitative understanding of saltation characteristics onMars still lacks important elements. Based upon image analysis and numerical predictions, aeolian ripples have been thought to consist of relatively large grains (diameter N 0.6mm) and that saltation occurs at high wind speeds (N26 m/s) involving trajectories that are significantly longer than those on Earth (by a factor of 10–100). However, this is not supported by recent observations from the surface of Mars, which shows that active ripples in their geometry and composition have characteristics compatible with those of terrestrial ripples (Sullivan et al., 2008). Also the highest average wind speeds on Mars have been measured to be b20 m/s, with even turbulent gusts not exceeding 25 m/s. Electrification is seen as a dominant factor in the transport dynamics of dust onMars, affecting the structure, adhesive properties and detachment/entrainment mechanisms specifically through the formation of aggregates (Merrison et al., 2012). Conversely for terrestrial conditions electric fields typically observed are not intense enough to significantly affect sand transport rates while little is known in the case of extra-terrestrial environments.

We present some of the main findings from simulation studies of the Magnetic Properties Experiment on the Mars Exploration Rovers. The results suggest that the dust has formed via mechanical breakdown of surface rocks through the geological history of the planet, and that liquid water need not have played any significant role in the dust formation processes.

We report on the determination of the mineralogy of the atmospherically suspended Martian dust particles using backscattering 57Fe Mossbauer spectroscopy on dust accumulated onto the magnets onboard the Mars Exploration Rovers. The spectra can be interpreted in terms of minerals of igneous origin, and shows only limited, if any, amounts of secondary minerals that may have formed in the presence of liquid water. These findings suggest that the dust has formed in a dry environment over long time in the history of the planet.

Windborne dust is one of the most important and dynamic factors affecting the Martian surface and its atmosphere, yet there lacks a detailed physical understanding how it is transported. We present a miniature laser-based optoelectronic instrument for use on a Mars lander. It integrates sensors capable of quantifying important parameters needed for the understanding and modeling of dust transport on Mars, these include wind speed, wind direction, suspended dust concentration, dust deposition and removal rates as well as the electrification of the Martian dust. Dust electrification has been seen from experimental simulations to be of considerable importance to the processes of adhesion and cohesion, specifically prompting the formation of low mass density dust aggregates. Testing of this prototype instrument has been performed under simulated Martian conditions in a wind tunnel facility. The results and analysis of its functionality will be presented.

Motivated by questions raised by the magnetic properties experiments on the NASA Mars Pathfinder and Mars Exploration Rover (MER) missions, we have studied in detail the capture of airborne magnetic dust by permanent magnets using a computational fluid dynamics (CFD) model supported by laboratory simulations. The magnets studied are identical to the capture magnet and filter magnet on MER, though results are more generally applicable. The dust capture process is found to be dependent upon wind speed, dust magnetization, dust grain size and dust grain mass density. Here we develop an understanding of how these parameters affect dust capture rates and patterns on the magnets and set bounds for these parameters based on MER data and results from the numerical model. This results in a consistent picture of the dust as containing varying amounts of at least two separate components with different physical properties.

X-ray analysis with the instruments on the rovers on Mars, landed in January 2004, and application to the thin dust layer accumulated on magnets on the rovers are discussed. Particle excitation and x-ray fluorescence have different effective depths and call for a more elaborate analysis of a thin surface layer. Measurements from Mars are presented and exhibit a similar elemental composition of the accumulated magnetic dust to that of the surrounding soil.

Suspended dust is a dominant component of the Martian environment. It has a major influence on atmospheric circulation and it is deposited widely over the planetary surface causing a serious hazard to instrumentation. In order to study dust transport, quantification of the wind flow and dust concentration are vital. A simple laser-based anemometer system is presented that is able to measure suspended dust grain velocity and turbulence from a landed spacecraft. This system has advantages over other techniques of wind speed determination in being insensitive to contamination or atmospheric conditions such as temperature, pressure or composition. For the first time it would allow direct measurement of the suspended dust concentration on Mars. A prototype instrument has been constructed and successfully tested in a wind tunnel facility under simulated Martian conditions. The optics are simple in design, light weight and the instrument has low power consumption. It is also robust and the output signal is easily interpreted, producing only a small data volume. Future improvements will be discussed, specifically modification to measure wind direction, the possibility of obtaining information about dust grain size and the construction of a flight model.

A new optical instrument has been developed to precisely measure the local accumulation of dust particles on a surface. This device can be used in combination with applied magnetic or electric fields in order to investigate physical properties of the dust and its interactions with the surface. In this prototype instrument, permanent magnets were used to capture suspended magnetic dust in a Mars simulation wind tunnel. The scientific objectives that may be addressed with such a device are discussed.

We describe the development of an instrument for the production of low energy positron beams that are bunched in time, and the use of a velocity selection device. The bunching unit was constructed from forty seven separate elements, coupled in series in a capacitor chain to reduce the delay time for propagation of the applied voltage pulse along the electrode system and to facilitate operation at frequencies up to 100 kHz. A parabolic potential distribution for time focusing was used. Tests with a dc positron beam produced from a radioactive source are described, together with measurements in which the buncher was used to compress positron pulses produced from an electron accelerator-based beam. Computer simulations of particle trajectories in the buncher have been performed resulting in a detailed evaluation of the factors that govern and limit the time resolution of the instrument. A sector magnet used to velocity-select intermediate energy positrons is described and its performance discussed. ©2003 American Institute of Physics.

The rare occurrence of magnetic soil in Denmark is normally explained by the hypothesis that the site has been burned. However, at some sites formation by means of organic processes has been suggested. In this contribution we present results of combined Mossbauer transmission and conversion electron spectroscopies in order to seek an answer to the question of the origin of magnetic soil in Denmark. It turns out that the sample preparation is of extreme importance, and we will document what precautions have to be taken in order to get meaningful results. When these issues are understood, and taken into consideration, Mossbauer spectroscopy seems to be a promising tool to gain insight in soil forming processes.

We have undertaken a set of wind erosion experiments on a simple and well defined mineral, quartz. In these experiments wind action is simulated by end over end tumbling of quartz grains in a sealed quartz flask. The tumbling induces collisions among the quartz grains and the walls of the flask. This process simulates wind action impact speed of ∼1.2 m/s. After several months of tumbling we observed the formation of a large number of spherical sand aggregates, which resemble small snowballs under optical microscopy. Upon mechanical load the aggregates are seen to be more elastic than quartz and their mechanical strength is comparable, though slightly lower than that of sintered silica aerogels. Aggregates of this kind have not been reported from field sites or from closed circulation systems. However, sparse occurrence might explain this, or in nature the concentration of the aggregate building particles is so low that they never meet and just appear as the most fine grained tail of the sediment particle size distribution.

The iron mineral thought to give the characteristic reddish color to martian dust could have formed through mechanical activation during sand transport. This has been demonstrated experimentally under conditions which are known to occur on Mars.

Cross sections for direct and total non-dissociative ionization of CO, CO2 and CH4 by positron impact have been measured for projectile energies ranging from threshold to 2000 eV. For CO and CO2 direct and total dissociative cross sections for several different fragments have been measured. The non-dissociative cross sections are observed to behave similarly to the single ionization cross sections of the light noble gases. The dissociative cross sections resemble that seen recently for N2, and can be related to models for double ionization of the light noble gases.

Single ionization of xenon and double ionization of helium, neon and xenon by positron impact have been studied at energies from threshold to ~1 keV. The total single ionization cross section of xenon is seen to behave as expected. In particular, single ionization with positronium formation is a strong channel at low energies. For double ionization we found that positronium formation is strongly suppressed and makes no contribution to the total cross section in the light noble gases, while some evidence for this channel is observed in xenon.

In support of the positronium based reaction scheme for antihydrogen formation an experiment has been performed which has demonstrated hydrogen formation following proton impact on positronium. The cross section has been experimentally determined at proton energies of 11.3 keV, 13.3 keV and 15.8 keV, values of σH = 26(±9), 7.8(±2.3) and 7.6(± 4.4) × 10−16 cm2 were obtained. The determination is in reasonable agreement with several recent calculations of the cross section and provides a well characterised process for antihydrogen formation.

Climate change and its consequences require immediate actions in order to safeguard the environment and economy in Europe and in the rest of world. Aiming to enhance data reliability and reduce uncertainties in climate observations, a joint research project called MeteoMet-Metrology for Meteorology started in October 2011 coordinated by the Italian Istituto Nazionale di Ricerca Metrologica (INRiM). The project is focused on the traceability of measurements involved in climate change: surface and upper air measurements of temperature, pressure, humidity, wind speed and direction, solar irradiance and reciprocal influences between measurands. This project will provide the first definition at the European level of validated climate parameters with associated uncertainty budgets and novel criteria for interpretation of historical data series. The big challenge is the propagation of a metrological measurement perspective to meteorological observations. When such an approach will be adopted the requirement of reliable data and robust datasets over wide scales and long terms could be better met. © 2013 AIP Publishing LLC.

In this study we investigated the polar cycling of sulfur (S) associated with the Werenskioldbreen glacier in Spitsbergen (Svalbard). Sulfide-derived S comprised 0.02-0.42wt% of the fine-grained fraction of proglacial sediments. These sediments originated from glacial erosion of Precambrian sulfide-rich quartz and carbonate veins. In summer 2008, the δ34S of dissolved SO4 in glacier melt waters (+9‰ to +17‰) was consistent with SO4 generation from oxidation of primary sulfide minerals in the bedrock (+9‰ to +16‰). The calculated monthly SO4 load was ~6881kg/month/km2 in the main glacier stream. Subsequent evaporation and freezing of glacial waters lead to precipitation, accumulation, and temporary storage of sulfate salt efflorescences in the proglacial zone. These salts are presumably ephemeral, as they dissolve during annual snow/glacial melt events.Hydrated sulfates such as gypsum are also important constituents of the low-elevation areas around the polar ice cap of Planum Boreum on Mars. The origin of this gypsum on Mars might be better understood by using the investigated polar S cycle in Spitsbergen as a foundation. Assuming a trace sulfide content in the basaltic bedrock on Mars, the weathering of sulfides within the fine, porous texture of the ancient aeolian strata (basal unit) underlying Planum Boreum could have created elevated SO4 fluxes (and gypsum precipitation) during episodic thawing/melting events in the past. Limited water activity and prevailing dry conditions on the surface of Mars are the likely factors that accounted for the larger accumulation and preservation of polar gypsum on the surface and its broad aeolian distribution around Planum Boreum. This suggestion is also supported by an experiment showing that gypsum sand can be transported, under dry conditions, over great distances (~2000km) without a significant loss of mass.

The transport of granular materials by wind has a major impact on our environment through sand/soil erosion and the generation and transport of atmospheric dust aerosols. Terrestrially the transport of dust involves billions of tons of material every year, influencing the global climate and impacting directly upon human health. Research in aeolian transport involves the inter-related fields of fluid dynamics, granular materials and electrification/electrostatics which are in themselves diverse and complex. This review only touches upon this intricacy, but aims to overview the latest work which is expanding our current understanding and outline the areas of advancement needed in the future. Presentation is made of current models for wind driven detachment/entrainment and the transport rates of sand and dust, including the effects of contact induced grain electrification. This ubiquitous phenomenon can affect grain transport through the generation of intense electric fields and processes of electrostatic assembly. Importantly the transport of sand is characterized by saltation, which is known to be an active process for erosion and therefore a source for dust and sand formation. Using novel erosion simulation techniques the link between grain transport rates and erosion rates has been quantified. Furthermore this can be linked to production rates for dust and has been associated with chemical and mineral alteration through a process of mechanical activation of fractured surfaces. This work has implications for the evolution of all terrestrial-like planetary surfaces. Studies in non-terrestrial environments force researchers to be less empirical, ultimately leading to a deeper understanding of these processes.

The electrification of wind-blown dust grains was studied in a series of laboratory experiments to examine how grain electrification depends on grain size, grain mineralogy, atmospheric composition, atmospheric pressure, and the method of dust dispersal. This work is intended to contribute to a deeper physical understanding of particle electrification on both Mars and Earth. Findings indicate that the amount of electrification per suspended particle generally is independent of dust entrainment process and atmospheric composition. As expected, the electrification process is grain size-dependent, with smaller grains predominantly electrifying negatively. Although there appears to be a weak dependence upon dust mineralogy, this work supports the expectation that dust suspended in the Martian atmosphere will be significantly electrified.

The effects of external electric fields upon the wind driven detachment of granular material has been investigated experimentally using an environmental wind tunnel facility. It has been shown that for sand sized grains on an electrically conductive surface there is a significant reduction in the threshold shear stress required for detachment at electric fields above 200 kV/m. However, if the surface is insulating then dielectric effects cause an increase in surface adhesion and an increase in the detachment threshold. This would be relevant in arid environments where the surface conductivity is low.

Wind tunnels have been used extensively in industry and research applications over the past 50 years. They vary greatly in scale and geometry, with some large enough to house and test small aircraft (see for example NASA, ATP facilities) and others are miniaturized flow generators used in the calibration of small sensors. However they invariably utilize the same basic technology and design elements. Similarly environmental simulators are also used widely in research, for example in climate and planetary studies. Here again they superficially vary greatly in size and configuration, but basically consist of a hermetic chamber with some form of temperature control [Jensen et al. 2008]. There is therefore a broad array of standard and often commercial technologies and construction techniques which have been successfully applied within the fields of wind tunnel and environmental simulator design. Some of these technologies and techniques will be outlined in this chapter to aid researchers or technology developers in their efforts to design or use environmental wind tunnels and also serve as an informative guide to those new to these fields of investigation. The fusion of an environmental simulator and a wind tunnel is a natural evolution of laboratory based technology to fulfill the need to reproduce specific physical conditions found in nature. Although facilities of this kind are only now being fully developed, they have the potential to expand into a new research field that could substantially contribute to our understanding of climate and mediate growth in advanced sensor technologies. In this chapter many of the challenges in designing and constructing environmental wind tunnels will be introduced and possible solutions presented, with some emphasis placed on extreme terrestrial and Martian planetary conditions. In addition some of the many and varied scientific and industrial applications will be discussed. Generally environmental wind tunnels are already in current use as a method of testing and calibrating meteorology sensors of various kinds especially wind flow sensors (anemometers). Application of wind tunnels in civil engineering and town planning is becoming common place. Here through wind tunnel simulation and modeling the flow of air around buildings and through built-up areas may be useful to avoid the generation of high wind shear and hazardous vortices at periods of high wind or storms. Such simulations can also aid in the design and placement of wind generation systems such as wind turbines. The formalized scaling laws developed by Reynolds (Reynolds equations) allows measurements, for example in smaller scale laboratory wind tunnels, which generate the same (or extremely similar) flow to that generated in the natural setting [Monin and Yaglom