Part I was about in-situ vertical grain size distributions of two dust devils sampled during a field campaign in the northern part of Morocco in 2012. The samples were analyzed in 2013 and 2014. During the project, the publication was written and submitted.
Main results are:
- The majority of all lifted particles were only lifted within the first meter. Nearly all sand grains occurred in the first meter which is the first directly measured evidence of the occurrence of the “sand skirt” of dust devils.
- Between ~60% to ~70% of all lifted particles were small enough to go into and stay in suspension, so these data will have an influence on studies of climate, weather, biogeochemistry, and (on Earth) human health.
- We get better information of the internal structure of dust devils and our sampled dust devils show comparable internal particle load structures despite the fact that they have different dimensions and intensities.
These results were presented in a peer-reviewed publication in the journal “Astrobiology” (J. Raack et al. (2017) Astrobiology 17) and at several scientific conferences.
Part II included two different field campaigns. The first field campaign was in 2016 to the desert in the northeast of Morocco. In-situ samples of six different dust devils were taken (Figs. 1, 2) and numerous dust devils were investigated with different meteorological instruments such as atmospheric pressure, vertical and horizontal wind speed, temperature, etc. During the second field campaign, in 2017 to a desert in Nevada, we made the same measurements of dust devils to compare these with measurements from Morocco.
Main (preliminary) results are:
- We measured in-situ pressure drop magnitudes and vertical wind speeds of dust devils in Morocco and Nevada. Plotting peak pressure drop magnitudes (P) versus peak vertical wind speeds shows that the vertical wind speed is about 0.06×ΔP. With this it could be possible to calculate wind speeds of dust devils only with the knowledge of the pressure drop (which is often the only measurement on Mars).
- Furthermore, we plotted the vertical winds speed versus the tangential wind speeds which shows that the vertical wind speed is about half the tangential wind speed. This is in good agreement with other studies.
To date, preliminary results were presented at international scientific conferences.
Part III consisted of laboratory experiments with the Mars Environmental Chamber (Figs. 3, 4). We investigated the behavior of liquid water flows over sandy surfaces at low pressures (~7-9 mbar, comparable to pressures on Mars) with different sediment and water temperatures (Fig. 6), as well as different slope angles and flow rates (unpublished). To date, two peer-reviewed publications (one in the high profile journal Nature Communications) were published.
Main results of the first laboratory campaign are:
- When the surface temperature is high enough (in this case ~15° C) “levitation” of saturated sediment pellets took place. The pellets levitate on a cushion of vapor released by boiling, comparable to the Leidenfrost effect (e.g. water drops “dancing” around on hot cooking plates). This was the first time that these observations were made.
- The effect of levitation with subsequent other transport mechanisms caused a higher transport capacity of the flow. This means that nine times more sediment was transported when the surface temperature was slightly higher (Figs. 7, 8).
- The experiments show that the amount of needed water to move comparable sediment amounts was an order of magnitude lower for warmer surfaces. This means that less water is used on Mars to transport material.
- Numerical scaling to the martian gravity imply that levitation could persist up to ~48 times longer on Mars, which will lead to an enhanced transport capacity.
To date, results were published in two peer-reviewed publications (J. Raack et al. (2017) Nature Communications 8, 1151 and C. Herny et al. (2018) GSL, Special Publications 467) and at scientific conferences.
