Improvement and Evaluation of a Parameterization Scheme for Assessing Dust Devils as Dust Emission in the Northern Margin of the Taklimakan Desert

Based on meteorological and dust devil intensification observation data in the desert transition zone of the Xiaotang region in the northern margin of the Taklimakan Desert, and combined with GPS sounding in the hinterland of the Taklimakan Desert, this study investigated the improvement and evaluation of the dust devil parameterization scheme. The results indicate that the thermodynamic efficiency of dust devils after improvement was significantly higher than that before improvement, improving the values by 84.7%, 63.9%, 25.6%, 13.3%, 12.5%, 22.7%, 26.6%, 26.9%, and 21.4% for the hourly intervals from 09:00–17:00, respectively. The annual occurrence of dust devils after improvement was 431 times, 55.2% more than before improvement. The correlation coefficients of convective boundary layer height after improvement was 0.96, higher than that before improvement (0.908). After the improvement, the total annual dust emission time was 181.3 h, 95.9% less than that calculated using the day length before improvement, and 31.8% more than that calculated using sunshine time before improvement. After the improvement, the average vertical dust flux of a single dust devil was 0.25 m2/s, 68.8% less than that before improvement. After the improvement, the average annual dust emission from dust devils per square kilometer was 15.3 t/km2, significantly lower than the value of 320.5 t/km2 before the improvement, approximately one-twentieth of the value.

The Site Tilt and Lander Transfer Function from the Short-Period Seismometer of InSight on Mars

ABSTRACT The National Aeronautics and Space Administration InSight mission has deployed the seismic experiment, SEIS, on the surface of Mars, and has recorded a variety of signals including marsquakes and dust devils. This work presents results on the tilt and local noise sources, which provide context to aid interpretation of the observed signals and allow an examination of the near-surface properties. Our analysis uses data recorded by the short-period sensors on the deck, throughout deployment and in the final configuration. We use thermal decorrelation to provide an estimate of the sol-to-sol tilt. This tilt is examined across deployment and over a Martian year. After each modification to the site, the tilt is seen to stabilize over 3–20 sols depending on the action, and the total change in tilt is <0.035°. Long-term tilt over a Martian year is limited to <0.007°. We also investigate the attenuation of lander-induced vibrations between the lander and SEIS. Robotic arm motions provide a known lander source in the 5–9 Hz bandwidth, yielding an amplitude attenuation of lander signals between 100 and 1000 times. The attenuation of wind sensitivity from the deck to ground presents a similar value in the 1.5–9 Hz range, thus favoring a noise dominated by lander vibrations induced by the wind. Wind sensitivities outside this bandwidth exhibit different sensitivity changes, indicating a change in the coupling. The results are interpreted through a finite-element analysis of the regolith with a depth-dependent Young’s modulus. We argue that discrepancies between this model and the observations are due to local compaction beneath the lander legs and/or anelasticity. An estimate for the effective Young’s modulus is obtained as 62–81 MPa, corroborating previous estimates for the top layer duricrust.

Expected first results from the SuperCam microphone onboard the NASA Perseverance rover

<p>The NASA Perseverance rover will land on Mars in February 2021, bringing with it a new suite of analytical instruments with which to explore its landing site in Jezero crater. The primary goal of this new mission is to assess the geology and past habitability in order to identify and cache samples with a high likelihood of preserving biosignatures, in preparation for a future sample return mission [1]. As part of its instrument payload, Perseverance will carry the SuperCam instrument [2-3]. SuperCam combines a number of analytical techniques, notably a laser-induced breakdown spectroscopy (LIBS) instrument for chemical analysis that is coupled with a microphone for acoustic studies. The SuperCam microphone is a commercial of-the-shelf electret (based on Knowles EK-23132) and is designed to record sounds in the audible range, from 100 Hz to 10 kHz, during the surface mission. There are three main science investigations of interest for the SuperCam microphone: 1) Analysis of the LIBS acoustic signal; 2) study of atmospheric phenomena; and 3) examination of rover mechanical sounds. Since the atmosphere will be the source of acoustic signals, the microphone may be used to better understand the nature of the atmosphere and related phenomena such as thermal gradient and convective behavior in the rover’s vicinity [4], the behavior of dust devils [5], and to refine current atmospheric attenuation models for Mars [6]. Under atmosphere, LIBS analysis produces an acoustic signal due to the creation of a shock wave during laser ablation of a target. This acoustic signal can provide critical information about a target’s hardness and ablation depth [7-8] and whether there are coatings or thin layers present [9]. Mechanisms on the rover itself will also provide a source of acoustic signal that may be examined by the SuperCam microphone, notably sounds produced by the Mars Oxygen ISRU Experiment (MOXIE, [10]) instrument pumps during oxygen production. By the time of the conference, the SuperCam microphone should have acquired the first sounds on Mars; we will report on these exciting initial results and compare them to our prelanding expectations.</p><p>[1] Farley K.A. et al. (2020) SSR 216, 142. [2] Wiens R.C. et al. (2021) SSR 217(4). [3] Maurice, S. et al. (in revision) SSR. [4] Chide, B. et al. (2020) 52<sup>nd</sup> LPSC. [5] Murdoch, N. et al. (2021) 52<sup>nd</sup> LPSC. [6] Chide, B. et al. (2020) AGU Fall meeting, S007-02. [7] Chide, B. et al. (2019) SAB 153, 50-60. [8] Chide, B. et al. (2020) SAB 174, 106000. [9] Lanza, N.L. et al (2020) 51<sup>st</sup> LPSC, no. 2807. [10] Hecht, M. H. et al. (2015) 46<sup>th</sup> LPSC, no. 2774.</p>

Mars surface dust activation at small meteoroid’s impacts

<p>We continue the analysis of HiRISE high resolution images of Mars to understand properties of dust covering the surface. The data on dust devils observed with Mars landers and surface traces of dust devils could be expanded with elongated albedo features imaged near “new” impact sites (“new” means that we have orbital images before and after the meteoroid impact, which give us an estimate of the impact date and the age of a feature). The age of these features is from 0.5 to 12 terrestrial years. From geometric reasons we could assume that the most possible mechanism of this elongated albedo details is the “footprint” of two or more colliding air shock waves, generated at the impact site. Of ~1200 “new” impacts known today, in 18 cases crater pairs or clusters, created with fragments of the same “parent” meteoroid, we recognize 24 thin “parabolas” with a width of 1 to 10 m (0.2 to 10 main crater diameters, <em>D</em>), extended to 100 – 400 m (3 to 100 <em>D</em>) from the impact site. In ~30 cases near a single crater we observe a curved albedo feature nick-named “scimitar”. These features have width, growing with a distance from the impact point. The length varies from 10 to 100 <em>D</em>, the width varies from 1 to 10 <em>D</em>. Our working hypothesis is that “scimitars” are footprints of ballistic and spherical air shock wave collision at the surface. Both “parabolas” and “scimitars” have an exact bilateral symmetry, which allows us to reconstruct the flight direction of projectiles.</p><p>We estimate the equivalent energy of spherical air blasts with two different assumptions for “parabolas” and “scimitars” formation. For parabolas we assume a mechanism, similar to dust devil track formation – the negative pressure excurse uplifts the upper fine dust layer. The main assumption is that the dark parabolic strip width corresponds the wave length of the negative pressure phase in the air shock wave. It gives us the minimum energy estimate as in reality the negative phase could be longer. The negative pressures here along the parabola length decay from about 10 to 5 Pa with the phase duration of a few milliseconds. Such a suction pulse is able to mobilize dust particles 50 to 100 microns in size.</p><p>For scimitars, which in contrast to “dark” parabolas are typically “brighter” than surrounding area, we have no a good mechanical explanation of origin. However, with limits of our current model, the spherical “explosion” air blast should be enough energetic, to overrun the ballistic shock wave. From non-linear motion of the shock wave front we can estimate the fraction of meteoroid’s kinetic energy, converted to the air blast energy. The model is able to reproduce approximately the scimitar’s curvature.</p>

A Galactic dust devil: far-infrared observations of the Tornado supernova remnant candidate

ABSTRACT We present complicated dust structures within multiple regions of the candidate supernova remnant (SNR) the ‘Tornado’ (G357.7–0.1) using observations with Spitzer and Herschel. We use point process mapping, ppmap, to investigate the distribution of dust in the Tornado at a resolution of 8 arcsec, compared to the native telescope beams of 5–36 arcsec. We find complex dust structures at multiple temperatures within both the head and the tail of the Tornado, ranging from 15 to 60 K. Cool dust in the head forms a shell, with some overlap with the radio emission, which envelopes warm dust at the X-ray peak. Akin to the terrestrial sandy whirlwinds known as ‘dust devils’, we find a large mass of dust contained within the Tornado. We derive a total dust mass for the Tornado head of 16.7 $\rm M_{\odot }$, assuming a dust absorption coefficient of κ300 = 0.56 $\rm m^2\, kg^{-1}$, which can be explained by interstellar material swept up by a SNR expanding in a dense region. The X-ray, infrared, and radio emission from the Tornado head indicate that this is a SNR. The origin of the tail is more unclear, although we propose that there is an X-ray binary embedded in the SNR, the outflow from which drives into the SNR shell. This interaction forms the helical tail structure in a similar manner to that of the SNR W50 and microquasar SS 433.