Field Measurements of Terrestrial and Martian Dust Devils

Surface-based measurements of terrestrial and martian dust devils/convective vortices provided from mobile and stationary platforms are discussed. Imaging of terrestrial dust devils has quantified their rotational and vertical wind speeds, translation speeds, dimensions, dust load, and frequency of occurrence. Imaging of martian dust devils has provided translation speeds and constraints on dimensions, but only limited constraints on vertical motion within a vortex. The longer mission durations on Mars afforded by long operating robotic landers and rovers have provided statistical quantification of vortex occurrence (time-of-sol, and recently seasonal) that has until recently not been a primary outcome of more temporally limited terrestrial dust devil measurement campaigns. Terrestrial measurement campaigns have included a more extensive range of measured vortex parameters (pressure, wind, morphology, etc.) than have martian opportunities, with electric field and direct measure of dust abundance not yet obtained on Mars. No martian robotic mission has yet provided contemporaneous high frequency wind and pressure measurements. Comparison of measured terrestrial and martian dust devil characteristics suggests that martian dust devils are larger and possess faster maximum rotational wind speeds, that the absolute magnitude of the pressure deficit within a terrestrial dust devil is an order of magnitude greater than a martian dust devil, and that the time-of-day variation in vortex frequency is similar. Recent terrestrial investigations have demonstrated the presence of diagnostic dust devil signals within seismic and infrasound measurements; an upcoming Mars robotic mission will obtain similar measurement types

History and Applications of Dust Devil Studies

Studies of dust devils, and their impact on society, are reviewed. Dust devils have been noted since antiquity, and have been documented in many countries, as well as on the planet Mars. As time-variable vortex entities, they have become a cultural motif. Three major stimuli of dust devil research are identified, nuclear testing, terrestrial climate studies, and perhaps most significantly, Mars research. Dust devils present an occasional safety hazard to light structures and have caused several deaths

Dust Devil Sediment Transport: From Lab to Field to Global Impact

The impact of dust aerosols on the climate and environment of Earth and Mars is complex and forms a major area of research. A difficulty arises in estimating the contribution of small-scale dust devils to the total dust aerosol. This difficulty is due to uncertainties in the amount of dust lifted by individual dust devils, the frequency of dust devil occurrence, and the lack of statistical generality of individual experiments and observations. In this paper, we review results of observational, laboratory, and modeling studies and provide an overview of dust devil dust transport on various spatio-temporal scales as obtained with the different research approaches. Methods used for the investigation of dust devils on Earth and Mars vary. For example, while the use of imagery for the investigation of dust devil occurrence frequency is common practice for Mars, this is less so the case for Earth. Modeling approaches for Earth and Mars are similar in that they are based on the same underlying theory, but they are applied in different ways. Insights into the benefits and limitations of each approach suggest potential future research focuses, which can further reduce the uncertainty associated with dust devil dust entrainment. The potential impacts of dust devils on the climates of Earth and Mars are discussed on the basis of the presented research results

Toward More Realistic Simulation and Prediction of Dust Storms on Mars

Global dust storms have major implications for the past and present climate, geologic history, habitability, and future exploration of Mars. Yet their mysterious origins mean we remain unable to realistically simulate or predict them. We identify four key Knowledge Gaps and make four Recommendations to make progress in the next decade

Mars-planeetan kaasukehästä, sen paineen mittauksista ja pölypyörteistä

The modeling of planetary atmospheres has become an increasingly important research topic for two reasons. First, the threat of climate change has increased the need for modeling the climate of our planet. Second, assessing the conditions of planets found outside our Solar System requires an understanding of the general processes of planetary atmospheres. High amounts of mineral dust are suspended in the atmosphere of planet Mars even if the mean atmospheric density at the surface is only about 2% of that on the Earth. As dust absorbs incoming and outgoing radiation, modeling the dynamics of the planet's atmosphere requires information on the processes which lift dust from the surface. Small-scale whirlwinds known as dust devils are one of those processes. This thesis work responds to two challenges related to the measurement and modeling of the Martian atmosphere: to improve the quality of barometric pressure measurements and to study the effect of dust devils on the atmosphere using the pressure data. Accurate and traceable pressure measurements by several successive Mars landers also enable studying slow changes in the Martian climate. The barometric pressure devices of NASA's Mars lander Phoenix and the rovers Mars ScienceLaboratory (MSL) and Mars 2020 are based on Barocap® sensor heads manufactured by the Vaisala Company. Furthermore, these sensor heads have been used in several failed Mars landers and are planned to be used in several upcoming landers. In this thesis work, sources of uncertainty affecting Barocap®-based pressure measurements on Mars are investigated through the analysis of the original test data of the devices, the analysis of the engineering data collected during past missions in space, and the laboratory tests with reference models. We conclude that the surface pressure of Mars can be measured using Barocap® sensors with an accuracy better than 3 Pascal, however it requires careful examination of and compensation for all possible error sources. Signs of dust devils and similar vortices not lifting dust are sought in this work from the time series of meteorological variables collected by the MSL rover. The statistics of the identified vortices are compared to forecasts from a numerical climate model. The dynamics of dust devil -like vortices are also studied by fitting a mathematical vortex model to the wind and pressure measurements of MSL, a first-of-its-kind study because previous Mars landers have not measured both pressure and wind simultaneously with adequate resolution. Our results show that the current schemes for calculating the amount of dust raised into the Martian atmosphere by dust devils lead to underestimating the spatial and seasonal variation in dust lifting. A more realistic scheme would require evaluating the distribution of vortex strengths and considering that the dust lifting capacity of a dust devil depends on its strength.Planeettojen kaasukehien mallinnus on noussut merkittäväksi tutkimusaiheeksi kahdesta syystä.Ensinnäkin ilmastonmuutoksen uhka on lisännyt tarvetta mallintaa oman planeettamme ilmastoa.Toiseksi oman aurinkokuntamme ulkopuolelta löytyneiden planeettojen olosuhteiden arvioiminen edellyttää ymmärrystä planeettojen kaasukehien yleisistä prosesseista. Mars-planeetan kaasukehässä leijailee suuri määrä mineraalipölyä, vaikka kaasukehän keskimääräinen tiheys pinnalla on vain noin 2 % Maan ilmakehän pintatiheydestä. Koska pöly absorboi saapuvaa ja lähtevää säteilyä, kaasukehän dynamiikan mallintaminen edellyttää niiden prosessien tuntemusta, jotka nostavat pölyä pinnalta kaasukehään. Pienen mittakaavan pölypyörteet ovat yksi näistä prosesseista. Tämä väitöskirja vastaa kahteen Marsin kaasukehän mittaamiseen ja mallintamiseen liittyvään haasteeseen: planeetan pinnalla mitatun ilmanpaineaineiston laadun parantamiseen sekä pölypyörteiden ilmastollisen vaikutuksen tutkimiseen ilmanpaineaineiston avulla. Perättäisten Mars-laskeutujien tarkkojen ja jäljitettävien ilmanpainemittausten ansiosta on mahdollista tutkia myös planeetan ilmaston hitaita muutoksia. NASAn Phoenix Mars-laskeutujan sekä Mars Science Laboratory (MSL) ja Mars 2020 -kulkijoiden ilmanpainemittalaitteet perustuvat Vaisala Oyj:n valmistamiin Barocap®-antureihin. Näitä antureita on lisäksi käytetty useissa epäonnistuneissa Mars-laskeutujissa ja niitä suunnitellaan käytettäväksi myös tulevissa laskeutujissa. Tässä työssä selvitetään Barocap®-antureihin pohjautuvien Marsin ilmanpaineen mittauksien epävarmuustekijöitä tutkimalla mittalaitteiden alkuperäisiä testiaineistoja, analysoimalla avaruuslentojen aikana kerättyjä teknisiä mittaustietoja ja testaamalla referenssimalleja laboratoriossa. Johtopäätös on, että Marsin kaasukehän pintapaine voidaan mitata Barocap®-antureiden avulla paremmalla kuin 3 Pascalin tarkkuudella mikäli kaikki mahdolliset virhelähteet selvitetään ja kompensoidaan. Pölypyörteiden ja muiden pyörretuulien aiheuttamia signaaleja etsitään tässä työssä MSL kulkijan meteorologisesta mittausaineistosta. Tilastoja havaituista pyörretuulista verrataan numeerisen ilmastomallin ennusteisiin. Lisäksi pyörretuulien dynamiikkaa tutkitaan sovittamalla matemaattista pyörremallia MSL-kulkijan tuuli- ja painemittauksiin. Tämä tutkimus on ensimmäinen laatuaan, sillä ilmanpainetta ja tuulta ei ole aiemmin mitattu Marsissa yhtäaikaisesti riittävällä erotuskyvyllä. Väitöskirjatyön tulokset osoittavat, että nykyiset menetelmät sen pölymäärän laskemiseksi, jonka pölypyörteet nostavat Marsin kaasukehään, johtavat tämän pölymäärän alueellisen ja ajallisen vaihtelun aliarvioimiseen. Realistisemmassa menetelmässä tulisi mallintaa pyörretuulien voimakkuusjakauma sekä ottaa huomioon pölypyörteen voimakkuuden vaikutus sen kykyyn nostaa pölyä

Modelling Martian dust devils using in-situ wind, pressure, and UV radiation measurements by Mars Science Laboratory

NASA's Mars Science Laboratory rover Curiosity (MSL) has measured simultaneous fluctuations in wind and atmospheric pressure caused by passing convective vortices, i.e. dustless dust devils. We study the dynamics of these vortices by fitting a mathematical vortex model to the wind and pressure measurements of MSL. The model matches the data adequately well in 29 out of the 33 studied vortex pass events having sufficient data quality. Clockwise and counterclockwise rotating directions are equally common among the studied convective vortices. The vortices seem to prefer certain trajectories, e.g. avoiding steep slopes. However, our results show that due to sensitivity constraints of the method, central pressure drops of Martian dust devils can usually not be accurately determined by fitting a theoretical vortex model to simultaneous pressure and wind measurements of a single station. We also present a methodology extension for further constraining the trajectories and the strengths of dust laden vortices (i.e. dust devils), based on concurrent in-situ solar irradiance measurements. We apply this methodology to the only evidently dust laden vortex in our data set and show that its dust lifting capacity is probably based not only on wind stress lifting.Peer reviewe

The quality of the Mars Phoenix pressure data

The Phoenix lander operated on the surface of Mars for circa 5 months in 2008. One of its scientific instruments is an atmospheric pressure sensor called MET-P. We perform a comprehensive study to identify all error sources affecting the data measured by MET-P and to generate methods for compensating these errors. Our results show that MET-P performed much better than was reported immediately after the mission (Taylor et al., 2010). The error limits of the original calibrated Phoenix pressure data currently available in NASA's Planetary Data System (Dickinson, 2008) are from −5.3 Pa to +3.5 Pa. Further, almost no temperature-dependent error exists in the original calibrated MET-P data. However, we identify a previously unknown error source, temperature hysteresis, which causes minor peaks in the measured pressure curve (<0.4 Pa). The electronic supplementary material of this article contains a version of the Phoenix pressure data generated by applying all the error compensations developed in this study (Online Resource 1). The study is based on the re-analysis of the original test data of MET-P, the analysis of the engineering data measured during the mission on Mars and during the interplanetary cruise, and laboratory tests with the Reference Model of the MET-P sensor. Temperature dependent errors are evaluated by comparing the readings of two sensor heads with different sensitivities, measuring the same quantity. The principle of this method is applicable also for other types of instruments.Peer reviewe

Convective vortex and dust devil predictions for Gale Crater over three Mars years and comparison with MSL‐REMS observations

Convective vortices and dust devils have been inferred and observed in Gale Crater, Mars, using Mars Science Laboratory (MSL) meteorological data and camera images. Rennó et al. [1998] modeled convective vortices as convective heat engines and predicted a ‘dust devil activity' (DDA) that depends only on local meteorological variables, specifically the sensible heat flux and the vertical thermodynamic efficiency which increases with the pressure thickness of the planetary boundary layer. This work uses output from the MarsWRF General Circulation Model, run with high‐resolution nests over Gale Crater, to predict DDA as a function of location, time of day, and season, and compares these predictions to the record of vortices found in MSL's Rover Environmental Monitoring Station pressure dataset. Much of the observed time of day and seasonal variation of vortex activity is captured, such as maximum (minimum) activity in southern summer (winter), peaking between 11:00 and 14:00. However, while two daily peaks are predicted around both equinoxes, only a late morning peak is observed. An increase in vortex activity is predicted as MSL climbs the northwest slopes of Aeolis Mons, as observed. This is attributed largely to increased sensible heat flux, due to (i) larger daytime surface‐to‐air temperature differences over higher terrain, enhanced by reduced thermal inertia, and (ii) the increase in drag velocity associated with faster daytime upslope winds. However, the observed increase in number of vortex pressure drops is much stronger than the predicted DDA increase, although a better match exists when a threshold DDA is used.Peer reviewe