Browsing by Author "Kallio, Esa, Prof., Aalto University , Department of Electronics and Nanoengineering, Finland"

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    On atmospheric pressure measurements and dust devils on planet Mars
    (Aalto University, 2022) Kahanpää, Henrik; Schmidt, Walter, Dr., Finnish Meteorological Institute, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Kallio, Esa, Prof., Aalto University , Department of Electronics and Nanoengineering, Finland
    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.