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The Devils You Know: Quantifying the Size-Frequency Distribution and Forward Velocities of Terrestrial Dust Devils, with Implications for Mars

Wednesday, October 31, 2012

Dust devils are particle-loaded vertical convective vortices commonly observed on Earth and especially Mars. Qualitative estimates of terrestrial dust devil frequency based upon visual field surveys have varied by several orders of magnitude. We will present the results of our quantitative characterization of the size-frequency distribution (SFD) of terrestrial dust devils, which utilizes stereo photography to calculate dust devil diameters via parallax displacement. Altogether, we were able to successfully stereo photograph approximately 40% of the more than 1000 dust devils that we observed within the study areas during the three field campaigns. We will also use the quantitative parallax-derived dust devil diameter measurements to assess the accuracy of our qualitative size estimates, accounting for a variety of factors such as distance, speed, duration, apparent dustiness, and number of observers. Our analysis will not only yield a more comprehensive SFD for terrestrial dust devils, but will also help constrain SFD parameterizations of Martian dust devils based on orbiter and lander observations. Lastly, we will show thatĀ that instantaneous dust devil translational velocity correlates well with instantaneous local ambient wind velocity: we found that dust devil horizontal speed is about 1.2 times the ambient 10 m height wind speed. This suggests that dust devil velocities can be used on Mars as proxy measurements for local wind speed, which would provideĀ an important tool for testing mesoscale climate models.

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