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  • A Framework for Mitigating the Biases in Barometric Dust Devil Surveys

    Background

    Dust devils are small-scale (few to many tens of meters) low-pressure vortices rendered visible by lofted dust. They usually occur in arid climates on the Earth and ubiquitously on Mars. Martian dust devils have been studied with orbiting and landed spacecraft and were first identified on Mars using images from the Viking Orbiter (Thomas et al., 1985). On Mars, dust devils may dominate the supply of atmospheric dust and influence climate (Basu 2004), pose a hazard for human exploration (Balme et al., 2006), and they may have lengthened the operational lifetime of Martian rovers (Lorenz et al., 2014). On the Earth, dust devils significantly degrade air quality in arid climates (Gillette et al., 1990) and may pose an aviation hazard (Lorenz 2005).

    The dust-lifting capacity of dust devils seems to depend sensitively on their structures, in particular on the pressure wells at their centers (Neakrase et al., 2006), so the dust supply from dust devils on both planets may be dominated by the seldom-observed larger devils. Using a martian global climate model, Basu (2004) showed that observed seasonal variations in Mars’ near-surface temperatures could not be reproduced without including the radiative effects of dust and estimated the dust contributes more than 10 K of heating to the heating budget. Thus, elucidating the origin, evolution, and population statistics of dust devils is critical for understanding important terrestrial and Martian atmospheric properties and for in-situ exploration of Mars.

    Studies of Martian dust devils have been conducted through direct imaging of the devils and identification of their tracks on Mars’ dusty surface (cf. Balme et al., 2006). Studies with in-situ meteorological instrumentation have also identified dust devils, either via obscuration of the Sun by the dust column (Zorzano et al., 2013) or their pressure signals (Ellehoj et al., 2010). Studies have also been conducted of terrestrial dust devils and frequently involve in-person monitoring of field sites. Terrestrial dust devils are visually surveyed (Pathare et al., 2010), directly sampled (Balme et al., 2003), or recorded using in-situ meteorological equipment (Sinclair, 1973; Lorenz, 2012).

    As noted in Lorenz (2009), in-person visual surveys are likely to be biased toward detection of larger, more easily seen devils. Such surveys would also fail to recover dustless vortices (Lorenz et al., 2015). Recently, terrestrial surveys similar to Martian dust devil surveys have been conducted using in-situ single barometers (Lorenz, 2012; Lorenz, 2014; Jackson et al., 2015) and photovoltaic sensors (Lorenz et al., 2015). These sensor-based terrestrial surveys have the advantage of being directly analogous to Martian surveys and are highly cost-effective compared to the in-person surveys (in a dollars per data point sense).

    In single-barometer surveys, a sensor is deployed in-situ and records a pressure time series at a sampling period \(\lesssim 1\) s. Since it is a low-pressure convective vortex, a dust devil passing nearby will register as pressure dip discernible against a background ambient (but not necessarily constant) pressure. Figure \ref{fig:conditioning_detection_b_inset} from Jackson et al. (2015) shows a time-series with a typical dust devil signal.

    \label{fig:conditioning_detection_b_inset} Example dust devil profile from Jackson et al. (2015). The black dots show the pressure \(p\) measurements (in hectoPascal hPa) as a function of local time in hours. The blue line shows the best-fit Lorentz profile model.