We report on an extremely well characterised encounter with a terrestrial dust devil, and its comparison with martian dust devils

Balme, M.

Greeley, R.

Metzger, S. M.

Patel, M. R

Ringrose, T. J.

Towner, M. C.

Zarnecki, J. C.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsA close encounter with a terrestrial dust devilConference or Workshop ItemHow to cite:Towner, M. C.; Ringrose, T. J.; Patel, M. R; Balme, M.; Metzger, S. M.; Greeley, R. and Zarnecki, J. C.(2004). A close encounter with a terrestrial dust devil. In: 35th Lunar and Planetary Science Conference, 15-19 Mar2004, Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1259.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukA CLOSE ENCOUNTER WITH A TERRESTRIAL DUST DEVIL.  M. C. Towner1, T. J. Ringrose1, M. R. Patel1, M. Balme2, S. M. Metzger3, R. Greeley2 and J. C. Zarnecki1, 1PSSRI, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK (m.c.towner@open.ac.uk), 2Arizona State University, Arizona, USA, 3Reno, Nevada, USA.   Introduction:  During August 03 a dust devil field investigation campaign was conducted in the El Do-rado Valley, Nevada. This field site has been well characterised previously [9], and has a well docu-mented record of dust devil events. We report on one particular encounter from this field campaign, whereby a dust devil was sampled by a large number of sensors. These measurements consist of wind speed at 8 heights up to 4m, wind direction at 5 heights, air temperature at 6 heights, air pressure at 2 heights, upward looking UV flux (opacity) and 2 dust impact sensors. As such this data set represents one of the best characterisations of a dust devil lower structure to date. Dust flux esti-mates obtained can be compared to those expected on Mars.  Figure 1  Results:  On 18 July 03 at around 14:40, a strong dust devil was encountered by DASHER. Figure 2 below shows the wind speed, direction and pressure during this encounter. A clear dust devil signature was seen, with a double peak in wind speed and a shift in wind direction indicative of the sensor suite passing through the core. From this signature it will be possi-ble to estimate the dust devil diameter, miss distance (minimum distance between the sensors and the geo-metric centre of the dust core), and maximum wind speed. Dust devils: Dust devils are a common occurrence both here on Earth and on Mars. They form when the correct conditions arise; these include convective plumes, and atmospheric vorticity. Convection occurs when the sun heats the ground, which in turn heats the air above. This heating will cause the air to become less dense and thus start to rise. These phenomenon have been observed on Mars by the Viking Orbiters and landers [1,2], Mars Pathfinder [3,4] and by Mars Global Surveyor[6]. A dust devil will have a rotating column of air, and a low-pressure area at the central core. Dust is lofted when wind speeds become suffi-ciently high [5]. The dust devil will then move across the landscape with the nominal ambient wind speed and may cause marks or scars on the surface. This is particularly noticeable on Mars where the surface mat-ter is removed by the dust devil revealing a darker or lighter material underneath [6]. The dust lofting proc-ess within a dust devil has recently been studied in more detail [7].  05010015020025030035051610 51615 51620 51625 51630 51635 51640Time (s)Wind speed*10 (m/s) Direction Pressure (arb. unit) Figure 2 Equipment: Figure 1 is an image of the equipment deployed, referred to as DASHER. The equipment and its operation is described in more detail in a compan-ion abstract[8]. A typical dust devil encounter during fieldwork would involve a chase, and deployment of the instruments in the oncoming path of the devil, al-lowing the dust devil to pass over the sensors.  In addition to the data shown, a vertical wind pro-file was recorded, and a UV flux drop was seen – shown in figure 3. We see a clear correlation between UV flux and Dust impacts, as the dust obscures the view of the Sun. UV flux was recorded in three spec-tral bands, and in combination with the dust flux data we hope to recover a dynamic particle distribution within the core, to investigate the dust lofting (and  Lunar and Planetary Science XXXV (2004) 1259.pdfdeposition) process. Further investigation of the dust lofting (and dust vertical transport) process will be further complemented by vertical wind profile infor-mation – as can be seen from figure 1, DASHER de-ployed 8 wind sensors, up to a height of 4m, giving detailed characterization of the vertical wind profile. When analysis of this event is complete, it will provide an comprehensive data set giving the signature of a dust devil encounter.  0100200300400500600700800900100051610 51615 51620 51625 51630 51635 51640Time (s)Arb. UnitUV flux (200-400nm) Dust impactsFigure 3  References:  [1] Ryan, J. A. and R. D. Lucich (1983), JGR 88, C15, 11005-11011. [2] Thomas, P. C. and P. J. Gierasch, (1985), Science 230, 175-177. [3] Schofield, J. T., et al., (1997), Science 278, 1752-1758. [4] Metzger et al. (1999), GRL 26,18, p2781. [5] Greeley, R and J. D. Iversen (1985) Wind as a geological proc-ess, ISBN 0-521-35962-7. [6] Edgett, K. S. and M. Malin (2000). JGR 105(E1): 1623-1650. [7] Greeley, R. et al. (2002) JGR 108, E5, p7-1, DOI 10.1029/2002JE001987. [8] Metzger, S. M. et al, this volume. [9] Metzger, S. M., (2003), LPS XXXIV, Ab-stract#2048 Lunar and Planetary Science XXXV (2004) 1259.pdf

A close encounter with a terrestrial dust devil

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A close encounter with a terrestrial dust devil

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