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Marswrf Convective Vortex and Dust Devil Predictions for Gale Crater

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Marswrf Convective Vortex and Dust Devil Predictions for Gale Crater RESEARC H ARTICLE Mars W RF Convective Vortex and Dust Devil Predictions 10.1029/2019J E006082 for Gale Crater Over 3 Mars Years a nd Co mpariso n Key Poi nts: Wit h MS L ‐RE MS Observations • Mars W RF output co mbined with ther modyna mic theory is used to C. E. Ne w man 1 , H. Kahanpää 2 , M. I. Ric hardso n 1 , G. M. Martí nez 3, 4 , predict te mporal a nd spatial tre nds 4 5 of “ d ust devil activity ” i n Gale Crater A. Vice nte ‐Ret ortill o , and M. T. Le m mon • Modeled activity a nd observed 1 2 3 vortex press ure drops are bot h Aeolis Research, Pasadena, C A, US A, Sc hool of Electrical E ngi neeri ng, Aalto U niversity, Espoo, Fi nla nd, Lunar and greatest i n local su m mer, peaki ng Pla netary I nstitute, U niversities Space Researc h Associatio n, Housto n, T X, US A, 4 College of E ngi neeri ng, U niversity of ~ 1 3: 0 0 ‐14:00, a nd s mallest i n wi nter Michigan, Ann Arbor, MI, US A, 5 Space Scie nce I nstit ute, College Statio n, T X, US A • Se nsible heat fl ux drives i ncrease d activity as MS L cli mbs, b ut press ure drop n u mbers i ncrease faster, u nless a t hres hol d activity is use d A bstract Convective vortices and dust devils have been inferred and observed in Gale Crater, Mars, using Mars Science Laboratory ( MS L) meteorological data and ca mera i mages. Rennó et al. (1998, https:// Supporti ng I nfor matio n: doi.org/10.1175/1520 ‐0469(1998)055 <3244:asttfd >2.0.co;2) modeled convective vortices as convective heat • Supporting Infor mation S1 e ngi nes a nd predicted a “ d ust devil activity ” ( D D A) that depends only on local meteorological variables, s p e ci fi cally t he se nsible heat fl ux and the vertical ther modyna mic ef fi cie ncy w hic h i ncreases wit h t he pressure thickness of the planetary boundary layer. This work uses output fro m the Mars W RF General Correspo nde nce to: C. E. Ne w man, Circ ulatio n Model, r u n wit h hig h ‐resol utio n nests over Gale Crater, to predict D D A as a f u nctio n of locatio n, claire @aeolisresearch.co m ti me of day, a nd seaso n, a nd co mpares t hese predictio ns to t he record of vortices fou nd i n MS L's Rover Environ mental Monitoring Station pressure data set. Much of the observed ti me ‐of ‐day a nd seaso nal Cit ati o n: variatio n of vortex activity is captured, suc h as maxi mu m ( mi ni mu m) activity i n sout her n su m mer ( wi nter), Ne w man, C. E., Kahanpää, H., peaking bet ween 11:00 and 14:00. Ho wever, while t wo daily peaks are predicted around both equinoxes, Ri c h ar ds o n, M. I., M arti n e z, G. M., o nly a late mor ni ng peak is observed. A n i ncrease i n vortex activity is predicted as MS L cli mbs t he nort h west Vice nte ‐Retortillo, A., & Le m mo n, M. (2019). Co nvective vortex a nd d ust devil slopes of Aeolis Mo ns, as observed. T his is attrib uted largely to i ncreased se nsible heat fl u x, d u e t o (i) l ar g er predictio ns for gale crater over 3 mars dayti me s urface ‐t o ‐air te mperature differe nces over hig her terrai n, e n ha nced by reduced t her mal i nertia, years and co mparison with MSL ‐RE MS a nd (ii) t he i ncrease i n drag velocity associated wit h faster dayti me upslope wi nds. Ho wever, t he observed observatio ns. Jour nal of Geophysical Rese arc h: Pl a nets , 1 2 4 , 3442 – 3 4 6 8. increase in nu mber of vortex pressure drops is much stronger than the predicted D D A increase, although a htt ps:// d oi. org/ 10.1029/2019J E006082 better match exists when a threshold D D A is used. Plain Language Su m mary The dayti me Martian at mosphere produces convective vortices called Received 9 J U N 2019 “ d ust devils ” w he n t hey are d ust ‐fi lled. Vortices produce rapid pressure drops, w hic h have bee n detected i n Accepted 6 N O V 2019 Accepted article online 15 N O V 2019 Gale Crater by Mars Science Laboratory instru ments. Observed vortex pressure drops are co mpared with Published online 28 D E C 2019 vortex activity predicted using a nu merical model, Mars W R F. Because vortices are far s maller than Mars W R F's grid spaci ng, t he model ca n't predict t he m directly. I nstead, t he t heory of Re n nó et al. (1998) is use d to calc ulate “ d ust devil activity ” ( D D A) – a meas ure of vortex activity – based o n t he large ‐s c al e at mosp heric state. Predicted D D A matc hes t he ge neral variatio n of vortex observatio ns wit h ti me of day a nd season, such as maxi mu m ( mini mu m) activity in southern su m mer ( winter), peaking bet ween 11:00 and 14:00. Ho wever, while t wo daily peaks are predicted around both equinoxes, only a late morning peak is observed. Predicted D D A also increases as Mars Science Laboratory cli mbs the slopes of Aeolis Mons, as observed. T his is attrib uted to (i) larger dayti me s urface ‐t o ‐air te mperat ure differe nces at hig her altit udes a nd (ii) faster dayti me upslope wi nds hig her up t he slopes. Ho wever, t he observed i ncrease i n nu mber of vortex pressure drops is muc h stro nger t ha n t he predicted D D A i ncrease, alt houg h t hey matc h better w he n a threshold D D A is used. 1. I ntrod uctio n Co nvective vortices occur duri ng periods of stro ng co nvective heati ng of t he surface, w he n t he grou nd te m- ©2019. T he Aut hors. perat ure exceeds t he air te mperat ure, war mi ng t he air above t he s urface. As t his air rises, existi ng vorticity T his is a n ope n access article u nder t he ter ms of the Creative Co m mons beco mes more vertical a nd i nte nsi fi es, wit h t he air spirali ng aro u nd a lo w ‐press ure regio n t hat develops i n Attrib utio n Lice nse, w hic h per mits use, t he vortex core ( Bal me & Greeley, 2006; Ka nak, 2005; Spiga et al., 2016; Toigo et al., 2003). Rotatio n is ra n- distrib utio n a nd reprod uctio n i n a ny do mly clock wise or co u nterclock wise, a nd vortices ofte n occ ur i n pairs or cl usters ( Bal me & Greeley, 2006). mediu m, provided t he origi nal work is pro perly cite d. They may extend to at least the height of the planetary boundary layer (P B L), which co m monly extends to NE W MA N ET AL. 3442 Jo ur nal of Geop hysical Researc h: Pla nets 10.1029/2019J E006082 ~ 2 – 3 k m i n Eart h's deserts a nd to ~10 – 12 k m over many parts of Mars and signi fi cantly higher in so me regio ns; dust devils wit h heig hts up to 16.5 k m have bee n ide nti fi ed i n so me regio ns ( Fe nto n et al., 2016; Fe nto n & Lore nz, 2015). D ust devils are vortices t hat co ntai n d ust, maki ng t he m visible; t his d ust is raised via stro ng ta nge ntial wi nds arou nd t he vortex core, assisted by t he “ s uctio n effect ” of t he press ure drop a nd ot her t her mop hysical factors (see, e.g., Neakrase et al., 2016 for a revie w of all processes t hat have bee n proposed). Mars vortices, he nce d ust devils, ca n gro w m uc h larger t ha n o n Eart h. He nce w hile t he largest o n Earth may reach a fe w tens of m in dia meter, on Mars they may reach or order a k m in dia meter (Fenton et al., 2016). Detectio n of vortices is typically acco mplis hed by detecti ng t heir press ure drop sig nat ure, wit h wind (speed and direction) and te mperature also measurably affected when a vortex passes close enough to t he se nsors (e.g., Ka ha npää et al., 2016; M urp hy et al., 2016; see also sectio n 2.1).
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