JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, D06113, doi:10.1029/2010JD014784, 2011 Dust storm over the Black Rock Desert: Larger‐scale dynamic signatures John M. Lewis,1,2 Michael L. Kaplan,2 Ramesh Vellore,2 Robert M. Rabin,1,3 John Hallett,2 and Stephen A. Cohn4 Received 19 July 2010; revised 3 December 2010; accepted 7 January 2011; published 29 March 2011. [1] A dust storm that originated over the Black Rock Desert (BRD) of northwestern Nevada is investigated. Our primary goal is to more clearly understand the sequence of dynamical processes that generate surface winds responsible for entraining dust from this desert. In addition to reliance on conventional surface and upper‐air observations, we make use of reanalysis data sets (NCAR/NCEP and NARR)—blends of primitive equation model forecasts and observations. From these data sets, we obtain the evolution of vertical motion patterns and ageostrophic motions associated with the event. In contrast to earlier studies that have emphasized the importance of indirect transverse circulations about an upper‐level jet streak, our results indicate that in this case the transition from an indirect to a direct circulation pattern across the exit region of upper‐level jet streak is central to creation of low‐level winds that ablate dust from the desert. It is further argued that the transition of vertical circulation patterns is in response to adjustments to geostrophic imbalance—an adjustment time scale of 6–9 h. Although unproven, we suggest that antecedent rainfall over the alkali desert 2 weeks prior to the event was instrumental in lowering the bulk density of sediments and thereby improved the chances for dust ablation by the atmospheric disturbance. We comprehensively compare/contrast our results with those of earlier investigators, and we present an alternative view of key dynamical signatures in atmospheric flow that portend the likelihood of dust storms over the western United States. Citation: Lewis, J. M., M. L. Kaplan, R. Vellore, R. M. Rabin, J. Hallett, and S. A. Cohn (2011), Dust storm over the Black Rock Desert: Larger‐scale dynamic signatures, J. Geophys. Res., 116, D06113, doi:10.1029/2010JD014784. 1. Introduction eterization of this widespread dust in the governing equa- tions for global circulation models. This is due in part to the [2] The impact of dust storms on human activity is often delicate interplay between reflection of sunlight by the dust dramatic as in the infamous San Joaquin Valley dust storms and the trapping of upwelling radiation by this same dust of 1977 [Wilshire et al., 1981] and 1991 (the “Interstate‐5 [Idso and Brazel, 1977; Miller and Tegan, 1998]. Despite Storm” [Pauley et al., 1996]) that caused a multitude of these uncertainties, the recent successful application of accidents and associated loss of life, and in the erosion of regional dynamical simulation to dust transport over the agricultural land so evident during the 1930s over the Gobi provides some encouragement [Liu et al., 2003]. Midwestern USA—the “Dust Bowl” years [Worster, 1979; [3] Prediction or analysis of a dust storm requires Schubert et al., 2004]. Further, the long‐term and wide- knowledge of the surface soil characteristics and the atmo- spread suspension of dust in the atmosphere that stems from spheric processes that give rise to the wind. Determination disturbances over the world’s gigantic deserts (such as the of soil characteristics—crustal roughness, bulk density, Gobi and Sahara) certainly impact climate [Idso, 1976; moisture content, etc.—and the relationship of these char- Washington et al., 2003; Goudie and Middleton, 2006; acteristics to the likelihood of dust storm generation is one Goudie, 2009]. Yet, significant uncertainty attends param- of the most challenging aspects of prediction. In part, this difficulty stems from reliance on remote observations from 1National Severe Storms Laboratory, NOAA, Norman, Oklahoma, space and the incompleteness and uncertainty of these USA. observations. But we are also ignorant of the micro- 2Division of Atmospheric Sciences, Desert Research Institute, Reno, meteorological processes that lead to lift of the sediments— Nevada, USA. 3 for example, sand/sediment entrainment and saltation [see Space Science and Engineering Center, Madison, Wisconsin, USA. Bagnold, 1973; Shao, 2000]. Laboratory work indicates that 4Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA. strong shear in the presence of unstable stratification, in essence a small Richardson number, is conducive to lift Copyright 2011 by the American Geophysical Union. [Richardson, 1920; Bagnold, 1973; Stull, 1988]. Unpublished 0148‐0227/11/2010JD014784 D06113 1of22 D06113 LEWIS ET AL.: LARGER-SCALE DYNAMIC SIGNATURES D06113 laboratory work by coauthor J. Hallett also indicates that a is then viewed macroscopically with the aid of satellite vortex ring whose axis is perpendicular to a dusty surface imagery and surface‐based measurements of particulate causes the dust to expand outward and upward while matter. Upper‐air analysis follows with support from the remaining undisturbed at the stagnation point directly beneath 6 h updates of NCEP (National Center for Environ- the ring. And although we know that drought conditions favor mental Prediction)/NCAR (National Center for Atmospheric dust storms, it has now become apparent that antecedent Research and 3 h updates of NARR (North American rainfall or run‐off, occurring on the order of several weeks Regional Reanalysis). The NCEP/NCAR data set is a before a dust storm event, is a positive contributor. This synoptic‐scale analysis with 2.5° grid resolution [Kalnay influence stems from salt efflorescence (production of pow- et al., 1996], and the NARR data set is a subsynoptic‐ dery salts) and swelling of certain clays that serve to reduce scale analysis with a 32 km grid resolution [Mesinger et al., the bulk density of the sediment [Gillies et al., 1999; Bullard 2006]. These archived data sets permit analysis of dynam- et al., 2008; J. A. Gilles, personal communication, 2009]. ically consistent vertical motion fields. The secondary ver- [4] The initial source of dust for our study comes from the tical circulations are viewed in the context of dynamic Black Rock Desert (BRD) located in northwestern Nevada. imbalance and adjustments to imbalance. We end with The BRD and its neighboring desert, the Smoke Creek section 7, where we present: (1) a comparison/contrast of Desert (SCD), are dry lakebeds (playa) that lie within our results with those from earlier investigations, and (2) a the late Pleistocene Lake Lahontan. A topographical map summary and schematic diagram of the physical processes including the area covered by these deserts is found in germane to the dust storm over the BRD appended by a list Figure 1. A panoramic view of the BRD from a mountain of key signatures that portend the likelihood of dust storms location west of the desert, and an aerial view of the BRD over the western United States. and the SCD are found in Figure 2. These deserts are often referred to as “alkali deserts” where the dominant elements are those associated with alumino‐silicate minerals (e.g., Si, 2. Background Information on Dust Storms: Al, K, and Ti) [Gillies et al., 1999]. In line with statements General and Case Specific ‐ above regarding the influence of antecedent rainfall and run [7] Throughout this research paper we make frequent off from neighboring mountains, we examine precedent reference to various upper air stations in the U.S. West conditions over these deserts; but our primary goal focuses Coast and surface weather stations in Nevada. These stations on understanding the atmospheric processes that produce the along with topographical and geographical features in low‐level winds responsible for raising dust from these northwestern Nevada are shown in Figures 1 and 3. deserts. [5] As shown by Danielsen [1968, 1974a, 1974b] and 2.1. Dynamics Linked to Dust Storms Pauley et al. [1996], large‐scale ascent/descent couplets in [8] Two categories of dynamical processes have been the vicinity of the jet stream or jet streaks (maxima in wind linked to dust storms: (1) storms associated with cyclogen- speed along the axis of the jet stream) were central to esis where Danielsen’s paradigm of large‐scale descending atmospheric processes that led to dust storms. Reviews of trajectories is the central theme [Danielsen, 1968, 1974a, these vertical circulations around the jet stream are provided 1974b; Pauley et al., 1996] (also http://marrella.meteor. by Keyser and Shapiro [1986] and Carlson [1991]. Eliassen’s wisc.edu/Martin_2008.pdf, and J. E. Martin, personal com- several‐decadal studies of vertical circulations—secondary munication, 2010), and (2) secondary vertical circulations circulations—were more general and not restricted to cou- where geostrophic adjustments around jet streaks are central plets near the jet stream. He viewed these circulations as to the generation of surface winds [Karyampudi et al., responses to imbalance in a variety of dynamical systems— 1995]. In both cases, deep mixed layers adjoining the sur- in the context of quasi‐static vortex motion [Eliassen, 1952], face are often present. The dust storms that originate over quasi‐geostrophic dynamics in the vicinity of frontal systems the world’s gigantic deserts are typically associated with [Eliassen, 1962] (Sawyer‐Eliassen circulations – primarily cyclogenesis in springtime [Liu et al., 2003]. In these based on Sawyer [1956] and Eliassen [1962]), and in the storms, the transport is often on a continental/hemispheric more general primitive equation dynamics [Eliassen, 1983; space scale as found for the April 2001 storm that formed T. Iversen, personal communication, 2010]. And it is fair to over the Gobi Desert. This voluminous dust plume was say that stimulation for this line of research came from the tracked for 9 days (6–14 April) as it moved from the Gobi to pioneering geostrophic adjustment studies of Rossby [1937, the western USA [Szykman et al., 2003].