Hindawi Advances in Meteorology Volume 2019, Article ID 2763153, 11 pages https://doi.org/10.1155/2019/2763153 Research Article Occurrence of Anticyclonic Tornadoes in a Topographically Complex Region of Mexico Noel Carbajal ,1 Jose´ F. Leo´n-Cruz ,1 Luis F. Pineda-Martı´nez ,2 Jose´ Tuxpan-Vargas ,1 and Juan H. Gaviño-Rodrı´guez 3 1Divisio´n de Geociencias Aplicadas, Instituto Potosino de Investigacio´n Cient´ıfica y Tecnolo´gica A.C., San Luis Potos´ı, SLP 78216, Mexico 2Unidad Acade´mica de Ciencias Sociales, Universidad Auto´noma de Zacatecas, Zacatecas, ZAC 98066, Mexico 3Centro Universitario de Investigaciones Oceanolo´gicas, Universidad de Colima, Manzanillo, COL 28860, Mexico Correspondence should be addressed to Noel Carbajal; [email protected] Received 3 September 2018; Accepted 21 November 2018; Published 9 January 2019 Academic Editor: Tomeu Rigo Copyright © 2019 Noel Carbajal et al. (is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tornadoes are violent and destructive natural phenomena that occur on a local scale in most regions around the world. Severe storms occasionally lead to the formation of mesocyclones, whose direction or sense of rotation is often determined by the Coriolis force, among other factors. In the Northern Hemisphere, more than 99% of all tornadoes rotate anticlockwise. (e present research shows that, in topographically complex regions, tornadoes have a different probability of rotating clockwise or anti- clockwise. Our ongoing research programme on tornadoes in Mexico has shown that the number of tornadoes is significantly higher than previously thought. About 40% of all tornadoes occur in the complex topographic region of the Trans-Mexican Volcanic Belt. Data collected (from Internet videos) on the rotation of tornadoes formed in this region showed that about 50% of them rotated in a clockwise direction, contradicting tornado statistics for most of North America. Time series of the helicity parameter showed that tornadoes formed in topographically complex areas exhibited different behaviours compared to those formed in plains that are related with supercell systems. 1. Introduction Coriolis parameter, Ω � 7:29 × 10−5 ·s−1 is the angular ve- locity of Earth, and φ is the latitude. (erefore, vorticity can Rotational phenomena in the atmosphere occur at a wide be related to circulation simply by dividing circulation by the range of scales, from turbulent motions at several centi- covered area. In this sense, vorticity can also be interpreted metres, dust swirls at several metres, tornadoes at hundreds as twice the angular velocity of the rotating system. Simple of metres, hurricanes at hundreds of kilometres, and, finally, solutions of the equation of motion in natural coordinates circulations associated with planetary perturbations at reveal that tornadoes of typical scales may have a cyclonic thousands of kilometres. Circulation and vorticity param- or anticyclonic rotational direction. (is solution is called eters essentially represent two ways of quantifying such cyclostrophic balance. rotational processes. Circulation is the line integral of the Tornadoes are an extremely powerful natural phenom- velocity vector around a closed curve, whereas vorticity is the enon defined as “a rotating column of air, in contact with the rotational of the velocity vector. In other words, circulation surface, pendant from a cumuliform cloud, and often visible is a measure of the size of a rotational event, whereas as a funnel cloud and/or circulating debris/dust at the vorticity defines the spinning rate [1]. (e vertical com- ground” [2]. Given their unpredictable frequency and scale, ponent of the relative vorticity, ς, is calculated from hori- as well as their high potential to cause damage, tornadoes are zontal gradients of the velocity vector. (e absolute vorticity categorised as extreme weather events [3]. Severe storms and is calculated as ω(a) � ς + f, where f � 2Ω sin φ is the tornadoes are closely related. Abundant lower-tropospheric 2 Advances in Meteorology moisture, steep mid-tropospheric lapse rates, and strong 3. Methodology tropospheric wind shear are important elements that influence the formation of tornadoes [4]. Also, high An official tornado database does not exist for Mexico, but vorticity values, i.e., rotating air masses produced by the some efforts have documented tornadoes [25]. We have interaction of cold and warm fronts, are one of the key directed an ongoing data collection programme on tornado factors leading to the development of supercell storms and events since 2013 based on official reports from the Na- tornadoes [5]. tional Weather Service of Mexico, eyewitness reports, Generally, the spatial distribution of severe storms and social media networks, and newspapers. Every tornado tornadoes coincides with large convergence zones of air report is validated and entered into our database. (is masses [6]. (ese processes often occur on plains, such as information can be later used as a starting point for re- on the plains of North America where supercell storms are search on tornadoes. In the present study, video evidence of common. Furthermore, tornadogenesis mainly occurs in the occurrence of tornadoes and their sense of rotation supercell systems that are affected by the Coriolis force, during the 2010–2017 period was obtained from the In- which causes tornadoes in the Northern Hemisphere to ternet (YouTube, Twitter, and Facebook). We only con- generally rotate in an anticlockwise direction. However, a sidered tornado records that had complete information on large number of tornadoes also occur in non-mesocyclonic the time of occurrence and the coordinates of the event and systems. It is important to mention that the possibility of that were associated with videos evidencing the sense of anticyclonic events cannot be ruled out. In this respect, rotation. To determine the prevailing meteorological Snider [7] carried out the first description of an anticy- conditions during these tornado events, we applied the clonic tornado, and Fujita [1] studied the characteristics of Weather Research and Forecasting (WRF) model. For this such events. Recently, the features of anticyclonic torna- analysis, 11 tornadoes, including 7 anticyclonic and 4 does were explained applying radar data [8]. Anticyclonic cyclonic tornadoes, were selected. In addition, the tornado tornadoes are generally found on the hook echo of anti- of Ciudad Acuña in 2015 is highlighted as reference of a cyclonic supercells in updrafts that take place within a mesocyclonic tornado in a flat region of Mexico. preexisting anticyclonic vortex [9]. Several publications (e WRF model is a numerical weather prediction and have additionally described the physical and dynamic atmospheric simulation system designed for research and aspects of tornadoes [10–13]. Recent data on the incidence operational applications [26]. Although the used resolution of tornadoes in the United States (U.S.) indicate that up to is not appropriated to resolve tornadoes themselves, the 1200 tornadoes may occur per year [14, 15]. But, countries WRF model is an important tool that can show how local such as Canada [16], India [17], Greece [18], China [19], systems (mountain-valley circulations or forced convection Spain [20], Brazil [21], and South Africa [22] also have by topography) and mesoscale systems (cold fronts or well-documented tornado events. Although statistics on moisture fluxes) interact with a tornado formation. Ac- anticyclonic tornadoes around the world are not available, cordingly, the WRF Model has been used in several studies studies have shown that these phenomena are rather rare. on tornadoes [17, 27–30]. In the present study, the selected Fujita [1] found that, in 27 years, only 29 clockwise- reanalysis dataset was the NCEP FNL Operational Model rotating tornadoes were detected in the U.S. Snider [7] Global Tropospheric Analyses. (ese data are expressed on a similarly found that, of 100 investigated tornadoes, only 1 1 × 1° grid every six hours [31]. All calculations were carried had an anticyclonic rotation. In recent research works, no out using similar domain characteristics and physical information on frequency of anticyclonic tornadoes was parameterisations. A mother domain (D1) was created with found. If one considers the abovementioned average 100 × 100 grid points, a 9 km resolution and outputs every number of tornadoes per year, a very small percentage 30 minutes. (en, a first nested domain (D2) was generated were anticyclonic. (is simple analysis demonstrates the with 88 × 88 grid points, a 3 km resolution, and outputs overwhelming dominance of cyclonic tornadoes in the every 30 minutes; finally, a second nested domain (D3) was Northern Hemisphere. generated with 76 × 76 grid points, a 1 km resolution, and outputs every 10 minutes. All simulations were carried out 2. Study Region so that the points where tornadoes occurred were centred in space and time. (e physical options were selected as fol- (e Trans-Mexican Volcanic Belt (TMVB) is a Neogene lows: WRF single-moment 3-class schemes for micro- volcanic arc built on the southern edge of the North physics; Dudhia shortwave scheme, RRTM longwave American plate [23]. It extends approximately 900 km from scheme, and MM5 similarity scheme for surface layer op- the Pacific Ocean in the west to the Gulf of Mexico in the tions; unified Noah land surface model for land surface east, crossing 13 states in Mexico; its width varies from 200 options; Yonsei University scheme (YSU) for planetary to 300 km. (e region is characterised by a complex to- boundary layer options; and Kain–Fritsch scheme for cu- pography, with mountains reaching heights of more than mulus parameterisation [32–38]. 5000 m (Figure 1). Also, the TMVB is considered as one of the 14 biogeographic provinces in Mexico and is defined as a 4. Results transition zone [24]. (e region selected for this analysis is located within the zone of influence of the TMVB from (e study of tornadoes in Mexico, a country with complex 18.80°N, 105.40°W to 21.52°N, 95.79°W.