DOCSLIB.ORG

Downloaded 09/24/21 01:00 PM UTC

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Downloaded 09/24/21 01:00 PM UTC 4220 MONTHLY WEATHER REVIEW VOLUME 136 The Effect of Mesoscale Heterogeneity on the Genesis and Structure of Mesovortices within Quasi-Linear Convective Systems DUSTAN M. WHEATLEY* AND ROBERT J. TRAPP Purdue University, West Lafayette, Indiana (Manuscript received 26 June 2007, in final form 2 January 2008) ABSTRACT This study examines the structure and evolution of quasi-linear convective systems (QLCSs) within complex mesoscale environments. Convective outflows and other mesoscale features appear to affect the rotational characteristics and associated dynamics of these systems. Thus, real-data numerical simulations of two QLCS events have been performed to (i) identify and characterize the various ambient mesoscale features that modify the structure and evolution of simulated QLCSs; and then to (ii) determine the nature of interaction of such features with the systems, with an emphasis on the genesis and evolution of low-level mesovortices. Significant low-level mesovortices develop in both simulated QLCSs as a consequence of mechanisms internal to the system—consistent with idealized numerical simulations of mesovortex-bearing QLCSs— and not as an effect of system interaction with external heterogeneity. However, meso-␥-scale (order of 10 km) heterogeneity in the form of a convective outflow boundary is sufficient to affect mesovortex strength, as air parcels populating the vortex region encounter enhanced convergence at the point of QLCS–boundary interaction. Moreover, meso-␤-scale (order of 100 km) heterogeneity in the form of interacting air masses provides for along-line variations in the distributions of low- to midlevel vertical wind shear and convective available potential energy. The subsequent impact on updraft strength/tilt has impli- cations on the vortex stretching experienced by leading-edge mesovortices. 1. Introduction In the idealized numerical simulations of QLCSs (e.g., Thorpe et al. 1982; Rotunno et al. 1988; Weisman An important unresolved issue in severe weather re- 1992, 1993; Skamarock et al. 1994; Weisman and Davis search is the relationship between quasi-linear convec- 1998; Weisman and Trapp 2003; Trapp and Weisman tive systems (QLCSs) such as squall lines and bow ech- 2003) and other convective storms, the initial condi- oes and the complex mesoscale environments within tions are supplied by a one-dimensional sounding that which they evolve. Some observational results (e.g., varies only with height; horizontal homogeneity along Klimowski et al. 2000; Przybylinski et al. 2000; model vertical levels is assumed. The resultant class of Schmocker et al. 2000) suggest that mesoscale variabil- solutions—while arising from an incomplete formula- ity in the wind and thermodynamic fields due, for ex- tion of deep moist convection (see Balaji and Clark ample, to convective outflows can significantly affect 1988)—agree with observations of highly organized, the rotational characteristics of severe QLCSs. Never- self-sustaining QLCSs (e.g., Burgess and Smull 1990; theless, idealized numerical simulations produce appar- Jorgensen and Smull 1993). Many hypotheses put forth ently severe QLCSs in the absence of environmental to explain the morphology, dynamics, and severe heterogeneity. weather potential of QLCSs are derived from idealized modeling, and some have been validated by subsequent * Current affiliation: NOAA/National Severe Storms Labora- studies. For example, a growing body of observational tory, Norman, Oklahoma. evidence (e.g., Atkins et al. 2005; Wheatley et al. 2006; Wakimoto et al. 2006) has confirmed the role of low- level mesovortices in the production of damaging sur- Corresponding author address: Dustan M. Wheatley, NOAA/ National Severe Storms Laboratory, National Weather Center, face winds within QLCSs, as described in Trapp and 120 David L. Boren Blvd., Norman, OK 73072. Weisman (2003). E-mail: [email protected] But idealized numerical simulations that develop me- DOI: 10.1175/2008MWR2294.1 © 2008 American Meteorological Society Unauthenticated | Downloaded 09/24/21 01:00 PM UTC MWR2294 NOVEMBER 2008 WHEATLEYANDTRAPP 4221 soconvective systems are unable to fully document the An issue especially in the latter observational studies environmental conditions affecting the life cycles of is the difficulty in establishing the unambiguous effect these systems, as they cannot reproduce the inherent of environmental heterogeneity, due to the lack of a four-dimensionality of the environment. homogeneous control. Toward this end, Atkins et al. (1999) used a cloud-resolving model to quantify the a. Conceptual models of storm–boundary influence of preexisting boundaries on supercell evolu- interactions that produce tornadoes tion. In their control “no-boundary” run, the model was A long series of modeling and observational studies initialized in the standard way, using a single-sounding have focused on the life cycles of convective storms in representation of a tornadic environment. Initial con- the presence of environmental heterogeneity. Consider ditions for the second, “boundary” experiment were the evidence that a kinematic boundary is at times a chosen to resemble the meteorological conditions near necessary condition for the development of nonsuper- Garden City, Kansas, on 16 May 1995, which was char- cell tornadoes (e.g., Carbone 1983; Brady and Szoke acterized by a preexisting trough line. In both sets of 1989; Wakimoto and Wilson 1989; Mueller and Car- experiments, warm thermal bubbles were used to initi- bone 1987; Lee and Wilhelmson 1997a,b). In the con- ate convection. ceptual model of nonsupercell tornadogenesis, small- The inception and evolution of low-level rotation scale circulations form along a convergence or shear [i.e, significant vertical vorticity of O(10Ϫ2 sϪ1) within boundary through the release of a horizontal shearing the primary updraft] within the storms simulated in instability. The circulations strengthen to tornadic in- the boundary runs tended to be earlier, stronger, and tensity through stretching in the updraft of overhead more persistent, when compared to the no-boundary convection. runs. Moreover, vorticity analyses of the two storms 1 A preexisting thermal boundary has been suggested revealed that the origin of rotation in the boundary as a necessary condition for the development of signif- runs differed in part from the usual conceptualization icant tornadoes [i.e., F2 or greater on the Fujita damage of low-level mesocyclogenesis (e.g., Rotunno and intensity scale (Fujita 1981)]. Maddox et al. (1980) de- Klemp 1985; Davies-Jones and Brook 1993), in which veloped a physical model of boundary layer wind fields streamwise horizontal vorticity along the forward- to explain the seeming natural tendency of thunder- (rear) flank gust front is vertically tilted by the primary storms to become more severe and even tornadic, upon updraft (rear-flank downdraft). Now, the low levels interaction with a synoptic-scale front or external thun- on the cool-air side of the boundary were a source re- derstorm outflow boundary. In their conceptual model, gion for parcels rich in horizontal baroclinic vorticity, boundary layer vertical wind profiles owing to shallow which then flowed into the updraft in a streamwise baroclinic zones enhance moisture content, conver- manner. This behavior was consistent in those simu- gence, and vertical vorticity, providing for tornadic lated storms that propagated along the boundary, thunderstorms in an otherwise unsupportive environ- sometimes at small angles toward the warm-air side of ment. the boundary. Observational studies born of the Verification of By employing an otherwise idealized model with me- the Origins of Rotation in Tornadoes Experiment soscale variability in the environmental conditions, the (VORTEX; Rasmussen et al. 1994) have considered a number of cases where tornadogenesis via thunder- experimental methodology of Atkins et al. (1999) and storm interactions with shallow baroclinic zones ap- more recently Richardson et al. (2007) represent the peared likely. In particular, Markowski et al. (1998) most robust treatments of numerically simulated con- found that nearly 70% of the significant tornadoes that vective storms interacting with their heterogeneous en- occurred during VORTEX were associated in some vironment. It should be noted, though, that their initial way with external shallow baroclinic zones. Moreover, conditions are defined analytically (without enhance- of this subset, most of the tornadoes occurred within ment by observations) to closely resemble desired en- the baroclinic zones of the boundaries, and generally vironmental conditions, and significant uncertainties within 30 km of the boundaries’ leading edges. exist within this input, as stated by the authors. Fur- thermore, the interaction is also necessarily “one way,” hence, the convective scale is not permitted to modify 1 Here, the qualifiers “preexisting” and “external” refer to a the mesoscale, which then cannot feedback to the con- thermal and/or kinematic boundary generated by a source outside the convective cell/system affected. Synoptic-scale fronts (i.e., vective scale. For these reasons, it is uncertain whether warm fronts and stationary fronts) and old thunderstorm outflow their idealized results can be generalized to the real boundaries are both examples of preexisting thermal boundaries. atmosphere. Unauthenticated | Downloaded 09/24/21 01:00 PM UTC 4222 MONTHLY WEATHER REVIEW VOLUME 136 b. Conceptual models of a QLCS interacting with
Load more

Recommended publications
  • Hurricane Outer Rainband Mesovortices
    Presented at the 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 31 2000 EXAMINING THE PRE-LANDFALL ENVIRONMENT OF MESOVORTICES WITHIN A HURRICANE BONNIE (1998) OUTER RAINBAND 1 2 2 1 Scott M. Spratt , Frank D. Marks , Peter P. Dodge , and David W. Sharp 1 NOAA/National Weather Service Forecast Office, Melbourne, FL 2 NOAA/AOML Hurricane Research Division, Miami, FL 1. INTRODUCTION Tropical Cyclone (TC) tornado environments have been studied for many decades through composite analyses of proximity soundings (e.g. Novlan and Gray 1974; McCaul 1986). More recently, airborne and ground-based Doppler radar investigations of TC rainband-embedded mesocyclones have advanced the understanding of tornadic cell lifecycles (Black and Marks 1991; Spratt et al. 1997). This paper will document the first known dropwindsonde deployments immediately adjacent to a family of TC outer rainband mesocyclones, and will examine the thermodynamic and wind profiles retrieved from the marine environment. A companion paper (Dodge et al. 2000) discusses dual-Doppler analyses of these mesovortices. On 26 August 1998, TC Bonnie made landfall as a category two hurricane along the North Carolina coast. Prior to landfall, two National Oceanographic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD) aircraft conducted surveillance missions offshore the Carolina coast. While performing these missions near altitudes of 3.5 and 2.1 km, both aircraft were required to deviate around intense cells within a dominant outer rainband, 165 to 195 km northeast of the TC center. On-board radars detected apparent mini-supercell signatures associated with several of the convective cells along the band.
    [Show full text]
  • Squall Lines: Meteorology, Skywarn Spotting, & a Brief Look at the 18
    Squall Lines: Meteorology, Skywarn Spotting, & A Brief Look At The 18 June 2010 Derecho Gino Izzi National Weather Service, Chicago IL Outline • Meteorology 301: Squall lines – Brief review of thunderstorm basics – Squall lines – Squall line tornadoes – Mesovorticies • Storm spotting for squall lines • Brief Case Study of 18 June 2010 Event Thunderstorm Ingredients • Moisture – Gulf of Mexico most common source locally Thunderstorm Ingredients • Lifting Mechanism(s) – Fronts – Jet Streams – “other” boundaries – topography Thunderstorm Ingredients • Instability – Measure of potential for air to accelerate upward – CAPE: common variable used to quantify magnitude of instability < 1000: weak 1000-2000: moderate 2000-4000: strong 4000+: extreme Thunderstorms Thunderstorms • Moisture + Instability + Lift = Thunderstorms • What kind of thunderstorms? – Single Cell – Multicell/Squall Line – Supercells Thunderstorm Types • What determines T-storm Type? – Short/simplistic answer: CAPE vs Shear Thunderstorm Types • What determines T-storm Type? (Longer/more complex answer) – Lot we don’t know, other factors (besides CAPE/shear) include • Strength of forcing • Strength of CAP • Shear WRT to boundary • Other stuff Thunderstorm Types • Multi-cell squall lines most common type of severe thunderstorm type locally • Most common type of severe weather is damaging winds • Hail and brief tornadoes can occur with most the intense squall lines Squall Lines & Spotting Squall Line Terminology • Squall Line : a relatively narrow line of thunderstorms, often
    [Show full text]
  • J5J.1 1. Introduction the Bow Echo and Mesoscale Convective Vortex
    J5J.1 Keynote Talk: BAMEX Observations of Mesoscale Convective Vortices Christopher A. Davis and Stanley B. Trier National Center for Atmospheric Research Boulder, Colorado 80307 1. Introduction and a Lear jet leased from Weather Modification Inc. (WMI). Mobile Ground- The Bow Echo and Mesoscale based facilities included the Mobile Convective Vortex (MCV) Experiment Integrated Profiling System (MIPS) from (BAMEX) is a study of life cycles of the University of Alabama (Huntsville) mesoscale convective systems using three and three Mobile GPS-Loran Atmospheric aircraft and multiple, mobile ground-based Sounding Systems (MGLASS) from instruments. It represents a combination of NCAR. The MIPS and MGLASS were two related programs to investigate (a) referred to as the ground based observing bow echoes (Fujita, 1978), principally system (GBOS). The two P-3s were each those which produce damaging surface equipped with tail Doppler radars, the winds and last at least 4 hours and (b) Electra Doppler Radar (ELDORA) being larger convective systems which produce on the NRL P-3. The WMI Lear jet long lived mesoscale convective vortices deployed dropsondes from roughly 12 km (MCVs) (Bartels and Maddox, 1991). The AGL. project was conducted from 20 May to 6 For MCSs, the objective was to sample July, 2003, based at MidAmerica Airport mesoscale wind and temperature fields in Mascoutah, Illinois. A detailed while obtaining high-resolution snapshots overview of the project, including of convection structures, especially those preliminary results appears in Davis et al. (2004). The reader wishing to view processed BAMEX data should visit http://www.joss.ucar.edu/bamex/catalog/. In this keynote address, I will focus on the study of MCVs, based particularly observations from airborne Doppler radar and dropsondes and wind profilers.
    [Show full text]
  • Template for Electronic Journal of Severe Storms Meteorology
    Lyza, A. W., A. W. Clayton, K. R. Knupp, E. Lenning, M. T. Friedlein, R. Castro, and E. S. Bentley, 2017: Analysis of mesovortex characteristics, behavior, and interactions during the second 30 June‒1 July 2014 midwestern derecho event. Electronic J. Severe Storms Meteor., 12 (2), 1–33. Analysis of Mesovortex Characteristics, Behavior, and Interactions during the Second 30 June‒1 July 2014 Midwestern Derecho Event ANTHONY W. LYZA, ADAM W. CLAYTON, AND KEVIN R. KNUPP Department of Atmospheric Science, Severe Weather Institute—Radar and Lightning Laboratories University of Alabama in Huntsville, Huntsville, Alabama ERIC LENNING, MATTHEW T. FRIEDLEIN, AND RICHARD CASTRO NOAA/National Weather Service, Romeoville, Illinois EVAN S. BENTLEY NOAA/National Weather Service, Portland, Oregon (Submitted 19 February 2017; in final form 25 August 2017) ABSTRACT A pair of intense, derecho-producing quasi-linear convective systems (QLCSs) impacted northern Illinois and northern Indiana during the evening hours of 30 June through the predawn hours of 1 July 2014. The second QLCS trailed the first one by only 250 km and approximately 3 h, yet produced 29 confirmed tornadoes and numerous areas of nontornadic wind damage estimated to be caused by 30‒40 m s‒1 flow. Much of the damage from the second QLCS was associated with a series of 38 mesovortices, with up to 15 mesovortices ongoing simultaneously. Many complex behaviors were documented in the mesovortices, including: a binary (Fujiwhara) interaction, the splitting of a large mesovortex in two followed by prolific tornado production, cyclic mesovortexgenesis in the remains of a large mesovortex, and a satellite interaction of three small mesovortices around a larger parent mesovortex.
    [Show full text]
  • Tornadogenesis in a Simulated Mesovortex Within a Mesoscale Convective System
    3372 JOURNAL OF THE ATMOSPHERIC SCIENCES VOLUME 69 Tornadogenesis in a Simulated Mesovortex within a Mesoscale Convective System ALEXANDER D. SCHENKMAN,MING XUE, AND ALAN SHAPIRO Center for Analysis and Prediction of Storms, and School of Meteorology, University of Oklahoma, Norman, Oklahoma (Manuscript received 3 February 2012, in final form 23 April 2012) ABSTRACT The Advanced Regional Prediction System (ARPS) is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes. The mesovortex was one of two tornadic meso- vortices spawned by a mesoscale convective system (MCS) that traversed southwestern and central Okla- homa on 8–9 May 2007. The simulation used 100-m horizontal grid spacing, and is nested within two outer grids with 400-m and 2-km grid spacing, respectively. Both outer grids assimilate radar, upper-air, and surface observations via 5-min three-dimensional variational data assimilation (3DVAR) cycles. The 100-m grid is initialized from a 40-min forecast on the 400-m grid. Results from the 100-m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex-scale tornado-like vortex (TLV). Closer examination of the genesis of the TLV suggests that a strong low-level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex. Vertical cross sections and backward trajectory analyses from this low-level updraft reveal that the updraft is the upward branch of a strong rotor that forms just northwest of the simulated TLV. The horizontal vorticity in this rotor originates in the near-surface inflow and is caused by surface friction.
    [Show full text]
  • Hurricane Andrew in Florida: Dynamics of a Disaster ^
    Hurricane Andrew in Florida: Dynamics of a Disaster ^ H. E. Willoughby and P. G. Black Hurricane Research Division, AOML/NOAA, Miami, Florida ABSTRACT Four meteorological factors aggravated the devastation when Hurricane Andrew struck South Florida: completed replacement of the original eyewall by an outer, concentric eyewall while Andrew was still at sea; storm translation so fast that the eye crossed the populated coastline before the influence of land could weaken it appreciably; extreme wind speed, 82 m s_1 winds measured by aircraft flying at 2.5 km; and formation of an intense, but nontornadic, convective vortex in the eyewall at the time of landfall. Although Andrew weakened for 12 h during the eyewall replacement, it contained vigorous convection and was reintensifying rapidly as it passed onshore. The Gulf Stream just offshore was warm enough to support a sea level pressure 20-30 hPa lower than the 922 hPa attained, but Andrew hit land before it could reach this potential. The difficult-to-predict mesoscale and vortex-scale phenomena determined the course of events on that windy morning, not a long-term trend toward worse hurricanes. 1. Introduction might have been a harbinger of more devastating hur- ricanes on a warmer globe (e.g., Fisher 1994). Here When Hurricane Andrew smashed into South we interpret Andrew's progress to show that the ori- Florida on 24 August 1992, it was the third most in- gins of the disaster were too complicated to be ex- tense hurricane to cross the United States coastline in plained by thermodynamics alone. the 125-year quantitative climatology.
    [Show full text]
  • A Preliminary Observational Study of Hurricane Eyewall Mesovortices
    AA PreliminaryPreliminary ObservationalObservational StudyStudy ofof HurricaneHurricane EyewallEyewall MesovorticesMesovortices Brian D. McNoldy and Thomas H. Vonder Haar Department of Atmospheric Science, Colorado State University e-mail: [email protected] ABSTRACT SATELLITE OBSERVATIONS The observational study of fine-scale features in A series of recent case studies will be presented that demonstrate the existence of mesovortices, vortex mergers, polygonal eyewalls, and vortex crystals. All cases were collected from the GOES-8 geosynchronous satellite centered over 0°N 75°W. Some cases were taken from “Normal Operations”, meaning images are taken every 15 or 30 minutes (depending on location). In special cases, the satellite images the storm every seven minutes; this is called “Rapid Scan Operations”. Finally, in high- the eye and eyewall of intense tropical cyclones (TC) priority situations, images can be taken every minute; this is called “Super Rapid Scan Operations”. has been made possible with high temporal and spatial To view loops of all the cases using the highest temporal resolution available, visit http://thor.cira.colostate.edu/tropics/eyewall/. The following four cases are small excerpts from the full loops. resolution imagery from geosynchronous satellites. The current Geosynchronous Operational Environmental BRET, 22Aug99 (1845Z-2010Z) ALBERTO, 12Aug00 (1445Z-1915Z) Satellite (GOES) Series is capable of producing 1-km resolution visible images every minute, resulting in an immense dataset which can be used to study convective cloud tops as well as transient low-level cloud swirls. Computer models have shown that vorticity redistribution in the core of a TC can result in the formation of local vorticity maxima, or mesovortices.
    [Show full text]
  • Severe Weather Forecasting Tip Sheet: WFO Louisville
    Severe Weather Forecasting Tip Sheet: WFO Louisville Vertical Wind Shear & SRH Tornadic Supercells 0-6 km bulk shear > 40 kts – supercells Unstable warm sector air mass, with well-defined warm and cold fronts (i.e., strong extratropical cyclone) 0-6 km bulk shear 20-35 kts – organized multicells Strong mid and upper-level jet observed to dive southward into upper-level shortwave trough, then 0-6 km bulk shear < 10-20 kts – disorganized multicells rapidly exit the trough and cross into the warm sector air mass. 0-8 km bulk shear > 52 kts – long-lived supercells Pronounced upper-level divergence occurs on the nose and exit region of the jet. 0-3 km bulk shear > 30-40 kts – bowing thunderstorms A low-level jet forms in response to upper-level jet, which increases northward flux of moisture. SRH Intense northwest-southwest upper-level flow/strong southerly low-level flow creates a wind profile which 0-3 km SRH > 150 m2 s-2 = updraft rotation becomes more likely 2 -2 is very conducive for supercell development. Storms often exhibit rapid development along cold front, 0-3 km SRH > 300-400 m s = rotating updrafts and supercell development likely dryline, or pre-frontal convergence axis, and then move east into warm sector. BOTH 2 -2 Most intense tornadic supercells often occur in close proximity to where upper-level jet intersects low- 0-6 km shear < 35 kts with 0-3 km SRH > 150 m s – brief rotation but not persistent level jet, although tornadic supercells can occur north and south of upper jet as well.
    [Show full text]
  • Quasi-Linear Convective System Mesovorticies and Tornadoes
    Quasi-Linear Convective System Mesovorticies and Tornadoes RYAN ALLISS & MATT HOFFMAN Meteorology Program, Iowa State University, Ames ABSTRACT Quasi-linear convective system are a common occurance in the spring and summer months and with them come the risk of them producing mesovorticies. These mesovorticies are small and compact and can cause isolated and concentrated areas of damage from high winds and in some cases can produce weak tornadoes. This paper analyzes how and when QLCSs and mesovorticies develop, how to identify a mesovortex using various tools from radar, and finally a look at how common is it for a QLCS to put spawn a tornado across the United States. 1. Introduction Quasi-linear convective systems, or squall lines, are a line of thunderstorms that are Supercells have always been most feared oriented linearly. Sometimes, these lines of when it has come to tornadoes and as they intense thunderstorms can feature a bowed out should be. However, quasi-linear convective systems can also cause tornadoes. Squall lines and bow echoes are also known to cause tornadoes as well as other forms of severe weather such as high winds, hail, and microbursts. These are powerful systems that can travel for hours and hundreds of miles, but the worst part is tornadoes in QLCSs are hard to forecast and can be highly dangerous for the public. Often times the supercells within the QLCS cause tornadoes to become rain wrapped, which are tornadoes that are surrounded by rain making them hard to see with the naked eye. This is why understanding QLCSs and how they can produce mesovortices that are capable of producing tornadoes is essential to forecasting these tornadic events that can be highly dangerous.
    [Show full text]
  • A Revised Tornado Definition and Changes in Tornado Taxonomy
    1256 WEATHER AND FORECASTING VOLUME 29 A Revised Tornado Definition and Changes in Tornado Taxonomy ERNEST M. AGEE Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana (Manuscript received 4 June 2014, in final form 30 July 2014) ABSTRACT The tornado taxonomy presented by Agee and Jones is revised to account for the new definition of a tor- nado provided by the American Meteorological Society (AMS) in October 2013, resulting in the elimination of shear-driven vortices from the taxonomy, such as gustnadoes and vortices in the eyewall of hurricanes. Other relevant research findings since the initial issuance of the taxonomy are also considered and in- corporated, where appropriate, to help improve the classification system. Multiple misoscale shear-driven vortices in a single tornado event, when resulting from an inertial instability, are also viewed to not meet the definition of a tornado. 1. Introduction and considerations from a cumuliform cloud, and often visible as a funnel cloud and/or circulating debris/dust at the ground.’’ In The first proposed tornado taxonomy was presented view of the latest definition, a few changes are warranted by Agee and Jones (2009, hereafter AJ) consisting of in the AJ taxonomy. Considering the roles played by three types and 15 species, ranging from the type I buoyancy and shear on a variety of spatial and temporal (potentially strong and violent) tornadoes produced by scales (from miso to meso to synoptic), coupled with the the classic supercell, to the more benign type III con- requirement in the latest definition that a tornado must vective and shear-driven vortices such as landspouts and be pendant from a cumuliform cloud, it is necessary to gustnadoes.
    [Show full text]
  • Using GLM Flash Density, Flash Area, and Flash Energy to Diagnose Tropical Cyclone Structure and Intensification Patrick Duran1,2, Christopher J
    Using GLM Flash Density, Flash Area, and Flash Energy to Diagnose Tropical Cyclone Structure and Intensification Patrick Duran1,2, Christopher J. Schultz1,2, Roger Allen2,3, Eric Bruning4, Stephanie N. Stevenson5, and David Pequeen4 1NASA Marshall Space Flight Center; 2NASA Short-Term Prediction Research and Transition Center ; 3Jacobs Space Exploration Group; 4Texas Tech University; 5NOAA NWS National Hurricane Center Background The Tropical Cyclone Diurnal Cycle as Observed by GLM • Increased lightning in tropical cyclones (TCs) is typically associated with intensification (e.g. Molinari et al. 1999; • Hurricane Dorian exhibited a classic “diurnal DC1 DC2 Stevenson et al. 2014), but significant lightning outbreaks are also observed in weakening storms (Xu et al. 2017). pulse” of cold cloud tops (Dunion et al. 2014). • The total number of lightning flashes in a TC is not always a reliable indicator of TC intensity evolution. • On both 30 and 31 August, a wave-like pulse • Issues with the range and detection efficiency of ground-based networks, particularly for intracloud lightning. propagated outward from the inner core, with • Physical processes such as vertical wind shear can intensify asymmetric convection while also weakening the TC. cooling infrared brightness temperatures on the • The commissioning of the Geostationary Lightning Mapper (GLM) aboard GOES-16 and GOES-17 marked, for the leading edge and warming infrared brightness first time, the presence of an operational lightning detector in geostationary orbit. temperatures behind (Fig. 5). • In addition to flash density (the number of flashes per unit area per unit time), GLM also provides continuous observations of flash area and total optical energy.
    [Show full text]
  • Low-Level Mesovortices Within Squall Lines and Bow Echoes. Part I: Overview and Dependence on Environmental Shear
    NOVEMBER 2003 WEISMAN AND TRAPP 2779 Low-Level Mesovortices within Squall Lines and Bow Echoes. Part I: Overview and Dependence on Environmental Shear MORRIS L. WEISMAN National Center for Atmospheric Research,* Boulder, Colorado ROBERT J. TRAPP1 Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, Oklahoma (Manuscript received 12 November 2002, in ®nal form 3 June 2003) ABSTRACT This two-part study proposes fundamental explanations of the genesis, structure, and implications of low- level meso-g-scale vortices within quasi-linear convective systems (QLCSs) such as squall lines and bow echoes. Such ``mesovortices'' are observed frequently, at times in association with tornadoes. Idealized simulations are used herein to study the structure and evolution of meso-g-scale surface vortices within QLCSs and their dependence on the environmental vertical wind shear. Within such simulations, signi®cant cyclonic surface vortices are readily produced when the unidirectional shear magnitude is 20 m s 21 or greater over a 0±2.5- or 0±5-km-AGL layer. As similarly found in observations of QLCSs, these surface vortices form primarily north of the apex of the individual embedded bowing segments as well as north of the apex of the larger-scale bow-shaped system. They generally develop ®rst near the surface but can build upward to 6±8 km AGL. Vortex longevity can be several hours, far longer than individual convective cells within the QLCS; during this time, vortex merger and upscale growth is common. It is also noted that such mesoscale vortices may be responsible for the production of extensive areas of extreme ``straight line'' wind damage, as has also been observed with some QLCSs.
    [Show full text]