DOCSLIB.ORG

Downloaded 10/07/21 07:51 PM UTC 1978 JOURNAL of ATMOSPHERIC and OCEANIC TECHNOLOGY VOLUME 35 Storms

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Downloaded 10/07/21 07:51 PM UTC 1978 JOURNAL of ATMOSPHERIC and OCEANIC TECHNOLOGY VOLUME 35 Storms OCTOBER 2018 L I M E T A L . 1977 Polarimetric Radar Signatures of a Rare Tornado Event over South Korea S. LIM,S.ALLABAKASH, AND B. JANG Korea Institute of Civil Engineering and Building Technology, Goyang, South Korea V. CHANDRASEKAR Colorado State University, Fort Collins, Colorado (Manuscript received 13 March 2018, in final form 28 August 2018) ABSTRACT The Korea Institute of Civil Engineering and Building Technology (KICT) made one of the first radar observations of a rare tornadic storm that occurred on 10 June 2014 in the Seoul metropolitan region, South Korea, using X-band dual-polarization radar. The tornado lasted for about 18 min, during which it destroyed about 20 greenhouses and injured several people. This tornado was rated at F0 on the Fujita scale. The KICT X-band dual-polarization radar was installed in the area northwest of Seoul to monitor storm development, measure rainfall, improve hazard mitigation, and disaster management. This paper presents the high- resolution (both spatial and temporal) polarimetric radar observations of the tornado, along with the radar parameters of reflectivity, differential reflectivity, Doppler velocity, and copolar correlation coefficient. The characteristic signatures of polarimetric variables, including the descending reflectivity core, weak echo hole, Doppler velocity couplet, and hook echo, are used to describe the tornado vortex and its development. In addition, the close range (about 5-km distance) observations of the hook echo show the high-resolution radar signatures of a weak echo region surrounded by high-reflectivity annular rings inside the tornado vortex. From development to dissipation, various finescale features are observed, including lofted tornadic debris and potential hail signatures. The high-resolution (close range) observations were also compared against low- resolution (long range) radar observations. The comparison shows that high-spatiotemporal, low-altitude, and close-range observations can be significantly advantageous for tornado detection and early warning. 1. Introduction Kumjian and Ryzhkov 2008; Lim et al. 2005). These polarimetric radar variables can also be used to distin- Weather radars are powerful remote sensing tools guish nonmeteorological scatterers (insects, dust, debris, for various meteorological applications, such as severe and birds) and hydrometeors (Ryzhkov et al. 2005). The weather monitoring and quantitative precipitation esti- polarimetric radars can be used to characterize tornadic mation. Over the last two decades, operational radars vortex signatures (Bluestein et al. 2007; Ryzhkov et al. have been significantly improved by the introduction of 2005). Dual-polarization radar transmits and receives dual-polarization capability. Dual-polarization radars electromagnetic waves in both vertical and horizontal have demonstrated the ability to discriminate between polarizations, which provides considerable information different types of hydrometeors. The combination of about the character of scatterers in the resolution vol- reflectivity factor at horizontal polarization Z , differ- h ume. The received polarimetric data can be used to ential reflectivity Z , and copolar correlation coefficient dr analyze and describe the structure of the tornadoes. r is used to extract information related to the size, hv The initial stage of the tornado may exhibit a descending shape, composition, and orientation of scatterers within reflectivity core (DRC) pattern (Rasmussen et al. 2006; the resolution volume (Bringi and Chandrasekar 2001; Byko et al. 2009). The DRC typically occurs prior to the development of the hook echo. The DRC signatures can Denotes content that is immediately available upon publication be used to detect tornadogenesis. DRCs may or may not as open access. be associated with tornadic storms. Rasmussen et al. (2006) performed the preliminary study on DRCs in which Corresponding author: S. Lim, [email protected] they described the characteristics of DRC in convective DOI: 10.1175/JTECH-D-18-0041.1 Ó 2018 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses). Unauthenticated | Downloaded 10/07/21 07:51 PM UTC 1978 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 35 storms. They also discussed the frequency of occurrence of supercell storm, which occurred on 4 May 2007, near DRCs prior to tornadic supercell storms. Subsequently, Greensburg, Kansas. They observed features such as WEH Kennedy et al. (2007) presented a statistical study of and WEC. The WEC is found in mode-1 (cyclic tornado DRCs and their relation to tornadic and nontornadic production) and mode-2 (long-track tornado production) storms. They suggested that DRCs are not necessarily tornadoes associated with low Zdr and low rhv, which in- present prior to tornadogenesis. Byko et al. (2009) also dicate lofted debris. They also found that high Zdr shield observed DRC features in various supercell thunder- and Zdr arc along the forward flank might represent large storms using mobile Doppler radar data. They described raindrops and size sorting, respectively. Houser et al. (2016) the classification of DRCs based on different precipitation observed the characteristics of a large violent tornado that events. According to this classification, type-I DRC are occurred on 24 May 2011, east of the dryline in western caused by stagnation of the midlevel flow, while type-II Oklahoma, using rapid scan X-band polarimetric mobile DRC results from supercell cycling, and the low-level ro- Doppler radar. They analyzed the TDS using rhv iso- tation generates type-III DRC. Tornadic debris signatures surfaces, in addition to the Zh, Zdr, and Doppler velocity (TDS) of larger storms have been studied by several re- V features. Kumjian and Ryzhkov (2008) discussed the searchers using polarimetric radar variables. Ryzhkov et al. efficiency of rhv over Zdr at TDS detection. Bodine et al. (2005) observed tornadic supercells near the Oklahoma. (2014) analyzed statistical properties of TDS using dual- City, Oklahoma, metropolitan area. They found that the wavelength (S band and C band) polarimetric radar data, strong vortex in Doppler velocity and inside the hook which may improve the capability of tornado detection echo, the presence of low Zdr (,0.5 dB), low rhv (,0.8), and its damage survey. The authors observed an EF4- and high Zh (.45 dB) are associated with lofted debris. rated tornado that occurred on 10 May 2010 in Moore, They also reported that the presence of high Zdr values Oklahoma, and Oklahoma City. They made comparisons at the inflow region of the forward flank downdraft between S- and C-band radar measurements. The com- (FFD) indicates raindrop size sorting. Wurman and Gill parisons exposed that the TDS at S band exhibited higher (2000) characterized the Dimmit, Texas, tornado that values of Zh and rhv than at C band. The presence of low occurred on 3 June 1995, using Doppler on Wheels values (Zh and rhv) for C-band radar relative to S-band (DOW) mobile radar. They noticed that circular rings radar is probably a result of non-Rayleigh scattering effects. near the tip of the hook echo accompanied a strong Snyder et al. (2010) presented the differences between velocity couplet and stated that the inner low-reflectivity S-band and X-band radar observations during severe con- rings represent tornadic debris signatures and outer vective storms. They described the tornadic supercell high-reflectivity rings indicate precipitation particles. structure that occurred on 29 May 2004 (tornado passed Bluestein et al. (2007) used dual-polarization X-band through the state of Oklahoma), and the one that traversed mobile Doppler radar to identify tornadoes in super- between the towns of Medicine Lodge, Kansas, and Harper cells. The authors observed F2- (east of Attica, Kansas) in southwestern Kansas on 12 May 2004. During these and F0-rated (southwest of Harper, Kansas) tornadoes two cases, they observed that the low values of rhv and Zdr on 12 May 2004, near southern Kansas. They also ob- in the tornado core indicate debris signatures, specifi- served the cyclonic (northeast of Geary and northwest cally that Zdr arc in FFD represents size sorting and that of Calumet, Oklahoma) and anticyclonic (north of high Zh (45–55 dBZ) and high Zdr (3–4 dB) values in FFD Calumet) tornadoes near central Oklahoma on 29 May indicate heavy precipitation. Burgess et al. (2002) observed 2004. In these tornado events, they found that the debris the characteristics of an Oklahoma City tornado that ring exhibited values of Zdr , 0.5 dB, rhv , 0.5, and occurred on 3 May 1999. They found that the minimum Zh ;40 dBZ. They also reported that precipitation wraps reflectivity in the tornado core describes the centrifuging around the weak echo hole. Wakimoto et al. (2015) pre- of radar scatterers. They also compared high-resolution, sented the relationship between the hook echo, weak close-range (8 km) observations (using DOW radars) to echo hole (WEH), weak echo column (WEC), and ro- low-resolution, long-range (17–59 km) observations [using tational couplet with visual tornadic characteristics. In Weather Surveillance Radar-1988 Doppler (WSR-88D)]. their study, they presented photogrammetric analysis of a From the comparison, they determined the advantage of devastating tornado that occurred near El Reno, utilizing close-range observations and presented the loss of Oklahoma, (on 31 May 2013) with X-band mobile polari- tornado information for long-range measurements. metric radar observations. They observed weak hook echo All of the above studies described tornadic storm and weak velocity couplet during the early stage of the features such as DRC, WEH or bounded weak echo tornado and strong hook echo and prominent velocity region (BWER), TDS, hook echo, velocity couplet, Zh couplet during the intensified tornado case. Tanamachi et al. rings, Zdr arc, and Zdr shield using polarimetric radar (2012) presented data from 10 tornado events by a single variables. We also observed all these features, which can Unauthenticated | Downloaded 10/07/21 07:51 PM UTC OCTOBER 2018 L I M E T A L .
Load more

Recommended publications
  • From Improving Tornado Warnings: from Observation to Forecast
    Improving Tornado Warnings: from Observation to Forecast John T. Snow Regents’ Professor of Meteorology Dean Emeritus, College of Atmospheric and Geographic Sciences, The University of Oklahoma Major contributions from: Dr. Russel Schneider –NOAA Storm Prediction Center Dr. David Stensrud – NOAA National Severe Storms Laboratory Dr. Ming Xue –Center for Analysis and Prediction of Storms, University of Oklahoma Dr. Lou Wicker –NOAA National Severe Storms Laboratory Hazards Caucus Alliance Briefing Tornadoes: Understanding how they develop and providing early warning 10:30 am – 11:30 am, Wednesday, 21 July 2010 Senate Capitol Visitors Center 212 Each Year: ~1,500 tornadoes touch down in the United States, causing over 80 deaths, 100s of injuries, and an estimated $1.1 billion in damages Statistics from NOAA Storm Prediction Center Supercell –A long‐lived rotating thunderstorm the primary type of thunderstorm producing strong and violent tornadoes Present Warning System: Warn on Detection • A Warning is the culmination of information developed and distributed over the preceding days sequence of day‐by‐day forecasts identifies an area of high threat •On the day, storm spotters deployed; radars monitor formation, growth of thunderstorms • Appearance of distinct cloud or radar echo features tornado has formed or is about to do so Warning is generated, distributed Present Warning System: Warn on Detection Radar at 2100 CST Radar at 2130 CST with Warning Thunderstorms are monitored using radar A warning is issued based on the detected and
    [Show full text]
  • Downloaded 09/30/21 06:43 PM UTC JUNE 1996 MONTEVERDI and JOHNSON 247
    246 WEATHER AND FORECASTING VOLUME 11 A Supercell Thunderstorm with Hook Echo in the San Joaquin Valley, California JOHN P. MONTEVERDI Department of Geosciences, San Francisco State University, San Francisco, California STEVE JOHNSON Association of Central California Weather Observers, Fresno, California (Manuscript received 30 January 1995, in ®nal form 9 February 1996) ABSTRACT This study documents a damaging supercell thunderstorm that occurred in California's San Joaquin Valley on 5 March 1994. The storm formed in a ``cold sector'' environment similar to that documented for several other recent Sacramento Valley severe thunderstorm events. Analyses of hourly subsynoptic surface and radar data suggested that two thunderstorms with divergent paths developed from an initial echo that had formed just east of the San Francisco Bay region. The southern storm became severe as it ingested warmer, moister boundary layer air in the south-central San Joaquin Valley. A well-developed hook echo with a 63-dBZ core was observed by a privately owned 5-cm radar as the storm passed through the Fresno area. Buoyancy parameters and ho- dograph characteristics were obtained both for estimated conditions for Fresno [on the basis of a modi®ed morning Oakland (OAK) sounding] and for the actual storm environment (on the basis of a radiosonde launched from Lemoore Naval Air Station at about the time of the storm's passage through the Fresno area). Both the estimated and actual hodographs essentially were straight and suggested storm splitting. Although the actual CAPE was similar to that which was estimated, the observed magnitude of the low-level shear was considerably greater than the estimate.
    [Show full text]
  • ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
    ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere.
    [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]
  • Near-Surface Vortex Structure in a Tornado and in a Sub-Tornado-Strength Convective-Storm Vortex Observed by a Mobile, W-Band Radar During VORTEX2
    VOLUME 141 MONTHLY WEATHER REVIEW NOVEMBER 2013 Near-Surface Vortex Structure in a Tornado and in a Sub-Tornado-Strength Convective-Storm Vortex Observed by a Mobile, W-Band Radar during VORTEX2 ,1 # @ ROBIN L. TANAMACHI,* HOWARD B. BLUESTEIN, MING XUE,* WEN-CHAU LEE, & & @ KRZYSZTOF A. ORZEL, STEPHEN J. FRASIER, AND ROGER M. WAKIMOTO * Center for Analysis and Prediction of Storms, and School of Meteorology, University of Oklahoma, Norman, Oklahoma # School of Meteorology, University of Oklahoma, Norman, Oklahoma @ National Center for Atmospheric Research, Boulder, Colorado & Microwave Remote Sensing Laboratory, University of Massachusetts, Amherst, Amherst, Massachusetts (Manuscript received 14 November 2012, in final form 22 May 2013) ABSTRACT As part of the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) field campaign, a very high-resolution, mobile, W-band Doppler radar collected near-surface (#200 m AGL) observations in an EF-0 tornado near Tribune, Kansas, on 25 May 2010 and in sub-tornado-strength vortices near Prospect Valley, Colorado, on 26 May 2010. In the Tribune case, the tornado’s condensation funnel dissipated and then reformed after a 3-min gap. In the Prospect Valley case, no condensation funnel was observed, but evidence from the highest-resolution radars in the VORTEX2 fleet indicates multiple, sub-tornado-strength vortices near the surface, some with weak-echo holes accompanying Doppler velocity couplets. Using high-resolution Doppler radar data, the authors document the full life cycle of sub- tornado-strength vortex beneath a convective storm that previously produced tornadoes. The kinematic evolution of these vortices, from genesis to decay, is investigated via ground-based velocity track display (GBVTD) analysis of the W-band velocity data.
    [Show full text]
  • Radar Artifacts and Associated Signatures, Along with Impacts of Terrain on Data Quality
    Radar Artifacts and Associated Signatures, Along with Impacts of Terrain on Data Quality 1.) Introduction: The WSR-88D (Weather Surveillance Radar designed and built in the 80s) is the most useful tool used by National Weather Service (NWS) Meteorologists to detect precipitation, calculate its motion, estimate its type (rain, snow, hail, etc) and forecast its position. Radar stands for “Radio, Detection, and Ranging”, was developed in the 1940’s and used during World War II, has gone through numerous enhancements and technological upgrades to help forecasters investigate storms with greater detail and precision. However, as our ability to detect areas of precipitation, including rotation within thunderstorms has vastly improved over the years, so has the radar’s ability to detect other significant meteorological and non meteorological artifacts. In this article we will identify these signatures, explain why and how they occur and provide examples from KTYX and KCXX of both meteorological and non meteorological data which WSR-88D detects. KTYX radar is located on the Tug Hill Plateau near Watertown, NY while, KCXX is located in Colchester, VT with both operated by the NWS in Burlington. Radar signatures to be shown include: bright banding, tornadic hook echo, low level lake boundary, hail spikes, sunset spikes, migrating birds, Route 7 traffic, wind farms, and beam blockage caused by terrain and the associated poor data sampling that occurs. 2.) How Radar Works: The WSR-88D operates by sending out directional pulses at several different elevation angles, which are microseconds long, and when the pulse intersects water droplets or other artifacts, a return signal is sent back to the radar.
    [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]
  • Glossary of Severe Weather Terms
    Glossary of Severe Weather Terms -A- Anvil The flat, spreading top of a cloud, often shaped like an anvil. Thunderstorm anvils may spread hundreds of miles downwind from the thunderstorm itself, and sometimes may spread upwind. Anvil Dome A large overshooting top or penetrating top. -B- Back-building Thunderstorm A thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction. Back-sheared Anvil [Slang], a thunderstorm anvil which spreads upwind, against the flow aloft. A back-sheared anvil often implies a very strong updraft and a high severe weather potential. Beaver ('s) Tail [Slang], a particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver's tail. It is attached to a supercell's general updraft and is oriented roughly parallel to the pseudo-warm front, i.e., usually east to west or southeast to northwest. As with any inflow band, cloud elements move toward the updraft, i.e., toward the west or northwest. Its size and shape change as the strength of the inflow changes. Spotters should note the distinction between a beaver tail and a tail cloud. A "true" tail cloud typically is attached to the wall cloud and has a cloud base at about the same level as the wall cloud itself. A beaver tail, on the other hand, is not attached to the wall cloud and has a cloud base at about the same height as the updraft base (which by definition is higher than the wall cloud).
    [Show full text]
  • Weather Radar Quiz Name
    Weather radar quiz Name: 1. Base velocity displays (select all that apply) 8. Targets that are ____ or ___ have no radial velocity (select all that apply) Select 2 answers Select 2 answers A Speed of the wind toward or away from the radar A stationary B Intensity of the precipitation B away from the radar C Movement of precipitation over the time C towards the radar D moving perpendicular to the radar beam 2. What are the values of reflectivity for precipitation mode? A From -28 dbz to +28 dbz B From 0 to 75 dbz C Above 45 dbz 3. Positive values (warm yellow to red colors) of velocities indicates movements 9. The higher gradient in the reflectivity values between the edge of the cell and core indicates a stronger storm. A perpendicular to the radar beam C towards the radar A True B False B away from the radar D parallel to the radar beam 10. What radar features indicate tropical cyclone? (select all that apply) Select 4 answers A Low reflectivity in the eye D High reflectivity band spiraling outward 4. Which non-meteorological targets can be detected by weather radars? (select all that apply) A Birds C Buildings E Dust B Small and circled shape echoes E Rotation B Trees D Smoke F All from the above C High reflectivity in eyewall 5. What factros enhance the radar reflectivity around the melting level? (select all that apply) Select 2 answers 11. What radar signature indicates that strong, straight-line winds are possible? A The targets become warmer A Hook echo B Bow echo C Rotation couplet B The targets increase in size 12.
    [Show full text]
  • Tornadogenesis: Our Current Understanding, Forecasting Considerations, and Questions to Guide Future Research
    Atmospheric Research 93 (2009) 3–10 Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmos Tornadogenesis: Our current understanding, forecasting considerations, and questions to guide future research Paul M. Markowski ⁎, Yvette P. Richardson Department of Meteorology, Pennsylvania State University, University Park, PA, United States article info abstract Article history: This paper reviews our present understanding of tornadogenesis and some of the outstanding Received 30 November 2007 questions that remain. The emphasis is on tornadogenesis within supercell thunderstorms. The Received in revised form 30 June 2008 origin of updraft-scale rotation, i.e., mesocyclogenesis, above the ground is reviewed first, Accepted 19 September 2008 followed by the requisites for the development of rotation near the ground. Forecasting strategies also are discussed, and some speculations are made about the relationships between Keywords: the dynamics of tornadogenesis and the forecasting parameters that have been somewhat Supercell successful discriminators between tornadic and nontornadic supercells. Thunderstorm Tornado When preexisting rotation is absent at the ground, a downdraft is required for tornadogenesis. Tornadogenesis Not surprisingly, decades of tornado observations and supercell simulations have revealed Mesocyclone that downdrafts are present in close proximity to tornadoes and significant nontornadic Mesocyclogenesis vortices at the surface. Tornadic supercells are favored when the outflow associated with Downdraft downdrafts is not too negatively buoyant. Cold outflow may inhibit vorticity stretching and/or lead to updrafts that are undercut by their own outflow. It may be for this reason that climatological studies of supercell environments have found that the likelihood of tornadic supercells increases as the environmental, boundary layer relative humidity increases (there is some tendency for supercell outflow to be less negatively buoyant in relatively humid environments).
    [Show full text]
  • Tornadoes – Forecasting, Dynamics and Genesis
    Tornadoes – forecasting, dynamics and genesis Mteor 417 – Iowa State University – Week 12 Bill Gallus Tools to diagnose severe weather risks • Definition of tornado: A vortex (rapidly rotating column of air) associated with moist convection that is intense enough to do damage at the ground. • Note: Funnel cloud is merely a cloud formed by the drop of pressure inside the vortex. It is not needed for a tornado, but usually is present in all but fairly dry areas. • Intensity Scale: Enhanced Fujita scale since 2007: • EF0 Weak 65-85 mph (broken tree branches) • EF1 Weak 86-110 mph (trees snapped, windows broken) • EF2 Strong 111-135 mph (uprooted trees, weak structures destroyed) • EF3 Strong 136-165 mph (walls stripped off buildings) • EF4 Violent 166-200 mph (frame homes destroyed) • EF5 Violent > 200 mph (steel reinforced buildings have major damage) Supercell vs QLCS • It has been estimated that 60% of tornadoes come from supercells, with 40% from QLCS systems. • Instead of treating these differently, we will concentrate on mesocyclonic versus non- mesocyclonic tornadoes • Supercells almost always produce tornadoes from mesocyclones. For QLCS events, it is harder to say what is happening –they may end up with mesocyclones playing a role, but usually these are much shorter lived. Tornadoes - Mesocyclone-induced a) Usually occur within rotating supercells b) vertical wind shear leads to horizontal vorticity which is tilted by the updraft to produce storm rotation, which is stretched by the updraft into a mesocyclone with scales of a few
    [Show full text]
  • Tornadogenesis: Our Current Understanding, Forecasting Considerations, and Questions to Guide Future Research
    Atmospheric Research 93 (2009) 3–10 Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmos Tornadogenesis: Our current understanding, forecasting considerations, and questions to guide future research Paul M. Markowski ⁎, Yvette P. Richardson Department of Meteorology, Pennsylvania State University, University Park, PA, United States article info abstract Article history: This paper reviews our present understanding of tornadogenesis and some of the outstanding Received 30 November 2007 questions that remain. The emphasis is on tornadogenesis within supercell thunderstorms. The Received in revised form 30 June 2008 origin of updraft-scale rotation, i.e., mesocyclogenesis, above the ground is reviewed first, Accepted 19 September 2008 followed by the requisites for the development of rotation near the ground. Forecasting strategies also are discussed, and some speculations are made about the relationships between Keywords: the dynamics of tornadogenesis and the forecasting parameters that have been somewhat Supercell successful discriminators between tornadic and nontornadic supercells. Thunderstorm Tornado When preexisting rotation is absent at the ground, a downdraft is required for tornadogenesis. Tornadogenesis Not surprisingly, decades of tornado observations and supercell simulations have revealed Mesocyclone that downdrafts are present in close proximity to tornadoes and significant nontornadic Mesocyclogenesis vortices at the surface. Tornadic supercells are favored when the outflow associated with Downdraft downdrafts is not too negatively buoyant. Cold outflow may inhibit vorticity stretching and/or lead to updrafts that are undercut by their own outflow. It may be for this reason that climatological studies of supercell environments have found that the likelihood of tornadic supercells increases as the environmental, boundary layer relative humidity increases (there is some tendency for supercell outflow to be less negatively buoyant in relatively humid environments).
    [Show full text]