DOCSLIB.ORG

Downloaded 10/02/21 06:08 AM UTC

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Downloaded 10/02/21 06:08 AM UTC 2344 MONTHLY WEATHER REVIEW VOLUME 136 Surface Analysis of the Rear-Flank Downdraft Outflow in Two Tornadic Supercells BRIAN D. HIRTH,JOHN L. SCHROEDER, AND CHRISTOPHER C. WEISS Atmospheric Science Group, Texas Tech University, Lubbock, Texas (Manuscript received 15 June 2007, in final form 15 November 2007) ABSTRACT The rear-flank downdraft regions of two tornadic supercells were sampled on 12 June 2004 and 9 June 2005 using four “mobile mesonet” probes. These rear-flank downdraft outflows were sampled employing two different data collection routines; therefore, each case is described from a different perspective. The data samples were examined to identify variations in measured surface equivalent potential temperature, virtual potential temperature, and kinematics. In the 12 June 2004 case, the tornadic circulation was accompanied by small equivalent potential temperature deficits within the rear-flank downdraft outflow early in its life followed by increasing deficits with time. Virtual potential temperature deficits modestly increased through the duration of the sample as well. The 9 June 2005 case was highlighted by heavy precipitation near the tornado itself and relatively small negative, or even positive, equivalent and virtual potential temperature perturbations. Large horizontal variations of surface thermodynamic properties were also noted within several regions of this rear-flank downdraft outflow. 1. Introduction small (large) equivalent potential temperature and vir- tual potential temperature deficits as compared to The existence of hook echoes and rear-flank down- those found in the storm inflow environment are drafts (RFDs) in supercell thunderstorms has been well thought to be associated with tornadogenesis success documented over the past several decades (Markowski (failure). These observational findings were all focused 2002b; Stout and Huff 1953; van Tassel 1955; Fujita on time periods very near tornadogenesis (Ϯ5 min). 1958, 1973, 1975; Browning and Donaldson 1963; These conclusions were further reinforced through a Browning 1964, 1965; Lemon 1977; Burgess et al. 1977; numerical simulation conducted by Markowski et al. Brandes 1978; Barnes 1978a,b). Initial investigations at- (2003). The present study attempts to examine the tem- tempted to directly link hook echoes with tornado oc- poral and spatial variability of the thermodynamic and currences, but recent research has confirmed that su- kinematic properties within RFDs while a tornado is percell thunderstorms possessing hook echoes often fail ongoing. to produce tornadoes (Markowski et al. 2002, hereafter Four “mobile mesonet” instrumented vehicles, mod- MSR02). Using direct surface measurements from the eled after those designed by Straka et al. (1996), were Verification of the Origins of Rotation in Tornadoes used by the Texas Tech University (TTU) Atmospheric Experiment (VORTEX; Rasmussen et al. 1994) and Science Group and the TTU Wind Science and Engi- subsequent endeavors, general conclusions have been neering Research Center to collect data during the made relating RFD thermodynamics (equivalent po- Wheeled Investigation of Rear-Flank Downdraft Life- tential temperature and virtual potential temperature) cycles (WIRL) project in May and June of 2004 and to tornadogenesis success and failure (MSR02; 2005. Project WIRL’s efforts yielded two RFD outflow Markowski 2002a, hereafter M02; Grzych et al. 2007, samples suitable for analysis. The first dataset was col- hereafter GLF07). RFD outflow parcels that possess lected from a supercell located west of Lehigh, Iowa, on 12 June 2004 (case 1). The second dataset was acquired from the 9 June 2005 supercell, which passed south of Corresponding author address: Brian D. Hirth, Atmospheric Science Group, Department of Geosciences, Texas Tech Univer- Hill City, Kansas (case 2). These cases offer differing sity, Box 42101, Lubbock, TX 79409. perspectives of the thermodynamic and kinematic vari- E-mail: [email protected] ability within tornadic RFDs. DOI: 10.1175/2007MWR2285.1 © 2008 American Meteorological Society Unauthenticated | Downloaded 10/02/21 06:08 AM UTC MWR2285 JULY 2008 HIRTHETAL. 2345 TABLE 1. Instrumentation and accessories used on the MM platform. Instrument Model Output Comment Wind monitor RM Young 05103 Wind Speed (m sϪ1) and wind direction (°) Temperature–relative Vaisala HMP45A Temperature (°C) and humidity relative humidity (%) Fast-response Campbell Scientific Temperature (°C) Susceptible to radio frequency interference temperature Thermistor 107-L5 resulting in data spikes. Aluminum flashing was added to the PVC housing to help alleviate this interference. Pressure sensor Vaisala PTB220B Pressure (hPa) Static pressure port RM Young 61002 GPS antenna Motorola ANT97-PGS 24 dB BNC-6 GPS receiver Motorola ONCORE Vehicle heading (°) and Vehicle must be in motion 8-channel vehicle speed (m sϪ1) Datalogger Campbell Scientific CR23X Enclosure Hoffman A-1214CHAL Houses the datalogger, pressure sensor, and GPS receiver Vehicle mounts Yakima Q-Towers and Q-Clips Electric fan Radio Shack 6250 Provides continuous aspiration to the PVC housing for the temperature–relative humidity and fast temperature probes Laptop computer Dell Latitude D505 Running LabVIEW software (Intel Celeron) HF radio ICOM IC-F320S Power inverter Tripp-Lite PV-5002 2. Methodology VIEW software. This real-time display allowed team members to better identify the RFD gust front and a. Data collection other noteworthy features. The entire system, including Mobile mesonet (MM) data were collected utilizing radio communications, was powered by the vehicle’s the instrumentation presented in Table 1. Instrumenta- battery. tion and hardware were mounted to an aluminum rack following the design of Straka et al. (1996) to limit the effects of vehicle motion on wind and pressure mea- surements. Consistent with the original design, a PVC housing was mounted to the rack mast to protect both temperature and relative humidity sensors from water, debris, and direct contact with sunlight. A sheet of alu- minum flashing was added surrounding the PVC hous- ing to shield the interior sensors from radio frequency (RF) noise. An electric fan was inserted into the bot- tom of the PVC housing to allow for a continuous as- pirated airflow through the entire enclosure. Because of erroneous measurements made by the flux gate com- pass as a result of RF noise, the compass was removed from the instrumentation suite. Data were collected at 0.5 Hz and were continuously processed and stored by a Campbell Scientific CR23X datalogger. The datalog- FIG. 1. TTU MM platform including wind monitor (A), static ger, pressure sensor, and GPS receiver were housed in pressure port (B), GPS antenna (C), PVC housing (D) containing a hail-resistant enclosure mounted to the mast just “fast” temperature and “slow” temperature–relative humidity probes, and hail-resistant enclosure (E) containing pressure sen- above the vehicle’s roof (Fig. 1). Data were simulta- sor, datalogger, and GPS receiver. The background tornado oc- neously transferred via serial interface from the data- curred in rural Kent County, TX, on 12 Jun 2005. Photo taken by logger to an on-board laptop computer running Lab- Ian Giammanco. Unauthenticated | Downloaded 10/02/21 06:08 AM UTC 2346 MONTHLY WEATHER REVIEW VOLUME 136 FIG. 2. Schematic diagram of the life cycle data collection rou- tine. The RFD boundary is indicated by a solid black line while individual MM teams are marked with an M. Location of the FIG. 3. Same as Fig. 2, but for the snapshot data collection low-level mesocyclone or tornado is denoted with a T. The storm routine. motion vector is provided. Vehicles were to utilize the road net- work to maintain their respective mesocyclone or tornado-relative positions as much as possible as the storm moved eastward. The sample was obtained, the probes attempted to reposi- ϫ idealized road grid spacing is approximately 1.6 km 1.6 km. tion themselves to repeat the procedure as roads al- lowed. In all cases during Project WIRL, the RFD was ini- Two primary data collection routines were executed tially identified visually through the manifestation of a through the duration of Project WIRL. The life cycle clear slot (Beebe 1959). Because of logistical chal- routine was executed for slow-moving supercells or lenges, the team was unable to conduct successful sam- storms following a densely gridded road network. The pling prior to the development of this feature, suggest- goal of this routine was to sample various regions of the ing that the processes driving the RFD were already RFD outflow for as long as logistically permitted. ongoing when the team made its initial measurements. Three individual MM probes attempted to position themselves with a 1- to 2-km spacing in the western, b. Analysis methodologies and techniques southern, and eastern portions of the RFD outflow. The fourth MM probe was dedicated to continuous To ensure data consistency among the four MM sampling of the inflow environment so direct thermo- probes, parameter value comparisons were made while dynamic comparisons could be made between the vari- the team was traveling in a caravan and in quiescent ous RFD sectors and the inflow “base state” (Fig. 2). conditions. Instrument offsets for each probe were The inflow probe was charged with helping to identify computed to remove any individual instrument biases potential low-level mesocyclogenesis, storm cycling, relative to the overall team mean calculated using data and storm transition
Load more

Recommended publications
  • Storm Spotting – Solidifying the Basics PROFESSOR PAUL SIRVATKA COLLEGE of DUPAGE METEOROLOGY Focus on Anticipating and Spotting
    Storm Spotting – Solidifying the Basics PROFESSOR PAUL SIRVATKA COLLEGE OF DUPAGE METEOROLOGY HTTP://WEATHER.COD.EDU Focus on Anticipating and Spotting • What do you look for? • What will you actually see? • Can you identify what is going on with the storm? Is Gilbert married? Hmmmmm….rumor has it….. Its all about the updraft! Not that easy! • Various types of storms and storm structures. • A tornado is a “big sucky • Obscuration of important thing” and underneath the features make spotting updraft is where it forms. difficult. • So find the updraft! • The closer you are to a storm the more difficult it becomes to make these identifications. Conceptual models Reality is much harder. Basic Conceptual Model Sometimes its easy! North Central Illinois, 2-28-17 (Courtesy of Matt Piechota) Other times, not so much. Reality usually is far more complicated than our perfect pictures Rain Free Base Dusty Outflow More like reality SCUD Scattered Cumulus Under Deck Sigh...wall clouds! • Wall clouds help spotters identify where the updraft of a storm is • Wall clouds may or may not be present with tornadic storms • Wall clouds may be seen with any storm with an updraft • Wall clouds may or may not be rotating • Wall clouds may or may not result in tornadoes • Wall clouds should not be reported unless there is strong and easily observable rotation noted • When a clear slot is observed, a well written or transmitted report should say as much Characteristics of a Tornadic Wall Cloud • Surface-based inflow • Rapid vertical motion (scud-sucking) • Persistent • Persistent rotation Clear Slot • The key, however, is the development of a clear slot Prof.
    [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]
  • The Garden City, Kansas, Storm During VORTEX 95. Part I: Overview of the Storm’S Life Cycle and Mesocyclogenesis
    The Garden City, Kansas, storm during VORTEX 95. Part I: Overview of the Storm’s life cycle and mesocyclogenesis Roger M. Wakimoto, Chinghwang Liu, Huaquing Cai Mon. Wea. Rev., 126, 372-392 The Garden City, Kansas, storm during VORTEX 95. Part II: The Wall Cloud and Tornado Roger M. Wakimoto, Chinghwang Liu Mon. Wea. Rev., 126, 393-408 Severe storm environment: Large CAPE and strong low level speed shear. Shear vector unidirectional with height, Helicity small. Trough and wind shift Intersection – focal point for storm initiation Dry line Visible satellite images Note warm inflow switches to cool outflow, probably in rear flank downdraft region Key observing system: ELDORA airborne dual-Doppler radar Flew at 300 m altitude next to the supercell and scanned with both antennas toward supercell PossiblePossible hook hook Tornado damage track Eldora aircraft track: Aircraft flying 300 m above surface Reflectivity (> 40 dBZ shaded), storm relative winds Heavy precipitation Uniform winds near surface Fine line in reflectivity field, believed to be synoptic scale trough line Updraft Cyclonic and anticyclonic mesocyclones aloft (splitting cells) Vertical velocity (gray) and vertical vorticity (dark) Reflectivity (> 40 dBZ shaded), storm relative winds Northerly winds start to develop Downdrafts in heavier precipitation Low level updraft intensifies Low level mesocyclone develops Cyclonic and anticyclonic cells continue to separate 30 m/s updraft becoming near coincident with cyclonic mesocyclone Vertical velocity (gray) and vertical vorticity
    [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]
  • PICTURE of the MONTH Some Frequently Overlooked Severe
    JUNE 2004 PICTURE OF THE MONTH 1529 PICTURE OF THE MONTH Some Frequently Overlooked Severe Thunderstorm Characteristics Observed on GOES Imagery: A Topic for Future Research JOHN F. W EAVER AND DAN LINDSEY NOAA/NESDIS/RAMM Team, Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, Colorado 23 October 2003 and 23 December 2003 ABSTRACT Several examples of Geostationary Operational Environmental Satellite (GOES) visible satellite images de- picting cloud features often associated with the transition to, or intensi®cation of, supercell thunderstorms are presented. The accompanying discussion describes what is known about these features, and what is left to learn. The examples are presented to increase awareness among meteorologists of these potentially signi®cant storm features. 1. Introduction dom 1976, 1983; Weaver 1980; Weaver and Nelson The role of satellite imagery in de®ning the near- 1982; Purdom and Sco®eld 1986; Weaver and Purdom storm environment of severe/tornadic thunderstorms has 1995; Browning et al. 1997; Weaver et al. 1994, 2000; been well documented over the past three decades (Pur- 2002; Bikos et al. 2002). Additionally, several papers have been written concerning storm-top characteristics of severe storms (Heyms®eld et al. 1983; McCann 1983; Corresponding author address: John F. Weaver, NOAA/NESDIS/ Adler and Mack 1986; SetvaÂk and Doswell 1991). Much RAMM, CIRA BuildingÐFoothills Campus, Colorado State Uni- versity, Fort Collins, CO 80523. less has been written concerning low-level,
    [Show full text]
  • Supercell Radar Signatures
    Supercell Radar Signatures OBJECTIVES 1. The student will understand how to use WxScope to access current and archived radar data. 2. The student will understand the reflectivity values frequently associated with hail and heavy rain. 3. The student will understand reflectivity patterns associated with hook echoes and tornadic circulations. 4. The student will understand the fundamentals of supercell storm motion. 5. Given a series of Doppler images from a supercell, the student will be able to identify the hook echo, presence of hail, heavy rain, and tornadic circulation. 6. The student will be able to predict storm locations relative to current radar images. 7. The student will be able to compare predictions to actual storm locations to determine if the storm moved as expected, moved right or left of predicted path. PREREQUISITES MATERIALS Basic understanding of WeatherScope. Computer Completion of Understanding Weather Radar WxScope software lecture in the OCS EarthStorm series Archived radar data VOCABULARY Hook echo: A pendant-shaped echo usually toward the right rear of the echo on a radar screen that indicates the presence of a mesocyclone and possible presence of a tornado. Radar: An electronic instrument used to detect objects (such as precipitation) by their ability to reflect and scatter microwaves back to a receiver. Reflectivity: A measure of the fraction of radiation reflected by a given surface; defined as a ratio of the radiant energy reflected to the total that is incident upon a surface. Generally “reflectivity” is used in place of the phrase “radar reflectivity factor” or “equivalent radar reflectivity factor.” Supercell: A large, long-lived (up to several hours) cell consisting of one quasi-steady updraft- downdraft couplet that is generally capable or producing the most sever weather (tornadoes, high winds, and giant hail).
    [Show full text]
  • Convective Storm Structure and Evolution Presented by the Warning Decision Training Branch
    Distance Learning Operations Course IC 5.7: Convective Storm Structure and Evolution Presented by the Warning Decision Training Branch Version: 0308.2 Distance Learning Operations Course Table of Contents Introduction ..................................................................................................... 1 Objectives ................................................................................................................................................ 3 Lesson 1....................................................................................................................................3 Lesson 2....................................................................................................................................3 Lesson 3....................................................................................................................................3 Lesson 1: Fundamental Relationships Between Shear and Instability on Convective Storm Structure and Type. ......................................................... 6 Objective 1 ............................................................................................................................................... 6 Effects of Shear .........................................................................................................................6 Objective 2 ............................................................................................................................................... 7 Objective 3 ............................................................................................................................................
    [Show full text]
  • Fundamentals of Spotting Part 2 – the Clear Slot
    Fundamentals of Spotting Part 2 – The Clear Slot Professor Paul Sirvatka College of DuPage Meteorology What you REALLY need to know! Gilbert’s Marital Status • Rumors are that he is checking out reception possibilities. Here he has found something that seems to make him happy. • Is it you? Over-emphasis on Wall Clouds You reported what?!?! Wall Clouds • Tell you the location of the updraft • Not easily identified sometimes • Over-identified by less- experienced spotters • Offer useless information to the NWS warn/no warn decision tree • What else does it matter? Characteristics of a Tornadic Wall Cloud • Surface-based inflow • Rapid vertical motion (scud- sucking) • Persistent • Persistent rotation • The key, however, is the development of a clear slot Clear Slot and Tornado Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather First Clue • No wall cloud • No apparent rotation • Only visible clue was a Horseshoe Updraft rain free base Clear Slot • Small scud tags started showing upward motion • Clear slot and horseshoe updraft clearly visible Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather A Storm’s Updraft Horseshoe Updraft The Clear Slot – Look for This! Horseshoe updraft Clear slot Preferred site for tornadogenesis Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Springfield, IL 1995 Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Less then 10 Minutes of Time Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Clear Slot is Visible Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather RFD – Rear Flank Downdraft RFD air is brought back into the tornado updraft! Courtesy Paul Markowski Prof.
    [Show full text]
  • Again, the Air Mass Thunderstorm Is the “Garden Variety” One… to Get More the More Organized, Longer Lived Severe Thunders
    Again, the air mass thunderstorm is the “garden variety” one… To get more the more organized, longer lived severe thunderstorms, we need a combination of more ingredients Ingredients for severe thunderstorms INGREDIENT 1: CONDITIONAL INSTABILITY Needs to be through the depth of the troposphere Make the atmosphere more conditionally unstable by: Warming and moistening near the surface Cooling and drying aloft INGREDIENT 2: WIND SHEAR Change in horizontal wind speed through a vertical depth. If the wind speed changes direction as well that’s even better! Why is wind shear a necessary ingredient for severe thunderstorms? CUMULUS STAGE MATURE STAGE Updraft only Updraft + downdraft NO WIND SHEAR MOST WITH FAVORABLE WIND FOR GROWTH SHEAR (Bluestein) Wind shear allows the updraft to be maintained in the cloud and not get choked off by the downdraft—so the thunderstorm keeps receiving the warm, moist air it needs to keep growing. Where to look for severe thunderstorms (in central and eastern U.S.) In the vicinity of a mid-latitude cyclone Strong upper level winds from the north and west Surface winds from the south to southeast (a low-level jet) Fronts, particularly in front of and at a cold front in the warm sector Drylines: transition zone between dry cT air and moist mT air Very common in the southern Great Plains. THESE CAN ENHANCE: 1. THE VERTICAL WIND SHEAR 2. CONDITIONAL INSTABILITY (i.e. CAPE) More Organized Severe Thunderstorm Types In approximate order of severity Multicell thunderstorms Less severe Squall lines Mesoscale Convective Complexes Supercells Most severe Multicell Thunderstorms In moderate shear, thunderstorms can get a bit more organized, numerous and have longer lifetimes.
    [Show full text]
  • Acronyms and Abbreviations
    ACRONYMS AND ABBREVIATIONS AGL - Above Ground Level AP - Anomalous Propagation ARL -Above Radar Level AVSET - Automated Volume Scan Evaluation and Termination AWIPS - Advanced Weather Interactive Processing System BE – Book End as in Book End Vortex BWER - Bounded Weak Echo Region CAPE - Conditional Available Potential Energy CIN – Convective Inhibition CC – Correlation Coefficient Dual Pol Product CR -Composite Reflectivity Product CWA -County Warning Area DP – Dual Pol dBZ - Radar Reflectivity Factor DCAPE - Downdraft Conditional Available Potential Energy DCZ - Deep Convergence Zone EL – Equilibrium Level ET -Echo Tops Product ETC - Extratropical Cyclone FAR - False Alarm Ratio FFD – Forward Flank Downdraft FFG – Flash Flood Guidance GTG – Gate-To-Gate HP - High Precipitation supercell (storm) HDA -Hail Detection Algorithm LCL -Lifting Condensation Level LEWP -Line Echo Wave Pattern LP - Low Precipitation Supercell (storm) MARC - Mid Altitude Radial Convergence MCC - Mesoscale Convective Complex MCS - Mesoscale Convective System MCV – Mesoscale Convective Vortex MESO -Mesocyclone MEHS -Maximum Expected Hail Size OHP -One-Hour Rainfall Accumulation Product POSH -Probability of Severe Hail QLCS - Quasi Linear Convective Systems R - Rainfall Rate in Z-R relationship RF – Range Folding RFD - Rear Flank Downdraft RIJ - Rear Inflow Jet RIN – Rear Inflow Notch SAILS - Supplemental Adaptive Intra-Volume Low-Level Scan SCP – Supercell Composite Parameter SRH – Storm Relative Helicity SRM -Storm Relative Mean Radial Velocity STP –Significant
    [Show full text]
  • Presentation of Storm Inflow
    4.3 OBSERVATIONS OF STORM SCALE BOUNDARY EVOLUTION WITHIN THE 23 MAY 2007 PERRYTON, TX SUPERCELL Patrick S. Skinner* and Christopher C. Weiss Texas Tech University, Lubbock, Texas 1. INTRODUCTION a boundary established in prior convection. Several studies over the past decade have established a link between tornadic 2. DATA COLLECTION AND QUALITY supercells and relatively low thermodynamic ASSURANCE deficits in both the Rear-Flank Downdraft (RFD) (Markowski et al. 2002; Grzych et al. 2007) and 2.1 StickNet the Forward-Flank Downdraft (FFD) (Shabbott and Markowski 2006). However, considerable Of the twenty-two total StickNet probes, heterogeneity has been observed within twenty were deployed on May 23 rd . Eleven type individual RFD’s (Finley and Lee 2004; Hirth et “A” probes employed a R.M. Young anemometer al. 2008) and the presence of a distinct with nine of these eleven also capable of kinematic and thermodynamic boundary within measuring temperature, humidity and barometric the forward flank has not always conformed to pressure. Though these probes are capable of the examples of observational schematics taking 5 or 10 Hz data, only 1 Hz data are (Lemon and Doswell 1979) and numerical considered in this study. Nine type “B” probes simulations (Wicker and Wilhelmson 1995). were equipped with a Vaisala all-in-one type In order to provide a higher spatial instrument that was capable of taking 1 Hz resolution of in-situ observations in hazardous, measurements of rain and hailfall as well as but potentially critical regions within supercell temperature, humidity, barometric pressure, thunderstorms, Texas Tech University has wind speed and direction.
    [Show full text]
  • Doppler Radar Observation of the Evolution of Downdrafts in Convective Clouds
    Doppler Radar Observation of the Evolution of Downdrafts in Convective Clouds by Nehzat Motallebi Department ofAtmospheric Science Colorado State University Fort Collins, Colorado DOPPLER-P..ADAR OBSERVATION OF THE EVOLUTIOH OF DOWNDRAFTS IN COl\rvECTIVE CLOUDS by Nehzat Motallebi Research supported by the National Science Foundation under Grant ATM76-83361 and National Aeronautics and Space Administration under Grant NSG-5011 Department of Atmospheric Science Colorado State University Fort Collins, Colorado Fall 1982 Atmospheric Science Paper No. 355 ABSTRACT DOPPLER-RADAR OBSERVATION OF THE EVOLUTION OF DOWNDRAFTS IN CONVECTIVE CLOUDS A detailed analysis of the 20 July 1977 thunderstorm oomplex which formed and evolved over the South Park region in Central Colorado is presented. This storm, extensively analyzed using multiple Doppler radar and surface mesonet data, developed within an environment having very weak wind shear. In this environment of weak flow, the storm owed its intensification to the strength of the downdraft, which was nearly coincident with the region where the cloud had grown. Some of the noteworthy features of this storm were its motion well to the right of the cloud-level winds, its multicellular nature and discrete propagation. its north-south orientation. and its relatively large storm size and high reflectivity factor (55 dBZ). The following scenario accounts for the ,observed mesoscale and cloud-scale event. During stage I, a line of convergence was generated at the interface between the easterly upslope winds and westerly winds. During stage II. the convergence line subsequently propagated down the slopes of the Mosquito Range, and was the main forcing mechanism for the development of updraft on the west flank of the storm.
    [Show full text]