correspondence
Real Time Doppler Isotach and Reflectivity contours on standard PPI scopes. On-line digital integrators, Signature of a Tornado Cyclone providing more reliable and accurate reflectivity field dis- 1 plays, are interfaced with NSSL's Doppler and WSR-57 sur- D. Sirmans, R. J. Doviak, D. Burgess, and L. Lemon, veillance radars (Sirmans and Doviak, 1973b). Reflectivity National Severe Storms Laboratory, NOAA, Nor- "hook" signatures are often used to indicate the possible pres- man, Oklahoma 73069 ence of a tornado cyclone. Now a relatively inexpensive mean velocity processor (MVP) that estimates, in real time, Dop- Abstract pler velocities at all contiguous range locations along a Digital processors estimate, in real time, precipitation echo radial, has been developed at NSSL (Sirmans and Doviak, strength and mean Doppler velocities to display simultane- 1973a). The full coverage of range locations obtained with ous reflectivity and isodop fields on standard PPI's. Reflec- this processor provides a complete Doppler field wherever tivity "hook" and isodop tornado signatures are displayed. targets are present. The statistical properties of the particu- lar estimation technique employed in the MVP are described Geographic location of severe storm winds and tornado by Doviak et al (1974). cyclones can be determined with increased reliability using The MVP was interfaced to NSSL's high resolution (0.8° Doppler radars if quantitative estimates of mean Doppler beamwidth), 10-cm Doppler radar to display isodops on a velocity fields can be conveniently made and displayed in a standard PPI during the 1973 severe storm season. PPI (Plan Position Indicator) format to complement existing A sample of reflectivity and isodop fields displayed simul- PPI displays of reflectivity estimates derived from echo power taneously on two PPI scopes is shown in Fig. 1. Shown in integration. Doppler radar has been utilized for meteorologi- isoecho contours is a reflectivity hook signature (199° AZ, cal research on a restricted basis for many years, but the 82 km) for a tornado cyclone which developed within a severe complexity and cost of processing Doppler data at speeds re- prefrontal squall line that moved across central Oklahoma quired to obtain real-time velocity fields have delayed opera- during the evening of 4 June 1973. Reflectivity values are tional implementation. coded by three PPI trace brightness levels that have the se- The National Severe Storms Laboratory has developed and quence noted in the caption. Fig. lb shows the tornado implemented on-line processors that estimate both mean cyclone's isodop signature. In this case, PPI trace brightness Doppler velocity and echo strength and display these esti- is used to indicate velocity magnitude, and brightness cate- mates as Doppler isotachs (isodops) and isoecho reflectivity gory boundaries form isodops. Because only three brightness levels are reliably resolved, the number of isodops have been i Lieutenant, NOAA Commissioned Corps. limited to five (zero and two for each radial velocity direc-
FIG. 1. PPI reflectivity (a) and isodops (b) at 2115 CST. The elevation angle is 1.9°, RM 60, 80, 100 km. Reflectivity categories are dim (<21 dBZ), bright (21-31), black (31-44), dim (44-57), and bright (>57 dBZ). Velocity categories are dim (<13 m sec-1), bright (13-21), and brightest (>21 m sec1). Positive radial velocities are angularly strobed. Mesocyclone type signature between 193°-203° and 75-90 km.
1126 Vol. 55, No. 9, September 1974
Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Bulletin Arnerican Meteorological Society
FIG. 2. Overlay of Fig. 1 reflectivity and isodop contours.
FIG. 3. Isodop contours of a stationary Rankine vortex. tion). To identify velocity sign, brightness for positive or radially outward velocities is alternately switched on and off Acknowledgments. The authors recognize the efforts of at 1° intervals. Because weak echoes bias the velocity estimate Mr. Glen Anderson whose care and dedication to the opera- toward zero (Doviak et al., 1974) and would make PPI isodop tion and maintenance of all aspects of the Doppler radar interpretation difficult, velocity estimates are not displayed made the reported results possible. We also acknowledge the where echo-to-receiver noise power ratio is less than 15 dB. support of the Federal Aviation Administration under Con- Line drawings of isodop and reflectivity fields are overlaid tract No. DOT FA72-WAI-265 and the Atomic Energy Com- in Fig. 2 to facilitate pattern comparison. Fig. lb shows a mission under Contract No. AT(49-5)-1289 which aided the -1 region of radially outward velocities greater than 21 m sec development of the basic ideas employed in the Mean (200° AZ, 80 km), and to this region's east a corresponding Velocity Processor. region of inbound velocities greater than 21 m sec-1 (195° AZ, 80 km). Shown in Fig. 3 is the isodop PPI signature for References a radar of infinite resolution viewing a stationary Rankine Doviak, R. J., D. Burgess, L. Lemon, and D. Sirmans, 1974: vortex at a distance large compared with the vortex diam- Doppler velocity and reflectivity structure observed within eter. The isodops form a symmetric couplet of closed lines a tornadic storm. (To be published in special May issue with equal number encircling positive and negative Dop- of Journal de Recherches Atmospheriques.) ier velocity maxima. The similarity of pattern in Fig. lb and Sirmans, D., and R. J. Doviak, 1973a: Pulsed-Doppler velocity Fig. 3 suggests that a small scale (10 km) vortex or meso- isotach displays of storm winds in real time. J. Appl. cyclonic type signature is resolved. The spatial coincidence of Meteor., 12, 694-697. the reflectivity hook and isodop vortex signatures occurring over regions where a confirmed tornado existed leads us to , 1973b: Meteorological radar signal intensity estimation. conclude that Fig. 1 shows the real-time signatures of a NOAA Technical Memorandum ERL NSSL-64, National tornado cyclone. Translational motion with a radial com- Severe Storms Laboratory, Norman, Okla., 80 pp. ponent will add equally to the isodop couplet causing asym- metry in magnitude, although symmetry of isodop contours should remain. The near symmetry of this isodop signature is due to vortex translation along a path perpendicular to Drop coalescence in zero-gravity environment the beam axis. of Skylab IV Several radar scans in azimuth and elevation showed that the average storm height was 16 km, and signature and storm O. H. Vaughan and C. Kelly Hill, Aerospace motion were equal (280°/13 m sec-1), but both were to the Environment Division, National Aeronautics and right of mean wind (250°/12.5 m sec"1). The tornado cyclone Space Administration, Marshall Space Flight Cen- signature was tracked for almost an hour as it moved east- ter, Alabama 35812 ward about 40 km. NASA's Skylab missions provided a unique laboratory setting During the spring 1973 season, several tens of storms were for performing cloud physics and fluid mechanics demon- scanned for evidence of vortex motion; of these, only nine strations in a near zero-gravity (< 10-3 g) environment. Sky- produced resolvable mesocyclone type signatures. Seven of lab IV Science Pilot, Dr. E. G. Gibson, conducted and photo- the nine storms were accompanied by tornado reports. graphed several science experiments with water drops. Spe- Storms that did not produce signatures were not accompanied cifically, these tests were designed "to obtain data on fluid by any confirmed tornado reports. oscillation times, dampening times, spherical rotational in-
1127
Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Vol. 55, No. 9, September 1974
C B S HH S 1B a* £ G G _ 553 ^ -PH * ^ v ^ ^ 88 J! "I O -O & 3 * a « « o w ° N rt Q rt gO sG Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Bulletin Arnerican Meteorological Society 1129 Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Vol. 55, No. 9, September 1974 stability, wetting characteristics of fluids in space, internal cause much of the circulation is precipitation free; it is pre- vortices, and fluid flow patterns" (Bannister, 1974). cipitation that scatters the radiation back to the radar One particularly interesting sequence of representative antennas, resulting in radar echoes. For this reason, we have photographs of the impaction and coalescence of two drops designed an experiment that utilizes a special radar-reflective of water of different colors taken by Gibson is shown on material called "chaff," a metalized plastic fiber, which, pages 1128-1129. Both had diameters of approximately 3.9 when distributed in clear air, will return "clear air" echo cm. One drop was stationary while the other was ejected signals to the radar. By distributing chaff through much of -1 toward it at about 3.4 cm sec . Recently, other interesting the volume of clear air adjacent to the natural echo of the photographs (Spengler, 1972) taken on earth of droplet mesoscale circulation, we can then use dual Doppler radars impactions were published in the January 1972 BULLETIN. to see the entire circulation. The difficulties of simulating and observing certain cloud A number of excellent meteorological tools have been used physics experiments in the earth's gravitational environ- in this research. The very fine NSSL 10-cm Dual Doppler ment are well known; thus, the potential for advancement radar system, one located at Norman and the second at from the zero-gravity cloud physics laboratory planned for Cimarron Field, 42 km northwest of Norman, is of course Space Shuttle (Spacelab) is encouraging and exciting the primary data acquisition tool. A chaff dispersal system, (Vaughan, 1973). capable of distributing 10-cm chaff in five discrete bundles through a 2600-m vertical column below the airplane flight References level, was a vital component to this research. The idea for Bannister, T. C., 1974: Skylab III and IV science demonstra- the vertical delivery of chaff is originally attributed to Mr. tions preliminary report. NASA TM X-64835, 20. P. H. Hildebrand of the University of Chicago. A more Spengler, J. D., 1972: Drop impaction and raindrop size. Bull. advanced unit was developed and manufactured for this Amer. Meteor. Soc., 53, 25-26. project by Flight Systems, Inc., of Burns Flat, Oklahoma. Vaughan, W. W., and O. H. Vaughan, 1973: Zero-gravity The University of Wyoming meteorological research Queen research potential in cloud physics and weather modifica- Air airplane, operated under subcontract to the University of tion. Bull. Amer. Meteor. Soc., 54, 552-555. Oklahoma, provided a highly sophisticated measurement platform, as well as a means of delivering the chaff to the appropriate environmental inflow regions of a tornado cyclone. Parameters sensed and digitally recorded on the airplane included dry-bulb and dew-point temperatures, Experiment to deduce tornado cyclone inflow airspeed, magnetic heading, static pressure, Aitken condensa- characteristics using chaff and NSSL tion particles, airplane position, and navigation Doppler dual Doppler radars radar ground track, wind drift angle, and airplane ground John McCarthy, Gerald M. Heymsfield, University of Oklahoma, Norman, Oklahoma, and Stephen P. Nelson, National Severe Storms Laboratory, Nor- man, Oklahoma The University of Oklahoma, in close cooperation with the National Severe Storms Laboratory (NSSL), has recently com- pleted its first year of active research on a grant entitled "Convection Research in Central Oklahoma." The primary objective is to combine several meteorological research tools to better understand the velocity and thermodynamic struc- ture of tornado-producing thunderstorms. Typically a tornado funnel varies in size from 30 to 300 m in diameter while embedded in a larger mesoscale cyclonic circulation ranging from 3 to 8 km in diameter. This parent circulation is usually identified as a tornado cyclone, and is typically situated near the right rear flank of the thunder- storm. While the presence of such a mesoscale circulation by no means assures that a tornado will form, there does ap- pear to be a high correlation between them. The tornado and its parent circulation have traditionally been difficult to detect with most meteorological sensors, but with the development of dual Doppler radars, such as the system at NSSL, there has been significant progress in better elucidating the tornado cyclone velocity structure. With dual Doppler radars we obtain data on storm intensity, measured in the conventional manner, as well as radial velocity compo- nents of the target from two separate antennas placed some FIG. 1. Intensity-contoured display of Cimarron Doppler distance apart. These data can be objectively analyzed to radar, taken at 1559 CST at 0° elevation angle. A marks the yield the quasi-horizontal velocity field. location of the center of the suspected mesoscale circulation Unfortunately, even with the NSSL radars, a significant and B indicates the positions of the chaff. (NSSL-NOAA portion of the mesoscale circulation may not be detected, be- photo.) 1130 Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Bulletin Arnerican Meteorological Society speed. An onboard mini-computer produced cockpit-displayed real-time values of dynamic heating-corrected temperature, dew point, potential, and equivalent potential temperatures, specific humidity, and horizontal wind speed and direction. The real-time display of these computed parameters en- hanced the ability of the flight scientist to make a real-time identification and to trace properties of the immediate thunderstorm environment. On 8 June 1974, a severe thunderstorm containing a meso- scale circulation produced a tornado at Harrah, Oklahoma (this storm was one of a number of similar storms occurring during a tornado outbreak in Central Oklahoma on that day). Chaff operations were conducted before and during this particular tornadic storm. While the storm was in its developmental stage, chaff operations were begun at 1539 CST and lasted 14 min, result- ing in the distribution of a chaff curtain extending from 3.35 km (flight level) to 0.75 km msl, with 11 chaff modules spaced horizontally along a 55-km length, while the air- plane was on a southwest heading. The curtain was placed approximately 20 km ahead of the inflow border of the storm. Figure 1 is a 1559 CST photograph of the intensity- contoured 1 Cimarron Doppler radar scope shown at 0° elevation angle, with range circles every 20 km. Position A marks the location of the suspected mesoscale circulation (hook), while B indicates the positions of the chaff. Whereas portions of the chaff appear to converge into the storms, the streamers are more accurately classified as vertical shear indicators. FIG. 2. Display of the mean radial velocity of the Norman Figure 2 is a display of the mean radial velocity of the Doppler taken at 1602 CST at 0° elevation angle. The display shows velocity-contoured radial velocity, with positive velocity Norman Doppler at 1602 CST. The presentation is velocity- (away from antenna) appearing strobed and negative velocity contoured radial velocity, with positive velocity (away from (toward the antenna) unstrobed. First level display intensity the antenna), appearing strobed,2 while negative velocity represents 0-13 m sec-1, next brightest 14-21 m sec-1, and (toward the antenna) is unstrobed. The brighter the in- brightest is above 22 m sec-1. A marks area of negative radial tensity of the echo, the greater the absolute value of radial velocity, a signature of suspected mesoscale cyclonic circula- velocity, with the brightest ranging above 22 m sec-1. tion. B marks chaff streamers. (NSSL-NOAA photo.) Since the storm was moving toward the northeast, most of of the mesoscale circulation. More specifically, we hope to the radial velocity indication of the echo is positive, or provide constant altitude maps of the complete tornado strobed, as would be expected. However, the circular area cyclone velocity flow field, at various intervals of 1 km be- marked A represents a negative velocity region, with a por- tween the surface and 3 km above the surface. The air- tion having the maximum brightness. The existence of an plane thermodynamic data will be used to further the under- area of strong northeast flow situated immediately northwest standing of the immediate environment of a tornadic storm. of strong southwest flow is a classical single Doppler radial Additional studies will concentrate on analyses of the syn- velocity signature of a mesoscale cyclonic circulation (see optic and subsynoptic dynamics on 8 June 1974. Sirmans et al, 1974). This is presumably a tornado cyclone, since the Harrah tornado was occurring at the photograph We have obtained what appears to be a unique set of data time, in the same location. The chaff streamers are indicated on the tornado cyclone. It is our expectation, when the data by B, again indicating vertical shear and at least a suggestion are fully analyzed, to be able to advance the understand- of converging of the environmental winds into the apparent ing of the structure of the tornado cyclone, and to see more circulation. clearly its interaction with the larger scales of motion. While dual Doppler data were being collected within both Acknowledgments. The broad scientific support of the the chaff and 10-cm precipitation return, the airplane personnel of the National Severe Storms Laboratory, directed collected dense horizontal wind and thermodynamic data by Dr. Edwin Kessler, is gratefully acknowledged. Dr. Donald in the southern, southwestern, and western flanks of the L. Veal of the University of Wyoming is acknowledged for immediate environment of the storm. The airplane wind his great skill in handling the airplane. The Federal Aviation data will be included in an objective analysis of the dual Administration is gratefully acknowledged for their vital Doppler data to give a quasi-horizontal kinematic description flight control support. This research was supported under Grants 04-4-022-3 from NSSL-NOAA, and GA-41844 from the 1 Equivalent radar reflectivity. National Science Foundation. 2 Strobed display refers to a highlight technique that alter- natively conceals the illumination of adjacent data gates. Reference Consequently a strobed display appears as light-dark-light bands of concentric rings about scope center. In this case, Sirmans, D., R. J. Doviak, D. Burgess, and L. Lemon, 1974: such a display refers to positive radial velocity, or targets Real time Doppler isotach and reflectivity signature of moving away from the antenna. a tornado cyclone. Bull. Amer. Meteor. Soc., 55, 1126-1127. 1131 Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Vol. 55, No. 9, September 1974 Multiple funnels at Nashville had visited the area, one moving across Nashville Metropoli- T tan Airport destroying and damaging 72 aircraft. The total Cecil M. Palmer, National Weather Service, A ash- damages in the area were estimated at more than $1,000,000. ville, Tenn. 37217 A special surface weather observation at 1920 CDT states Now called the dates of "The Jumbo Tornado Outbreak," "Tornado overhead moving northeast." This funnel pro- 3-4 April 1974 brought tornadoes to Nashville and the duced 82 kt winds at the centerfield instrument location, Tennessee area. Two nights before, on 1 April, tornadoes and as the funnel moved overhead produced enough vacuum 1132 Unauthenticated | Downloaded 10/06/21 10:22 PM UTC Bulletin American Meteorological Society to empty water bowls in rest rooms, where station personnel proached the area of his home, which was not damaged. had taken refuge. There were several reports of multiple funnels in the area Wednesday, 3 April, severe weather began developing on both the nights of 1 April and 3 April. However, these across Tennessee by afternoon, and moved into the Nashville pictures are the only concrete documentation of their area. Tornado watches, severe thunderstorm warnings, and occurrence. tornado warnings were issued that began before noon and The tornado activity continued to move through Tennessee continued throughout the day as storm and damage reports throughout the night, with 37 hook echoes being identified from the public and indications by radar became numerous. by Nashville radar. By 2:15 a.m. 4 April, 21 tornado warnings, At 1718 CDT a tornado was again sighted from the NWS Office to the southeast, moving northeastward. It was this 7 severe thunderstorm warnings, and one flash flood warning tornado(es) that damaged the Edge-of-Lake area of Nashville had been issued within a 14 hr period for the mid-Tennessee and produced the multiple funnels in the pictures (p. 1132). area. Fifty-five persons were killed in Tennessee alone, as Mr. James D. Tatum, of 516 Clearwater Drive, stepped out- destruction and death resulted from the "Widespread side his home and took the pictures as the tornado ap- Tornado Outbreak." (Continued from announcements, page 1094) NSF report on federal funds for R&D, Effects of acid precipitation symposium science activities The First International Symposium on Acid Precipitation Federal R&D funding rose from $17.0 billion in 1973 to an and the Forest Ecosystem will be held 12-16 May 1975 at the estimated $17.4 billion in FY 1974, according to a report Ohio State University, Columbus, Ohio, sponsored by the released recently by the National Science Foundation (NSF). U.S. Forest Service and Atmospheric Sciences Program, the The report, Federal Funds for Research, Development, Ohio State University. The Symposium will provide a forum and Other Scientific Activities, FY 1972, 1973, and 1974, Vol- for the consideration of all aspects of acid precipitation and ume XXII, (NSF 74-300), provides statistical information on its possible effects on the forest ecosystem, including atmo- the size and scope of federal R&D programs. It is the 22nd spheric transport and chemistry, forest vegetation, soil en- in an annual series and is based on information furnished vironment, and water resources and hydrology. For further to NSF by federal agencies supporting research and develop- information contact: Dr. Leon S. Dochinger, U.S. Forest ment, R&D plant, and scientific information activities. The Service Laboratories, P.O. Box 365, Delaware, Ohio 43015. R&D data, which form the main body of the report, are shown by character of work, type of performer, field of sci- Portable automated mesonet at NCAR ence, and geographic distribution. Copies of the report are available from the Superintendent A portable automated mesonet (PAM) designed to meet the of Documents, U.S. Government Printing Office, Washington, needs of the National Hail Research Experiment and poten- D.C. 20402, for $1.45 per copy. tially useful for various university activities is now being developed and tested at the National Center for Atmospheric Meetings of interest Research (NCAR). NCAR's Research Systems Facility would 29-31 October 1974: The 7th Annual Meeting of the Sea like input on the needs of university scientists early in PAM's Grant Association will be held at the Olympic Hotel in developmental stage. This information should be directed to Seattle, Washington. The theme of the conference will be: Fred Brock at NCAR, P.O. Box 3000, Boulder, Colo. 80303 "Sea Grant—an Action Catalyst." For further information (tel: 303-494-5718). contact: Sea Grant Conference Coordinator, Division of The PAM will be a mesoscale data logger comprising a Marine Resources, University of Washington, 3716 Brooklyn trailer-mounted base station and a network of 40 remote Ave., N.E., Seattle, Washington 98195. stations. These will have basic sensors for measuring wind speed and direction, air temperature and humidity, rain, and 18-22 November 1974: The Tenth American Water Resources pressure, as well as the capability for additional sensors. Conference will be held in San Juan, Puerto Rico, sponsored The system will be useful for studying sea breezes, hail- by the American Water Resources Association. Contact An- storms, squall lines, and regional air pollution. It will also tonio Santiago-Vasques, President, Environmental Systems serve as a ground reference for remote sensors. Engineering of Puerto Rico, Calle Canals, 270-G.P.O. 6061, The PAM base station will have a minicomputer to record Santurce, P.R. 00936. data on magnetic tape, and for real-time data analysis, dis- 4-6 November 1974: An International Conference on Toxic play, and quality verification. The remote stations will sam- Dinoflagellate Blooms will be held in the Boston, Mass., ple data synchronously and telemeter them back to the base area, sponsored by the Massachusetts Science and Technol- station; strip chart recording at the remote stations will be ogy Foundation, Massachusetts Institute of Technology Sea unnecessary. Data transmission links between the base and Grant Program, and other organizations. Topics to be covered remote stations will incorporate a comprehensive error-check - include oceanographic conditions affecting such blooms, in- ing procedure. cluding red tides. Contact: Mass. Science and Technology Foundation, Lakeside Office Park, Door 10, Wakefield, Mass. The PAM will be tested for about a year using Boulder as 01880. the test base station and the Marshall Field site, approxi- mately 19 km away, as the remote station. (More announcements on page 1155) 1133 Unauthenticated | Downloaded 10/06/21 10:22 PM UTC cn — > * " , I-* :: m ELECTRIC CHART DRIVES fp • Three output shafts and appropriate time-scale gearing (pinion and gear) provide aii chart periods previously available plus one of 35.9 days/rev of chart cylinder. • 31-day charts are available for hygrothermographs, thermographs, microbarographs, rain gage, and water-stage recorders. tf • The Chart Drives are interchangeable with Belfort and Friez spring-powered drives. • A timing accuracy including a chart of 5 sec/hr but no greater than 14 min/wk. • A battery life up to 4 months over a temperature range of -40 to +125 F. with one alkaline-manga- nese dioxide C-cell. ' Hii n 4---H « ' f- I ' f 4 Chart Drive complete with LI!-.,.. cylinder and time-scale jW gearing but w/o battery j * •Uj ; BELFORT INSTRUMENT COMPANY 1600 S. CLINTON STREET BALTIMORE, MARYLAND 21224 U.S.A. VfttriMrmm Tel: (301)-342-2626 1134 Vol. 55, No. 9, September 1974 Unauthenticated | Downloaded 10/06/21 10:22 PM UTC