CONVECTIVE WEATHER RESEARCH

Burgess, D. W., T. D. Crum, R. J. Vogt, 2008: Impact of wind farms on WSR-88D radars. Extended Abstracts, 24rd Conference on Interactive Information Processing Systems (IIPS), New Orleans, LA, USA, AMS, CD-ROM, bB.3.

Davies-Jones, R. P., 2008: An efficient and accurate method for computing the wet-bulb temperature along pseudoadiabats. Monthly Weather Review, 136, 2764-2785.

A new technique for computing the wet-bulb potential temperature of a parcel and its temperature after pseudoadiabatic ascent or descent to a new pressure level is presented. It is based on inverting Bolton’s most accurate formula for equivalent potential temperature θE to obtain the adiabatic wet-bulb temperature Tw on a given pseudoadiabat at a given pressure by an iterative technique. It is found that Tw is a linear function of equivalent temperature raised to the −1/κd (i.e., −3.504) power, where κd is the Poisson constant for dry air, in a significant region of a thermodynamic diagram. Consequently, Bolton’s formula is raised to the −1/κd power prior to the solving. A good “initial-guess” formula for Tw is devised. In the pressure range 100 ≤ p ≤ 1050 mb, this guess is within 0.34 K of the converged solution for wet-bulb potential temperatures θw ≤ 40°C. Just one iteration reduces this relative error to less than 0.002 K for −20° ≤ θw ≤ 40°C. The upper bound on the overall error in the computed Tw after one iteration is 0.2 K owing to an inherent uncertainty in Bolton’s formula. With a few changes, the method also works for finding the temperature on water- or ice-saturation reversible adiabats.

The new technique is far more accurate and efficient than the Wobus method, which, although little known, is widely used in a software package. It is shown that, although the Wobus function, on which the Wobus method is based, is supposedly only a function of temperature, it has in fact a slight pressure dependence, which results in errors of up to 1.2 K in the temperature of a lifted parcel. This intrinsic inaccuracy makes the Wobus method far inferior to a new algorithm presented herein.

Davies-Jones, R. P., 2008: Can a descending rain curtain in a supercell instigate tornadogenesis barotropically?. Journal of the Atmospheric Sciences, 65, 2469-2497.

This paper investigates whether the descending rain curtain associated with the hook echo of a supercell can instigate a tornado through a purely barotropic mechanism. A simple numerical model of a mesocyclone is constructed in order to rule out other tornadogenesis mechanisms in the simulations. The flow is axisymmetric and Boussinesq with constant eddy viscosity in a neutrally stratified environment. The domain is closed to avoid artificial decoupling of a vortex from the storm-scale circulation. In the principal simulation, the initial condition is a balanced, slowly decaying, Beltrami flow describing an updraft that is rotating cyclonically at midlevels around a low pressure center surrounded by a concentric downdraft that revolves cyclonically but has anticyclonic vorticity. The boundary conditions are no slip on the tangential wind and free slip on the radial or vertical wind to accommodate this initial condition and to allow strong interaction of a vortex with the ground.

Precipitation is released through the top above the updraft and falls to the ground near the updraft–downdraft interface in an annular curtain. The downdraft enhancement induced by the precipitation drag upsets the balance of the Beltrami flow. The downdraft and its outflow toward the axis increase low-level convergence beneath the updraft and transport air with moderately high angular momentum downward and inward where it is entrained and stretched by the updraft. The resulting tornado has a corner region with an intense axial jet and low pressure capped by a vortex breakdown and a transition to a broader vortex aloft (a tornado cyclone). A clear slot of subsiding air with anticyclonic vorticity surrounds the vortex. The vertical kinetic energy of the entire circulation declines dramatically prior to tornado formation.

Kuhlman, K. M., D. R. MacGorman, M. I. Biggerstaff, 2008: Spatial distribution of lightning data relative to kinematics in a HP tornadic supercell storm during TELEX. Preprints, 3rd Annual Conference on Applications of Lightning Data, New Orleans, LA, USA, American Meteorological Society, P1.3.

The Thunderstorm Electrification and Lightning Experiment (TELEX) observed a high-precipitation tornadic supercell storm on 29 May 2004. The available observation systems included the Oklahoma Lightning Mapping Array (LMA), the KOUN S-Band polarimetric radar, and two mobile SMART-R C-Band radars. Thunderstorm charge is thought to be produced by microphysical interactions between graupel and cloud ice followed by differential sedimentation to produce regions of net charge. If so, the kinematics of the storm govern spatial relationships between regions of microphysical charging and the location and geometry of those charge regions.

On 29 May 2004, lightning flashes near the core of this storm, although quite frequent, tended to have shorter duration and smaller horizontal extent than typical flashes in other storms having less frequent lightning. We suggest that this is due, at least in part, to small pockets of opposite charge lying in close proximity to each other. Thus, each polarity of lightning leader propagates only a relatively short distance before reaching regions of unfavorable electrical potential. In the anvil, however, lightning extended tens of kilometers from the reflectivity cores in roughly horizontal layers, consistent with the charge spreading through the anvil in broad sheets. Though lightning has been previously observed in anvils, typically this lightning is initiated in or near the core of the storm and extends out into the anvil. Yet, in the 29 May 2004 storm, flashes initiated in the anvil region and the subsequent leaders progressed back towards the core of the storm. Some of these flashes were negative cloud-to-ground flashes that initiated over 50 km away from the core and struck ground beneath the anvil close to the initiation point. We hypothesize that interaction between the anvil of this supercell and a somewhat lower anvil of opposite polarity from a weaker left-moving cell to the north was responsible for initiating this lightning.

Available online at ://http://www.ametsoc.org.

MacGorman, D. R., W. D. Rust, T. J. Schuur, M. I. Biggerstaff, J. M. Straka, C. L. Ziegler, E. R. Mansell, E. C. Bruning, K. M. Kuhlman, N. R. Lund, N. S. Biermann, C. Payne, L. D. Carey, P. R. Krehbiel, W. Rison, K. B. Eack, W. H. Beasley, 2008: TELEX: The Thunderstorm Electrification and Lightning Experiment. Bulletin of the American Meteorological Society, 89, 997-1013.

The field program of the Thunderstorm Electrification and Lightning Experiment (TELEX) took place in central Oklahoma, May–June 2003 and 2004. It aimed to improve understanding of the interrelationships among microphysics, kinematics, electrification, and lightning in a broad spectrum of storms, particularly squall lines and storms whose electrical structure is inverted from the usual vertical polarity. The field program was built around two permanent facilities: the KOUN polarimetric radar and the Oklahoma Lightning Mapping Array. In addition, balloon-borne electric-field meters and radiosondes were launched together from a mobile laboratory to measure electric fields, winds, and standard thermodynamic parameters inside storms. In 2004, two mobile C-band Doppler radars provided high-resolution coordinated volume scans, and another mobile facility provided the environmental soundings required for modeling studies. Data were obtained from twenty-two storm episodes, including several small isolated thunderstorms, mesoscale convective systems, and supercell storms. Examples are presented from three storms. A heavy-precipitation supercell storm on 29 May 2004 produced greater than 3 flashes per second for 1.5 h. Holes in the lightning density formed and dissipated sequentially in the very strong updraft and bounded weak echo region of the mesocyclone. In a small squall line on 19 June 2004, most lightning flashes in the stratiform region were initiated in or near strong updrafts in the convective line and involved positive charge in the upper part of the radar bright band. In a small thunderstorm on 29 June 2004, lightning activity began as polarimetric signatures of graupel first appeared near lightning initiation regions.

Available online at ://http://ams.allenpress.com/archive/1520-0477/89/7/pdf/i1520-0477-89-7-997.pdf.

MacGorman, D. R., K. M. Kuhlman, E. C. Bruning, W. D. Rust, P. R. Krehbiel, M. I. Biggerstaff, 2008: Small, continual lightning activity in the overshooting turret of supercell storms. Proc. 3rd Annual Conference on Applications of Lightning Data, New Orleans, LA, USA, American Meteorological Society, 4.7.

Several supercell storms have occurred within the region in which the Oklahoma Lightning Mapping Array (OKLMA) maps all three spatial dimensions of lightning. These storms span much of the supercell spectrum -- from non-tornadic storms to storms that produced strong tornadoes and from low-precipitation to heavy-precipitation morphologies. As noted by several studies, supercell storms tend to have much larger flash rates than ordinary isolated thunderstorms; maximum rates are typically hundreds of flashes per minute, even when considering only flashes that produce at least ten mapped points per flash. However, the OKLMA indicates that most of the flashes occurring within the main body of the storm during periods of high flash rates have quite small spatial extents, many with a long dimension of 5 km or less. Not usually included in these flash rates are a large number that appear to be isolated points (sometimes called singletons), each failing criteria of distance or time for associating it with other points in a flash. Often determining whether these isolated points are artifacts of the OKLMA is difficult, but in the overshooting top, they present a coherent pattern that appears plausible. They are distributed throughout a cap having horizontal dimensions comparable to that of the overshooting top and sitting near or on the upper surface. They occur continually, though they are too far apart in time or space to be associated in a flash with each other. A comparison with high-resolution reflectivity data for one storm observed by the two mobile 5-cm wavelength SMART-R radars shows that these isolated points were most concentrated near the top of the 40 dBZ echo in the overshooting turret, but some occurred higher, in regions of small reflectivity or just above the overshooting top. These points may be similar to the continual lightning noted by Bill Taylor in the upper region of a severe storm in the early 1980s.

Available online at ://http://www.ametsoc.org.

MacGorman, D. R., T. Mansell, C. Ziegler, J. Straka, 2008: Detailed storm simulations by a numerical cloud model with electrification and lightning parameterizations. Preprints, 20th International Lightning Detection Conference, Tucson, AZ, USA, Vaisala, 28.

We have further developed our three-dimensional cloud model, which includes parameterizations of lightning, corona from ground, ion production and capture, and inductive and noninductive electrification mechanisms, as well as advanced treatments of advection, microphysics, and dynamics. Our most recent improvements have been to improve the model's treatment of microphysics, particularly particle size distributions. This model has been used to simulate many types of storms, from small isolated storms to extensive storm systems, supercell storms, and an idealized hurricane, with excellent similitude to observed kinematic structure in many cases. We will show examples of our simulations and will discuss relationships among the model fields, particularly between lightning and other storm properties. Lightning usually is correlated with precipitation ice mass and with the mass flux through the mixed phase region for updrafts >10 m/s.

MacGorman, D., K. Kuhlman, W. D. Rust, M. Biggerstaff, P. Krehbiel, B. Rison, 2008: Lightning and electrical structure of a heavy-precipitation supercell storm during TELEX. Preprints, 2nd International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, 10.

The Thunderstorm Electrification and Lightning Experiment (TELEX) observed a heavy-precipitation (HP) supercell storm in central Oklahoma on 29 May 2004. In a HP supercell storm, the initial location of the mesocyclone, which is the parent rotation of tornadoes, is embedded well within the precipitation of the storm, instead of being on the edge of the storm(as in classic and low-precipitation supercell storms). Two 5-cm wavelength mobile Doppler radars were positioned near the storm and collected volume scans every 3 minutes for 3 h beginning as the storm became supercellular. The storm had supercell characteristics for this entire period. The Oklahoma Lightning Mapping Array provided three-dimensional data throughout the storm’s supercellular stage and provided two-dimensional data from the time of storm initiation in western Oklahoma. A 10-cm wavelength polarimetric radar also provided data for much of this period.
Lightning flash rates became extraordinarily large as the storm evolved into a supercell and its motion turned rightward. Flash rates increased again (to an estimated peak value of almost 500 flashes per minute) shortly before the storm produced a tornado rated F2 on the Fujita scale. During this period, an upward pulse in lightning density extended as high as 18 km MSL in a plume extending above the equilibrium level. Most flashes in the main body of the storm had small spatial extent (3-10 km). Lightning in the overshooting top consisted of continual single-point flashes.
The region of lightning activity pulsed eastward far into the anvil, up to 100 km from the convective core. Up to 5 -CG flashes per minute were initiated in the anvil more than 40 km from the main storm core, and typically came to ground within a few kilometers horizontally of the location of initiation. Because these -CG strikes occur far from the deep convection, they pose a generally unexpected danger to personnel.
A series of minimums in the plan projection of lightning density (i.e., lightning holes) formed just above the bounded weak echo region. A dual-Doppler synthesis of wind during one volume scan shows the lightning hole was co-located with large vertical wind speeds in the rotating updraft. The hole apparently occurred because precipitation particles had little time to grow and gain charge in the strong updraft before they were lifted to upper regions of the storm and advected outward by flow from the diverging updraft. Lightning mapping data suggest that the vertical polarity of the storm’s electrical structure was inverted from the usual polarity, and this appears to be why CG flashes that began in the anvil were -CG flashes.

MacGorman, D., T. Schuur, M. Kumjian, 2008: Total lightning activity during the re-intensification of Tropical Storm Erin over Oklahoma on 18–19 August 2007. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, 7A.5.

The remnants of Tropical Storm Erin made landfall on the Texas coast on 16 August 2007 and reached Oklahoma on 18 August, where it produced tornadoes, severe straight-line winds, and flooding. In west-central Oklahoma (roughly 800 km from the coast), the system re-intensified and formed an eye and rainband structure characteristic of tropical cyclones. The Oklahoma Mesonet indicated that the system eventually produced greater sustained winds (26 m s-1, 58 mph) and a lower central pressure (1001.3 hPa) than it had produced over open water.

The eye, which fluctuated from 5 to 25 km in diameter, was first apparent on lightning and radar displays at 4:50 am local time and began dissipating over Oklahoma City at 9:50 am. Throughout the period during which the eye formed and dissipated, the eye and the majority of the area of rainbands were well within the region in which the Oklahoma Lightning Mapping Array maps lightning in three dimensions and in which the KOUN S-Band radar provides polarimetric data. Both radar displays and displays of lightning density delineated the formation of the eye and rainband well. Convection extended highest and lightning rates were greatest in the rainband on the southeast flank. The height of convection in the rainband decreased as one approached the eye, and the decrease in height extended around the eye as the eye formed. Some long, horizontal flashes extended eastward from storms along the east side of the eye into the region of widespread light precipitation east of the rainband. The appearance of these long horizontal flashes was similar to the lightning structure observed in the stratiform precipitation regions of mesoscale convective systems. As the cyclone structure weakened, convection on the west side of the eye dissipated, and the remnants of the rainband on the east side propagated eastward as a line of storms.

Though the lightning in this system was probably influenced by being over land, this case still may provide clues to what happens electrically in tropical cyclones over open water, where continuous observations of total lightning activity during tropical cyclone intensification and dissipation are not yet available.

Available online at ://http://www.ametsoc.org.

Payne, C., T. J. Schuur, D. R. MacGorman, W. D. Rust, M. Biggerstaff, K. Kuhlman, E. Bruning, N. Lund, 2008: Electrical and polarimetric radar observations of an HP supercell on 29 May 2004 during TELEX. Preprints, 3rd Conference on Meteorological Applications of Lightning Data, New Orleans, LA, USA, American Meteorological Society, 4.6.

Rabin, R. M., J. Hanna, 2008: GOES winter precipitation efficiency algorithm.. Extended Abstracts, Fifth GOES Users Conference, 88th AMS meeting, New Orleans, LA, USA, AMS, P1.34.

Wood, V. T., 2008: Improvement of WSR-88D VAD Winds: Cyclonic Wind Fields. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, AMS, P2B.3. [Available from Vincent T. Wood, 120 David L. Boren Blvd., National Severe Storms Laboratory, Norman, OK, USA, 73072.]

Hurricanes pose a serious threat to life and property along the Gulf and Atlantic coastal regions of the United States. The WSR-88D network provides the potential to improve hurricane forecasts and warnings by monitoring changes in a hurricane’s track, eye diameter, radar eyewall and rainband reflectivities. The WSR-88D Velocity-Azimuth Display (VAD) Wind Profile (VWP) display is a useful tool for diagnosis of wind fields at different altitudes as a hurricane is approaching a coastal WSR-88D.

The causes of missing winds on the VWP display were related to cyclonic flow from the approaching hurricane. The missing data arose because the extreme positive and negative Doppler velocity values around the VAD circle were inherently not 180 degrees apart and, therefore, the first-harmonic Fourier sine curve used in the operational WSR-88D VAD algorithm was a poor fit to the data. This resulted in root-mean-square (RMS) differences that exceeded the threshold value. In this situation, most of the winds on the VWP display were set equal to missing in spite of the fact that there were strong radar returns.

A new solution to recover or improve VAD winds has been developed. A higher-order polynomial regression technique employs least-squares fit of the Doppler velocity data distributed on the VAD circle. Wind speed is computed from the average of the magnitudes of the positive and negative peaks of the quasi-sine curve. Wind direction is determined from the average of the magnitudes of maximum and minimum azimuths (at which positive and negative Doppler velocity peaks occur, respectively) minus ninety degrees. After applying the experimental technique to a couple of hurricane cases such as Hurricane Katrina (29 August 2005) and Hurricane Rita (20 September 2005), the technique examines a standard deviation about a regression line which agrees well with the RMS value. The higher-order polynomial regression VAD curve fits the measurements with low RMS difference values. It is indicated that the technique does a good job of fitting the curve to the data points with low RMS difference between the curve and data points.

Wood, V. T., L. W. White, 2008: A Skirted Rankine Combined Vortex Model. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P3.4.

Brown, R. A., T. A. Niziol, N. R. Donaldson, P. I. Joe, V. T. Wood, 2007: Improved Detection Using Negative Elevation Angles for Mountaintop WSR-88Ds. Part III: Simulations of Shallow Convective Activity Over and Around Lake Ontario. Weather and Forecasting, 22, 839-852.

During the winter, lake-effect snowstorms that form over Lake Ontario represent a significant weather hazard for the populace around the lake. These storms, which typically are only 2 km deep, frequently can produce narrow swaths (20–50 km wide) of heavy snowfall (2–5+ cm/hr) that extend 50–75 km inland over populated areas. Subtle changes in the low-altitude flow direction can make the difference between accumulations that last for 1–2 hr and accumulations that last 24 hr or more at a given location. Therefore, it is vital that radars surrounding the lake are able to detect the presence and strength of these shallow storms.
Starting in 2002, the Canadian operational radars on the northern side of the lake at King City, ON (WKR) and Franktown, ON (XFT) began using elevation angles as low as -0.1 deg and 0.0 deg, respectively, during the winter to more accurately estimate snowfall rates at the surface. Meanwhile, WSR-88D radars in New York State on the southern and eastern sides of the lake—Buffalo (KBUF), Binghamton (KBGM), and Montague (KTYX)—all operate at 0.5 deg and above. KTYX is located on a plateau that overlooks the lake from the east at a height of 0.5 km. With its upward-pointing radar beams, KTYX’s detection of shallow lake-effect snowstorms is limited to the eastern quarter of the lake and surrounding terrain.
The purpose of this paper is to show—through simulations—the dramatic increase in snowstorm coverage that would be possible if KTYX were able to scan downward toward the lake’s surface. Furthermore, if KBUF and KBGM were to scan as low as 0.2 deg, detection of at least the upper portions of lake-effect storms over Lake Ontario and all of the surrounding land area by the five radars would be complete. Over-lake coverage in the lower half (0-1 km) of the typical lake-effect snowstorm would increase from about 40% to about 85%, resulting in better estimates of snowfall rates in landfalling snowbands over a much broader area.

Brown, R. A., V. T. Wood, cited 2007: A Guide for Interpreting Doppler Velocity Patterns: Northern Hemisphere Edition, 2nd ed.. [Available online at ://http://www.nssl.noaa.gov/papers/dopplerguide/.]

Brown, R. A., R. M. Steadham, 2007: Developing site-specific scanning strategies for WSR-88Ds: Important considerations. Preprints, Annual Meeting, Reno, NV, USA, National Weather Association, 94-95.

Burgess, D. W., T. Crum, R. J. Vogt, 2007: Impacts of wind turbine farms on WSR-88D radars. Preprints, 33rd Int. Conf. on Radar Meteor., 6-10 August, 2007, Cairns, Australia, AMS, CD-ROM, 13B.6.

Kuhlman, K., D. MacGorman, D. Rust, P. Krehbiel, B. Rison, 2007: Lightning in the anvil region of a supercell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, PS5-8.

The Thunderstorm Electrification and Lightning Experiment (TELEX) took place in central Oklahoma during the 2003 and 2004 convective seasons to study the lightning, dynamics and microphysics of thunderstorms. One storm from this field project, a high-precipitation tornadic supercell occurred on 29 May 2004. In this storm, the Oklahoma Lightning Mapping Array detected lightning extending over one hundred kilometers away from the core of the supercell. Lightning is known to occur in the anvil region of supercells; typically this lightning is initiated in the core of the storm and extends out through the anvil. In the 29 May 2004 storm, however, some flashes actually initiated in the anvil region and the subsequent leaders progressed back towards the core of the storm. Some of these flashes were negative cloud-to-ground flashes that initiated over 50 km away from the core and struck ground beneath the anvil close to the initiation point. It appears that interaction between the anvil of this supercell and an anvil of opposite polarity from a weaker left-moving cell to the north was responsible for initiating this lightning.

MacGorman, D. R., T. Filiaggi, R. L. Holle, R. A. Brown, 2007: Negative Cloud-to-Ground Lightning Flash Rates Relative to VIL, Maximum Reflectivity, Cell Height, and Cell Isolation. Journal of Lightning Research, 1, 132-147.

This study relates storm cell parameters derived automatically from the Doppler radars of the United States National Weather Service to negative cloud-to-ground lightning activity detected by the United States National Lightning Detection Network. Data from the central United States were processed for over 1200 cells from seventeen days. Each cell’s maximum ground flash rate was compared to a subjective rating of the degree of cell isolation and to three radar-derived cell parameters: maximum reflectivity, maximum vertically integrated liquid (VIL), and the maximum vertical thickness having at least 30 dBZ reflectivity above the 0 deg C isotherm (similar to 30-dBZ cell height). Of the three parameters, the maximum 30-dBZ thickness of cells had the most useful relationship: The mean and modal values of ground flash rates increased with increasing 30-dBZ thickness, and the mean and modal values of 30-dBZ thickness increased with increasing flash rates. However, large ground flash rates provided a better diagnostic for large 30-dBZ thickness than large 30-dBZ thickness provided for large ground flash rates. The degree of cell isolation and the complexity of cell evolution also had a large effect: Cells which were less isolated or whose evolution was more complex were more likely to produce a ground flash and larger ground flash rates. Besides effects of storm complexity and size suggested by previous investigators, we suggest that the more complex charge distribution produced by having older cells nearby improves a cell’s probability of access to the lower positive charge typically needed to initiate negative ground flashes.

MacGorman, D., K. Kuhlman, D. Rust, M. Biggerstaff, T. Schuur, J. Straka, P. Krehbiel, B. Rison, L. Carey, 2007: Lightning and electrical structure of a heavy-precipitation supercell storm during TELEX. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, OS5-1.

The Thunderstorm Electrification and Lightning Experiment (TELEX) observed a heavy-precipitation (HP) supercell storm in central Oklahoma on 29 May 2004. In a HP supercell storm, the initial location of the mesocyclone, which is the parent rotation of tornadoes, is embedded well within the precipitation of the storm, instead of being on the edge of the storm (as in classic and low-precipitation supercell storms). Two 5-cm wavelength mobile Doppler radars were positioned near the storm and collected volume scans every 3 minutes for 3 h beginning as the storm became supercellular. The storm had supercell characteristics for this entire period. The Oklahoma Lightning Mapping Array provided three-dimensional data throughout the storm’s supercellular stage and provided two-dimensional data from the time of storm initiation in western Oklahoma. A 10-cm wavelength polarimetric radar also provided data for much of this period.
Lightning flash rates became extraordinarily large as the storm evolved into a supercell and its motion turned rightward. Flash rates increased again (to an estimated peak value of almost 500 flashes per minute) shortly before the storm produced a tornado rated F2 on the Fujita scale. During this period, an upward pulse in lightning density extended as high as 18 km MSL in a plume extending above the equilibrium level, and the region of lightning activity pulsed eastward far into the anvil, up to 150 km from the western edge of the storm. A series of minimums in the plan projection of lightning density (i.e., lightning holes) formed just above the bounded weak echo region. A dual-Doppler synthesis of wind during one volume scan shows the lightning hole was co-located with large vertical wind speeds in the rotating updraft. The hole apparently occurred because precipitation particles had little time to grow and gain charge in the strong updraft before they were lifted to upper regions of the storm and advected outward by flow from the diverging updraft. Cloud-to-ground lightning activity in and near heavy precipitation was dominated initially by negative ground flashes, but during part of the supercell phase, evolved to become dominated by positive ground flashes. Lightning mapping data suggest that, when positive ground flashes dominated, the vertical polarity of the storm’s electrical structure was inverted from the usual polarity.

MacGorman, D., K. Kuhlman, E. Bruning, D. Rust, P. Krehbiel, M. Biggerstaff, 2007: Small, continual lightning activity in the overshooting turret of supercell storms. Preprints, 2007 Annual Fall Meeting, San Francisco, CA, USA, American Geophysical Union, AE41A-03.

Ramig, N., D. MacGorman, D. Rust, T. Schuur, P. Krehbiel, W. Rison, T. Hamlin, J. Straka, M. Biggerstaff, 2007: Relationship between lightning location and polarimetric radar signatures in an MCS. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, PS5-2.

The relationship of lightning initiation and structure to the storm microphysics and structure depicted by polarimetric radar has been analyzed for a small mesoscale convective system (MCS) that occurred on 19 June 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX). Horizontal reflectivity (Z), differential reflectivity (Zdr), specific differential phase (Kdp) and correlation coefficient (ρHV) data were gathered by a 10-cm, polarimetric radar located in Norman, Oklahoma. Three-dimensional lightning structure was mapped by the Oklahoma Lightning Mapping Array (OK-LMA), and ground strike points were mapped by the United States National Lightning Detection Network. OK-LMA data were processed to group mapped points into flashes and to determine the initiation location of each flash that contained more than 10 mapped points. The initiation location was calculated by sequentially eliminating outliers among the first 10 points that occurred in a flash, with no fewer than 5 points being used in the final initiation location. The initiation location and mapped points for each flash were superimposed on polarimetric radar data in order to investigate lightning relationships with storm structure. The lightning initiation points tended to cluster together in one of two altitude ranges and were almost all in the convective line. Initial results show a relationship between the lightning initiation locations and radar signatures in both Z and Kdp. In the lower altitude range, between 3 and 5 km MSL, initiation locations tended to cluster around updraft cores, in regions characterized by a transition in Z from 50 to 55 dBZ and a transition in Kdp from 0.4 to 0.5 deg/km. In the upper range, between 8 and 10 km MSL, initiation points tended to cluster directly above the updrafts, in regions characterized by a transition in Z from 42.5 to 47.5 dBZ and in Kdp from 0.075 to 0.150 deg/km. The two-layer nature of the initiation points is consistent with grossly tripolar structure of the charge distribution involved in lightning in the convective line. Also, the horizontal pattern of the initiation locations has a quasi-periodic horizontal structure which is 180 degrees out of phase with the maximum updraft locations for the lower region and is in phase with the maximum updraft locations for the upper region. There were also a few flash initiations within the stratiform region, possibly associated with decaying cells. The values of Z and Kdp associated with these initiation points were smaller than in the convective line, but as in the convective line, the initiations also occurred along gradients, above a local maximum, in these parameters.

Wood, V. T., 2007: OK-WARN: Oklahoma Weather Alert Remote Notification. Preprints, 16th Symposium on Education, San Antonio, TX, USA, Amer. Meteor. Soc., CD-ROM P1.25.

Oklahoma Weather Alert Remote Notification (OK-WARN) is a new service that provides timely notification of weather hazards and emergencies to people with hearing loss via pager, e-mail or cell phone. This program was developed as a partnership between Oklahoma Department of Emergency Management, NOAA National Weather Service, NOAA National Severe Storms Laboratory, Oklahoma Department of Rehabilitation Services, Communication Services for the Deaf of Oklahoma, and Weather Affirmation, LLC. OK-WARN was made possible by a federal grant from the Federal Emergency Management Agency, now a division of the Department of Homeland Security. Since the inception of OK-WARN in 2001, the program has been expanded statewide to serve the deaf and hard-of-hearing community. Information about how OK-WARN operates will be presented.

Wood, V. T., 2007: Impact of Severe Weather on People with Hearing Loss. Weather and Society Watch Vol. 1, No. 4, July 20, 2007, 3 pp.

Brown, R. A., T. A. Niziol, N. R. Donaldson, P. I. Joe, V. T. Wood, 2006: WSR-88D monitoring of shallow lake-effect snowstorms over and around Lake Ontario: Simulations of improvements using lower elevation angles. Preprints, 22nd Conference on Interactive Information Processing Systems, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P2.7. [Available from Rodger A. Brown, National Severe Storms Laboratory, 1313 Halley Circle, Norman, OK, USA, 73069.]

Winner, best poster presentation of conference.

Currently, National Weather Service (NWS) WSR-88D radars do not operate below +0.5 deg. Consequently, shallow lake-effect snowstorms over and around Lake Ontario pose a detection (and warning) challenge for the Buffalo, NY, NWS Forecast Office. Limited measurements in the lower portions of the storms preclude reliable quantitative precipitation estimation (QPE) in much of the coverage area.

This presentation will show how we use simulated scanning strategies to investigate how much detections and QPE would improve using lower elevation angles for the three closest New York State WSR-88Ds: Montague (KTYX), Buffalo (KBUF), and Binghamton (KBGM). Canadian radars at King City and Franktown on the north side of the lake—that operate as low as –0.1 and 0.0 deg, respectively—also are considered.

The Montague radar is located east of Lake Ontario on top of the Tug Hill Plateau 520 m above the lake. Using current scanning strategies, 2-km-deep snowstorms are detectable to a range of only 100 km from the radar (covering the eastern quarter of the lake). The Buffalo radar covers the western half of the lake. Being farther from the lake, the Binghamton radar covers snowstorms that extend southeastward from Lake Ontario.

Simulations show that, when the lowest elevation angle for KTYX is decreased to –0.4 deg, the range of detection of 2-km-deep snowstorms increases from 100 to 220 km. Lowering the lowest elevation angle for KBUF and KBGM to +0.2 deg increases the coverage area (2 km above the surface) by about 60%. Lowering the scanning strategies for these three radars and operating in conjunction with the Canadian radars, shallow lake-effect storms would be detected over the entire lake and surrounding coastal regions and reliable QPE information would be available over nearly the entire region.

Brown, R. A., V. T. Wood, D. C. Dowell, 2006: Interpretation of simulated WSR-88D Doppler velocity signatures of tornadoes associated with nonuniform reflectivities. Preprints, 23rd Conference on Severe Local Storms, St. Louis, MO, USA, Amer. Meteor. Soc., CD-ROM, P9.10.

Typically, when simulated Doppler velocity measurements are made across a tornado, one assumes that the associated reflectivity field is uniform. However, recent measurements made by mobile Doppler radars in the immediate vicinity of tornadoes reveal the presence of a low-reflectivity eye centered on the tornado. The eye arises from the centrifuging of debris and hydrometeors within the tornadic circulation.

Dowell et al. (2005) employed an axisymmetric numerical model to study particle motions and concentrations in tornadoes. We used 1.5-mm-diameter raindrops in the model to produce flow and reflectivity patterns for three different sized tornadoes: medium, large, and very large. The model output then was scanned with a WSR-88D emulator to produce simulated reflectivity and Doppler velocity measurements within the tornadoes.

We found that, except for the rare very large tornado, peak Doppler velocity values associated with a low-reflectivity eye at close range occurred at a smaller radius than in the model tornado. These peak Doppler velocity values also were at a smaller radius than peak values associated with a uniform reflectivity pattern. As distance from the radar increased, the widening radar beam smeared the low-reflectivity eye to produce a more uniform distribution of reflectivity. At the same time, the peak Doppler velocity values approached those obtained for a uniform reflectivity distribution. Thus, in a typical tornado near a WSR-88D, we would expect the presence of a low-reflectivity eye to cause the peak Doppler velocity values to appear at a smaller radius than the radius of the true peak tangential velocities.

Brown, R. A., R. M. Steadham, 2006: Site-specific scanning strategies for WSR-88Ds: Planning for field tests.. Preprints, Annual Meeting, Cleveland, OH, USA, National Weather Association, 46-47.

The lowest elevation angle scanned by all radars in the Weather Surveillance Radar–1988 Doppler (WSR-88D) network is 0.5 deg. Users of Terminal Doppler Weather Radars (TDWRs) and research Doppler radars find that scanning at 0.0 deg reveals the presence of boundaries of forecasting significance that frequently are not evident at 0.5 deg elevation angles. Furthermore, forecasters who prepare warnings based on mountaintop WSR-88D measurements frequently find that the radar overshoots hazardous weather phenomena that threaten the surrounding populace. Simulations indicate that the use of negative elevation angles at mountaintop sites would permit the detection of hazardous weather and would greatly improve the accuracy of surface rainfall and snowfall estimates.
With a basic need for WSR-88Ds to scan at lower elevation angles, the WSR-88D Radar Operations Center—in collaboration with National Weather Service Forecast Offices, National Severe Storms Laboratory, and Federal Aviation Administration—is proposing that each WSR-88D collect data at elevation angles that are best suited for its locale. To test the operational feasibility of lowering elevation angles, a two-year field test is being proposed for six WSR-88Ds, three located on mountaintops and three located on relatively flat terrain. The test plan currently is being evaluated at various administrative levels within the National Weather Service.

Davies-Jones, R. P., 2006: Integrals of the vorticity equation. Part I: General three- and two-dimensional flows.. Journal of the Atmospheric Sciences, 63, 598-610.

The integral of the vector vorticity equation for the vorticity of a moving parcel in 3D baroclinic flow with friction is cast in a new form. This integral of the vorticity equation applies to synoptic-scale or mesoscale flows and to deep compressible or shallow Boussinesq motions of perfectly clear or universally saturated air. The present integral is equivalent to that of Epifanio and Durran in the Boussinesq limit, but its simpler form reduces easily to Dutton’s integral when the flow is assumed to be isentropic and frictionless.
The integral for vorticity has the following physical interpretation. The vorticity of a parcel is composed of barotropic vorticity, baroclinic vorticity, which originates from solenoidal generation, and vorticity stemming from frictional generation. Its barotropic vorticity is the result of freezing into the fluid the w field (specific volume times vorticity) that is present at the initial time. Its baroclinic vorticity is the vector sum of contributions from small subintervals of time that partition the interval between initial and current times. In each subinterval, the baroclinic torque generates a small vector element of vorticity and hence w. The contribution to the current baroclinic vorticity is the result of freezing this element of w into the fluid immediately after its formation. The physical interpretation of vorticity owing to frictional generation is identical except the torque is frictional rather than solenoidal.
The baroclinic vorticity is decomposed into a part that would occur if the current entropy of the flow were conserved materially backward in time to the initial time and an adjustment term that accounts for production of entropy gradients in material coordinates during this interval. A method for computing all the vorticity parts in an Eulerian framework within a 3D numerical model is outlined.
The usefulness of the 3D vorticity integral is demonstrated further by deriving Eckart’s, Bjerknes’ and Kelvin’s circulation theorems from it in relatively few steps, and by showing that the associated expression for potental vorticity is an integral of the potential-vorticity equation and implies conservation of potential vorticity for isentropic frictionless motion of clear air (Ertel’s theorem). Lastly, a formula for the helicity density of a parcel is obtained from the vorticity integral and an expression for the parcel’s velocity, and verified by proving that it is an integral of the equation for helicity density.

Davies-Jones, R. P., 2006: Integrals of the vorticity equation. Part II: Special two-dimensional flows.. Journal of the Atmospheric Sciences, 63, 611-616.

In Part I, a general integral of the 2D vorticity equation was obtained. This is a formal solution for the vorticity of a moving tube of air in a 2D unsteady stratified shear flow with friction. This formula is specialized here to various types of 2D flow. For steady inviscid flow, the integral reduces to an integral found by Moncrieff and Green if the flow is Boussinesq and to one obtained by Lilly if the flow is isentropic. For steady isentropic frictionless motion of clear air, several quantities that are invariant along streamlines are found. These invariants provide another way to obtain Lilly’s integral from the general integral.

Davies-Jones, R. P., 2006: Tornadogenesis in supercell storms – what we know and what we don’t know. Preprints, Symposium on the Challenges of Severe Convective Storms,, Atlanta, GA, USA, Amer. Meteor. Soc., CD-ROM, 2.2.

invited paper

Davies-Jones, R. P., V. T. Wood, 2006: Simulated Doppler velocity signatures of evolving tornado-like vortices. Journal of Atmospheric and Oceanic Technology, 23, 1029-1048.

Exact solutions of the Navier-Stokes or Euler equations of motion and the continuity equation in cylindrical coordinates for 3D, axisymmetric, inviscid or laminar flows are utilized to represent evolving vortices that roughly model tornado cyclones or misocyclones contracting to tornadoes. These solutions are unsteady versions of the diffusive Burgers-Rott vortex and the inviscid Rankine combined vortex. They satisfy the free-slip condition at the ground. Different vortices are obtained by choosing different values of the constant eddy viscosity and uniform horizontal convergence while holding the circulation at infinity constant. A simulated WSR-88D radar is employed to generate time-varying Doppler velocity signatures in uniform reflectivity of these analytical vortices at ranges of 25 and 50 km from the radar. Mean Doppler velocities are determined by computing 3D integrals over effective resolution volumes. Magnitudes of Doppler vortex signatures at different times in the evolution of the stationary vortices are computed for effective beamwidths of 1.02º and 1.39º, which correspond to azimuthal sampling intervals of 0.5º and 1.0º, respectively. Four tornado predictors, rotational velocity, shear, excess rotational kinetic energy, and circulation, are examined.
Results of the simulations show that for smaller effective beamwidths, Doppler vortex signatures are stronger and exceed fixed threshold values of rotational velocity and shear earlier. With finer azimuthal resolution, tornado-cyclone, misocyclone, or tornado signatures switch to tornadic vortex signatures later. Circulations of the vortex signatures give good estimates of the circulations of the simulated tornadoes and tornado cyclones with relative insensitivity to range, effective beamwidth, and stage of evolution High circulation and convergence values of a rotation signature reveal the potential for a tornado earlier than all the other predictors, which increase significantly during tornadogenesis.

Davies-Jones, R. P., 2006: Global properties of a simple axisymmetric simulation of tornadogenesis. Preprints, 23rd Conference on Severe Local Storms, St Louis, MO, USA, American Meteorological Society, P10.2.

Kuhlman, K. M., C. L. Ziegler, E. R. Mansell, D. R. MacGorman, J. M. Straka, 2006: Numerically Simulated Electrification and Lightning of the 29 June 2000 STEPS Supercell Storm. Monthly Weather Review, 134, 2734-2757.

A three-dimensional dynamic cloud model incorporating airflow dynamics, microphysics, and thunderstorm electrification mechanisms is used to simulate the first 3 h of the 29 June 2000 supercell from the Severe Thunderstorm Electrification and Precipitation Study (STEPS). The 29 June storm produced large flash rates, predominately positive cloud-to-ground lightning, large hail, and an F1 tornado. Four different simulations of the storm are made, each one using a different noninductive (NI) charging parameterization. The charge structure, and thus lightning polarity, of the simulated storm is sensitive to the treatment of cloud water dependence in the different NI charging schemes. The results from the simulations are compared with observations from STEPS, including balloon-borne electric field meter soundings and flash locations from the Lightning Mapping Array. For two of the parameterizations, the observed “inverted” tripolar charge structure is well approximated by the model. The polarity of the ground flashes is opposite that of the lowest charge region of the inverted tripole in both the observed storm and the simulations. Total flash rate is well correlated with graupel volume, updraft volume, and updraft mass flux. However, there is little correlation between total flash rate and maximum updraft speed. Based on the correlations found in both the observed and simulated storm, the total flash rate appears to be most representative of overall storm intensity.

Available online at ://http://www.ametsoc.org.

Kuhlman, K., D. MacGorman, M. Biggerstaff, W. D. Rust, T. Schuur, C. Ziegler, P. Krehbiel, 2006: Lightning and radar observatons of the 29 May 2004 supercell during TELEX. Preprints, 2nd Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 3.3.

MacGorman, D., I. Apostolakopoulos, A. Nierow, J. Cramer, N. Demetriades, P. Krehbiel, 2006: Improved Timeliness of Thunderstorm Detection from Mapping a Larger Fraction of Lightning Flashes. Preprints, 1st International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, CD-ROM, N/A. [Available from Vaisala, Inc., Tucson Operations, 2705 E. Medina Rd., Tucson, AZ, USA, 85706.]

One application of lightning ground strike mapping systems has been thunderstorm detection. However, the climatological ratio of in-cloud flashes to cloud-to-ground flashes typically is greater than 2:1. Thus, systems that map either cloud flashes or all types of flashes will detect storms more quickly and reliably. The improvement typically is even greater than would be expected simply from the greater number of samples, because the first flashes produced by a storm usually are cloud flashes. However, the improvement obviously is affected by the fraction of flashes that a lightning mapping system detects. Because it costs substantially more to detect a larger fraction of all flashes, one would like to know how much lead time will be added by various levels of lightning detection. The U.S. National Lightning Detection Network (NLDN) being used by the National Weather Service is now capable of detecting roughly 10-20% of cloud flashes, in addition to a much larger fraction of cloud-to-ground flashes, over the contiguous United States. So far, this cloud flash option has been turned on only in a test region. The optical lightning mapper being planned for GOES-R is expected to detect 80-90% of cloud flashes. Some research mapping systems can detect essentially all but the smallest flashes throughout their coverage region. We analyzed the test cloud flash data from the NLDN network to see how much that system’s cloud flash detection would improve thunderstorm detection. Furthermore, we analyzed data from VHF lightning mapping systems that detect almost all flashes, to evaluate how much the timeliness of thunderstorm detection can be improved over what is now achieved with ground strike mapping systems. In north Texas and Oklahoma, 50% of thunderstorms produced a cloud-to-ground flash within 5-10 minutes of their first cloud flash, but in roughly 10% of storms, no cloud-to-ground flash occurred within an hour of the first cloud flash. Behavior was much different in storms over the High Plains of northwest Kansas and northeast Colorado. There it required 30 minutes after the first cloud flash for 50% of storms to produce a cloud-to-ground flash, and 20% of storms produced no cloud-to-ground flash within their first hour of lightning activity. One might expect such a result on the basis of climatological studies showing that cloud flashes comprise at least 90% of all lightning over much of the High Plains and in a few other regions of the country.

MacGorman, D. R., I. Apostolakopoulos, A. Nierow, J. Cramer, N. Demetriades, P. Krehbiel, 2006: Improved timeliness of thunderstorm detection from mapping a larger fraction of lightning flashes. Preprints, International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, 7.

MacGorman, D., K. Kuhlman, M. Biggerstaff, D. Rust, P. Krehbiel, 2006: Lightning and radar observations of the 29 May 2004 tornadic HP supercell during TELEX. Preprints, Annual Fall Meeting, San Francisco, CA, USA, American Geophysical Union, AE343A-1056.

Rabin, R. M., T. J. Schmit, 2006: Estimating soil wetness from the GOES sounder. Journal of Atmospheric and Oceanic Technology, 23, 991-1003.

Rabin, R. M., T. Whittaker, 2006: Tool for Storm Analysis Using Multiple Data Sets. Advances in Visual Computing, G. Bebis, R. Boyle, D. Koracin, B. Parvin, Ed(s)., Springer, 571-578.

Wood, V. T., L. W. White, C. R. Alexander, R. L. Tanamachi, 2006: An analytical model of one- and two-celled vortices: Preliminary testing. Preprints, 23rd Conference on Severe Local Storms, St. Louis, MO, USA, American Meteorological Society, CD-ROM, P10.1.

Brown, R. A., V. T. Wood, 2005: Interpretation of Doppler velocity patterns. Doppler Radar Theory and Meteorology, Part B, Doppler Radar Meteorological Observations, Federal Meteorological Handbook No. 11 (Revised), NOAA, 6-1-6-20.

Brown, R. A., 2005: Thunderstorms. The Encyclopedia of World Climatology, Springer, 719-724.

Brown, R. A., K. Tarp, 2005: The National Severe Storms Laboratory: 40 Years Young and Going Strong. Preprints, 21st International Conference on Interactive Information and Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology, San Diego, CA, USA, American Meteorological Society, CD-ROM, XXXX.

In 1964, the U.S. Weather Bureau's National Severe Storms Project (NSSP) moved from Kansas City to Norman and changed its name to the National Severe Storms Laboratory (NSSL). For the next 25 years, NSSL continued NSSP's (and its predecessors') long-standing tradition of improving understanding of severe storms by conducting a data collection program each spring that included surface and upper air mesonetworks, research aircraft, and radars. Over the years, Doppler radars (including dual polarization), an instrumented TV transmitter tower, storm intercept teams, and storm electricity measurements were added. In more recent years, spring programs have become more intermittent because of funding constraints, with many associated with national research programs (involving airborne Doppler radars) in the southern Plains. Since the early 1990s, various NSSL sensors have become mobile with the addition of mobile rawinsonde release vehicles, balloon-borne storm electricity sensors, mesonetwork instruments on the tops of cars, and Doppler radars mounted on trucks.

Early NSSL research has had a positive impact on improved public safety. Aircraft studies of turbulence in severe thunderstorms, called Project Rough Rider, during the 1960s, 1970s, and early 1980s led to improved commercial airline safety guidelines in the vicinity of thunderstorms. NSSL Doppler radar studies of thunderstorm mesocyclones and tornadoes during the 1970s led to the decision by the National Weather Service (NWS), U.S. Air Force's Air Weather Service, and Federal Aviation Administration (FAA) to include Doppler capability in their updated operational WSR-88D and Terminal Doppler Weather Radar networks. The WSR-88D has helped forecasters significantly improve severe thunderstorm and tornado warnings, saving countless lives. NSSL continues to support the NWS and FAA by developing and refining radar algorithms for identifying severe weather phenomena and estimating precipitation accumulations, and by helping to design better radar acquisition and processing equipment. A program is currently underway to collect data much faster using a newly-constructed phased array Doppler radar.

By the mid 1980s, NSSL was developing an expertise in numerical modeling. Various techniques, including ensembles, are being investigated to improve the numerical prediction of storm-scale, mesoscale, and synoptic-scale processes. In 1997, soon after the National Severe Storms Forecast Center in Kansas City changed its name to the Storm Prediction Center (SPC), it moved to Norman. With the SPC being collocated with NSSL, there have been many opportunities for NSSL meteorologists to help SPC forecasters develop improved severe storm forecasting techniques, including the application of probabilistic forecasting techniques. Thus, through its various research activities during the past 40 years, NSSL has been instrumental in advancing the state of the art of severe storm detection and prediction.

Brown, R. A., B. A. Flickinger, E. Forren, D. M. Schultz, D. Sirmans, P. L. Spencer, V. T. Wood, C. L. Ziegler, 2005: Improved detection of severe storms using experimental fine-resolution WSR-88D measurements. Weather and Forecasting, 20, 3-14.

Doppler velocity and reflectivity measurements from WSR-88D (Weather Surveillance Radar - 1988 Doppler) radars provide important input to forecasters as they prepare to issue short-term severe storm and tornado warnings. Current-resolution data collected by the radars have an azimuthal spacing of 1.0° and range spacing of 1.0 km for reflectivity and 0.25 km for Doppler velocity and spectrum width. To test the feasibility of improving data resolution, National Severe Storms Laboratory's test-bed WSR-88D (KOUN) collected data in severe thunderstorms using 0.5° azimuthal spacing and 0.25 km range spacing,resulting in eight times the resolution for reflectivity and twice the resolution for Doppler velocity and spectrum width. Displays of current-resolution WSR-88D Doppler velocity and reflectivity signatures in severe storms were compared with displays showing finer-resolution signatures. At all ranges, fine-resolution data provided better depiction of severe storm characteristics. Eighty-five percent of mean rotational velocities derived from fine-resolution mesocyclone signatures were stronger than velocities derived from current-resolution signatures. Likewise, about 85% of Doppler velocity differences across tornado and tornadic vortex signatures were stronger than values derived from current-resolution data. In addition, low-altitude boundaries were more readily detected using fine-resolution reflectivity data. At ranges greater than 100 km, fine-resolution reflectivity displays revealed severe storm signatures, such as bounded weak echo regions and hook echoes, which were not readily apparent on current-resolution displays. Thus, the primary advantage of fine-resolution measurements over current-resolution measurements is the ability to detect stronger reflectivity and Doppler velocity signatures at greater ranges from a WSR-88D.

Brown, R. A., R. M. Steadham, B. A. Flickinger, R. R. Lee, D. Sirmans, V. T. Wood, 2005: New WSR-88D volume coverage pattern 12: Results of field tests. Weather and Forecasting, 20, 385-393.

For the first time since the installation of the national network of WSR-88D radars, a new scanning strategy -- Volume Coverage Pattern 12 -- has been added to the suite of scanning strategies. VCP 12 is a faster version of VCP 11 and has denser vertical sampling at lower elevation angles. This note discusses results of field tests in Oklahoma and Mississippi during 2001 - 2003 that led to the decision to implement VCP 12. Output from meteorological algorithms for a test-bed radar using an experimental VCP were compared with output for a nearby operational WSR-88D using VCP 11 or 21. These comparisons were made for severe storms that were at comparable distances from both radars. Findings indicate that denser vertical sampling at lower elevation angles leads to earlier and longer algorithm identifications of storm cells and mesocyclones, especially those more distant from a radar.

Brown, R. A., J. M. Lewis, 2005: Path to NEXRAD: Doppler radar development at the National Severe Storms Laboratory. Bulletin of the American Meteorological Society, 86, 1459-1470.

In this historical paper, we trace the scientific- and engineering-based steps at the National Severe Storms Laboratory (NSSL) and in the larger weather radar community that led to the development of NSSL's first 10-cm wavelength pulsed Doppler radar. This radar was the prototype for the current NEXRAD (NEXt generation weather RADar) or WSR-88D (Weather Surveillance Radar-1988 Doppler) Network.

We track events, both political and scientific, that led to the establishment of NSSL in 1964. The vision of NSSL's first director, Edwin Kessler, is reconstructed through access to historical documents and oral history. This vision included the development of Doppler radar where research was to be meshed with the operational needs of the U.S. Weather Bureau and its successor the National Weather Service.

Realization of the vision came through steps that were often fitful, where complications arose due to personnel concerns, and where there were always financial concerns. The historical research indicates that: (1) the engineering prowess and mentorship of Roger Lhermitte was at the heart of Doppler radar development at NSSL; (2) key decisions by Kessler in the wake of Lhermitte's sudden departure in 1967 proved crucial to the ultimate success of the project; (3) research results indicated that Doppler velocity signatures of mesocyclones are a precursor of damaging thunderstorms and tornadoes; and (4) results from field testing of the Doppler-derived products during the 1977-1979 Joint Doppler Operational Project -- especially the noticeable increase in the verification of tornado warnings and an associated marked decrease in false alarms -- led to the government decision to establish the NEXRAD network.

Brown, R. A., K. L. Torgerson, 2005: Interpretation of single-Doppler radar signatures in a V-shaped hailstorm: Part II – Evolution of updraft interactions with ambient midaltitude flow. National Weather Digest, 29, 65-80.

Part II of this two-part descriptive study documents characteristics and evolution of the midaltitude flow field arising from interactions of ambient flow with the updraft region of a North Dakota multicell hailstorm. While only single-Doppler radar measurements were available, there were sufficient details in reflectivity and Doppler velocity features to provide interesting deductions about the interactions. The updraft region, located at the upstream end of the storm, typically consisted of two or three actively growing updrafts. Maximum wind speeds occurred along the lateral flanks of the updraft region. The center of the resulting wake region was characterized by a midaltitude channel of low-speed air extending downstream from the middle of the updraft region. Characteristics of the resultant midaltitude vorticity couplet straddling the updraft region did not appear to support the theoretical concept that couplets arise from vertical tilting of low-altitude horizontal vortex tubes. Rather, the vertical momentum of individual updrafts appeared to have collectively presented enough resistance to the approaching midaltitude environmental flow that air slowed down as it flowed through the porous updraft region. As air farther upstream approached the wall of slower-moving air, some of the air was diverted, increasing speed as it flowed around the sides of the updraft region.

Brown, R. A., T. A. Niziol, V. T. Wood, 2005: Improved WSR-88D detection of shallow lake-effect snowstorms over Lake Ontario: Simulations of lowered elevation angles. Preprints, Annual Meeting, St. Louis, MO, USA, National Weather Association, 22-23.

Currently, National Weather Service WSR-88D radars do not operate below +0.5 deg. Consequently, shallow lake-effect snowstorms over and around Lake Ontario pose a detection and warning problem for the Buffalo NWS Forecast Office. We use simulated scanning strategies to investigate how much detections would increase using lower elevation angles for the three closest New York State WSR-88Ds: Montague (KTYX), Buffalo (KBUF), and Binghamton (KBGM). Two Canadian radars on the north side of the lake—that operate as low as 0.0 deg—also are considered.

The Montague radar is located east of Lake Ontario on top of the Tug Hill Plateau 520 m above the lake. Using the current scanning strategies, 2-km-deep snowstorms are detectable to a range of only 100 km from the radar (covering the eastern quarter of the lake). The Buffalo radar covers the western half of the lake. Being farther from the lake, the Binghamton radar covers snowstorms over the southern lake shore.

Simulations show that, when the lowest elevation angle for KTYX is decreased to –0.3 deg, the range of detection of shallow snowstorms increases by 100 km. Lowering the lowest elevation angle for KBUF and KBGM to +0.3 deg increases the coverage range by 20 km. By lowering the scanning strategies for these three radars and operating in conjunction with the Canadian radars, lake-effect storms would be detected over the entire lake and surrounding coastal regions.

Burgess, D. W., D. C. Dowell, L. J. Wicker, A. Witt, 2005: Detailed comparison of observed and modeled tornadogenesis. Preprints, 32nd Conf. on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 10R.4.

Davies-Jones, R. P., V. T. Wood, 2005: Simulated Doppler velocity signatures of evolving tornado-like vortices.. Preprints, 32nd Conf. on Radar Meteorology,, Albuquerque, NM, USA, Amer. Meteor. Soc., CD-ROM, P15R.8.

Dowell, D. C., C. R. Alexander, J. M. Wurman, L. J. Wicker, 2005: Centrifuging of hydrometeors and debris in tornadoes: Radar-reflectivity patterns and wind-measurement errors. Monthly Weather Review, 133, 1501-1524.

High-resolution Doppler radar observations of tornadoes reveal a distinctive tornado-scale signature with the following properties: a reflectivity minimum aloft inside the tornado core (described previously as an "eye"), a high-reflectivity tube aloft that is slightly wider than the tornado core, and a tapering of this high-reflectivity tube near the ground. The results of simple one-dimensional and two-dimensional models demonstrate how these characteristics develop. Important processes in the models include centrifugal ejection of hydrometeors and/or debris by the rotating flow and recycling of some objects by the near-surface inflow and updraft.

Doppler radars sample the motion of objects within the tornado rather than the actual airflow. Since objects move at different speeds and along different trajectories than the air, error is introduced into kinematic analyses of tornadoes based on radar observations. In a steady, axisymmetric tornado, objects move outward relative to the air and move more slowly than the air in the tangential direction; in addition, the vertical air-relative speed of an object is less than it is in still air. The differences between air motion and object motion are greater for objects with greater characteristic fall speeds (i.e., larger, denser objects) and can have magnitudes of tens of meters per second. Estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one-dimensional model.

Doppler On Wheels observations of the 30 May 1998 Spencer, South Dakota, tornado demonstrate how the apparent tornado structure can change when the radar-scatterer type changes. When the Spencer tornado entered the town and started lofting debris, changes occurred in the Doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size.

Hane, C. E., D. L. Andra Jr., K. Trammell, F. H. Carr, 2005: Development of a tool to aid in forecasting the evolution of Great Plains MCSs during late morning hours. AIRMASS 2005 Conference, Wichita, KS, USA, American Meteorological Society, CD-ROM, XXXX.

Hane, C. E., D. L. Andra, Jr., J. A. Haynes, T. E. Thompson, F. H. Carr, 2005: On the Importance of Environmental Factors in Influencing the Evolution of Morning Great Plains MCS Activity during the Warm Season. Extended Abstracts, Eleventh Conference on Mesoscale Processes, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P3M.6.

MacGorman, D. R., W. D. Rust, P. Krehbiel, W. Rison, E. Bruning, K. Wiens, 2005: The electrical structure of two supercell storms during STEPS. Monthly Weather Review, 133, 2583-2607.

Balloon soundings were made through two supercell storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) in summer 2000. Instruments measured the vector electric field, temperature, pressure, relative humidity, and balloon location. For the first time, soundings penetrated both the strong updraft and the rainy downdraft region of the same supercell storm. In both storms, the strong updraft had fewer vertically separated charge regions than found near the rainy downdraft, and the updraft's lowest charge was elevated higher, its bottom being near the 40-dBZ boundary of the weak-echo vault. The simpler, elevated charge structure is consistent with the noninductive graupel-ice mechanism dominating charge generation in updrafts. In the weak-echo vault, the amount of frozen precipitation and the time for particle interactions are too small for significant charging. Inductive charging mechanisms and lightning may contribute to the additional charge regions found at lower altitudes outside the updraft. Lightning mapping showed that the in-cloud channels of a positive ground flash could be in any one of the three vertically separated positive charge regions found outside the updraft, but were in the middle region, at 6-8 km MSL, for most positive ground flashes. Our data are consistent with the electrical structure of these storms having been inverted in polarity from that of most storms elsewhere. We hypothesize that the observed inverted-polarity cloud flashes and positive ground flashes were caused by inverted-polarity storm structure, possibly due to a larger than usual rime accretion rate for graupel in a strong updraft.

MacGorman, D., D. Rust, T. Schuur, M. Biggerstaff, J. Straka, C. Ziegler, E. Mansell, P. Krehbiel, W. Rison, T. Hamlin, L. Carey, E. Bruning, K. Kuhlman, N. Ramig, C. Payne, 2005: Lightning Relative to Storm Structure and Microphysics in TELEX. Polarimetric radar and electrical structure of a multicell storm. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 10R.7.

MacGorman, D., 2005: Relationships among electrification, lightning, kinematics, and microphysics: Lessons from the interaction of observations and numerical storm simulations. Extended Abstracts, 2005 Annual Fall Meeting, San Francisco, CA, USA, American Geophysical Union, CD-ROM, AE32A-01.

MacGorman, D., C. L. Ziegler, E. Mansell, W. Beasley, B. Fiedler, 2005: Retrieval and assimilation of storm characteristics from both in-cloud and cloud-to-ground lightning data to improve mesoscale model forecasts. Final report to the Office of Naval Research (ONR Grant # N00014-00-1-0525) 1, 54 pp.

MacGorman, D., C. Ziegler, T. Mansell, J. Straka, P. Krehbiel, B. Rison, T. Hamlin, 2005: Applications of advanced lightning mapping technologies to storm research and weather operations. Preprints, Conference on Meteorological Applications of Lightning Data, San Diego, CA, USA, American Meteorological Society, 2.1.

MacGorman, D. R., W. D. Rust, C. L. Ziegler, T. J. Schuur, E. R. Mansell, M. I. Biggerstaff, J. M. Straka, E. C. Bruning, K. M. Kuhlman, N. R. Ramig, C. D. Payne, N. S. Biermann, P. R. Krehbiel, W. Rison, T. Hamlin, L. D. Carey, 2005: Lightning relative to storm structure, evolution, and microphysics in TELEX. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, 10R.7.

Rabin, R. M., 2005: Tool for storm analysis using multiple data sets. Published in "Advances in Visual Computing", Lecture Notes in Computer Science (#3804), Bebis et. al, Editors. Published by Springer.. Proc. First International Symposium on Visual Computing., Lake Tahoe, NV, USA, University of Nevada-Reno, Desert Research Institute, Berkeley L, 571-578. [Available from Robert Rabin, 120 David L. Boren, Norman, OK, USA, 73072.]

Available online at ://http://www.springeronline.com.

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