Browsing by Subject "lightning"
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Item Enlightening lightning! Producing and directing a multimedia planetarium show(Texas A&M University, 2005-02-17) Fowler, Sarah MarieStarting with a group of lightning researchers, planetarium staff, and visualization specialists, an academically diverse group was formed through a grant from the National Science Foundation to develop a planetarium show on lightning. The show target audience is middle school aged children. The goal of the show is to teach lightning safety and lightning facts in an immersive environment. Through the use of video, an animated character, and a meteorologist, the curriculum is presented to the audience. I fulfilled the roles of producer and director through all aspects of production. My role also included maintaining group organization and communication throughout show production. This paper discusses my experiences in producing Enlightening Lightning! by starting with outlining the curriculum and finishing with putting it all together at the planetarium. The goal of this paper is to discuss the techniques and organizational methods used to manage a diverse group and produce a multimedia show.Item Environmental control of cloud-to-ground lightning polarity in severe storms(2009-05-15) Buffalo, Kurt MatthewIn this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and CG flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong updrafts and associated large liquid water contents in severe storms lead to enhanced positive charging of graupel and hail via the noninductive charging mechanism, the generation of an inverted charge structure, and increased positive CG lightning production. The corollary is that environmental conditions favoring these kinematic and microphysical characteristics should support severe storms generating an anomalously high (> 25%) percentage of positive CG lightning (i.e., positive storms), while environmental conditions relatively less favorable should sustain storms characterized by a typical (? 25%) percentage of positive CG lightning (i.e., negative storms). Forty-eight inflow proximity soundings were analyzed to characterize the environments of nine distinct mesoscale regions of severe storms (four positive and five negative) on six days during May ? June 2002 over the central United States. This analysis clearly demonstrated significant and systematic differences in the mesoscale environments of positive and negative storms, which were consistent with the stated hypothesis. When compared to negative storms, positive storms occurred in environments associated with a drier low to midtroposphere, higher cloud base height, smaller warm cloud depth, stronger conditional instability, larger 0-3 km AGL wind shear, stronger 0-2 km AGL storm-relative wind speed, and larger buoyancy in the mixed-phase zone, at a statistically significant level. Differences in the warm cloud depth of positive and negative storms were by far the most dramatic, suggesting an important role for this parameter in controlling CG lightning polarity. Subjective visual inspection of radar imagery revealed no strong relationship between convective mode and CG lightning polarity, and also illustrated that positive and negative severe storms can be equally intense.Item Low-level convergence and its role in convective intensity and frequency over the Houston lightning and rainfall anomaly(Texas A&M University, 2007-09-17) McNear, Veronica AnnAn increase in the amount of lightning and rainfall over the Houston area, compared to the surrounding rural areas, has been well documented in previous studies. The placement of a Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) in the Houston area during the summer season of 2005 presented a unique opportunity to investigate the role of boundary-layer convergence in modulating convective frequency and intensity and, thereby, likely causing the rainfall and lightning anomalies. The role of the urban heat island (UHI) and the sea-breeze, as a source of low-level convergence leading to enhanced convection over Houston, was examined. Hourly average dual-Doppler wind and convergence maps were created on 1 X 1 km grids for an eleven-week period. By using these images along with average lightning, rainfall, and reflectivity for a large Houston-centered domain, it was possible to discern a correlation between low-level convergence and convection. Also, past findings of enhancement in lightning and rainfall over Houston and downwind of Houston were validated. High convergence levels for the Houston area in the mid-morning were followed closely by a peak in convection in the early afternoon. The enhancement of rainfall and lightning over and downwind of downtown was found to be primarily from a large increase in frequency of deep convective events when compared to the surrounding domain. Also, it was found that UHI, rather than sea-breeze, was likely the primary causative mechanism in the development of convection over the Houston area because of the lack of deep convection in areas equally affected by the sea-breeze and the timing of the convection compared to time of peak sea-breeze. An area of weaker enhancement south of Houston, not discussed in previous studies, was found to be present, possibly from the interactions between the bay-breeze off of the Galveston Bay and the seabreeze.Item Radar Nowcasting of Total Lightning over the Kennedy Space Center(2011-08-08) Seroka, Gregory NicholasThe NASA Kennedy Space Center (KSC) is situated along the east coast of central Florida, where a high frequency of lightning occurs annually. Although cloud-to-ground (CG) lightning forecasting using radar echoes has been thoroughly analyzed, few studies have examined intracloud (IC) and/or total (IC CG) lightning. In addition to CG lightning, IC flashes are of great concern to KSC launch operations. Four years (2006-2009) of summer (June, July, August) daytime (about 14-00 Z) Weather Surveillance Radar ? 1988 Doppler data for Melbourne, FL were analyzed. Convective cells were tracked using a modified version of the Storm Cell Identification and Tracking (SCIT) algorithm and then correlated to CG lightning data from the National Lightning Detection Network (NLDN), as well as grouped IC flash data acquired from the KSC Lightning Detection and Ranging (LDAR) networks I and II. Pairs of reflectivity values (30, 35, and 40 dBZ) at isothermal levels (-10, -15, -20 and updraft -10 degrees C), as well as a vertically integrated ice (VII) product were used to optimize criteria for radar-based forecasting of both IC and CG lightning within storms. Results indicate that the best radar-derived predictor of CG lightning according to CSI was 25 dBZ at -20 degrees C, while the best reflectivity at isothermal predictor for IC was 25 dBZ at -15 degrees C. Meanwhile, the best VII predictor of CG lightning was the 30th percentile (0.840 kg m-2), while the best VII predictor of IC was the 5th percentile (0.143 kg m-2), or nearly 6 times lower than for CG! VII at both CG and IC initiation was higher than at both CG and IC cessation. VII was also found to be lower at IC occurrence, including at initiation, than at CG occurrence. Seventy-six percent of cells had IC initiation before CG initiation; using the first IC flash as a predictor of CG occurrence also statistically outperformed other predictors of CG lightning. Even though average lead time for using IC as a predictor of CG was only 2.4 minutes, when taking into account automation processing and radar scan time for the other methods, lead times are much more comparable.Item The evolution of total lightning and radar reflectivity characteristics of two mesoscale convective systems over Houston, Texas(2009-05-15) Hodapp, Charles LeeTwo mesoscale convective systems (MCSs) passed over the Houston Lightning Detection and Ranging (LDAR) network on 31 October 2005 and 21 April 2006. As the MCSs traverse the LDAR network, the systems slowly mature with a weakening convective line and a developing stratiform region and radar bright band. The intensification of stratiform region precipitation, including the bright band, is thought to play an important role in stratiform lightning structure, charge structure, and total lightning production of MCSs. The stratiform areas quadruple in size and the mean reflectivity values increase substantially by ~ 6 dB. As the stratiform region matures, VHF source density plots show a lightning pathway that slopes rearward and downward from the back of the convective line and into the stratiform region. At early times for both MCSs, the pathway extends horizontally rearward 40 to 50 km into the stratiform region at an altitude of 9 to 12 km. Near the end of the analysis time period, the pathway slopes rearward 40 km and downward through the transition zone before extending 40 to 50 km in the stratiform region at an altitude of 4 - 7 km. The sloping pathway likely results from charged ice particles advected from the convective line by storm relative front-to-rear flow while the level pathway extending further into the stratiform region is likely caused by both charge advection and local in-situ charging. As the stratiform region matures, the stratiform flash rates double and lightning heights decrease. The percentage of lightning flashes originating in the stratiform region increases significantly from 10 - 20% to 50 - 60%. Overall, the number of positive cloud-to-ground flashes in the stratiform region also increases. Between both MCSs, 60% of the positive CGs originated in the convective or transition regions. Both in-situ charging mechanisms created by the development of the mesoscale updraft and charge advection by the front-to-rear flow likely contribute to the increased electrification and lightning in the stratiform region.Item The warning time for cloud-to-ground lightning in isolated, ordinary thunderstorms over Houston, Texas(2009-05-15) Clements, Nathan ChaseLightning detection over Houston, Texas is possible with the Lightning Detection and Ranging (LDAR-II) network and the National Lightning Detection Network (NLDN). A comparison of the two datasets in conjunction with 37 isolated, ordinary thunderstorms reveals a time separation of 3.1 minutes between the first detected Very High Frequency (VHF) source (i.e. first intracloud discharge) and the first cloud-toground (CG) lightning flash. This CG warning time is increased to 16.1 minutes when using the radar-defined criterion of when the 30-dBZ contour first reaches the -10?C isotherm level. Several attempts were made to establish a similar characteristic that could be used to forewarn the occurrence of the final CG in this storm type. Based on the average radar characteristics during the last CG flash in each thunderstorm case, CG activity comes to an end when the 45-dBZ echo falls below the -10?C isotherm. Detection efficiencies that remain slightly less than perfect for each network may have allowed for some error when analyzing VHF sources and ground flashes for each convective case. Exhibiting this possible error, four cases actually recorded a greater number of CG flashes than intracloud flashes, which is contrary to typical lightning characteristics. Future studies hope to increase the number of thunderstorm cases to analyze as the LDAR network continues to observe more lightning events. Also, similar approaches could be implemented in differing geographic regions of the country to observe if these lightning characteristics vary depending on latitude, longitude, or climate.Item Thunderstorm lightning and radar characteristics: insights on electrification and severe weather forecasting(Texas A&M University, 2007-04-25) Steiger, Scott MichaelTotal lightning mapping, along with radar and NLDN cloud-to-ground lightning data, can be used to diagnose the severity of a storm. Analysis of the 13 October 2001 supercell event (Dallas-Fort Worth, Texas), some supercells of which were tornadic, shows that LDAR II lightning source heights (quartile, median, and 95th percentile heights) increased as the storms intensified. Most of the total lightning occurred where reflectivity cores extended upwards and within regions of reflectivity gradient rather than in reflectivity cores. A total lightning hole was associated with an intense, nontornadic supercell on 6 April 2003. This feature was nonexistent from all supercells analyzed during the 13 October case. During tornadogenesis, the radar and LDAR II data indicated updraft weakening. The height of the 30 dBZ radar top began to descend approximately 10 minutes (2 volume scans) before tornado touchdown in one storm. Total lightning and CG flash rates decreased by up to a factor of 5 to a minimum during an F2 tornado touchdown associated with this storm. LDAR II source heights all showed descent by 2-4 km during a 25 minute period prior to and during this tornado touchdown. This drastic trend of decreasing source heights was observed in two tornadic storms prior to and during tornado touchdown, but did not occur in non-tornadic supercells, suggesting that these parameters can be useful to forecasters. These observations agree with tornadogenesis theory that an updraft weakens and the mesocyclone can become divided (composed of both updraft and downdraft) when a storm becomes tornadic. LDAR II source density contours were comma-shaped in association with severe wind events within mesoscale convective systems (MCSs) on 13 October 2001 and 27 May 2002. This signature is similar to the radar reflectivity bow echo. Consistent relationships between severe weather, radar and lightning storm characteristics (i.e., lightning heights) were not found for cells within MCSs as was the case for supercells. Cell interactions within MCSs are believed to weaken these relationships as reflectivity and lightning from nearby storms contaminate the cells of interest. It is also more difficult to clearly define a cell within an MCS.Item Total lightning observations of severe convection over North Texas(2009-05-15) McKinney, Christopher MichaelFive severe convective cells over North Texas from three separate dates were examined to determine what three dimensional, or ?total? lightning data can add to the understanding of a convective cell?s intensity, propagation, and severe weather potential. Total lightning data were obtained from Vaisala Inc.?s Dallas/Fort Worth (D/FW) Lightning Detection and Ranging (LDAR) network. Radar data from two Weather Surveillance Radar ? 1988 Doppler (WSR-88D) sites were used for position data and information regarding the intensity and kinematic properties of each cell. Total lightning products used by the National Weather Service Forecast Office in Fort Worth, Texas were compared to total lightning flash rate; a quantity that has been shown to be correlated to changes in cell intensity inferred from other sources, such as radar and satellite data. These products, specifically flash extent density (FED) were also compared to CG flash rate and radar derived measures from the WSR-88D sites. The results of this work show that FED and total flash rate are well correlated, with an average Pearson correlation value of 0.73, indicating that previous total flash rate results may also apply to FED. Lightning hooks, holes, and notches in FED displays indicated likely updraft regions, while appendages were observed to develop prior to deviant motion with two supercells. These results, combined with a greater update frequency provided a useful complement to radar data in the warning decision process. FED jumps were observed prior to several severe weather reports, indicating that total lightning activity may be related to updraft strength as found in past studies. However, FED jumps were sometimes observed without any associated severe event. More work is clearly needed to define what FED changes are of most importance in the short-term prediction of storm severity. The usefulness of the total lightning data on these dates was dependant upon LDAR network status and distance of the cell from the network center. The results of this study suggest that combining total flash rate trends with visual displays of FED provides the greatest added benefit to forecasters in maintaining situational awareness during warning operations.