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Author's Kit
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Differences in Winter Lighting Activity over Land and Sea across the Eastern Coast of the Mediterranean |
| Orit Altaratz,
Zev Levin Yoav Yair and Baruch Ziv |
| We will present a study of the characteristics of lightning activity during the Cyprus Low winter storms across the eastern coast of the Mediterranean. The focus is on changes in the nature of thunderstorms crossing the coastline from the sea into the northern and central parts of Israel, as manifested in their electrical activity. Our results are based on LPATS measurements of lightning ground strikes during four winter seasons between 1995 and 1999. The spatial distribution shows a maximum of lightning ground strikes over Mount Carmel, possibly due to its topographical forcing. The annual variation shows a major maximum in January with two minor peaks, one in November and another in March, which can be explained by changes in the static instability of the atmosphere throughout the rainy period. The average fraction of positive ground flashes was found to be 6% and their average peak current +41 kA. The average peak current of negative ground flashes was -27 kA. The diurnal variation shows that the maximum in maritime lightning activity was at 0500 LST and over land at 1300 LST. The mean peak current of positive ground flashes was higher over land and of negative ground flashes, over the sea. Higher frequencies of ground flashes were detected over the sea than over land during the study period. This is probably due to the large heat and humidity fluxes from the sea surface, which destabilize the colder air that passes above and drives cloud convection. The annual distribution shows that during midwinter (D-J-F) there is higher flash density over the sea, while during autumn and spring the flash density is similar above the two regions. |
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The Rondonia
Lightning Detection Network: |
| R. J. Blakeslee J. C. Bailey O. Pinto A. Athayde N. Renno C. D. Weidman |
| A four station Advanced Lightning Direction Finder (ALDF) network was established in the state of Rondonia in western Brazil in 1999 through a collaboration of U.S. and Brazilian participants from NASA, INPE, INMET, and various universities. The network utilizes ALDF IMPACT (Improved Accuracy from Combined Technology) sensors to provide cloud-to-ground lightning observations (i.e., stroke/flash locations, signal amplitude, and polarity) using both time-of-arrival and magnetic direction finding techniques. The observations are collected, processed and archived at a central site in Brasilia and at the NASA/ Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Initial, non-quality assured quick-look results are made available in near real-time over the internet. The network is still operational and will remain deployed for several years to provide ground truth data for the Lightning Imaging Sensor (LIS) on the Tropical Rainfall Measuring Mission (TRMM) satellite that was launched in November 1997. The measurements are also being used to investigate the relationship between the electrical, microphysical and kinematic properties of tropical convection. In addition, the long-time series observations produced by this network will help establish a regional lightning climatological database, supplementing other databases in Brazil that already exist or may soon be implemented. Analytic inversion algorithms developed at NASA/ Marshall Space Flight Center (MSFC) have been applied to the Rondonian ALDF lightning observations to obtain site error corrections and improved location retrievals. The data will also be corrected for the network detection efficiency. The processing methodology and the results from the analysis of four years of network operations will be presented.
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The Advantages of Total Lightning over CG Lightning for Thunderstorms Cell Identification and Tracking and its Complements to Radar Reflectivity |
| Nicholas W. S. Demetriades,
Martin J. Murphy, and Phillippe Richard |
| Radar reflectivity data and the algorithms used to help meteorologists interpret these data are extremely important in nowcasting. However, a number of inherent problems arise when tracking thunderstorm cells using 2-dimensional and 3-dimensional reflectivity. These problems include: (1) analyzing thunderstorm cells at close range from the radar, Vaisala-GAI has two total (cloud and cloud-to-ground) lightning detection technologies that can help address some of these problems. Both technologies provide a much richer dataset than cloud-to-ground (CG) lightning data alone. The SAFIR technology detects total lightning at VHF in 2-dimensions and the Lightning Detection and Ranging (LDAR II) technology detects lightning at VHF in 3-dimensions. Vaisala-GAI has compared thunderstorm cell identification and altitude trends from radar algorithms with lightning data provided by SAFIR, LDAR II and CG only lightning detection networks. Lightning density plots were used for cell identification and many different methods were employed for tracking lightning cell altitude trends. Thunderstorm cell identification and tracking were greatly improved with the use of total lightning density over CG lightning density. Comparisons of the spatial extent of lightning activity within thunderstorms showed that total lightning extended the lightning boundary of cells by 10's of kilometers over CG lightning cell boundaries. Total lightning was able to identify cells that produced severe weather that were too close to radar to be properly identified. Total lightning has also been able to identify thunderstorm cells more accurately in complex multi-cellular environments such as squall lines. In a number of thunderstorms, altitude trends obtained from echo tops exhibited unrealistic growth and decay and were better represented by lightning altitudes. Finally, the continuous data stream provided by both the SAFIR and LDAR II technologies allowed cells to be tracked with more rapid update cycles than the typical 5-minute update time of radar. This provided a higher level of detail for both thunderstorm growth and decay. |
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Lightning evolution in the severe storms in Texas on 7 April 2002 |
| Nikolai Dotzek Robert M. Rabin, Donald R. MacGorman Nicholas W. Demetriades and Ronald L. Holle |
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The severe Texas storms of 7 April 2002 are investigated using GOES 8, NLDN, and 3D total lightning data from the LDAR II network in the Dallas--Ft. Worth region. Storms developed from an unstable surface boundary and quickly evolved into tornadic supercells, later merging into a squall line with flash floods and large hail. Satellite data reveal possible predictive potential of cloud top structures prior to tornado formation. The 3D lightning data characterizes the storms as normal polarity dipoles with main charge layers at about 7 and 11 km AGL. Horizontal flash extent and branching both increase as the squall line develops a trailing stratiform part. |
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Relationship between variations of the atmospheric electric field in the southern polar region and thunderstorm activity |
| A.Frank-Kamenetsky,
O.Troshichev V. Morozov G.Burns M.Fuellekrug A.Rodger |
| High and dry regions with no thunderstorms, such as the Antarctic plateau, are ideal sites for monitoring the global geoelectric circuit. Additional solar influences on the geoelectric field occur at high latitudes, via the same processes that generate the aurora. In conjunction with Australian and American colleagues, we measure the geoelectric field at the Russian station, Vostok, on the Antarctic plateau. We have shown that solar variability can influence the geoelectric field measured at ground level in Polar Regions. Comparative analysis of the near surface electric field variations at Vostok station (Antarctica) and the thunderstorm activity has been fulfilled for 10 days in April 1998. As a measure of thunderstorm activity we take VLF emission amplitude at 9.3 KHz, measured at Halley Bay (Antarctica) and intensity of the lightning flashes. No any good correlation is found between Ez, delta Ez and thunderstorm activity. The correlation between VLF and flashes is rather good. Conclusion is made, that steady conduction currents connected with the thunderstorm clouds, whereas flashes related to the explosive process, cannot provide essential effect in region far from the thunderstorm, generate the main geoelectric field. Estimations of the global flush effects at great distances, made for non-stationary model of the electric field in the atmosphere, showed that the flush input in Antarctica does not exceed 5 V/m. This effect of flushes registered in tropical zone turned out to be insignificant in comparison with the regular ionospheric electric fields in the polar region (about 20 - 30 V/m).
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Lightning
Research in Brazil: recent results |
| I.R.C.A. Pinto, O.
Pinto Jr., M.A.S. Santos, F.J. Miranda,
K. P. Naccarato, W. A. Fernandes
and E.C. Ferraz |
| The lightning research in Brazil is reviewed based on recent indirect measurements of electromagnetic radiation of natural lightning. The measurements were obtained by lightning networks and single electric field antennas, located at different parts of the country, and by the LIS (Lightning Imaging Sensor) optical sensor launched on board the TRMM satellite in 1997. The lightning characteristics are revised and compared with similar data obtained outside the tropics by other lightning networks and single-antenna observations. In particular, the following topics will be discussed: multiplicity and peak current estimates of negative and positive cloud-to-ground (CG) flashes and intracloud/cloud-to-ground flash ratio at different parts of the country. The present situation of the efforts to have an integrated network in Brazil (Brazilian Lightning Detection Network - BLDN) will be also presented. This network would be the largest one in the tropics. |
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Positive Lightning Activity During an Intense Derecho |
| Colin Price Brian Murphy |
| A derecho is an extratropical mesoscale convective system (MCS) that produces damaging winds from a series of downbursts. These damaging downbursts occur with bow echoes observed in conventional radar imagery. A derecho must have a damage path of at least 450 km in length, with at least three reports of hurricane force winds, each separated by at least 75 km, and with no more than three hours between successive wind damage events. On 4 July 1999, a severe derecho caused extensive damage to forested regions along the United States/Canada border, west of Lake Superior. There were 665,000 acres of forest destroyed in the Boundary Waters Canoe Area Wilderness (BWCAW) in Minnesota and Quetico Provincial Park in Canada, with approximately 12.5 million trees blown down. This storm resulted in additional severe weather (hail, wind and tornados) before and after the occurrence of the derecho, with continuous cloud-to-ground (CG) lightning occurring for more than 34 hours during its path across North America. At the time of the derecho the percentage of positive cloud-to-ground (+CG) lightning measured by the Canadian Lightning Detection Network (CLDN) was greater than 70% for more than three hours, with peak values reaching 97% positive CG lightning. Such high ratios of +CG are rare, and may be useful indicators for short-term forecasts of severe weather. |
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Detection Efficiency Contours for Regions Serviced by Lightning Detection Networks of Limited Scope |
| John T. Rompala,
Richard J. Blakeslee Jeffery C. Bailey |
| Advances in lightning detection systems and associated software have prompted groups worldwide to establish regional lightning detection networks (LDN). The placement and limited number of sites making up such a network can result in less than ideal detection efficiency over the region serviced. This constraint does not limit the expectations of local and global investigators that these networks can provide complete and reliable data sets. As an illustration of how these expectations might be realized, the authors investigated data from a four station LDN in Brazil's Rhodonian region. The area considered covers more than a million square kilometers with intersite separation varying between 150 km and 605 km. Detection efficiency contours where developed to illustrate the regional variation in the portion of events for which detection information would be insufficient to prompt a location "solution". These contours were formulated by distributing a pool of simulated CG events of varying peak currents over the region. In one application the distribution followed a Monte Carlo process. In another, the event pool was applied uniformly to each regional segment. The event pool for both processes was formulated using observed CG event statistics within a regional segment near the network center assumed to have nearly perfect detection efficiency. This peak current spectrum was then modeled by a variation of the gamma probability distribution. Application algorithms were designed to account for variation in detection thresholds among sites, signal attenuation, the character of the "solution" software, and various permutations of site operational status. For investigators employing data from an existing LDN of limited scope, this process serves as an initial step in estimating and correcting for the count and strength of undetected events. For LDN planners, it can serve as a tool in determining optimal site configuration. |
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Severe Storm Lightning Evolution Pattern and Associated Weather Hazards |
| V.N.Stasenko, S.M.Galperin
and G.G.Shchukin |
| Severe storm lightning evolution pattern correlate apparently well with weather hazards produced by that storm (hail, tornado, excessive precipitation etc.). However lightning flash (LF) sensors of different design exploring the same storm will portray clouds of different severity. To evaluate diagnostic and forecasting potential of such an information, for example, for Risk Evaluation and Emergencies Management, comparative analysis of particular features of thunderstorm activity generated by different type sensors and lightning-weather hazards correlation are to be done. Close interconnection of microphysic, dynamic and electrical properties of a cloud, owing to appropriate physical mechanisms (need further study and clarification), lead to certain time and space sequence of the above processes during severe storm evolution. Every LF sensor has own performance characteristics (POD, lead time etc), influencing its ability to forecast weather hazards. An integration of satellite, radar, DFs data makes it possible to identify lead times of the upcoming severe weather what is of a great importance for timely warning. As access to more information increases, information management will become a major factor. Expert system can be developed and implemented to provide guidance for decision - making by disaster managers or in guiding on appropriate response for specific types of hazards (for example, cloud modification for hail and tornado suppression). Lightning mapping system data in combination with multi wavelength radar products can gain new insight to the problem. Evidently, cloud particles of various size, concentration and physical properties contribute to charge separation and growth, and finally to LF release. LF illuminates the charge structure of a cloud. Assuming low enough conductivity inside of a thundercloud, h.e. low probability of charge supply form other cloud volumes, we can consider LF as the volume where particles of different physical properties are concentrated and charge generation process maximized. This assumption most probably holds true for places of LF origin (active electric zones) so far as further LF branching is influenced by the superposition of electric fields of the main cloud charges. Results of multi wave thunderstorm investigation of such an active electric zones in St Petersburg area are presented, including comparative analysis of radar and DF data on LF evolution in single- and multi-cell storms. Rationales for such an expert system are discussed as well as informational products would be generated. |
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| Last Update : May 7, 2003 |
Full program for Monday
