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48 endangers airport workers, they only represent a small frac- should therefore only be used to generate "advisory" products tion of the total lightning in a storm. The majority of the that call attention to the potential for storm development. lightning discharges stay within the cloud or strike adjacent Such an advisory would serve as a "heads-up" and not in itself clouds and are generally described as IC strikes. Measurement call for a "stand down." Predictive systems may be valuable systems that can detect and locate both CG and IC lightning for operational planning, but are not likely to replace or elim- are termed total lightning systems. inate the need for lightning-specific detection and warning CG lightning strikes are predominantly vertically orientated systems. and can be associated with a single geographical position, essentially their impact point. IC lightning, on the other Making Use of Existing Data hand, often extends in complicated patterns over long hori- Integration Systems zontal distances. The most sophisticated total lightning detection systems can track the full path of an IC stroke and, Integrating multiple data sets into a decision support by combining the tracks of several successive strokes, can pro- system can be a difficult and expensive process. Data access duce two-dimensional coverage plots. Because there are many and latency are particularly critical issues. One way to mini- more IC lightning strokes than CG strokes, and since their mize these efforts and costs is to make use of existing data positions can be mapped in a two-dimensional grid, they integration systems instead of developing new systems that provide a valuable description of the overall extent of active process much the same information. lightning in a cloud system. Total lightning patterns can Potentially valuable additions to airport lightning detec- be monitored and tracked with more precision than can be tion and warning systems include meteorological radar data, done with CG strokes alone, and since IC strokes are gener- cell identification and tracking algorithms, and observations ally observed several minutes before the first CG strokes they from regional total lighting detection systems. may be able to be used to identify potential hazards in storms Radar data and associated cell identification and tracking that are developing overhead before the first CG stroke is algorithms are fundamental to both the FAA-sponsored observed. ITWS developed by Raytheon (33) and Vaisala's WSDDM Total lightning systems require special VHF sensors to system that was developed at NCAR (34). Because both track the IC strokes and are currently only available over a few systems already include access to real-time NLDN lightning regional areas where they are being tested. Because the IC reports, it should be relatively straightforward to transfer spe- lightning patterns identify areas that have already developed cific lightning warning algorithms to these existing opera- active charge separation processes and are actively producing tional systems for easy access to their extended data sets and lightning strikes, they represent a uniquely valuable enhance- processing algorithms. The expanded weather systems, how- ment to operational lightning warning systems. Integrated ever, would need to support additional communication links, systems based on total lightning detection networks may be lightning user displays, and integration of electric field mill able to provide significantly improved lightning warnings, in data, as well as be able to trigger the needed alarms and noti- terms of a better delineated hazard area and a reduction in fication systems. An ITWS-based integration would also total downtime for airport operations. extend the government's use of lightning data beyond the While it is not yet clear to what extent total lightning systems limits of the current U.S. contract with Vaisala and directly will become available, or who will install, operate, and fund compete with Vaisala's commercial lightning warning prod- their operation, they may eventually provide significant im- ucts. The terms and conditions of the NLDN contract, how- provements for lightning detection and warning systems, as ever, could be renegotiated when the contract comes up for well as enhancing short-term weather forecasts for the entire renewal in 2010. terminal area. On the other hand, customized products or output fields could be generated by ITWS, WSDDM, or other data inte- gration platforms for export to existing lightning warning Predicting Lightning Hazards systems, with the final integration being done there. Mesoscale "nowcasting" systems are quite effective at iden- In both cases, the technical challenges for these types of tifying the growth and motion of developing convective sys- integration should not be too difficult, but the issues of data tems and are used by the FAA for both terminal and en route rights and the generation of customized products for use by air traffic management. These forecasting systems can also be other, separately funded systems could become a major used to identify developing storms that are likely to produce impediment. Integrating aviation-related weather decision lightning. support systems into unified systems, however, should be the Airline operations are time-sensitive and have a very low most efficient and cost-effective way to ensure a higher level tolerance for false alarms. Most lightning prediction products of operational safety.