Recent improvements in lightning reporting at 45th Weather Squadron

Several significant improvements have been made recently to the systems and procedures used in producing lightning reports for customers of the 45th Weather Squadron (45 WS). These lightning reports include the distance to, and peak current of, cloud-to-ground lightning return strokes near key facilities at Cape Canaveral Air Force Station and NASA Kennedy Space Center (KSC) in east central Florida. Customers use these reports to determine if induced current damage is possible in the electronics of their space launch vehicles, their payloads, or ground processing equipment, as well as which level of inspection is required to recertify those electronics. These inspections can be costly, both financially and in delays to launch processing. The recent improvements in these lightning reports began when the Four Dimensional Lightning Surveillance System (4DLSS) became operational in April 2008. One of the many benefits of 4DLSS is that all return strokes per flash are detected. The previous cloud-to-ground lightning system used by 45 WS only reported one stroke per flash. However, cloud-to-ground lightning has an average of 3.5 strokes per flash and 50% or more of these strokes have multiple ground strike locations. These multiple ground strike locations have an average spacing of 3 km and can extend up to 12 km. In addition, a truncation error in the computer database used to generate the daily lightning reports was discovered. This error was causing up to a 4% underestimate of the peak current of each stroke for average lightning. This problem was corrected.

Another significant improvement in the 45 WS lightning reporting procedures derived from the realization that the quoted location accuracy assumed that all six cloud-to-ground lightning sensors were used in the solution. However, solutions often use less than all six sensors, resulting in larger location errors and more eccentric error ellipses than previously believed. Reporting a single location accuracy and implied circularity of the error was misleading. In addition, customers were being provided the 50th percentile location accuracy, which was inappropriate for space launch applications. To address this shortfall, the location accuracy and detection efficiency across the local area was obtained as a function of all possible sensor combinations. However, the error characteristics for each individual return stroke were still needed since these error characteristics varied based upon the geometry of the stroke location relative to the sensors used in the solution of that stroke. This led 45 WS and their mission partners to develop an interim procedure where the raw data from 4DLSS was used to estimate the 95th or 99th percentile error ellipse for each stroke, depending on the customer, and to calculate the distance from a specific point of interest to the most likely lightning location as well as the closest edge of the error ellipse. Customer points of interest can include, but are not limited to, launch pads or payload processing facilities. If the closest possible strike, considering the error ellipse, has a peak current which does not violate the threshold for induced current damage, then the customer can be confident that no action is required. A new direct connection from 4DLSS to a local workstation in 45 WS now allows on-demand lightning reports without system administrator support. In addition, on their own initiative, KSC provided automatic e-mail notification in near real-time to specific customers whenever a return stroke exceeded that customer's distance or distance/intensity threshold. As part of their initiative, KSC also displays the return stroke locations at a website.

Further improvements to the 45 WS lightning reporting process are planned. MatLabŪ software was installed to improve accuracy in calculating the distance to the closest point on the ellipse, reduce the time required for data analysis processing, and generate more efficient customer reports. The Fault Analysis Lightning Location System (FALLS) from Vaisala, Inc. is being acquired with implementation scheduled for Oct 09 to provide advanced analysis capabilities as well as display of the error ellipses. KSC may extend their initiative by adding the error ellipses to their website displaying the return strokes so the customers can see this important data in near real time. Finally, efforts are underway to ingest data from nine surrounding National Lightning Detection Network sensors into 4DLSS in real-time to improve the detection of strong strokes that can sometimes overwhelm the 4DLSS sensors. This will also improve the location accuracy and detection efficiency of the 4DLSS system.