Lightning Mapping Array (LMA)
The Lightning Mapping Array is an instrument installed in two locations: North Alabama and Washington, D.C. Each card on this page represents one of these two arrays. The array on a green card, marked as "Transitioned Product," is being used by at least one National Weather Service Forecast Office. The array on a blue card, marked as "Research," exists mainly for academic purposes and research. To see actual real-time data, click the link at the bottom right of the card.
TRANSITIONED PRODUCT
NALMA
Real-time 2 minute source densities on a 2 x 2 km grid from the North Alabama Lightning Mapping Array.
RESEARCH
DCLMA
Washington D.C. Lightning Mapping Array with source densities on a 1 x 1 km grid with a 1-minute update.
NALMA Overview
The North Alabama Lightning Mapping Array (NALMA) was first established as a ground verification site for the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. The NALMA's mission has evolved since the initial deployment in 2001. Today, SPoRT provides NALMA data to four National Weather Service Offices, to assist in short-term forecasting. These offices are Huntsville and Birmingham, Alabama as well as Nashville and Knoxville, Tennessee. Additionally, SPoRT utilizes the NALMA as a risk reduction system for the GOES Lightning Mapper (GLM) set for launch aboard GOES-R in 2014. SPoRT researchers are using the NALMA to develop algorithms for and bring awareness to the forecasting community about the GLM's capabilities.
Figure 1. NALMA Network
The NALMA is a three-dimensional VHF detection network that consists of 11 VHF receivers deployed across northern Alabama with a base station and receiver located at the National Space Science and Technology Center (NSSTC). The NSSTC is located on the campus of the University of Alabama in Huntsville. The NALMA system locates the sources of impulsive VHF radio signals from lightning by accurately measuring the time that the signals arrive at the different receiving stations. Each station records the magnitude and time of the peak lightning radiation signal in successive 80 microsecond intervals within a local unused television channel (channel 5, 76-82 MHz). Typically, hundreds of sources per flash can be reconstructed, which in turn produces accurate 3-dimensional lightning image maps (normally <50 m error within 200 km range). The NALMA detects total lightning and not just the cloud-to-ground stike locations. Figure 1 shows the location of the NALMA sites. Solid green circles indicate a VHF receiver, while open green circles are wireless relay stations. The blue dot is the base station located at the NSSTC.
Figure 2. NALMA Coverage
SPoRT provides a three dimensional total lightning data set that is updated every 2 minutes. Figure 2 shows that the NALMA product provides full coverage to the Huntsville and Nashville Weather Service county warning areas as well as partial coverage to Birmingham and Knoxville offices. The lightning source density grids have a horizontal extent of 460 x 460 km, with a 2 x 2 km resolution centered on the NSSTC. The vertical grid resolution is 1 km from 0-17 km. SPoRT provides these gridded data to the National Weather Service through their Local Data Acquisition and Dissemination (LDAD) system. This allows the National Weather Service to ingest the near real-time source density grids into the Advanced Weather Information Processing System (AWIPS). AWIPS is the workstation used by forecasters to integrate varied weather data in order to issue forecasts and warnings. By providing the NALMA data in AWIPS, forecasters can interrogate the data on any of the 17 horizontal levels or examine the cumulative source density maps. With AWIPS, forecasters can readily compare the NALMA data to NEXRAD radar and other data set loops to enhance situational awareness during severe weather episodes.
Figure 3. Example Display in AWIPS
Typically, as shown in Figure 3, forecasters use the cumulative source density map (upper left), along with various radar parameters. These include 0.5 degree base reflectivity (upper right), mid level layer reflectivity maximum (lower right), and 0.5 storm relative motion (lower left). This example is from the 6 February 2008 "Super Tuesday" outbreak and shows the Jackson County EF-4 tornado that struck in the Huntsville county warning area. Note the very large NALMA source density values (upper right) associated with this tornadic supercell. The NALMA data coupled with other data sources led to WFO Huntsville forecasters issuing life saving tornado warnings with an average lead time in excess of 20 minutes.
In the forecast environment, the NALMA provides additional information on storm kinematics and updraft evolution that offers the potential to improve severe storm warning lead times by up to 50%. Additionally, the false alarm rate (for non-tornado producing storms) can be decreased. Our prior studies suggest a rapid increase in the "in-cloud" lightning frequency is associated with the invigoration of the storm updraft followed by a rapid decrease in lightning activity associated with the weakening of the storm updraft and descent of the storm angular momentum from aloft. This has been utilized to warn (or not to warn) of tornadic and hail producing thunderstorms. Additionally, NALMA data can provide a 3-5 minute lead time on the occurrence of the first cloud-to-ground strike of a storm.
