LMA data are still up and running in AWIPS II here at the Huntsville WFO and I had the opportunity to view the data yesterday morning as a narrow band of convection moved across the area. It is nice to have these data back in operations and the utility can be seen in the series of images below. In these images, the KHTX reflectivity data are overlaid with North Alabama Lightning Mapping Array (NALMA) data and 1-minute NLDN data. The NALMA data are generally white and pinkish in color and lay atop the radar imagery. The NLDN data appear as “-” or “+” based on the polarity of the cloud-to-ground flash. In the first image below, the NALMA data indicated intra-cloud lightning prevalent in Lincoln County, TN, stretching westward into Giles County. No cloud-to-ground lightning was occurring at the time with this area of convection.
A little later at 1435Z, the area of convection had moved downstream to Bedford County, TN. Intra-cloud lightning activity had been sporadic through the period, but can be seen increasing again with a forming area of deep convection in the eastern portion of the county at 1435Z. Notice a negative cloud-to-ground strike can be seen in west central portions of Bedford County (just to the upper-left of the “B” in Bedford).
Later, at 1443Z, as the developing area of deep convection enters western Coffee County, a small jump appears in the LMA data, likely correlated with a strengthening updraft. Still, no cloud-to-ground lightning has occurred with this storm.
Finally, at 1449Z, the NLDN data indicate a negative cloud-to-ground strike in northwestern Coffee County, as seen in the image below (the negative sign may be a little difficult to see, but is located in the NW part of the county on the western fringe of the area of high reflectivity).
In this case, the NALMA data showed that electrical activity was occurring in the intra-cloud region and that a thunderstorm was in progress well before (~35 minutes) the NLDN data alone would have indicated. These data can be invaluable during real-time weather watches for our Emergency Manager partners and for the general public during outdoor events and can also alert a forecaster that a thunderstorm is indeed in progress when there are no cloud-to-ground strikes observed by the NLDN data alone.
Now, for something a little different…
I also noticed some unusual data that appeared well ahead of the line of convection yesterday in Madison and Limestone Counties. While intra-cloud lightning could take place well ahead of the deep convection within the cirrus shield, this didn’t seem to be the case yesterday. After some consultation with Dr. Geoffrey Stano of SPoRT/ENSCO, he believes the NALMA was detecting an aircraft traveling east to west through the region. He wrote to me that, “the speed of the propogation in successive images and the “line” the sources make all point to an aircraft.”
Here are the images…
The NALMA page maintained by the lightning group showed the linear streak very well too, as seen in this image provided by Dr. Stano…
Dr. Stano described this as a corona discharge that is generated by an aircraft flying through clouds that are electrically active (although not necessarily producing lightning). The corona discharge can go into very high frequency range (VHF), which can be observed by an LMA. We’re not sure at this point if we’re going to observe this more in AWIPS II. Nevertheless, forecasters will have to be made aware of this type of phenomena and not be falsely alarmed by sudden increases or appearences of source data from the NALMA.
Acknowledgement: I would like to thank Dr. Geoffrey Stano for his consultation with this post.