One major focus on this project is to how to understand the polarization of lightning radio sources and how to use that information to perform near-field interferometry (both WP1 and WP2). However, in the time between the grant being awarded and the project started, we serendipitously discovered how to simultaneously solve both of these problems (publication is Scholten and Hare et al., “Interferometric imaging of intensely radiating negative leaders”, Phys Rev D, doi:https://doi.org/10.1103/PhysRevD.105.062007 ), called TRI-D. TRI-D is capable of reconstructing both the location and polarization of 10,000 lightning radio sources per millisecond of data. Thus, in this project we have so-far focused on validating this new technique.
We’ve developed two techniques to test the accuracy of our TRI-D: a monte-carlo error analysis and a serendipitous observation of an airplane. The monte-carlo simulation, pursued by a PhD student, consists of modeling the radio emission from an input distribution of dipole point sources, adding background noise, and passing the result back through our TRI-D analysis to compare the output with the input. Thus far, the result is that in-general we can reconstruct the dipole direction of the emitting source current within 10 degrees of the input dipole current. A manuscript on this work is being prepared. The second technique to validate TRI-D involves the serendipitous observation of an airplane; possibly due to VHF emitted from sparks off the aircraft. We have discovered that TRI-D is not only capable of locating the airplane, but actually imaging its shape (location of both engines and tail). This presents an ideal scenario to test our techniques, as an airplane is a much simpler environment than a lightning flash. We have used this data to show that the relative location accuracy of TRI-D can be less than a meter, and the polarization accuracy is consistent with what has been modeled in the monte-carlo analysis. A manuscript on these results is also being prepared.
We have also designed the online mapping system for LOFAR2.0 (in WP3). This has proven a challenge, as my original implementation concept (writing firmware to do pulse-detection online during observation) has proven too difficult to implement. However, I discovered an alternative method where the antenna voltages could be streamed to a central large server, and the pulse-detection could be performed by the large server. I have designed this method for online lightning mapping with LOFAR2.0 and had it reviewed by ASTRON (host institute) personnel to
insure it can actually be easily implemented. I will implement this online mapping system when LOFAR2.0 comes online.
I have tried to maximize the output and impact of LIFT by pursuing collaborations. In the first such collaboration a lightning research group in Prague combined LOFAR data with lower-frequency magnetic loop antenna they measured, to explore how a certain lightning phenomena (dart leaders) can emit strong radio burst; which resulted in a publication. Another completed successful collaboration was with the plasma modeling group situated in Amsterdam. I helped advise a PhD student who was interested in attempting to model how radio waves are emitted from lightning (which is a major question in LIFT, but taken from an experimental direction). This resulted in publication 4 in section 1.3 below. In addition, I have worked with an American lightning scientist and his PhD student to produce a new numerical plasma model of a dart leaders. This collaboration has proceeded very will, and the results are currently being written into a manuscript.
Multiple future collaborations are being planned. A lightning researcher from China will visit our group for one year. This researcher will focus on comparing how results seen with LOFAR compare to his lightning observations in China. This collaboration will help us validate our results against other instruments and interpretations, as well as explore how lightning could behave differently in other climates. And, we are planning a joint observation campaign with a second lightning research group. In summer 2026, during thunderstorms, this will park an instrumented car near industrial wind-turbines in the Netherlands. This instrumented car contains high speed cameras, low-frequency electric field antennas, and high-energy particle scintillators. It will send signals to the newly upgraded LOFAR2.0 to record data when there is lightning on a wind-turbine . This will allow us to explore how lightning attaches to tall objects and emits energetic radiation.
