VHF lightning detection and storm tracking from GPS orbit

Over the last few decades, there has been a growing interest to develop and deploy an automated and continuously operating satellite-based global lightning monitor. Lightning is a direct consequence of the electrification and breakdown processes that take place during the convective stages of thunderstorm development. Satellite-based lightning monitors are designed to exploit this relationship by using lightning detection as a proxy for remotely identifying, locating and characterizing strong convective activity on a global basis.

To date, efforts to develop a satellite-based lightning detection system have mostly focused on the deployment of optical sensors that can provide high-detection-efficiency, single-platform, two-dimensional geolocation of conventional lightning flashes. Over the last several years, measurements of radio-frequency (RF) lightning radiation using very high frequency (VHF) radio receivers aboard the Fast On-Orbit Recording of Transient Events (FORTE) satellite have shown that satellite-based VHF lightning detection may also present a practical means of global lightning monitoring. VHF lightning detection techniques provide a complementarity to optical detection techniques in that they are most sensitive to a meteorologically important type of in-cloud lightning that produces sub-threshold optical emissions. Additionally, VHF detection provides geolocation of lightning events into the third dimension (altitude) and can easily discriminate between cloud-to-ground (CG) and intra-cloud (IC) activity based on the power-versus-time profile of the signal. The opportunity to locate lightning sources in altitude may be particularly useful in quantifying the vertical extent (strength) of the convective development and in possibly deducing vertical charge distributions.

This paper presents the scientific and technical foundations for satellite-based VHF global lightning detection and storm tracking from Global Positioning System (GPS) orbit. Lightning data collected by VHF receivers currently in orbit aboard GPS satellites is used to demonstrate the detection and tracking of generic thunderstorm activity, tropical storms and severe weather. The detected VHF lightning events are analyzed with respect to NEXRAD scans, Lightning Mapper Array (LMA) data, Los Alamos Sferic Array (LASA) data and World Wide Lightning Location (WWLL) array data to determine the meteorological context of the detected events. Multiple satellite observations of lightning/storm activity over the western hemisphere are used to demonstrate the geolocation ability of the GPS-based VHF receivers. We conclude that GPS-based VHF lightning detection presents a viable means of mapping global deep convection and thunderstorm activity from space. A proposal to use a planned constellation of GPS-based VHF receivers as a real-time global lightning mapper is presented.