Global lightning and severe storm monitoring 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 stage of thunderstorm development. Not surprisingly, lightning flash rates have been shown to be statistically correlated to the strength of the convective updraft and can be used as a proxy for locating and nowcasting severe weather. This paper details an ongoing effort to develop a satellite-based Very High Frequency (VHF) Global Lightning And Severe Storm monitor (V-GLASS) based on the detection of VHF emissions from lightning. The proposed system would be an outgrowth of an already-funded constellation of broadband VHF receivers to be flown on the upcoming Block IIF Global Positioning System (GPS) satellite constellation beginning in 2006. A VGLASS system would provide the user with a global three-dimensional geolocation capability for detected lightning events by way of a multi-satellite time-difference-of-arrival (TDOA) technique and in this manner, could be used to detect and track severe convection on a global basis.

The scientific and technical foundations for satellite-based VHF global lightning detection and storm mapping from GPS orbit will be presented. Lightning data collected by experimental VHF receivers currently in orbit aboard two GPS satellites (SVN 54 and SVN 56) will be used to demonstrate and explore the potential use of GPS-based VHF receivers for such purposes. Ground-truthing for the GPS-detected events is provided by the Los Alamos Sferic Array (LASA) for lightning activity in the Florida area and by the World Wide Lightning Location Network (WWLL) for storm activity in the central and western Pacific Ocean. Analysis of GPS/LASA correlated events indicates that the majority of GPS-detected VHF emissions (about 80%) are associated with positive-polarity narrow bipolar events (NBEs). NBEs are a ubiquitous type of in-cloud lightning found in most thunderstorms, are associated with deep convective processes, and their occurrence rates are excellent statistical indicators of thunderstorm convective strength. The remaining 20% of the GPS events are due to intense VHF return stroke attachment transients occurring primarily over sea water. The detectability of each emission type from GPS orbit is a function of the receiver sensitivity, the source strength and the source radiation pattern (the statistical VHF radiation pattern associated with NBE activity is shown to peak at an angle of about 40 degrees from the horizontal).

Two-satellite observations of lightning/storm activity, ground-truthed with the WWLL network, demonstrate the ability of GPS-based VHF receivers to routinely identify, locate and track generic storm activity. GPS storm detection and tracking statistics will be presented from a 3-month study of storm activity in the central and western Pacific Ocean. We conclude that GPS-based VHF lightning detection presents a viable means of monitoring global severe weather from space.