FORTE Measurements of Global Lightning Altitudes

While multiple lightning detection systems provide geographical locations of lightning events across the globe, robust lightning altitude measurements on a global scale have proven elusive. Space‐based platforms have an advantageous viewing geometry for making these measurements, but prior studies with the Fast On‐orbit Recording of Transient Events (FORTE) satellite were limited to a few thousand events. In this study, we apply the same technique for calculating source altitude from the previous efforts to a large catalog of hundreds of thousands of global FORTE in‐cloud lightning events that were coincident with flashes geolocated by its lightning imager between 1997 and 2003. We use this new data set to document global variations in lightning altitude. As in previous studies, we find that FORTE primarily resolves sources from the upper (positive) charge layer at ∼11 km altitude in normal thunderstorms. However, sources are also recorded from other charge layers in the storm and from leaders developing between layers. In particular, we note a pronounced increase in source altitude in the first 20 ms of FORTE flashes from the negative leader developing upward into the upper positive charge layer. Regions known for wintertime and/or stratiform lightning have increased contributions from low‐altitude sources, while tropical regions particularly around Panama and the Maritime Continent have the greatest concentrations of high‐altitude sources. Plain Language Summary After many years of observing lightning from multiple sensors, we have a good understanding of how the global frequency of lightning varies from region to region. However, the lightning that we witness on the ground (which is also the primary phenomenon detected by the global lightning detection networks) is only a small portion of the expansive lightning channels. Most of the flash extends through the clouds, hidden from view. The altitudes of lightning flashes in the clouds are particularly important because they reveal changes to convection and play a key role in atmospheric chemistry. In this study, we use a large catalog of in‐cloud lightning events recorded by the Fast On‐orbit Recording of Transient Events satellite to document variations in lightning altitudes across the globe. Key Points A new robust data set of very high frequency (VHF) source altitudes from lightning is presented that covers the global Fast On‐orbit Recording of Transient Events (FORTE) satellite domain Source altitude