Terrestrial gamma ray flashes due to particle acceleration in tropical storm systems

Abstract

Terrestrial gamma ray flashes (TGFs) are submillisecond flashes of energetic radiation that are believed to emanate from intracloud lightning inside thunderstorms. This emission can be detected hundreds of kilometers from the source by space‐based observatories such as the Fermi Gamma‐ray Space Telescope (Fermi). The location of the TGF‐producing storms can be determined using very low frequency (VLF) radio measurements made simultaneously with the Fermi detection, allowing additional insight into the mechanisms which produce these phenomena. In this paper, we report 37 TGFs originating from tropical storm systems for the first time. Previous studies to gain insight into how tropical cyclones formed and how destructive they can be include the investigation of lightning flash rates and their dependence on storm evolution. We find TGFs to emanate from a broad range of distances from the storm centers. In hurricanes and severe tropical cyclones, the TGFs are observed to occur predominately from the outer rainbands. A majority of our sample also show TGFs occurring during the strengthening phase of the encompassing storm system. These results verify that TGF production closely follows when and where lightning predominately occurs in cyclones. The intrinsic characteristics of these TGFs were not found to differ from other TGFs reported in larger samples. We also find that some TGF‐producing storm cells in tropical storm systems far removed from land have a low number of WWLLN sferics. Although not unique to tropical cyclones, this TGF/sferic ratio may imply a high efficiency for the lightning in these storms to generate TGFs.

The First Fermi‐GBM Terrestrial Gamma Ray Flash Catalog

“…Once the source region was identified, the gamma ray properties are calculated. Similar analysis has been performed previously by Roberts et al () for a subset of the TGFs in this catalog that were found to be affiliated with tropical cyclones.…”

“…The source location of a TGF detected by GBM is limited to a ∼800‐km region centered on the subsatellite nadir. However, measurements of very low frequency (VLF) radio signals detected within several milliseconds of the TGF can be used to determine the location of the TGF to an accuracy of ∼10–20 km, critical for many studies that require an accurate source location (Chronis et al, ; Cohen et al, ; Collier et al, ; Connaughton et al, , ; Cummer, ; Inan et al, ; Roberts et al, ).…”

Analysis of Sub-threshold Short Gamma-Ray Bursts in Fermi GBM Data

“…An offline blind search of the CTTE data, which uses a multidetector rate analysis similar to that employed by the GBM flight software, but over a much larger range of energy bands and timescales, has been shown to find an additional ∼80 SGRB candidates per year. This technique was pioneered for the sub-threshold search of terrestrial gamma-ray flashes (TGFs) (Briggs et al 2013), which are much shorter than SGRBs, resulting in substantial detection improvements compared to the in-orbit method, increasing from ∼30 to ∼800 TGFs per year (Roberts et al 2018).…”

A Terrestrial Gamma‐Ray Flash inside the Eyewall of Hurricane Patricia

“…This is the first reported observation of a TGF associated with a hurricane eyewall, although TGFs have been seen from a very wide range of storm types (Chronis et al, ; Splitt et al, ). All previously observed TGFs associated with tropical storms have been observed in the rainbands, predominately during the strengthening phase of the storm (Roberts et al, )…”