Special Classes of Terrestrial Gamma Ray Flashes From RHESSI

Abstract

We report on three classes of terrestrial gamma ray flashes (TGFs) from the (RHESSI) satellite. The first class drives the detectors into paralysis, being observed usually through a few counts on the rising edge and the later tail of Comptonized photons. These events-and any bright TGF-reveal their true luminosity more clearly via their Compton tail than via the main peak, since the former is unaffected by the unknown beaming pattern of the unscattered radiation, and Comptonization mostly isotropizes the flux. This technique could be applied to TGFs from any mission. The second class is more than usually bright and long in duration. When the magnetic field at the conjugate point is stronger than at the nearby footpoint, we find that 4 out of 11 such events show a significant signal at the time expected for a relativistic electron beam to make a round trip to the opposite footpoint and back. We conclude that a large fraction of TGFs lasting more than a few hundred microseconds may include counts due to the upward moving secondary particle beam ejected from the atmosphere. Finally, using a new search algorithm to find short TGFs in RHESSI, we see that these tend to occur more often over the oceans than land, relative to longer-duration events. In the feedback model of TGF production, this suggests a higher thunderstorm potential, since more feedback per avalanche implies fewer "generations" of avalanches needed to complete the TGF discharge.

Determining a Lower Limit of Luminosity for the First Satellite Observation of a Reverse Beam Terrestrial Gamma Ray Flash Associated With a Cloud to Ground Lightning Leader

“…Is this brightness estimate reasonable? There are several examples in the literature of TGFs with luminosities of orders of magnitude similar to our estimate of 2 × 10 18 (Mailyan et al., 2016; Smith et al., 2020). In particular, we refer to a TGF over the Mediterranean basin estimated to be as bright as 3 × 10 18 photons with energy >1 MeV (Gjesteland et al., 2015).…”

Production of Terrestrial Gamma‐Ray Flashes During the Early Stages of Lightning Flashes

“…The TGF catalogs are obtained from the TGF detecting space missions RHESSI, Fermi, AGILE, and ASIM. There are 2824 TGFs (August 2004 to November 2013) from the RHESSI TGF catalog (Smith et al, 2020), 4774 TGFs (August 2008 to July 2016) from the first Fermi-GBM TGF catalog (Roberts et al, 2018), 3473 TGFs (March 2015 to October 2020) from the 3rd AGILE TGF catalog (Lindanger et al, 2020;Maiorana et al, 2020), and 729 ASIM TGFs (June 2018 to September 2020) available from https://asdc.space.dtu.dk. The ASIM instrument is described in detail in Chanrion et al (2019); Neubert et al (2019); Østgaard, Balling, et al (2019).…”

Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers

“…• Do these high-energy atmospheric phenomena have any impact on atmospheric chemistry and dynamics? Although large catalogs of TGFs counting thousands of events are now available from most of the TGF-detecting missions [1010][1011][1012][1013], major advancements in the field now come from simultaneous observations at different frequency bands, ranging from the radio to optical (see [1014,1015] for instance). A breakthrough in the field for example could come from observation of TGFs from space coupled with simultaneous high spatial and time resolution lightning measurements by ground-based interferometers (a goal so far eluded because of the sporadic nature of TGFs events and the limited range of lightning interferometers).…”