Simultaneous detections of TGFs and Elves by ASIM

Credit: Birkeland Centre for Space Science and MountVisual

In a new paper by Bjørge-Engeland et al. [2022], an investigaton has been performed on simultaneous detections of Terrestrial Gamma-ray Flashes (TGFs) and Elves by the ASIM instrument. TGFs are short and highly energetic bursts of gamma photons associated with lightning discharges, and Elves are Transient Luminious Events (TLEs) that are observed from space as concentric rings of light in UV and visible light at ionospheric altitudes and are produced when an electromagnetic pulse hits the base of the ionosphere.

“We have identified 17 simultaneous observations of these phenomena between the launch of ASIM in April 2018 and the end of 2020”, Ingrid Bjørge-Engeland explains. “We have compared properties of these events with both other TGFs detected by ASIM and lightning detections in general. In addition to data from ASIM, we used data from lightning location networks, to obtain information about the lightning discharges associated with the events and their locations”.

The results obtained by Bjørge-Engeland et al. [2022] shows that the TGFs with accompanying Elves all have very short durations (with core durations less than 75 us), and that the events are associated with very high peak current lightning (typically of several hundred kA), compared to both lightning in general and to other TGFs detected by ASIM. “We also show that TGFs can be associated with a wide range of peak currents, and that short duration TGFs tend to be associated with higher peak currents than longer TGFs”, Ingrid Bjørge-Engelands says.

In the image below (Figure 17 in Bjørge-Engeland et al., 2022), the key results are highlighted, showing peak currents associated with ASIM TGFs versus TGF core durations. The TGFs with Elves are highlighted in red.