Investigating the relationship between TGF durations and the onset times of the optical pulses and the TGFs

<p><em>We investigate and determine the sequence of the Terrestrial Gamma-ray Flashes (TGFs) and the observed optical emissions associated with lightning flashes, as well as the connection between the duration of TGFs and the time between the onset of the TGFs and the observed main optical pulses. Over 200 observations from the instruments of the Atmosphere-Space Interactions Monitor (ASIM) on board the International Space Station (ISS) are used, together with data from the lightning detection networks GLD360 and WWLLN. The ASIM data consist of two separate recordings: High energy measurements from the Modular X- and Gamma-ray Sensor (MXGS), and optical measurements from the Modular Multi-Spectral Imaging Array (MMIA). The optical measurements are from photometers operating in the 337 and 777.4 nm bands, and the temporal uncertainty between the two instruments of ASIM is +- 5 µs.</em></p>

ASIM TGFs with accompanying elves

<p><span>The Atmospheric Space Interactions Monitor (ASIM) was launched in 2018, and has since then observed Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs). ASIM consists of the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA). Using data from both MXGS and MMIA, we investigate observations of TGFs (detected by MXGS) with accompanying elves (detected by MMIA). We study the optical signatures of the elves detected by a photometer of MMIA operating in the 180-230 nm band. Lightning sferics associated with these events have been detected by WWLLN and GLD360. Several TGFs have associated lightning sferics outside the field of view of MMIA, but due to the expanding rings of the elves we can still observe optical signatures from accompanying elves. Using GLD360 data we also study properties of the lightning strokes. </span></p>

Comparison of lightning observed by ASIM on the International Space Station and GLM on the GOES-16 geostationary satellite

<p>The Atmosphere-Space Interactions Monitor includes an optical imaging array consisting of 5 nadir-viewing  sensors , dedicated to monitor electrical discharges in and above thunderstorms. Three photometers sample in 337.0/4 nm, the VUV band 180-230 nm and 777.4/5 nm with a sample rate of 100 kHz while the 2 cameras record in 337.0/3 nm and in 777.4/3 nm with a temporal and spatial resolution of 12 frames per second and ~400 m, respectively. The Geostationary Lightning Mapper (GLM) on the GOES-16 satellite is the first operational space-based lightning detector in geostationary orbit measuring in 777.4/1 nm, with a pixel size of ~8-14 km and temporal resolution of up to 500 frames per second.<br>We present an analysis of the signal amplitudes and detection efficiencies of ASIM and GLM based on three mutually detected storms: one in the center and two on the edges of GLM field of view. We find a dependence of the amplitudes and detection efficiencies on the cloud structure and the observation angles of ASIM and GLM. The best agreement between the instruments appears when ASIM detects towards the nadir, but differences in amplitudes may vary by several orders of magnitude.  The cloud structure offers a potential explanation for these differences which we will explore in the presentation.</p>