Height Determination of a Blue Discharge Observed by ASIM/MMIA on the International Space Station

We analyze simultaneous photometric observations of thundercloud discharges from the Modular Multispectral Imaging Array of the Atmosphere-Space Interactions Monitor (ASIM) on board the International Space Station with ground-based vertical electric field measurements in South Africa on 3 February 2019 at 23:00-23:05 UTC. During this time, ASIM flew over an extended thunderstorm front of several hundreds of kilometers and recorded a blue discharge with the photometer at 337 nm which emitted strong electric fields. It is found that the rising edge of the blue photomultiplier tube light pulse allows the estimation of the blue discharge height: similar to 10.9-16.5 km which is constrained by cloud top height in a range of similar to 13.3-16.7 km deduced from infrared radiometry on board the geostationary Meteosat satellite. The electric field measurements are used to infer the height of the blue discharge to be similar to 16.0-18.8 km by use of skywave arrival times. It is shown that the height determinations are consistent with each other within the measurement uncertainties and the possible presence of an overshooting cloud top is discussed. The height of blue discharges is important to better understand how they can affect the chemistry in the upper troposphere. Plain Language Summary Recently, Transient Luminous Events (TLEs) and lightning activity from thunderstorm tops above thunderstorms have attracted great interest. The Atmosphere-Space Interactions Monitor (ASIM) and the Modular Multispectral Imaging Array (MMIA) are on board the International Space Station to record the lightning activity and TLEs in the UV band (180-230 nm) as well as the blue (337 nm) and the red (777.4 nm) emissions. In total, 188 MMIA triggers were recorded and more than 2,000 lightning strokes were reported by the lightning detection and location network during 23:00-23:05 UTC on 3 February 2019. We focus on a blue discharge event that happened at 23:02:41 UTC. The novelty of this work is that the height determination is carried out by using ground-based electric field measurements and space-based optical measurements from ASIM. This study can help to understand the chemistry effects at the tropopause level caused by such blue discharge events.