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.

Automated summary

Simultaneous photometric observations of thundercloud discharges from ASIM on the International Space Station and ground-based electric field measurements in South Africa were analyzed. A blue discharge with strong electric fields was recorded by ASIM during its flight over an extended thunderstorm front. The height of the blue discharge was estimated to be around 10.9-16.5 km based on the rising edge of the photomultiplier tube light pulse and was inferred to be around 16.0-18.8 km using skywave arrival times. The height determinations were found to be consistent with each other and the possibility of an overshooting cloud top was discussed. The height of blue discharges plays a significant role in understanding their impact on upper tropospheric chemistry.