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

Abstract

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: ∼10.9–16.5 km which is constrained by cloud top height in a range of ∼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 ∼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.