Analysis of Blue Corona Discharges at the Top of Tropical Thunderstorm Clouds in Different Phases of Convection

Polarity transitions of narrow bipolar events in thundercloud tops reaching the lower stratosphere

Blue corona discharges are often generated in thunderclouds penetrating into the stratosphere and are the optical manifestation of narrow bipolar events (NBEs) observed in radio signals. While their production appears to depend on convection, the cause and nature of such discharges are not well known. Here we show the observations by a lightning detection array of unusual amounts of 982 NBEs during a tropical storm on the coastline of China. NBEs of negative polarity are predominantly observed at the cloud top reaching the stratosphere, and positive NBEs are primarily at lower altitudes. We find that the dominant polarity changes with the typical time of development of thunderstorm cells, suggesting that the polarity depends on the phase of the storm cells. Furthermore, we find that the lightning jump of negative NBEs is associated with above-anvil cirrus plumes of ice crystals and water vapor in the lower stratosphere. We propose that variations in updrafts induce changes in the altitude and charge concentrations of the cloud layers, which lead to the polarity transition. Our results have implications for studies of the chemical perturbations of greenhouse gas concentrations by corona discharges at the tropopause.

Optical observations of thunderstorms from the International Space Station: recent results and perspectives

The International Space Station (ISS) is in the lowest available orbit at ~400 km altitude, bringing instruments as close to the atmosphere as possible from the vantage point of space. The orbit inclination is 51.6°, which brings the ISS over all the low- and mid-latitude regions of the Earth and at all local times. It is an ideal platform to observe deep convection and electrification of thunderstorms, taken advantage of by the Lightning Imaging Sensor (LIS) and the Atmosphere Space Interaction Monitor (ASIM) experiments. In the coming years, meteorological satellites in geostationary orbit (~36,000 km altitude) will provide sophisticated cloud and lightning observations with almost complete coverage of the Earth's thunderstorm regions. In addition, Earth-observing satellite instruments in geostationary- and low-Earth orbit (LEO) will measure more atmospheric parameters at a higher resolution than we know today. The new infrastructure in space offers an opportunity to advance our understanding of the role of thunderstorms in atmospheric dynamics and climate change. Here, we discuss how observations from the ISS or other LEO platforms with instruments that view the atmosphere at slanted angles can complement the measurements from primarily nadir-oriented instruments of present and planned missions. We suggest that the slanted viewing geometry from LEO may resolve the altitude of electrical activity and the cloud structure where they occur, with implications for modelling thunderstorms' effects on the atmosphere's radiative properties and climate balance.