Model studies on chemical effects of sprites in the mesosphere in relation with satellite measurements
Final Report Abstract
Sprites are large scale electrical discharges in the mesosphere above active thunderstorm clouds. It is known that electrical discharges cause chemical effects in the atmosphere, and in recent years several model studies on the chemical processes in sprites have been carried out. However, until recently, there were no observations of the chemical impact of single sprites. New measurement data from the satellite instrument SMILES indicate an increase of HO2 above sprite producing thunderstorms. These are the first direct observations of chemical sprite effects, and provide a unique opportunity to test our understanding of the processes in sprites. The aim of this project was to investigate chemical impact of sprites by means of numerical modeling, and comparisons with the SMILES observations. Almost all previous model studies on this topic used box models (chemistry only, neglecting atmospheric transport). As the SMILES measurements are taken a few hours after the sprite events, and at distances of several kilometers from the sprite locations, it was necessary to perform chemistry-transport simulations to compare with the observations. A one-dimensional (vertical) chemistry and transport model was developed and used to simulate sprites corresponding to the SMILES observations. According to the model results, the main production mechanism of hydrogen radicals after a sprite event involves reactions of positive proton hydrates. The net effect is conversion of water molecules into H + OH. Eventually, this leads to a formation of HO2. Several previously used models do not account for proton hydrates and therefore underestimate the production of hydrogen radicals in sprites. Our model prediction of the total amount of HO2 produced by a sprite is small compared to the observed HO2 enhancements. A possible explanation is an accumulation of HO2 released by several sprites. This is supported by our model simulations which show that the HO2 produced by a sprite is stable for several hours in the night-time mesosphere. Additionally, horizontal transport and dispersion simulations of sprite volumes have been performed for the first time. Also these calculations hint that observed HO2 enhancement are due to more than one sprite each.
Publications
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Model studies on chemical effects of sprites in relation with satellite measurements, DPG-Tagung München, 2019
H. Winkler, J. Notholt, T. Yamada, Y. Kasai
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HO2 enhancements due to sprite discharges - observations and model simulations, Online-Präsentation, EGU-Konferenz, 2020
H. Winkler, T. Yamada, Y. Kasai, J. Notholt
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HO2 generation above sprite-producing thunderstorms derived from lownoise SMILES observation spectra, Geophys. Res. Lett.
T. Yamada, T.O. Sato, T. Adachi, H. Winkler, K. Kuribayashi, R. Larsson, N. Yoshida, Y. Takahashi, M. Sato, A.B. Chen, R.R. Hsu, Y. Nakano, T. Fujinawa, S. Nara, Y. Uchiyama, and Y. Kasai
