University of Oulu

Baumann, C., Kero, A., Raizada, S., Rapp, M., Sulzer, M. P., Verronen, P. T., and Vierinen, J.: Arecibo measurements of D-region electron densities during sunset and sunrise: implications for atmospheric composition, Ann. Geophys., 40, 519–530,, 2022

Arecibo measurements of D-region electron densities during sunset and sunrise : implications for atmospheric composition

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Author: Baumann, Carsten1; Kero, Antti2; Raizada, Shikha3;
Organizations: 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Solar Terrestrische Physik, Neustrelitz, Germany
2Sodankylä Geophysical Observatory, Oulu University, Sodankylä, Finland
3National Astronomy and Ionosphere Center, Arecibo Observatory, Arecibo, Puerto Rico
4Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Wessling, Germany
5Meteorologisches Institut, Ludwig-Maximilians Universität, Munich, Germany
6Space and Earth Observation Centre, Finnish Meteorological Institute, Helsinki, Finland
7Department of Physics and Technology, UiT The Arctic University of Norway, Tromsø, Norway
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 8.5 MB)
Persistent link:
Language: English
Published: Copernicus Publications, 2022
Publish Date: 2023-06-02


Earth's lower ionosphere is the region where terrestrial weather and space weather come together. Here, between 60 and 100 km altitude, solar radiation governs the diurnal cycle of the ionized species. This altitude range is also the place where nanometre-sized dust particles, recondensed from ablated meteoric material, exist and interact with free electrons and ions of the ionosphere. This study reports electron density measurements from the Arecibo incoherent-scatter radar being performed during sunset and sunrise conditions. An asymmetry of the electron density is observed, with higher electron density during sunset than during sunrise. This asymmetry extends from solar zenith angles (SZAs) of 80 to 100. This D-region asymmetry can be observed between 95 and 75 km altitude. The electron density observations are compared to the one-dimensional Sodankylä Ion and Neutral Chemistry (SIC) model and a variant of the Whole Atmosphere Community Climate Model incorporating a subset SIC's ion chemistry (WACCM-D). Both models also show a D-region sunrise–sunset asymmetry. However, WACCM-D compares slightly better to the observations than SIC, especially during sunset, when the electron density gradually fades away. An investigation of the electron density continuity equation reveals a higher electron–ion recombination rate than the fading ionization rate during sunset. The recombination reactions are not fast enough to closely match the fading ionization rate during sunset, resulting in excess electron density. At lower altitudes electron attachment to neutrals and their detachment from negative ions play a significant role in the asymmetry as well. A comparison of a specific SIC version incorporating meteoric smoke particles (MSPs) to the observations revealed no sudden changes in electron density as predicted by the model. However, the expected electron density jump (drop) during sunrise (sunset) occurs at 100 SZA when the radar signal is close to the noise floor, making a clear falsification of MSPs' influence on the D region impossible.

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Series: Annales geophysicae
ISSN: 0992-7689
ISSN-E: 1432-0576
ISSN-L: 0992-7689
Volume: 40
Issue: 4
Pages: 519 - 530
DOI: 10.5194/angeo-40-519-2022
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The work of Antti Kero is funded by the Tenure Track Project in Radio Science at Sodankylä Geophysical Observatory, University of Oulu. The work of Pekka T. Verronen is supported by the Academy of Finland grant no. 335555 (ICT-SUNVAC). The radar observation itself was funded at the time by National Astronomy and Ionosphere Center (NAIC), National Science Foundation (NSF), and SRI International based on proposal T3087. The article processing charges for this open-access publication were covered by the German Aerospace Center (DLR).
Dataset Reference: The raw radar data (power profiles and plasma line measurements), processed data, and plotting routines for Figs. 3 and 4 have been made available on Zenodo (, Baumann et al., 2022).
Copyright information: © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License.