31 Mar 2022
31 Mar 2022
Status: this preprint is currently under review for the journal ANGEO.

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

Carsten Baumann1, Antti Kero2, Shikha Raizada3, Markus Rapp4,5, Michael P. Sulzer3, Pekka T. Verronen2,6, and Juha Vierinen7 Carsten Baumann et al.
  • 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 München, Universität München, Munich, Germany
  • 6Space and Earth Observation Centre, Finnish Meteorological Institute, Helsinki, Finland
  • 7UiT The Arctic University of Norway, Department of Physics and Technology, Tromso, Norway

Abstract. 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 nanometersized dust particles, recondensated 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 (SZA) 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 WACCM-D, a GCM incorporating the SIC ion chemistry. 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.

Carsten Baumann et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2022-12', Anonymous Referee #1, 26 Apr 2022
  • RC2: 'Comment on angeo-2022-12', Anonymous Referee #2, 27 Apr 2022
  • RC3: 'Comment on angeo-2022-12', Anonymous Referee #3, 30 Apr 2022

Carsten Baumann et al.

Carsten Baumann et al.


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Short summary
The Arecibo radar was used to probe free electrons of the ionized atmosphere between 70 and 100 km altitude. This is also the altitude region were meteors evaporate and form secondary particulate matter the so called meteor smoke particles (MSP). Free electrons attach to these MSPs when the sun is below the horizon and cause a drop in the amount of free electrons which subject of these measurements. Furthermore we identified a different amount of free electrons during sunset and sunrise here.