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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-57
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-57
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 29 Apr 2019

Regular paper | 29 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Comparing high-latitude thermospheric winds from FPI and CHAMP accelerometer measurements

Anasuya Aruliah1, Matthias Förster2, Rosie Hood1, Ian McWhirter1, and Eelco Doornbosa,b Anasuya Aruliah et al.
  • 1Atmospheric Physics Laboratory, University College London, Gower Street, London, WC1E 6BT, UK
  • 2Helmholtz-Zentrum Potsdam, GFZ German Research Centre for Geosciences,Telegrafenberg, 14473 Potsdam, Germany
  • aformerly at: Faculty of Aerospace Engineering, Delft University of Technology (TU Delft), Kluyverweg 1, 2629 HS Delft, the Netherlands
  • bcurrently at: Royal Netherlands Meteorological Institute (KNMI), Utrechtseweg 297, 3731 GA De Bilt, the Netherlands

Abstract. It is generally assumed that horizontal wind velocities are independent of height above the F1-region (> 300 km) due to the large viscosity of the upper thermosphere. This assumption is used to compare two completely different methods of thermospheric neutral wind observation, using two distinct locations in the high-latitude Northern Hemisphere. The measurements are from ground-based Fabry-Perot Interferometers (FPI), and from in-situ accelerometer measurements onboard the CHAMP satellite, which was in a near polar orbit. The UCL KEOPS FPI is located in the vicinity of the auroral oval at the ESRANGE site near Kiruna, Sweden (67.8° N, 20.4° E). The UCL Longyearbyen FPI is a polar cap site, located at the Kjell Henriksen Observatory on Svalbard (78.1° N, 16.0° E). The comparison is done in a statistical sense, comparing a longer time series obtained during nighttime hours in the winter months (November to January); with overflights of the CHAMP satellite between 2001 and 2007 over the observational sites, within ±2° (±220 km horizontal range). The FPI is assumed to measure the Doppler shift along the line-of-sight of winds at ~ 240 km height, i.e. the peak emission height of the atomic oxygen 630.0 nm emission. The components of winds at right angles to the CHAMP orbit are derived from state-of-the-art precision accelerometer measurements at altitudes. CHAMP was at altitudes between 450 km (in 2001) to 330 km (in 2007); i.e. 100–200 km above the FPI wind observations. We show that CHAMP winds at high latitudes are systematically 1.5–2 times larger than FPI winds. In addition to testing the consistency of the different measurement approaches, the study aims to clarify the effects of viscosity on the height dependence of thermospheric winds.

Anasuya Aruliah et al.
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Short summary
Winds near the top of the atmosphere are expected to be the same at all heights for a given location. This is due to assuming high viscosity in rarefied gases. However, wind measurements from satellite drag at 350–400 km altitude are found to be up to 2 times larger than optical measurements at ~ 240 km. Satellites provide global measurements, and ground-based optical instruments provide long-term monitoring at single sites. So we must understand this inconsistency for correct physics prediction.
Winds near the top of the atmosphere are expected to be the same at all heights for a given...
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