Abstract. It is generally assumed that horizontal wind velocities are
independent of height above the F1 region (> 300 km) due to
the large molecular 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 challenging mini-satellite payload (CHAMP) satellite, which was in a near-polar orbit. The University College London (UCL) Kiruna Esrange Optical Platform Site (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 carried out in a
statistical sense, comparing a longer time series obtained during night-time
hours in the winter months (DOY 300–65) with overflights of the CHAMP
satellite between 2001 and 2007 over the observational sites, within ±2∘ latitude (±230 km horizontal range). The FPI is assumed
to measure the line-of-sight winds at a height of ∼240 km, i.e.
the peak emission height of the atomic oxygen 630.0 nm emission. The
cross-track winds are derived from state-of-the-art precision accelerometer
measurements at altitudes between ∼450 km (in 2001) and
∼350 km (in 2007), i.e. 100–200 km above the FPI wind
observations. We show that CHAMP wind values at high latitudes are typically 1.5 to 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.
Investigation of the variability of night-time equatorial thermospheric winds over Nigeria, West Africa
