Comparison between thermospheric winds measured by a ground-based Fabry-Perot spectrometer at Mawson, Antarctica, and winds determined in-situ from satellite drag

Abstract:

Two of the main techniques currently in use for measuring winds in Earth's middle and upper thermosphere are satellite drag, and optical remote sensing using ground-based Doppler spectrometers viewing thermospheric airglow or auroral emissions. Recent comparisons done by the University College London Fabry-Perot group indicates that, at least in the Northern Hemsphere and for the periods studied, the satellite drag method yielded wind speeds that were 1.5 to 2 times stronger than those measured from optical Doppler shifts. The origin of this discepancy is currently unknown, as indeed are any dependencies that it may have on geophysical drivers such as season, solar or geomagnetic activity, altitude, latitude, etc. Here we will present a similar comparison between optical and satellite data using observations from our all-sky imaging Fabry-Perot spectrometer located at Mawson in Antarctica, to determine whether a similar discrepancy is observed in the southern hemisphere. While the Mawson Fabry-Perot is not identical to those used by the UCL group, there is typically very little uncertainty in the absolute calibration of Doppler shifts measured using Fabry-Perot instruments. This means that ground-based winds measured in the two hemispheres should be directly comparable, and it is likely that the same discrepancy will manifest when comparing the Mawson data to satellite drag winds. If, by contrast, the Mawson data behaves differently to that from the northern hemisphere, it would suggest that some as-yet unidentiifed aspect of the optical remote sensing method can lead to biased wind measurements.