Fig. 1From: Thermospheric wind variations observed by a Fabry–Perot interferometer at Tromsø, Norway, at substorm onsetsField-of-view for Fabry–Perot interferometer (FPI) measurement. The FPI scans the sky in the five directions of north, west, south, east, and zenith. The elevation angle is 45°. We plot the field-of-view of the five directions over the all-sky auroral image, as indicated by the small white circles. The field-of-view in each direction is 5°Back to article page