Thermospheric neutral wind velocities measured by a Fabry-Perot interferometer at Shigaraki, Japan. Eastward (b) and northward (c) wind were measured through the Doppler shift of the 630-nm airglow emission at altitudes of 200 to 300 km. The count rate (per pixel) of the interferometer is also shown in (a) to indicate the data quality. Two interference fringes (inner and outer) were used independently to determine these wind velocities. The horizontal arrow indicates the time interval (approximately 1600 to 1900 UT) during which the plasma bubble was observed in the airglow images.