Geomagnetic conjugate observations of plasma bubbles and thermospheric neutral winds at equatorial latitudes

Plasma bubbles are plasma-density depletion which is developed by the Rayleigh-Taylor instability on the sunset terminator at equatorial latitudes. They usually propagate eastward after the sunset. The eastward propagation of the plasma bubbles is considered to be controlled by background eastward neutral winds in the thermosphere through the F-region dynamo effect. However, it is not clear how the F-region dynamo effect contributes to the propagation of the plasma bubbles, because plasma bubbles and background neutral winds have not been simultaneously observed at geomagnetic conjugate points in the northern and southern hemispheres. In this study, geomagnetic conjugate observations of the plasma bubbles at low latitudes with thermospheric neutral winds were reported. The plasma bubbles were observed at Kototabang (0.2S, 100.3E, geomagnetic latitude (MLAT): 10.0S), Indonesia and at Chiang Mai (18.8N, 98.9E, MLAT: 8.9N), Thailand, which are geomagnetic conjugate stations, on 5 April, 2011 from 13 to 22 UT (from 20 to 05 LT). These plasma bubbles were observed in the 630-nm airglow images taken by using highly-sensitive all-sky airglow imagers at both stations. They propagated eastward with horizontal velocities of about 100-125 m/s. Background thermospheric neutral winds were also observed at both stations by using two Fabry-Perot interferometers (FPIs). The eastward wind velocities were about 70-130 m/s at Kototabang, and about 50-90 m/s at Chiang Mai. We estimated ion drift velocities by using these neutral winds observed by FPIs and conductivities calculated from the IRI and MSIS models. The estimated velocities were about 60-90 % of the drift velocities of plasma bubbles. This result shows that most of the plasma bubble drift can be explained by the F-region dynamo effect, and additional electric field effect may come in to play.