We study nighttime medium-scale travelling ionospheric disturbances (MSTIDs) observed at Kototabang (0.2S, 100.3E, geomagnetic latitude : 10.6S), Indonesia during 7 years from 26 October 2002 to 25 October 2009. The MSTIDs were observed in 630-nm night airglow images which were taken with exposure times of 105-165 s and time resolutions of 4.5-5.5 min by using a highly-sensitive all-sky airglow imager. The average and standard deviation of the horizontal phase velocity and period of the MSTIDs were 316.7, 166.0 m/s and 42.1, 10.5 min, respectively. The previous study suggested that acoustic gravity waves in the thermosphere caused the observed MSTIDs, because the observed MSTIDs mostly had east-west phase fronts. In this observation during 7 years from solar maximum to minimum, the airglow emission became weaker and the observation rate of MSTIDs decreased year by year. This fact may suggest that the gravity waves are difficult to propagate when the solar activity is weaker because neutral viscosity in the thermosphere increases for decreasing solar activities. However the decrease of the signal-to-noise ratio and the decline of the imager sensitivity may also affect this positive correlation. We also found positive correlation between the propagation directions of the observed MSTIDs and the location of tropospheric convection activity identified by hourly maps of equivalent black body temperature (TBB). The propagation directions of MSTIDs were usually southward or southwestward and they were most frequently observed between May and July when intertropical convergence zone (ITCZ) locates north of Kototabang. These facts suggest that acoustic gravity waves generated in the troposphere are one of the source of observed MSTIDs.