Abstract: Ghosts are a newly discovered category of transient luminescence events (TLEs) occurring in the middle and upper atmospheres above energetic thunderstorms. Due to the high requirements of optical shooting, the observation data that can be investigated are very scarce and are all obtained from the ground-based observations at single station. Based on the ground-based observation of seven ghost events with original optical data, in this paper we present a methodology to estimate the altitude of ghosts from single-station observation in conjunction with star-field background, and determine the altitude range of five ghosts (two of which are at the same place and time) to be 90 to 100 km. So far, ghost events are known to be accompanied by two different types of TLEs, namely "red sprite" or "gigantic jet". The accompanying relationship between ghost events and these two TLEs phenomena shows that the occurrence of ghost events may be closely related to the altitude and the strong electric field and energy release during the thunderstorm. This paper further examined the atmospheric background conditions (i.e., neutral particle density, ion concentration and electron density, etc.) upon the observations of the aforementioned seven ghost events. The density profile of neutral particles (O, N₂, O₂), ion (O₂⁺ and NO⁺) and electron density were obtained by means of the MSIS-E-90 model and the IRI model. It was found that the mutation of N₂, O₂ and electron density played a key role in the occurrence of ghosts. These mutations of density may provide necessary medium conditions for the occurrence of ghosts. In this paper, by calculating the diffusivity of ghosts, it is found that the diffusivity of ghost is much lower than that of streamer discharge, which confirms that ghost emission is a form of glow discharge. Finally, the characteristics of the parent thunderstorms of ghosts are analyzed, and it is found that ghosts occur in the phase of weakening convective activity, which implies that the formation of ghost might require the existence of lightning flashes with relatively high energy release. In the weakening stage of thunderstorm activity, although the convective activity decreases, the electric field of the thunderstorm cloud top may still be strong, thus providing the necessary energy conditions for the occurrence of ghost events.