# Airglow Observation and Statistical Analysis of Plasma Bubbles over China
###### Abstract  
Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products of equatorial plasma bubbles (EPBs) were obtained. Based on the optical data of the airglow imager in Hainan, we investigated the main optical features of EPBs, and statistically analyzed the occurrence of EPBs from September 2014 to August 2015. The observation results show that EPB exhibits plume-shaped structures, usually tilting westward, and EPB extends to a long distance along the geomagnetic field lines. It is found that the west wall of EPB is relatively stable, while there are some bifurcations on the east wall of EPB, and the bifurcation of EPB becomes more pronounced with time. Moreover, the spatial scale of EPB gradually increases with time, which is about several hundred kilometers, and the drift velocity of EPB is in the range of 40-130 m/s (\(+/-20\) m/s). The statistical results show that EPBs mainly occur in the months of September to November and February to April, with a higher occurrence rate. In terms of seasonal occurrence, EPBs tend to appear more frequently in spring and autumn, and the occurrence rate of EPBs is relatively low in winter and summer. plasma bubbles; image processing method; optical features; statistical analysis +
Footnote †: journal:  
simultaneously observed by two all-sky imagers, located at the geomagnetic conjugate points of two hemispheres. [PERSON] et al. [11] statistically analyzed the seasonal variation of equatorial plasma bubbles by using airglow data and GPS scintillation data for two years. Based on ground-based airglow images and satellite data, [PERSON] et al. [12] revealed the zonal drift velocities of plasma bubbles and plasma blobs in low latitudes. Using the data obtained from the airglow imager from 2011 to 2015 in India, [PERSON] et al. [13] reported the evolution and dynamics of ionospheric plasma bubbles at low latitudes, including the bifurcation, merging, and detachment of plasma bubbles. In terms of the optical observation of plasma bubbles, some research work has been carried out recently in China. By using the airglow data in China, [PERSON] et al. [14] investigated the main optical features of plasma bubbles, such as morphology and drift, and obtained the optical observation results of plasma bubbles for the first time in Hainan, China. Based on several all-sky airglow imagers in China, [PERSON] et al. [15] revealed the irregular structure characteristics and statistical characteristics of plasma bubbles. The all-sky airglow imager [16; 17] can observe the airglow depletions caused by plasma bubbles in the equatorial regions [18]. The advantage of the airglow imager [19; 20] is that it can display the two-dimensional horizontal structures of plasma bubbles on a large scale. In this study, we utilized the optical data of the all-sky airglow imager at Fuke station in Hainan (19.5\({}^{\circ}\) N, 109.2\({}^{\circ}\) E), which is part of the Meridian project in China. Moreover, the geomagnetic latitude of Fuke is 9.9\({}^{\circ}\) N; thus, Fuke is a station located near the northern crest of the Equatorial Ionospheric Anomaly (EIA). The airglow imager has a large field of view and can observe the airglow emission with a large range of 180 degrees. Moreover, digital airglow images can be obtained using the imager, and the resolution of the airglow image is 1024 \(\times\) 1024 pixels. The all-sky airglow imager in Fuke usually works at night for observation. The observation time is generally 18:00 LT-6:00 LT at Fuke station, and the observation duration is nearly 12 h in each day. In this study, we employed the optical data in Hainan during the period from September 2014 to August 2015.