ROTI Keograms based on CMONOC to characterize the ionopsheric irregularities in 2014

Abstract Ionospheric irregularities have been studied since ~70 years ago. With the development of global navigation satellite system (GNSS), GNSS networks have been used to get the characteristics of the irregularities, including the drift velocity, the structure, and the evolution and so on. In this paper, keograms based on the Crustal Movement Observation Network of China (CMONOC) were used to characterize the irregularities over the area from 85 to 125°E in longitude and 11 to 35°N in latitude in 2014. Keograms were obtained for the rate of TEC index (ROTI) in each 0.5 longitude degrees and 30 minutes universal time pixel. The results showed that the occurrence rate of irregularities was high in the equinox months and December, and lowest in June in 2014. In equinox months the irregularities often appeared after sunset. In March the irregularities usually had long lifetime of ~5-7 hours and ~5 degrees apparent longitude scales. The long lifetime usually was accompanied by obvious eastward drift of ~100m/s and large vROTI. In September the irregularities had weaker ROTI and shorter lifetime than those in March. In June, they appeared ~2-3 hours later than those in equinoxes and drifted westward. And the summer irregularities had weakest ROTI and their latitude was ~30°N, much higher than those in equinoxes. In December, the irregularities had small patches with a longitude scale of ~2 degrees and short lifetime of ~2 hours. Different from the equatorial irregularities in equinox months, the solstice irregularities mainly appeared should be local phenomenon.