Nighttime enhancements in the VTEC at anomaly crest region Bhopal: Solar and Magnetic activity effects

Abstract Nighttime enhancement in the Vertical Total Electron Content (VTEC) of the ionosphere near equatorial ionization anomaly crest region in the Indian ionospheric sector has been studied during May 2016 to August 2017, a solar minimum period. VTEC data is obtained from a multi-frequency multi-constellation global navigation satellite system (GNSS) receiver installed at Bhopal (23.2° N, 77.4° E & MLAT 14.2° N). Only those enhancements which show VTEC enhancement ≥10% compared to the background has been considered in the study. Out of the total 105 cases of enhancement recorded during this period, 86 events occurred during pre-midnight and 19 during post-midnight hours. Enhancements in VTEC occurred in all seasons; more frequent however during summer than winter and equinox months. Some of the nighttime enhancements in VTEC resulted in the scintillations in the satellite signals as well. Peak amplitude of the enhancement maximizes in summer whereas its half amplitude duration maximizes during equinox month. The number of occurrences of nighttime enhancement in VTEC shows negative correlation with peak amplitude while they are positively correlated with half amplitude duration. We have found that the peak amplitude of nighttime enhancements in VTEC shows strong positive correlation while percentage occurrence shows strong negative correlation with solar and magnetic activities respectively. Other characteristics like half amplitude duration, time of peak and occurrence time of nighttime enhancement in VTEC show positive correlation with solar activity while they are insignificant with magnetic activity. The peak amplitude of pre-midnight enhancements in VTEC is highly correlated with the strength of equatorial electrojet strength. The results are compared with the earlier observations and possible mechanism is also discussed.