Ionospheric quasi-biennial oscillation of the TEC amplitude of the equatorial ionization anomaly crests from continuous GPS data in the Southeast Asian region

The quasi-biennial oscillation (QBO) signals at two Equatorial ionization anomaly (EIA) crests of the ionosphere have been studied using continuous GNSS network data in Vietnam and adjacent regions during 2008- 2021 period. monthly mean EIA amplitudes are calculated. Lomb-Scargle periodogram method was applied to residuals magnitudes, DTEC, which obtained from subtracting fittings with solar index, F10.7. spectrum shows component DTEC picks 18, 25, 29-30 months. QBO found out by band-pass filter centered 25 months haft-power points 17 33 zonal wind 50 hPa (~ 20 km) tropical equatorial stratosphere is used as (SQBO) consider relationship between SQBO QBO. direct comparison cross wavelet transform series show that 2008-2009, signal low, phase 2010-2013 2018-2021 periods, but anti-phase 2014-2017 For 2010-2013, correlation coefficients 0.623, 0.637, -0.646 northern crest, 0.571, 0.53, -0.530 southern respectively. Furthermore, we also observed were shortened 2015-2016 period, approximately 1.5 years. Previous studies showed ENSO (El Niño - Southern Oscillation) warm phase, known El-Niño existed 2015-2016. results this study allow us assume influences Our main factor affecting ionospheric crests. However, physical theoretical interpretation mechanisms action a challenge for scientists requires further research.