Ionospheric Response to 2013 SSW under High Solar Activity in Middle Latitude Observed by an Ionosonde Chain in China

Abstract:

Sudden stratospheric warming (SSW) in 2013 is a major warming event under moderate-high solar activity. Based on the observations of a meridianal chain of ionosondes covering a latitude range from 30.5°N to 42.8°N in China, we find ionospheric response to 2013 SSW is latitude dependent and comparable to that of low-latitude and equatorial region with f₀F2 enhancement more than 80% and h_mF2 elevation more than 60km. Typical semidiurnal variations are found consistently in all the 8 stations in early and middle January during SSW. However, the expected depressions in afternoon hours are not so impressive and the enhancements after sunset become more frequent and evident, which may be due to the higher F region Pedersen conductivity during high solar activity. Wavelet results show that f₀F2 perturbations during SSW exhibit rich oscillations like tidal components especially semidiurnal tides and planetary waves (< 5 days), especially 3-day periodicities maybe associated to ‘Ultra-fast’ Kelvin waves (UFKW) in lower atmosphere and the average of f₀F2 in 8-18LT displays 16-day planetary wave like oscillations, suggesting interaction of tides and planetary waves . Also, diurnal, semidiurnal and termidiurnal tides in f₀F2 are amplified during the warming in good agreement with earlier studies. Importantly, the amplitudes of semidiurnal tides in f₀F2 exhibit 16-day periodicities, confirming the theory that the modulated semidiurnal tides bring the 16-day planetary wave like oscillations to the F region through electrodynamic effects during the SSW event.