Midlatitude ionospheric responses to the 2013 SSW under high solar activity

Ionospheric responses to sudden stratospheric warming (SSW) are not well understood, particularly in the midlatitudes and under high solar conditions. During the 2013 SSW, ionospheric disturbances were observed in eight locations on the meridional chain from 30.5 degrees N to 42.8 degrees N in northern China. The midlatitude ionosphere responded strongly to the SSW despite being under high solar flux. The F-2 layer maximum electric density increased by more than 80%, and the peak height was elevated more than 60km. Well-set and organized semidiurnal variations were recorded in early and middle January during the SSW in eight observation locations. The expected f(o)F(2) decrease in the afternoon hours was not clearly discernible; however, nighttime enhancements occurred frequently. The time-period spectra of the average f(o)F(2) and zonal winds and meridional winds at altitudes of 86-95km presented quasi-16day planetary wave-like oscillations during the warming event. The coupling between the atmosphere and ionosphere may be strengthened by the quasi-16day waves. The amplified diurnal, semidiurnal, and terdiurnal tides in f(o)F(2) were also recorded during the warming, in good agreement with earlier observations. Importantly, the variations in the semidiurnal tides included a 16day periodic component, indicating that the modulated semidiurnal tides may transmit these 16day planetary wave-like oscillations to the F region through wind dynamo. Although the PW-tide interaction theory is not novel, it is of significance in the midlatitude ionospheric response to SSW.