Seasonal Variability of the Midlatitude Traveling Ionospheric Disturbances From Wallops Island, VA, Dynasonde Data: Evidence of a Semiannual Variation

Abstract

We investigate the ionospheric variability due to traveling ionospheric disturbances (TIDs) over Wallops Island, VA, using Dynasonde-derived measurements of ionospheric tilts and vertical Doppler speed between May 2013 and August 2016, covering the bottomside ionospheric F layer. The mean power spectral density is determined separately for each month for both ionospheric tilts and for the Doppler speed, with a 2 km resolution in a broad altitude range. This is accomplished using a spectral analysis technique based on the Lomb-Scargle and Welch methods, with an added filtering criterion. The analysis is performed separately for the daytime and nighttime data. By investigating the seasonal variability of the power spectral density integral, a semiannual variation is highlighted in the overall level of daytime TID activity, with increased activity during summer and winter seasons in the northern hemisphere. This result provides a more complete picture than other recent publications that only highlighted a winter peak in the same geographical sector. Finally, the relative amplitude of the two peaks in TID activity is shown to vary significantly during the three years investigated and also as a function of the altitude.