The day‐to‐day longitudinal variability of the global ionospheric density distribution at low latitudes during low solar activity

Abstract

One important characteristic of longitudinal variability of the ionosphere is the global wavenumber‐4 signature. Recent investigations have focused mainly on the climatological pattern during daytime and evening sectors. We investigate the day‐to‐day variability of the wavenumber‐4 structure of the longitudinal ionospheric density distribution using the global total electron content (TEC) measurements from Global Positioning Systems receivers on the ground. The quiet time (Kp ≤ 3) day‐to‐day occurrence of the wavenumber‐4 is obtained during periods of low solar flux conditions for the years 2008 and 2009. We find that the wavenumber‐4 structure occurs at all local time sectors; however, the daytime TEC wavenumber‐4 structures are clearer and can persist until the midnight hours. The most significant occurrence is observed during the 1000–2400 LT sector while the minimum number of wavenumber‐4 structure is observed between the 0400 and 0600 LT sector. Around the nighttime sector, more wavenumber‐4 occurrence is observed during the premidnight sector than the postmidnight hours. The seasonal occurrence probability of the wavenumber‐4 pattern is at a maximum during the March–April equinox and June–July solstice. December–January is the period when the wavenumber‐4 occurrence is less dominant than the rest of the year.