First observation of topside ionization ledges using radio beacon measurements from low Earth orbiting satellites

Ionization ledges in the topside ionosphere have been observed from Trivandrum (8.5 degrees N, 77 degrees E, 0.5 degrees N dip) using single station Total Electron Content (TEC) measurements. These measurements are made using a ground based radio beacon receiver. The receiver measures the relative phase between 150 MHz and 400 MHz beacon transmissions from a Low Earth Orbiting Satellite (LEOS). The ionization ledges, which could be observed, using only topside sounders so far, are seen to have their clear signatures in relative TECs derived using differential Doppler measurements. Simulations were also carried out to understand how the ionospheric topside ledges of various intensities would manifest in the latitudinal profiles of the relative TEC. The magnetometer observations indicate the presence of the Equatorial Counter Electrojet (CEJ) on the days when the ledge is observed. The study demonstrates the potential of radio beacon measurements for observing topside ionization ledges, and phenomena similar to it.