Two-windows Ionospheric Drift Measurement at Heights 90-150 km During Sporadic E-layer Occurrence Using Digisonde DPS-4

Our contribution is focused on the ionospheric plasma motion in the height range 90 km - 150 km (corresponding to the E-region ionosphere). Study involves observations from midlatitude ionospheric station Pruhonice (50N, 14.6E) using DPS4 equipment during period of low solar activity (2006-2007). Raw data are manually checked and controlled using skymap points selection method (Kouba et al., 2008) consisting of robust reflection height range selection, setting limits on the Doppler frequency shift, and restriction of the echo arrival angle. During summer periods of 2006 and 2007 we performed special campaigns of 'Es drift' measurement. Together with a standard E measurement (2-2.6 MHz) we recorded plasma motion each 15 minutes also in a higher frequency window (3.2-4.7 MHz). Our results show different behavior of plasma motion in the 'E' and 'Es' layers. This fact confirms height dependence of drift velocity in the interval 90-150 km and calls for careful interpretation of the E-drift during presence of Es layer.