Range rate variation studies of the low-altitude quasi-periodic radar echoes during seek-2 campaign

The first experimental evidence on range rate reversal of lowaltitude quasi-periodic (LQP) echoes from nighttime midlatitude sporadic E region with systematic characteristics in their occurrences for the echoes observed during SEEK- 2 (Sporadic-E Experiment over Kyushu) campaign with 24.515 MHz frequency agile radar located at Tanegashima in southern Japan (30.75oN, 130.03oE, geomagnetic latitude 20.97oN, dip angle 43.2oN) is presented. Four reversal cases of LQP echoes are found during the observation period. The reversal times of these echoes from positive QP to negative QP are found between 2000 and 2400 hrs LT and negative QP to positive QP around 0200 hrs LT. Besides, Doppler velocities associated with these echoes show preferential directions meaning that they are consistent with the sign of range rate of QP echoes in most cases. As the backscatter echoes studied are confined to the collision dominated lower E region and semidiurnal tide is most pronounced at latitude higher than 300, large-period neutral winds such as tidal and planetary waves in addition to atmospheric gravity waves play a role in the generation and control of these backscatter echoes.