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In the post-sunset ionosphere, plasma depleted bubbles with associated irregularity structures of scale sizes varying from centimeters to kilometers are generated due to plasma instability processes which causes the ionospheric irregularities. Ionospheric spread-F was discovered some decades ago. The variation in spread-F occurrence percentages continues to be an active area for scientific investigations at the present time. The spread-F presents a large dependence on the solar flux, the local time, the season, the latitude and longitude and the magnetic disturbances. In this paper, we present simultaneous ionosonde observations carried out at Chongqing (29.51°N, 106.42°E), which is located at the middle latitude in China, to study the characteristics of spread-F occurrence percentages and variations with local time, season and solar activity during 1997 to 2016. The results show that the onset time of spread-F seems to start at around 20 LT and continue till 05 LT at middle latitude. The spread-F occurs during summer most frequently at Chongqing. The spread-F occurrences decrease with the increase of solar and geomagnetic activity at middle latitude. These observations may improve our understanding of the factors responsible for the generation, growth and dynamics of the middle latitude spread-F events.

The ever-increasing space debris circling over geospace can be hard to detect by use of ground-based radar due to its small size and high-order radial motion, which can easily lead to considerable integration loss. In this paper, we propose an efficient method that can achieve good integration performance for moving targets like space debris, of up to second-order dynamics, meaning only velocity and acceleration be taken into account. Overall, range migration can be resolved by limiting the integration number so that all echoes of different pulses are within the same range unit. As for doppler migration problem, we use the combination of Fast Fourier Transform (FFT) and Inverse Fourier Transform (IFFT) to compute and compensate for velocity and acceleration terms, respectively.

The ionospheric plasma temperatures in March and June measured by the Qujing incoherent scatter radar have been used to study the diurnal variation of electron and ion temperatures with altitude (193-513km). It is found that there exist the morning and sunset enhancement and the daytime constant valley in electron temperature in March. The features like morning overshoot, day time valley (about 1000K) and sunset enhancement (with the maximum 3500K) show larger values at higher altitudes. The electron temperature above 1000K decreases with an increase in density. The sunset peak occurs earlier at higher altitudes. These above characteristic isn't prominent for electron temperature in June and ion temperature in all seasons. Both the electron and ion temperature reach a peak at about 200km and then decreases. The possible mechanism is also presented.

Incoherent scatter radar (ISR) detects the Thomson scatter echo of free electrons to inverse ionosphere parameters and is thought as the most powerful instrument to observe the ionosphere on the ground. In fact there are usually severe ground clutters around altitude 100km in the echo data. This paper introduces pulse subtraction to deal with ground clutter by using the Qujing incoherent scatter radar data. The results show that this pulse subtraction suppresses ground clutter well.