This paper brings analysis of spread-F echoes along the years of 2003 to 2012 from Christmas Island radar. We organize our data with the objective of observing the peak time and altitude distribution. Our results indicate the peak time occurrence of echoes to be distributed closer to local sunset during solar maximum and around midnight during solar minimum; meanwhile, the peak altitude echoes show higher altitude occurrences during solar maxima and lower altitudes during solar minima.

Sub-auroral polarisation streams (SAPSs) are very fast plasma flows that occur at mid-latitudes, which can affect the atmosphere. In this paper, we use four ground-based radars to obtain a wide coverage of SAPSs that occurred over the USA, along with interferometer cameras in Virginia and Massachusetts to measure winds. The winds are strongly affected but in different ways, implying that the balance forces on the atmosphere is strongly dependent on proximity to the disturbance.

The solar eclipse of 5–6 January 2019 perturbed the ionospheric electron density, N, observed with the receiver at the Harbin Engineering University and 14 HF broadcasting stations ~1 000 km around. It was accompanied by ±1.5 Hz Doppler-spectrum broadening, ±0.5 Hz Doppler shift, f_D, variations, 15 min period variations in f_D caused by 1.6–2.4 % perturbations in N, and period changes of 4–5 min in f_D caused by 0.2–0.3 % disturbances in N. The decrease in N attained ~15 % (vs. modeled 16 %).

We investigate the local time behaviour of auroral structures and emission height. Data are collected from the Fennoscandian Lapland and Svalbard latitutes from 7 identical auroral all-sky cameras over about 1 solar cycle. The typical peak emission height of the green aurora varies from 110 km on the nightside to about 118 km in the morning over Lapland but stays systematically higher over Svalbard. During fast solar wind, nightside emission heights are 5 km lower than during slow solar wind.