This study concerns postmidnight ionospheric irregularities observed during low solar activity conditions. We analyze data from digisondes and optical imaging systems located in an equatorial region over Brazil. The results show that they occur under unfavorable and unexpected conditions. This work can be useful for space weather forecasting during low solar activity.

The present study examines the role of tropical cyclones in the enhancement of tropospheric ozone. The most significant and new observation reported is the increase in the upper-tropospheric ozone by 20–50 ppbv, which has extended down to the middle and lower troposphere. The descent rate of enhanced ozone layer during the passage of tropical cyclone is 0.8–1 km day⁻¹. Enhancement of surface ozone concentration by ~ 10 ppbv in the daytime and 10–15 ppbv at night-time is observed.

We present the longest (1998 to 2013) cirrus cloud climatology over a tropical station using a ground-based lidar. A statistically significant increase is found in the altitude of sub-visible cirrus clouds. Also a systematic shift from thin to sub-visible cirrus cloud type is observed. Ground-based lidar is found to detect more number of sub-visible cirrus clouds than space-based lidar. These findings have implications to global warming and stratosphere-troposphere water vapour exchange studies.