For the first time, long-term data sets of ground-based observations of noctilucent clouds (NLC) around the globe have been analyzed in order to investigate a response of NLC to solar UV irradiance variability on a day-to-day scale. NLC brightness has been considered versus variations of solar Lyman-alpha flux. We have found that day-to-day solar variability, whose effect is generally masked in the natural NLC variability, has a statistically significant effect when considering large statistics for more than ten years. Average increase in day-to-day solar Lyman-α flux results in average decrease in day-to-day NLC brightness that can be explained by robust physical mechanisms taking place in the summer mesosphere. Average time lags between variations of Lyman-α flux and NLC brightness are short (0–3 days), suggesting a dominant role of direct solar heating and of the dynamical mechanism compared to photodissociation of water vapor by solar Lyman-α flux. All found regularities are consistent between various ground-based NLC data sets collected at different locations around the globe and for various time intervals. Signatures of a 27-day periodicity seem to be present in the NLC brightness for individual summertime intervals; however, this oscillation cannot be unambiguously retrieved due to inevitable periods of tropospheric cloudiness.

Detailed tracing of an exhaust plume from a rocket's initial trajectory is a scientifically and diagnostically useful technique. It can provide detailed information on the atmosphere's mean winds, wind shears, turbulent regime, and physical state over a wide altitude range from 50 to 200km. We analyze Soyuz rocket exhaust plumes from Plesetsk on 21 May 2009 and 27 June 2011, which uncovered significantly different atmospheric states and underlying dynamics. The first case showed highly dynamical conditions in the mesosphere, characterized by vortex structures, wind shears, and small-scale turbulent eddies. The estimated turbulent energy dissipation rates ranged 330-460mWkg(-1). A characteristic balloon-shaped trail was observed at altitudes between 105 and 160km, having rapid expansion rates of 500-800ms(-1) over the time period of 2min which can be explained by complex gas dynamic processes in the rocket wake involving the collision of shock waves. In the second case, we show evidence that the rocket exhaust trail persisted without any changes during its motion from Plesetsk via Denmark to the UK for 9h, indicating extremely stable atmospheric conditions. This case introduces a new state of the summer mesosphereremarkably quiet conditions, probably never observed before. The rocket plumes studied, related to the initial rocket trajectory, are essentially twilight phenomena as seen from the ground using wideband spectrum cameras, that is, the Sun should be below the horizon by 6 degrees. For the first time, we analyze the dynamics of rocket exhaust products at the initial trajectory in the mesosphere and lower thermosphere using detailed photographic imaging taken from the ground.

We report on the first common volume ground‐based and space measurements of the mesospheric front in noctilucent clouds (NLCs). The detailed ground‐based observations were performed with automated digital cameras located at the Athabasca University Geophysical Observatory (Canada) on the night of 29–30 June 2012, while simultaneous space measurements were conducted onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite using the Sounding of the Atmosphere using Broadband Emission Radiometry instrument. The large temperature difference of 20–25 K between two different air masses at about 85 km altitude was responsible for the front jump separating the area filled with NLCs from the area with no NLCs. The front jump (soliton) had a pronounced elevation of 12 km up to the altitude of 96 km relative to the undisturbed NLC layer located between 84.5 and 86.3 km. Considering present and previous ground‐based measurements of the NLC height, we conclude that altitude of 96–97 km is the upper limit of possible heights of NLCs.

A comparison is made between ground-based observations of noctilucent clouds (NLCs), obtained with a network of automated digital cameras, and Aura satellite data (the MLS instrument). The Aura data (water vapor and temperature) demonstrate reasonable values around the summer mesopause fostering NLC formation in June through August, when supersaturated air conditions occur. The temperature decrease leads, in general, to amplification of the NLC brightness. The 2- and 5-day planetary waves, extracted from the Aura temperature field, have definite influence on the brightness variations of NLCs. The temperature behavior around the summer mesopause at 60°N demonstrated a remarkable feature, namely, in 2007 the minimum of a Gaussian fitted seasonal temperature variation was observed, on average, 14 days earlier and was broader than the corresponding minimum in 2008. The different temperature climatology resulted in different seasonal variation of NLCs in 2007 and 2008; in particular, the maximum of a Gaussian fitted seasonal variation of the NLC brightness cycle in 2007 was advanced by 12–29 days relative to that in 2008.