Lobachevsky University researchers describe a mysterious phenomenon in the Earth's atmosphere
The way the Earth's ionosphere reacts to powerful radio waves can be understood by examining an exceptionally rare phenomenon recorded by radiophysicists from Lobachevsky University as part of a research team. Their findings have been published in the international journal Sensors.
Scientists distinguish the following consistently existing layers in the Earth's ionosphere based on height above the surface: D (during the daytime, at altitudes from 60 to 90 km), E (90–120 km), and F (above 130 km).
Additionally, at altitudes around 100 km, the so-called sporadic E-layer (Es) — which has a concentration of charged particles 3 to 10 times higher — can suddenly emerge and vanish in the ionosphere. Its thickness varies from hundreds of meters to a kilometer in height, and horizontally, Es can stretch for hundreds of kilometers.
Since the 1970s, physicists have been conducting systematic research on artificial disturbances in the Earth's ionosphere caused by powerful short-wave radio waves (with wavelengths between 30 and 100 meters) using specialised heating facilities.
Currently, there are only three such facilities in operation around the world: EISCAT heating in northern Norway and HAARP in Alaska, both located in polar latitudes, as well as Lobachevsky University’s SURA facility, situated in middle latitudes near the settlement of Vasilsursk in the Nizhny Novgorod region.
One of the observed phenomena is the generation of airglow in visible light at the heights of the F layer, including in red (wavelength 630 nm), green (557.7 nm), and blue (391.4 nm) spectral lines. This phenomenon is sometimes referred to as artificial aurora, although its brightness is significantly lower than that of natural auroras, and special sensitive equipment is required for its study.
During the experiment on August 5, 2024, while conducting regular observations of artificial glow at the SURA facility, which was carried out by radiophysicists from UNN in collaboration with colleagues from the Institute of Solar-Terrestrial Physics of the RASSiberian Branch(Irkutsk) and the Institute of Physics at Kazan Federal University, an exceptionally intense and dense sporadic E-layer was observed at altitudes of about 105–110 km. This layer completely blocked the penetration of powerful radio waves into the heights of the F region.
The concentration of charged particles (electrons) in this sporadic layer was approximately ten times higher than in the surrounding E layer. At that time, an extreme increase in the brightness of the artificial glow in the green line was noted — from about five to fifty times the brightness of the airglow occurring in the F layer, and approximately ten times the brightness of the glow in the Es layer observed in previous experiments.
At the same time, a significant increase in the brightness of the airglow (approximately by a factor of two) was observed in the blue spectral line. According to one of the authors of the study, Professor Savely Grach from the Department of Radio Wave Propagation and Radio Astronomy at the UNN Radiophysics Faculty, such brightness of artificial optical luminescence was recorded in exposure experiments for the first time.
The scientist noted that the goal of the experiment was to study the patterns of occurrence of artificial optical luminescence of the ionosphere under the influence of radio waves. The appearance of energetic electrons that cause luminescence at altitudes of 250–300 km during collisions with atoms and ions of the Earth's atmosphere is well explained as a result of their acceleration by plasma waves generated under the influence of radio waves. However, the cause of the extremely intense airglow in the Es layer is currently unclear to researchers.
The emergence of such powerful Es layers is a unique phenomenon that, apparently, occurs only during periods close to the peak of solar activity," professor Grach said.
He noted that the data obtained help to gain a deeper understanding of the processes taking place in the upper atmosphere and lower ionosphere during high solar activity. The research broadens the knowledge of the mechanisms of radio wave interaction with ionospheric plasma and the formation of artificial optical phenomena in near-Earth space.
The findings from this study provide a basis for developing new methods to diagnose the ionosphere and investigate its dynamic processes under the impact of both natural and human-made factors.
Moving forward, scientists intend to conduct further experimental and theoretical research into the observed abnormal rise in optical luminescence caused by radio waves in the presence of a blocking Es layer. They believe this will enhance our understanding of the physical processes occurring in Earth's atmosphere due to solar radiation.
