Using the Digisonde data this paper shows that the small variation in the geomagnetic activity during low solar activity can affect both the parameter of height and the frequency of the intermediate layer (ILs) over the low-latitude Brazilian sector. The most expressive responses of the ILs to geomagnetic activity were observed during the summer when the height of the ILs suffered a significant decrease with the increase of the magnetic activity magnetic in the first hours of the day.

Exospheric Ly-α observations of UVIS/HDAC at CASSINI on its Earth swing-by and TWINS are combined to derive the exospheric H-density profile of the ecliptic dayside between 3–15 R_E. At 10 R_E n_H=35 cm⁻³ is found in the vicinity of the subsolar point for quiet space weather conditions. Also a faster radial fall of the dayside H density above 8 R_E (r⁻³) compared to lower distances of 3–7 R_E (r^−2.37) is found and possibly indicates enhanced loss of H atoms near the magnetopause and beyond.

Despite the solar wind being turbulent in nature, numerical models of its interaction with obstacles have until now assumed it to be laminar. The code \textit{Menura} allows for the global simulation of the interaction between a fully turbulent solar wind and various bodies of the solar system. The code is illustrated by a first example: the interaction between a turbulent solar wind and a comet.

We report that the ionospheric plasma flow patterns associated with the J-shaped transpolar arc (a type of nightside distorted TPA), detected by the SuperDARN radar, reveal the formation process of the nightside distortion of a TPA. Equatorward flows at the TPA growth point were observed flowing out of the polar cap and then turning toward the pre-midnight main auroral oval along the TPA nightside distortion. These ionospheric flow patterns would cause the distortion at the TPA nightside end.

The acceleration, or energisation, of particles is a common and fundamental process throughout the universe. This study presents new observations of the acceleration of protons by waves at the bow shock upstream of the Earth, where the solar wind first encounters Earth’s magnetic field. The results are important, because they provide insight into acceleration processes that can create high-energy particles both near the Earth and at other astrophysical systems.

There is great scientific interest in extending atmospheric models, such as the Met Office’s Unified Model, upwards to include the upper atmosphere. Atmospheric tides are an important driver of circulation at these greater heights. This study provides a first in-depth analysis of the migrating and non-migrating components of these tides, examining important tidal properties. Our results show that the ExUM produces a rich spectrum of spatial components, with significant non-migrating components.

We investigated the possible widening of the tropical belt along with the probable drivers and impacts based on high-accuracy, high-resolution GNSS RO data (2001–2020). The results show that the tropical belt has significant expansion in the Northern Hemisphere, while the Southern Hemisphere has no significant expansion.

The radial diffusion mechanism is of utmost importance to both the acceleration and loss of relativistic electrons in the outer radiation belt and, consequently, for physics-based models, which provide nowcasting and forecasting of the electron population. In the framework of the "SafeSpace" project, we have created a database of calculated radial diffusion coefficients, and, furthermore, we have exploited it to provide insights for future modelling efforts.

We developed a new approach for validation of the numerical models of electromagnetic wave propagation in the Earth–ionosphere waveguide. We compared the parameters of the waveguide (i.e., characteristic electric and magnetic altitudes, resonance frequencies, phase velocity, and attenuation rate) obtained from numerical models with correspondent analytical calculations. We tested such validation for various conductivity profiles and found good agreement between analytical and numerical results.

We investigate the influence of different parameters on the colour of noctilucent clouds (highest clouds in the atmosphere), using radiative transfer calculations. We determined the effect of the particle size, optical depth, single scattering/multiple scattering and ozone. For sufficiently large optical depth and for specific viewing geometries, ozone plays only a minor role in the blueish colour of noctilucent clouds (new result).

Although the 1991 eruption of Mt Pinatubo had a severe impact on Earth's climate, the effect of this event on the mesosphere is not well understood. We investigated satellite-borne temperature measurements from the HALOE instrument and found indications that a positive temperature anomaly is present in the tropical upper mesosphere at the beginning of the HALOE time series, which may be related to the eruption of Mt. Pinatubo.