Global total electron content data derived from the assimilated thermosphere–ionosphere model are analyzed using empirical orthogonal function (EOF) decomposition and the principal component analysis technique. The spectral analysis of the time series of the EOF coefficients reveals how different mechanisms such as solar flux variation, change in the orbital declination, nonlinear mode coupling and geomagnetic activity are separated and expressed in different EOFs.

Meteoroids entering the atmosphere produce trails of ionized particles which can be detected with radar. The weakest ones are called underdense (the most common), the strongest are called overdense, and intermediate ones are transitional. Meteor radar signatures are used to determine atmospheric parameters like temperature and winds. We present new results which show the effect of ozone on the transitional trail lifetimes, which may eventually allow radar to measure mesospheric ozone.

The paper develops a consistent model for the anisotropic Maxwell–Jüttner distribution. This is the velocity distribution in a gas of relativistic particles, where the temperature is not equi-distributed in all degrees of freedom. The physical requirements necessary for modeling this distribution are provided. The known models are examined showing that they do not fulfill these requirements, while a new model is constructed and studied that is consistent with all the required conditions.

We use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE index during various phases of different solar cycles between 1960 and 2014. Results show that, particularly during the solar minimum of 23–24 in 2008, the 27-day period is no longer detectable above the 95 % CI, while auroral geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics.

Magnetic field and motion of charged particles are examined near two parallel current sheets with non-uniformly distributed currents theoretically. Results can be applied to study of Birkeland currents which flow in the ionosphere along magnetic field lines and are connected to auroral phenomena.

Using Cluster data we have noted observations of diffusion-like signatures in the energy range where the the solar wind halo and strahl populations overlap. This includes the development of a proto-halo. At present the source of this diffusion is not known or understood. The prime analysis was carried out through the use of phi–theta plots at individual energy steps. The motivation was to understand if repartitioning in energy was occurring at these locations.

Global climate change affects the whole atmosphere, including the thermosphere and ionosphere. Calculations of long-term trends in the ionosphere are critically dependent on solar activity correction of ionospheric input data. The main result of this study is the finding that the solar activity correction used in calculating ionospheric long-term trends is not stable, as was assumed in all previous investigations of ionospheric trends.

This study examines variation in wave power off the central west coast of India at water depths 30, 9 and 5 m based on buoy measured data. The study shows a significant reduction (~ 10–27 %) in wave power at 9 m depth compared to 30 m and the power at 5 m depth is 20–23 % less than that at 9 m. At 9 m water depth, the mean annual wave power is 6 kW m⁻¹ and interannual variations up to 19.3 % are observed during 2009–2014; 75 % of the total annual wave energy is from this narrow directional sector.

Turbulence is an essential process in the atmosphere and ocean. Clear-air turbulence is a well-known threat for the safety of aviation. Using a powerful MST radar, we detected turbulence and compared it with the results from radiosondes. The correlation between turbulence and background conditions, e.g., Richardson number and wind shears, is determined. There is a nearly negative correlation between turbulence and Richardson number independent of the length scale over which it was calculated.

Radar echoes from mesospheric altitudes (80–90 km) are called polar mesospheric summer echoes (PMSEs). These echoes can be used to derive wind velocities and turbulence strength estimations in a region where measurements are hard to perform. The small-scale structure of PMSEs has not been analysed before but, as we will show, has a major influence on wind and turbulence measurements. We also present a method to improve these measurements by using software beam-steering methods.

A significant number of studies published over the last 15 years demonstrate that there is strong two-way coupling between the magnetosphere and ionosphere during geomagnetic activity; not only does the ionosphere respond to magnetospheric forcing during storms, but through its impact on wave generation, wave-particle interactions, ion outflow and mass loading at the dayside magnetopause and in the magnetotail, dense plasma plumes modulate the subsequent magnetospheric dynamics.