It is well known that occasional eruptions of very high energy protons from the Sun directly impact the middle atmosphere in the polar regions. This paper shows that much more frequent high-speed streams in the plasma wind from the Sun can also modify the same parts of the atmosphere. Their effects are made "visible" by strong enhancement of radar echoes in polar winter and were found to affect half of the days when observations were made at Troll, Antarctica, in 2012 and 2013.

In this paper we analyze 21 conjunctions between the Cluster and CHAMP satellites while they were passing magnetic cusp during relatively quiet solar activity. Only three of the conjunctions reveal field-aligned currents on both satellites as well as neutral density enhancement in the thermosphere. Poynting and electron energy fluxes (EEF) as well as Joule heating were computed and the conclusion is that for these weak events EEF has the strongest contribution to the observed density increase.

Rapid fluctuations in amplitude and phase of radio waves passing through the ionosphere degrade GPS positional accuracy and can lead to navigational errors, particularly during geomagnetic storms. As a function of magnetic latitude and local time, regions of GPS phase scintillation at high latitudes are identified in the context of coupling between the solar wind and the magnetosphere-ionosphere system, which primarily depends on the interplanetary magnetic field magnitude and orientation.

A series of interplanetary coronal mass ejections in the period 7–17 March 2012 caused geomagnetic storms that strongly affected the high-latitude ionosphere in the Northern and Southern Hemisphere. Interhemispheric comparison of GPS phase scintillation reveals commonalities as well as asymmetries, as a consequence of the coupling between the solar wind and magnetosphere. The interhemispheric asymmetries are primarily caused by the dawn-dusk component of the interplanetary magnetic field.

In this paper a Himalayan cloudburst event is investigated. The conditions of formation, evolution, and triggering mechanisms of this cloudburst are studied, looking at varieties of observed data sets and simulation with the Weather Research and Forecasting (WRF) model. This cloudburst event is attributed to two mesoscale convective systems originating from Madhya Pradesh and Tibet which interacted over Uttarkashi, and under orographic uplifting in the presence of favorable moisture conditions.

Solar wind impacts the Earth’s magnetic cavity driving waves in the magnetosphere. The waves in the range of few mHz are important for the dynamics of energetic particles trapped inside the magnetosphere. The average solar wind parameters are known to control of magnetospheric wave power. Here the variability of solar wind parameters, rather than average properties, is analysed. It is shown that the magnetospheric wave power is most sensitive to variations in the interplanetary magnetic field.

In magnetic reconnection in collisionless plasmas, a quadrupole structure of the magnetic field component in the direction of current supporting the reconnecting magnetic field is generated down to electron scales. This paper shows that the magnetic field can develop a "nested structure of quadrupoles" at the electron scales and identifies the nested structure in Cluster observations. Results are useful in interpreting the electron physics in observations, in particular by the NASA/MMS mission.

The first in-flight results from a new design of miniaturised magnetometer (MAGIC - MAGnetometer from Imperial College), aboard the first CINEMA (Cubesat for Ions, Neutrals, Electrons and MAgnetic fields) spacecraft in low Earth orbit, are presented. Not only can this sensor be used for determining attitude, but it is also able to detect the extremely small (20-40 nT) magnetic field signatures of field-aligned currents at the auroral oval. Thus, there are science capabilities with such sensors.

Noctilucent clouds were observed by two radars at different wavelengths. Artificial electron heating was applied. As predicted by modelling, there is a general difference between the observations by the two radars. However, for some heater cycles we observed an exceptionally strong, rapid and similar increase in backscatter for both radars when the heater was on. Models predict a considerable difference in reaction. Our observation indicate that the charging models may not be complete.

We explore two new modifications of the magnetotail magnetic flux calculation algorithm based on the pressure balance approach for the tail radius determination. The new modifications extend the scope of the algorithm to the inner magnetosphere, which is possible due to the approximate uniformity of the magnetic field of external sources. A new empirical formula for the tail radius at the terminator is also presented.

The composite analysis of major sudden stratospheric warmings (SSW) showed changes in atmospheric parameters at mid-latitudes about 1-2 months before the central date of the SSW. Polar ozone is enhanced during the half year after the SSW event.