Low-latitude aurorae (LLA) were an uncommon phenomenon not well known or understood in 1780. During our historical manuscript research of high atmospheric phenomena, we came across a document reporting an observation made by the abbot Rozier in Beausejour, France, on 15/08/1780. Thanks to the accuracy of his report, we were able to confirm it was a white, two-band structure LLA. Due to the few existing geomagnetic and solar observations, this is useful new geomagnetic activity proxy data.

Travelling ionospheric disturbances behave like waves in the ionosphere, the ionised upper part of the atmosphere. In this study, we use an ionospheric tomography technique to map the electron content as affected by the passage of a large-scale travelling ionospheric disturbance launched during the largest geomagnetic storm observed by modern instruments. This is the first such imaging using this software and to the authors' knowledge the first study of this travelling ionospheric disturbance.

The paper reports a new finding on space weather effects at around 70–75 ° geographic latitudes. We found that X flares cause an unexpectedly strong ionospheric current driven by solar flares. The effect is as large as a substorm that is known to cause strong auroras and may enhance ongoing substorms. However, it has been overlooked in the past due to the narrow latitudinal range at high latitudes. Since severe magnetic storms often occur with X flares, this may cause geomagnetic hazards.

We focus on reconstructing the topside ionosphere and plasmasphere and assimilating the space-based Global Navigation Satellite System slant total electron content (STEC) measurements with an ensemble Kalman filter (EnKF). We present methods for realizing the propagation step without a physical model. We investigate the capability of our estimations to reconstruct independent STEC and electron density measurements. We compare the EnKF approach with SMART+ and the 3D ionosphere model NeQuick.

In this study, we present the ionization level from EISCAT radar experiments and cosmic noise absorption level from KAIRA riometer observations during pulsating auroras. We found thick layers of ionization that reach down to 70 km (harder precipitation) and higher cosmic noise absorption during patchy pulsating aurora than during amorphous pulsating and patchy auroras.

This study developed a model of total electron content (TEC) over the African region. The TEC data were derived from radio occultation measurements done by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. Data during geomagnetically quiet time for the years 2008–2011 and 2013–2017 were binned according to local time, seasons, solar flux level, geographic longitude, and dip latitude. Cubic B splines were used to fit the data for the model.

Numerical simulations have been used to investigate some acceleration mechanisms in order to explain the origin of the energized back-streaming ions observed at the Earth's bow shock. This paper used test particles in two different configurations with self-consistent and fixed shock front profiles. The comparison of these two configurations allows us to analyze, in detail, the impact of the shock front nonstationarity and the role of the built-up electric field in the acceleration process.

Predicting geomagnetic activity intensity for an upcoming solar cycle is important in space weather service and for planning future space missions. The maximum aa geomagnetic index for the solar cycle is found to be well correlated with the preceding minimum. The maximum aa index of solar cycle 25 is estimated to be about 29 % stronger than that of solar cycle 24. The maximum amplitude of the sunspot cycle is much better correlated with high geomagnetic activity than low geomagnetic activity.

Solar atmospheric tides are natural oscillations of 24, 12, 8... hours that contribute to the circulation of the atmosphere from low to high altitudes. The Sun heats the atmosphere periodically because, mainly, water vapor and ozone absorb solar radiation between the ground and 50 km height during the day. Tides propagate upward and they can be observed in, for example, the wind field. This work presents diurnal tides observed by meteor radars which measure wind between 80 and 100 km height.

Global-scale wind measurements from the upper regions of the atmosphere are used to isolate those atmospheric waves that follow the apparent motion of the sun over the course of a day. We present 16 years of near-continuous measurements, demonstrating the unique capabilities of the array of high-latitude SuperDARN radars. The validation steps outlined in our work also provide a methodology for future studies using wind measurements from the (expanding) network of SuperDARN radars.

We used multipoint magnetic field, electric field, plasma, and energetic particle observations to study the spatial, temporal, and spectral characteristics of compressional Pc5 pulsations observed deep within the magnetosphere at the end of a strong magnetic storm. We investigated the mode of the waves and their nodal structure. The energetic particles responded directly to the compressional Pc5 pulsations. We interpret the compressional Pc5 waves in terms of drift-mirror instability.

Plasma waves are ubiquitous in the Earth's magnetosphere. They are responsible for many energetic processes happening in Earth's atmosphere, such as auroras. In order to understand these processes, thorough investigations of these waves are needed. We use a state-of-the-art numerical model to do so. Here we investigate the impact of different spatial resolutions in the model on these waves in order to improve in the future the model without wasting computational resources.

The atmospheric impacts of energetic particle precipitation (EPP) can be useful in understanding the uncertainties of measuring the precipitation. Hence, information on how strong of an EPP flux has observable atmospheric impacts is needed. In this study, we find such threshold flux values using odd hydrogen concentrations from both satellite observations and model simulations. We consider the effects of solar proton events and radiation belt electron precipitation in the middle atmosphere.