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On the importance of middle-atmosphere observations on ionospheric dynamics using WACCM-X and SAMI3

This study shows how middle-atmospheric data (starting at 40 km) affect day-to-day ionospheric variability. We do this by using lower atmospheric measurements that include and exclude the middle atmosphere in a coupled ionosphere–thermosphere model. Comparing the two simulations reveals differences in two thermosphere–ionosphere coupling mechanisms. Additionally, comparison against observations showed that including the middle-atmospheric data improved the resulting ionosphere.

Does high-latitude ionospheric electrodynamics exhibit hemispheric mirror symmetry?

In studies of the Earth’s ionosphere, a hot topic is how to estimate ionospheric conductivity. This is hard to do for a variety of reasons that mostly amount to a lack of measurements. In this study we use satellite measurements to estimate electromagnetic work and ionospheric conductances in both hemispheres. We identify where our model estimates are inconsistent with laws of physics, which partially solves a previous problem with unrealistic predictions of ionospheric conductances.

Analysis of in situ measurements of electron, ion and neutral temperatures in the lower thermosphere–ionosphere

The relation between electron, ion and neutral temperatures in the lower thermosphere–ionosphere (LTI) is key to understanding the energy balance and transfer between species. However, their simultaneous measurement is rare in the LTI. Based on data from the AE-C, AE-D, AE-E and DE-2 satellites of the 1970s and 1980s, a large number of events where neutrals are hotter than ions are identified and statistically analysed. Potential mechanisms that could trigger these events are proposed.

Solar wind magnetic holes can cross the bow shock and enter the magnetosheath

Magnetic holes are curious localized dropouts of magnetic field strength in the solar wind (the flow of ionized gas continuously streaming out from the sun). In this paper we show that these magnetic holes can cross the bow shock (where the solar wind brake down to subsonic velocity) and enter the region close to Earth’s magnetosphere. These structures may therefore represent a new type of non-uniform solar wind–magnetosphere interaction.

The Lehtinen–Pirjola method modified for efficient modelling of geomagnetically induced currents in multiple voltage levels of a power network

The Lehtinen-Pirjola (LP) method is widely used for modelling geomagnetically induced currents (GIC) in power systems but was developed when the main aim was to model GIC in only the highest voltage level of a power network. Here we present a modification to the LP method designed to provide an efficient method for modelling GIC in multiple voltage levels. We also show how existing software can easily be converted to the new method and provide examples of calculations.

Magnetospheric response to solar wind forcing: ultra-low-frequency wave–particle interaction perspective

Magnetospheric physics is in an extremely vibrant phase, with a number of ongoing and highly successful missions, e.g., Cluster, THEMIS, Van Allen Probes, and the MMS spacecraft, providing the most amazing observations and data sets. Since there are many fundamental and unsolved problems, in this paper I have addressed selected topics of ULF wave-charged particle interactions which encompass many special fields of radiation belt, ring current and plasmaspheric physics.

Dynamics of variable dusk–dawn flow associated with magnetotail current sheet flapping

The sun’s magnetic field is carried across space by the solar wind – a hot plasma “stream” of ions and electrons – forming the interplanetary magnetic field (IMF). The IMF can introduce asymmetries in the Earth’s magnetic field, giving plasma flowing within it a direction dependent on IMF orientation. Electric currents in near-Earth space can also influence these plasma flows. We investigate these two competing mechanisms and find that the currents can prevent the IMF from controlling the flow.

Steepening of magnetosonic waves in the inner coma of comet 67P/Churyumov–Gerasimenko

Plasma waves are an integral part of cometary physics, as they facilitate the transfer of energy and momentum. From intermediate to strong activity, nonlinear asymmetric plasma and magnetic field enhancements dominate the inner coma of 67P/CG. We present a statistical survey of these structures from December 2014 to June 2016, facilitated by Rosetta’s unprecedented long mission duration. Using a 1D MHD model, we show they can be described as a combination of nonlinear and dissipative effects.

Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard

This study analyses the observations of a new type of small-scale aurora-like feature, which is further referred to as fragmented aurora-like emission(s) (FAEs). One possible explanation for this is Farley–Buneman instabilities of strong local currents. In the present study, we provide an overview of the observations and discuss their characteristics and potential generation mechanisms.

Lower-thermosphere response to solar activity: an empirical-mode-decomposition analysis of GOCE 2009–2012 data

Forecasting the thermosphere (atmosphere’s uppermost layer from 90 to 800 km altitude) is crucial to space mission design, spacecraft operations and space surveillance. The thermosphere is controlled by the Sun through variable solar extreme-ultraviolet radiation and the solar wind. We show how the solar indices Mg II and Ap may be used in forecasting thermospheric density at 260 km, a very low altitude, where the GOCE satellite operated from 2009 to 2013, during the full rise of solar cycle 24.

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