Temperatures at 85 km around Earth's poles in summer can be so cold that small ice particles form. These can become charged, and, combined with turbulence at these altitudes, they can influence the many electrons present. This can cause large radar echoes called polar mesospheric summer echoes. We use radio waves to heat these echoes on and off when the sun is close to or below the horizon. This allows us to gain some insight into these ice particles and how the sun influences the echoes.

Collisional fragmentation of asteroids, comets and meteoroids is the main source of dust in the solar system. The dust distribution is however uncharted and the role of dust in the solar system is largely unknown. At present, the interplanetary medium is explored by the Solar Orbiter spacecraft. We present a novel method, based on artificial intelligence, that can be used for detecting dust impacts in Solar Orbiter observations with high accuracy, advancing the study of dust in the solar system.

We have investigated the nucleation process of noctilucent clouds observed in the mesosphere using a theoretical approach, where we adopt a more accurate model called the semi-phenomenological model for the nucleation process. We obtained an important result that rejects one of the two dominant nucleation mechanisms that have been proposed. Our results show it is extremely difficult for homogeneous nucleation of water to occur in the mesosphere, while heterogeneous nucleation occurs effectively.

Our model calculations indicate that meteoric smoke particles (MSPs) influence both the magnitude and shape of the electron temperature during artificial heating. Others have found that current theoretical models most likely overestimate heating in the D-region compared to observations. In a future study, we will compare our results to observations of the electron temperature during heating to investigate if the presence of MSPs can explain the discrepancy between model and observations.

This paper discusses the charge generation for impacts of nano- to micro-scale dust on metal surfaces at speeds below a few kilometres per second. By introducing a model of capacitive coupling between the dust and the impact surface, we find that at such low speeds, the charge can be dominated by contact charging as opposed to plasma generation.

Agglomeration of ice and dust particles in the mesosphere are studied, using classical electrostatic approaches which are extended to capture the induced polarisation of surface charge. The instances of strong attraction between particles of the same sign of charge are predicted, which take place at small separation distances and also lead to the formation of stable aggregates.

In the past, additional sodium peaks occurring above the main sodium layer of the upper mesosphere were discussed. Here, formation of an additional sodium peak below the main sodium layer peak is discussed in detail. The event coincided with passage of multiple mesospheric bores, which are step-like disturbances occurring in the upper mesosphere. Hence, this work highlights the importance of such mesospheric bores in causing significant changes to the minor species concentration in a short time.

Dust grains exist throughout our solar system. This dust is subject to destruction processes like sublimation and sputtering. Sputtering is the erosion of dust through the impact solar wind and can be very effective near the Sun. We performed calculations to find out how important the sputtering process is compared to the sublimation of dust. Recently launched spacecraft will probe the proximity of the Sun and measure the dust population. Our work will help to understand these measurements.

We discuss the design of a rocket instrument to collect mesospheric dust consisting of ice with embedded non-volatile meteoric smoke particles. The instrument consists of a collection device and an attached conic funnel. We consider the dust trajectories in the airflow and fragmentation at the funnel. For summer atmospheric conditions at 85 km and assuming that the ice components vaporize we estimate that up to 10¹⁴ to 10¹⁵ amu of non-volatile dust material can be collected.

This work presents a review of dust measurements from spacecraft Cassini, STEREO, MMS, Cluster, Maven and WIND. We also consider the details of dust impacts and charge generation, and how different antenna signals can be generated. We compare observational data to laboratory experiments and simulations and discuss the consequences for dust observation with the new NASA Parker Solar Probe and ESA Solar Orbiter spacecraft.

In a simulation study of the downward current region of the aurora, i.e. where electrons are accelerated upward, double layers are seen to form at low altitude and move upward until they are disrupted at altitudes of ten thousand kilometres or thereabouts. When one double layer is disrupted a new one forms below, and the process repeats itself. The repeated demise and reformation allows ions to flow upward without passing through the double layers that otherwise would have kept them down.

In this paper, we simulate the plasma on a magnetic field line above the aurora. Initially, about half of the acceleration voltage is concentrated in a thin double layer at a few thousand km altitude. When the voltage is lowered, electrons trapped between the double layer and the magnetic mirror are released. In the process we see formation of electron beams and phase space holes. A temporary reversal of the polarity of the double layer is also seen as well as hysteresis effects in its position.