The magnetosphere of Mercury is highly dynamic, a consequence of its small size, weak intrinsic magnetic field, and proximity to the Sun. One intriguing phenomenon is the presence of magnetic field fluctuations around 1 Hz. Here, we present a comprehensive statistical survey of these waves using the full span of the MESSENGER magnetometer measurements from 2011 to 2015. We find that ~1 Hz waves are observed during 10-20 % of the time that the spacecraft spent on closed field lines in Mercury’s magnetosphere, as determined from the KT17 magnetic field model. Wave occurrence is increased under magnetospheric conditions that favour an expanded closed field line region. We present the first global characterisation of the ~1 Hz waves at Mercury and demonstrate their dependence on both external drivers, such as upstream IMF conditions, and internal magnetospheric activity, such as the occurrence of identified dipolarization events. These results are discussed in the context of the BepiColombo mission, which will provide new opportunities to identify the nature of these waves and to assess their role in Mercury’s highly dynamic plasma environment.

Despite heat flux's role in regulating energy conversion in collisionless plasmas, its properties and evolution in the magnetosheath downstream of the Earth's bow shock are scarcely explored. We use Magnetospheric Multiscale in situ measurements to quantify and characterize the electron heat flux in the magnetosheath. We find that the heat flux is shaped by the magnetosheath magnetic field as it drapes around the magnetosphere. While it is affected by solar wind upstream conditions and increases with magnetic field strength, it is not substantially changed by local magnetosheath processes. Also, the heat flux is limited by whistler instability thresholds.

The Earth's magnetosheath is a dynamic region of shocked solar wind plasma downstream of the bow shock. Depending on the upstream magnetic field orientation, the magnetosheath usually has one of two distinct configurations: a more variable magnetosheath with strong fluctuations and structures propagating from upstream to downstream, or a more stationary magnetosheath characterized by compression and high ion temperature anisotropy. The more variable magnetosheath is usually observed for quasi-parallel shocks (the angle between the shock normal and the upstream magnetic field theta(Bn)<45 degrees), but the limit can vary for 40 degrees <=theta(Bn)<= 70 degrees. These differences facilitate studies of how different plasma environments affect various processes such as turbulence and heating, and these require an accurate magnetosheath classification. Since theta(Bn) can rarely be determined correctly in the absence of upstream monitors, local measurements have been suggested to classify the magnetosheath. However, this has not yet been verified for Magnetospheric Multiscale (MMS) data. We investigate this approach with MMS using locally measured magnetic field variability, ion temperature anisotropy, and suprathermal ion flux. We find the more variable magnetosheath at normalized magnetic fluctuations above 0.29 and ion temperature anisotropy below 0.18. We also find that the suprathermal ion flux can complement the classification given that MMS burst-mode data is used. Our findings provide a method to determine the magnetic connectivity of the magnetosheath with the upstream solar wind in the case of MMS and classify the downstream region into different configurations.

Plasma inside Earth's magnetosphere can have a substantial effect in the efficiency of magnetic reconnection at the magnetopause, specially if it is rich in cold and heavy ions. We have analyzed 9 years of data gathered by the Magnetospheric Multiscale (MMS) mission to locate and characterize one magnetospheric plasma population with such features, the warm plasma cloak (WPC). The WPC has an ion temperature that ranges between tens of eV to a few keV and is mainly composed of electrons, protons, and O+ ions. Our statistical study has shown that 51% of MMS observations in the outer magnetosphere correspond to WPC population, and that 15% of the WPC is rich in O+ ions. The presence of heavy ions in the WPC is related to strong geomagnetic activity. We have found that the detections of O+ rich WPC take place 9 hours after geomagnetic events with Kp index larger than 6. The duration of such time gap is in accordance with the prediction of previous models on the formation of the WPC in the dayside magnetosphere.

Whistler waves are found in various space plasma environments, such as the Earth’s magnetosheath, where they affect particle dynamics and energy transfer. Through wave-particle interactions, they contribute to changes in both the energy and pitch angle of electrons. However, the significance of whistler waves in different plasma regions is not fully known. In this work, we use MMS measurements to calculate the occurrence and properties of whistler waves in the Earth’s magnetosheath. Based on selected MMS orbits, we compare the plasma conditions offered by the more stationary quasi-perpendicular (Q⊥) to the more fluctuating quasi-parallel (Q॥) magnetosheath. We show that the whistler waves occur in local magnetic dips and density peaks and are not necessarily correlated with electron temperature anisotropy. Also, there is an elevated occurrence downstream of Q⊥ shocks, compared to the Q॥ configuration. Further, by calculating pitch-angle diffusion coefficients, we find that whistler waves can significantly reshape the electron velocity distribution during the time a plasma parcel spends in the magnetosheath, which has important implications for the plasma dynamics of the magnetosheath region.

The warm plasma cloak (WPC) is a plasma population located in the outer magnetosphere. It is composed primarily of electrons and H+ ${\mathrm{H}}<^>{+}$ ions with energies of tens to hundreds electronvolts and can contain significant amounts of O+ ${\mathrm{O}}<^>{+}$. We conduct a statistical survey of the WPC using 9 years of observations in the dayside magnetosphere from the Magnetospheric Multiscale mission. WPC is found in 51% $51\%$ of the observations and it is 1.6 times more abundant in the dawn than in the dusk sector. O+ ${\mathrm{O}}<^>{+}$-rich WPC is detected in 7.5% $7.5\%$ of the observations, being 3 times more probable in the dawn sector. We find that after a peak of strong geomagnetic activity, it takes approximately 9 hr to detect the WPC in the dayside magnetosphere.

Electromagnetic Ion Cyclotron (EMIC) waves mediate energy transfer from the solar wind to the magnetosphere, relativistic electron precipitation, or thermalization of the ring current population, to name a few. How these processes take place depends on the wave properties, such as the wavevector and polarization. However, inferring the wavevector from in-situ measurements is problematic since one needs to disentangle spatial and time variations. Using 8 years of Magnetospheric Multiscale (MMS) mission observations in the dayside magnetosphere, we present an algorithm to detect proton-band EMIC waves in the Earth's dayside magnetosphere, and find that they are present roughly 15% of the time. Their normalized frequency presents a dawn-dusk asymmetry, with waves in the dawn flank magnetosphere having larger frequency than in the dusk, subsolar, and dawn near subsolar region. It is shown that the observations are unstable to the ion cyclotron instability. We obtain the wave polarization and wavevector by comparing Single Value Decomposition and Ampere methods. We observe that for most waves the perpendicular wavenumber (k(perpendicular to)) is larger than the inverse of the proton gyroradius (rho(i)), that is, k(perpendicular to)rho(i) > 1, while the parallel wavenumber is smaller than the inverse of the ion gyroradius, that is, k(& Vert;)rho(i) < 1. Left-hand polarized waves are associated with small wave normal angles (theta(Bk) < 30 degrees), while linearly polarized waves are associated with large wave normal angles (theta(Bk) > 30 degrees). This work constitutes, to our knowledge, the first attempt to statistically infer the full wavevector of proton-band EMIC waves observed in the outer magnetosphere.

In the Earth's magnetosphere wave-particle interaction is a major ion energization process, playing an important role for the atmospheric escape. A common type of ion heating is associated with low-frequency broadband electric wave fields. For such waves the energy is not concentrated to a certain narrow frequency range and exhibits no peaks or dips in a power spectrum. If there are enough fluctuations close to the ion gyrofrequency the electric field may still come in resonance with gyrating ions and heat them perpendicular to the background magnetic field. We perform a proof-of-concept study to investigate if this heating mechanism may contibute significantly to the energization of planetary ions also in the induced magnetosphere of Venus. We assume Alfv & eacute;nic fluctuations and estimate the electric field spectral density based on magnetic field observations. We find typical estimated electric spectral densities of a few (mV/m)2 ${(\text{mV/m})}<^>{2}$/Hz close to Venus. This corresponds to a heating rate of a few eV/s. We consider an available interaction time of similar to ${\sim} $ 300 s and conclude that this mechanism could increase the energy of an oxygen ion by about a keV. Observed thermal energies are in the range 100-1,000 eV and thus, resonant wave heating may also be important at Venus.

Ion-acoustic waves (IAWs) commonly occur near interplanetary (IP) shocks. These waves are important because of their potential role in the dissipation required for collisionless shocks to exist. We study IAW occurrence statistically at different heliocentric distances using Solar Orbiter to identify the processes responsible for IAW generation near IP shocks. We show that close to IP shocks the occurrence rate of IAW increases and peaks at the ramp. In the upstream region, the IAW activity is highly variable among different shocks and increases with decreasing distance from the Sun. We show that the observed currents near IP shocks are insufficient to reach the threshold for the current-driven instability. We argue that two-stream proton distributions and suprathermal electrons are likely sources of the waves. Ion-acoustic waves (IAWs) are fluctuations in the electric field that occur at frequencies close to the ion plasma frequency. These waves are commonly found in the solar wind and often cluster around interplanetary (IP) shock waves. In this study, we investigate and quantify how common IAWs are in the vicinity of IP shocks. Our research revealed that IAW activity is enhanced before and after most IP shock passages. Furthermore, IAWs are more likely to be observed preceding IP shocks that are closer to the Sun. We find that the occurrence rate of IAWs shows no clear dependence on the IP shock parameters. We explore the possible mechanisms that could explain the presence of these IAWs. For instance, IAW modes can be excited by electric currents if the associated drift velocity between ions and electrons is above a certain threshold. However, the currents alone are not strong enough to generate the IAWs found near IP shocks. We discuss other potential generation mechanisms, such as velocity distributions of ions and electrons deviating from thermodynamic equilibrium. The occurrence of Ion-acoustic waves (IAWs) is enhanced at interplanetary (IP) shocks, peaking at the shock ramp The occurrence rate of IAWs in the upstream region of IP shocks increases with decreasing radial distance from the Sun IAWs are observed upstream of an IP shock together with two-stream protons and an electron strahl

In the Earth's magnetosheath (MSH), several processes contribute to energy dissipation and plasma heating, one of which is wave-particle interactions between whistler waves and electrons. However, the overall impact of whistlers on electron dynamics in the MSH remains to be quantified. We analyze 18 hours of burst-mode measurements from the Magnetospheric Multiscale (MMS) mission, including data from the unbiased magnetosheath campaign during February-March 2023. We present a statistical study of 34,409 whistler waves found using automatic detection. We compare wave occurrence in the different MSH geometries and find three times higher occurrence in the quasi-perpendicular MSH compared to the quasi-parallel case. We also study the wave properties and find that the waves propagate quasi-parallel to the background magnetic field, have a median frequency of 0.2 times the electron cyclotron frequency, median amplitude of 0.03-0.06 nT (30-60 pT), and median duration of a few tens of wave periods. The whistler waves are preferentially observed in local magnetic dips and density peaks and are not associated with an increased temperature anisotropy. Also, almost no whistlers are observed in regions with parallel electron plasma beta lower than 0.1. Importantly, when estimating pitch-angle diffusion times we find that the whistler waves cause significant pitch-angle scattering of electrons in the MSH.

The Earth’s magnetosheath is a dynamic region and its properties strongly depend on the angle between the bow shock normal and the solar wind magnetic field (θbn). If the shock is quasi-parallel (θbn < 45°), the magnetosheath is magnetically connected to the foreshock, causing strong fluctuations and structures propagating from upstream to downstream. A quasi-perpendicular shock (θbn > 45°) produces a less structured and more stationary magnetosheath characterized by compression and high ion temperature anisotropy. These distinct configurations make it possible to study how different plasma environments affect various processes such as turbulence, heating, and wave-particle interactions. Therefore, such studies require an accurate classification of the magnetosheath. This is not easily achieved, especially close to the magnetopause where the shock crossing for the plasma of interest cannot be observed.Previously, Karlsson et al. (2021) used data from the Cluster mission to propose a promising classification method using local measurements of the magnetic field standard deviation, high-energy ion flux, and ion temperature anisotropy. In this work, we are building on this study and extending it to the Magnetospheric Multiscale (MMS) mission, having a different orbit than Cluster. We compare this local classification to θbn estimated from upstream conditions and well-known bow shock models, and discuss the advantages and disadvantages of the different methods. Reference: Karlsson, T., Raptis, S., Trollvik, H., & Nilsson, H. (2021). Classifying the magnetosheath behind the quasi-parallel and quasi-perpendicular bow shock by local measurements. Journal of Geophysical Research: Space Physics, 126, e2021JA029269.

The magnetosheath is a region downstream of the bow shock filled with turbulent, decelerated solar wind plasma which is flowing earthwards. This solar wind flow sometimes shows signatures of localized structures with enhanced dynamic pressure, so called magnetosheath jets. These jets are often associated with low angles between the bow shock normal and the interplanetary magnetic field (IMF) direction, the so called quasi-parallel bow shock. Less often they are also found behind the quasi-perpendicular bow shock.As jets propagate through the magnetosheath, they interact with the surrounding plasma. Studying waves inside, and in the vicinity of, jets is a step towards understanding the interaction of jets with the surrounding plasma. So far whistler waves, electrostatic waves, waves in the lower hybrid frequency range as well as low frequency waves have been reported. However, the sources of these waves are unknown. In addition, further types of waves may be associated with the jets.We conduct a study on waves in magnetosheath jets using burst mode data of the Magnetospheric Multiscale (MMS) mission. The magnetic and electric field data are provided with a sampling rate of 8 kHz, while previous studies used data sets with much lower sampling rates. The high time resolution allows us to study different waves over a large frequency range and investigate properties of these waves. In addition, we discuss possible generation mechanisms.

Context. Langmuir waves (electrostatic waves near the electron plasma frequency) are often observed in the solar wind and may play a role in the energy dissipation of electrons. The largest amplitude Langmuir waves are typically associated with type II and III solar radio bursts and planetary foreshocks. In addition, Langmuir waves not related to radio bursts occur in the solar wind, but their source is not well understood. Langmuir waves have been observed inside isolated magnetic holes, suggesting that magnetic holes play an important role in the generation of Langmuir waves. Aims. We provide the statistical distribution of Langmuir waves in the solar wind at different heliocentric distances. In particular, we investigate the relationship between magnetic holes and Langmuir waves. We identify possible source regions of Langmuir waves in the solar wind, other than radio bursts, by analyzing the local plasma conditions. Methods. We analyzed data from Solar Orbiter’s Radio and Plasma Waves (RPW) and Magnetometer (MAG) instruments. We used the triggered electric field snapshots and onboard statistical data (STAT) of the Time Domain Sampler (TDS) of RPW to identify Langmuir waves and investigate their properties. The plasma densities were derived from the spacecraft potential estimated by RPW. The MAG data were used to monitor the background magnetic field and detect magnetic holes, which are defined as regions with an isolated decrease in | B | of 50% or more compared to the background level. The statistical analysis was performed on data from 2020 to 2021, comprising heliocentric distances between 0.5 AU and 1 AU. Results. We show that 78% of the Langmuir waves in the solar wind not connected to radio bursts occur in regions of local magnetic field depletions, including the regions classified as isolated magnetic holes. We also show that the Langmuir waves occur more frequently inside magnetic holes than in any other region in the solar wind, which indicates that magnetic holes are important source regions of solar wind Langmuir waves. We find that Langmuir waves associated with magnetic holes in the solar wind typically have lower amplitudes than those associated with radio bursts.

Planetary atmospheres are very dynamic in geological timescales, with their composition and physical characteristics changing significantly throughout the history of a stellar system.These changes can cause for a warm and wet planet to become cold and dry (Mars), or for the surface of a planet to become so hot and its atmospheric pressure so high as to melt lead (Venus).A key part of this evolution is the coupling of the atmosphere to space through the release of atmospheric particles in form of ions and neutrals as a response to solar wind, auroral processes, solar heating, and other space weather phenomena.The way these atmospheres evolve with time is far from being fully understood, and while the community counts with advanced threedimensional models of these atmospheres, significant differences remain between the limited observations we have and the results produced by those models.These differences hint at a lack of understanding of some important physical processes that are taking place, and that the most advanced models fail to capture.The only way to improve our understanding is by filling the observational gaps that exist to date.We present an attractive mission architecture to fill this gap by studying (and quantifying) atmospheric escape from our own planet, Earth.

Plasma waves and instabilities driven by temperature anisotropies are known to play a significant role in plasma dynamics, scattering the particles and affecting particle heating and energy conversion between the electromagnetic fields and the particles. Among these instabilities, the electron firehose instability is driven by electron temperature anisotropy Te, > Te,perp (with respect to the background magnetic field) and produce nonpropagating oblique modes. Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities - including the electron firehose instability - affecting the particle dynamics and the energy conversion of the process. Yet, the electron firehose instability and its role in the reconnection process is still rather unexplored, especially with in situ measurements. We report MMS observations of electron firehose fluctuations observed in the exhaust region of a reconnection site in the magnetotail. The fluctuations are observed in the Earthward outflow relatively close (less than 2 di distance) to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique electron firehose fluctuations, the associated firehose instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. The wave analysis in the EDR suggests that the firehose instability could be active at the reconnection site. We suggest that the firehose fluctuations observed in the outflow region may have been originated at the EDR, where the electron temperature anisotropy exceeds the threshold values, and then advected in the outflow region.

Magnetosheath jets are localized dynamic pressure enhancements in the magnetosheath. We make use of the high time resolution burst mode data of the Magnetospheric Multiscale mission for an analysis of waves in plasmas associated with three magnetosheath jets. We find both electromagnetic and electrostatic waves over the frequency range from 0 to 4 kHz that can be probed by the instruments on board the MMS spacecraft. At high frequencies we find electrostatic solitary waves, electron acoustic waves, and whistler waves. Electron acoustic waves and whistler waves show the typical properties expected from theory assuming approximations of a homogeneous plasma and linearity. In addition, 0.2 Hz waves in the magnetic field, 1 Hz electromagnetic waves, and lower hybrid waves are observed. For these waves the approximation of a homogeneous plasma does not hold anymore and the observed waves show properties from several different basic wave modes. In addition, we investigate how the various types of waves are generated. We show evidence that, the 1 Hz waves are connected to gradients in the density and magnetic field. The whistler waves are generated by a butterfly‐shaped pitch‐angle distribution and the electron acoustic waves by a cold electron population. The lower hybrid waves are probably generated by currents at the boundary of the jets. As for the other waves we can only speculate about the generation mechanism due to limitations of the instruments. Studying waves in jets will help to address the microphysics in jets which can help to understand the evolution of jets better.

Waves at the electron plasma frequency are found throughout the heliosphere. They provide indicators of unstable electron distributions, are routinely used to estimate the local electron number density, and can lead to radio wave emission at the plasma frequency and its harmonics. Although they have been studied extensively in various solar and heliospheric plasma regions, there is a lack of statistical studies of plasma frequency waves in Earth’s magnetotail. Here, the occurrence and properties of plasma frequency waves, namely Langmuir and upper hybrid waves, are investigated in Earth’s magnetotail using the four Magnetospheric Multiscale spacecraft. In Earth’s magnetotail plasma frequency waves are observed about $1$~\% of the time. About $80$~\% of the waves are identified as Langmuir waves, while about $20$~\% are identified as upper hybrid waves. The waves are primarily found in the plasma sheet boundary layer. By comparing with the local electron distributions it is shown that the Langmuir waves are generated by the bump-on-tail instability, while upper hybrid waves are typically associated with broad electron beams or loss-cone-like distributions. The majority of the waves are found in close proximity to ion outflow regions associated with magnetic reconnection in the magnetotail. The waves are likely generated by plasma sheet electrons escaping along newly reconnected magnetic field lines or electron beams propagating toward the distant magnetotail.

We argue that many studies in space physics would benefit from putting a detailed investigation into a wider perspective. Three examples of theoretical and observational studies are given. We argue that space physics should aim to be less of an isolated branch of science. Rather, by putting the scientific space results into a wider perspective these results will become more interesting and important than ever. We argue that diversity in a team often is favourable for work on complicated problems and helps to present the results in a wider perspective.

Venus' relatively small induced magnetosphere enables the solar wind to interact directly with the upper atmosphere (Stenberg Wieser et al., 2015), and one could guess that this would yield a larger escape rate compared to a magnetized planet. However, the escape rates reported from Earth are somewhat larger than from Venus. Singly charged oxygen dominates the ion mass outflow from Earth and the average escape rate is estimated to be a few times 1025 s-1 (André, 2015, and references therein). A strong intrinsic magnetic field creates a huge magnetosphere, which prevents direct solar wind access to the atmosphere, but the big structure instead provides a larger interaction cross section to transfer solar wind energy and momentum into the magnetosphere (e.g., Gunell et al., 2018). This can lead to a larger ion energization and atmospheric escape. In the absence of a direct interaction between the ionosphere and the solar wind, wave-particle interaction has been identified as a major ion energization process at Earth. Several wave modes at different frequencies are able to heat ions. (André & Yau, 1997). A common type of ion heating is associated with low-frequency broadband electric wavefields (André et al., 1998). The spectral density of such broadband waves does not exhibit a peak at a certain frequency but the wave power available at the ion gyrofrequency may nevertheless efficiently energize the ions (Chang et al., 1986). At Earth this heating mechanism is definitely effective and important (André et al., 1998). We investigate if ions originating from the Venusian ionosphere can be energized by electric wave power in a similar way as is observed at Earth. References André, M. (2015). Previously hidden low-energy ions: a better map of near-earth space and the terrestrial mass balance. Physica Scripta, 90 (12), 128005. André, M., Norqvist, P., Andersson, L., Eliasson, L., Eriksson, A. I., Blomberg, L. Waldemark, J. (1998). Ion energization mechanisms at 1700 km in the auroral region. Journal of Geophysical Research: Space Physics, 103 (A3), 4199-4222. André, M., & Yau, A. (1997). Theories and observations of ion energization and outflow in the high latitude magnetosphere. Space Science Reviews, 80 (1), 27-48. Chang, T., Crew, G. B., Hershkowitz, N., Jasperse, J. R., Retterer, J. M., & Winningham, J. D. (1986). Transverse acceleration of oxygen ions by electromagnetic ion cyclotron resonance with broad band left-hand polarized waves. Geophysical Research Letters, 13 (7), 636-639 Gunell, H., Maggiolo, R., Nilsson, H., Stenberg Wieser, G., Slapak, R., Lindkvist, J., De Keyser, J. (2018). Why an intrinsic magnetic field does not protect a planet against atmospheric escape. A&A, 614. Stenberg Wieser, G., Ashfaque, M., Nilsson, H., Futaana, Y., Barabash, S., Diéval, C., Zhang, T. L. (2015). Proton and alpha particle precipitation onto the upper atmosphere of venus. Planetary and Space Science, 113-114 , 369-377.