The Structure of the Large-Scale Heliosphere as Seen by Current Models.

This review summarizes the current state of research aiming at a description of the global heliosphere using both analytical and numerical modeling efforts, particularly in view of the overall plasma/neutral flow and magnetic field structure, and its relation to energetic neutral atoms. Being part of a larger volume on current heliospheric research, it also lays out a number of key concepts and describes several classic, though still relevant early works on the topic. Regarding numerical simulations, emphasis is put on magnetohydrodynamic (MHD), multi-fluid, kinetic-MHD, and hybrid modeling frameworks. Finally, open issues relating to the physical relevance of so-called "croissant" models of the heliosphere, as well as the general (dis)agreement of model predictions with observations are highlighted and critically discussed

Raising awareness on mental health in the heliophysics community

To foster greater diversity, equity, and inclusion within the field of space sciences, it is crucial that we recognize and proactively address the mental health challenges experienced by our community. The purpose of this article is to raise awareness about mental health, assess the current state of our community in this regard, and explore ways to better safeguard and support our community members. We present a compelling argument for conducting surveys to evaluate the mental health and overall wellbeing of our community. Additionally, we offer several recommendations aimed to improve the mental health within our research community such as promoting honest conversations and programs on stress management and resilience building, training to notice and respond, and rethinking sick days. We recommend reevaluating our definition of success and reconsidering the existing strategies aimed at addressing the issues related to power imbalances. By promoting mental health awareness, fostering an open and supportive culture, and implementing policies that prioritize the wellbeing of all individuals, we can create an environment that is more inclusive and conducive to the thriving of every member

Energetic Ion Moments and Polytropic Index in Saturn’s Magnetosphere using Cassini/MIMI Measurements: A Simple Model Based on κ‐Distribution Functions

Moments of the charged particle distribution function provide a compact way of studying the transport, acceleration, and interactions of plasma and energetic particles in the magnetosphere. We employ κ‐distributions to describe the energy spectra of H+ and O+, based on >20 keV measurements by the three detectors of Cassini’s Magnetospheric Imaging Instrument, covering the time period from DOY 183/2004 to 016/2016, 5 < L < 20. From the analytical spectra we calculate the equatorial distributions of energetic ion moments inside Saturn’s magnetosphere and then focus on the distributions of the characteristic energy (Ec=IE/In), temperature, and κ‐index of these ions. A semiempirical model is utilized to simulate the equatorial ion moments in both local time and L‐shell, allowing the derivation of the polytropic index (Γ) for both H+ and O+. Primary results are as follows: (a) The ∼9 < L < 20 region corresponds to a local equatorial acceleration region, where subadiabatic transport of H+ (Γ∼1.25) and quasi‐isothermal behavior of O+ (Γ∼0.95) dominate the ion energetics; (b) energetic ions are heavily depleted in the inner magnetospheric regions, and their behavior appears to be quasi‐isothermal (Γ<1); (c) the (quasi‐) periodic energetic ion injections in the outer parts of Saturn’s magnetosphere (especially beyond 17–18 RS) produce durable signatures in the energetic ion moments; (d) the plasma sheet does not seem to have a ground thermodynamic state, but the extended neutral gas distribution at Saturn provides an effective cooling mechanism that does not allow the plasma sheet to behave adiabatically.Key PointsDerivation of energetic ion moments, κ‐index, characteristic energy, temperature, and polytropic index in Saturn’s magnetospherePresentation of a semiempirical analytical model for the 20 keV energetic ion Pressure, density, and temperatureThe neutral gas at Saturn provides an effective cooling mechanism and does not allow the plasma sheet to behave adiabaticallyPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146558/1/jgra54546.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146558/2/jgra54546_am.pd

On the Energy Dependence of Galactic Cosmic Ray Anisotropies in the Very Local Interstellar Medium

We report on the energy dependence of galactic cosmic rays (GCRs) in the very local interstellar medium (VLISM) as measured by the Low Energy Charged Particle (LECP) instrument on the Voyager 1 (V1) spacecraft. The LECP instrument includes a dual-ended solid state detector particle telescope mechanically scanning through 360 deg across eight equally-spaced angular sectors. As reported previously, LECP measurements showed a dramatic increase in GCR intensities for all sectors of the >=211 MeV count rate (CH31) at the V1 heliopause (HP) crossing in 2012, however, since then the count rate data have demonstrated systematic episodes of intensity decrease for particles around 90{\deg} pitch angle. To shed light on the energy dependence of these GCR anisotropies over a wide range of energies, we use V1 LECP count rate and pulse height analyzer (PHA) data from >=211 MeV channel together with lower energy LECP channels. Our analysis shows that while GCR anisotropies are present over a wide range of energies, there is a decreasing trend in the amplitude of second-order anisotropy with increasing energy during anisotropy episodes. A stronger pitch-angle scattering at the higher velocities is argued as a potential cause for this energy dependence. A possible cause for this velocity dependence arising from weak rigidity dependence of the scattering mean free path and resulting velocity-dominated scattering rate is discussed. This interpretation is consistent with a recently reported lack of corresponding GCR electron anisotropies

Desalination Technologies: Hellenic Experience

Beyond doubt, desalination is growing rapidly worldwide. However, there are still obstacles to its wider implementation and acceptance such as: (a) high costs and energy use for fresh water production; (b) environmental impacts from concentrate disposal; (c) a complex, convoluted and time-consuming project permitting process; and (d) limited public understanding of the role, importance, benefits and environmental challenges of desalination. In this paper, a short review of desalination in Greece is being made. Data on the cost of desalination shows a decrease in the future and the potential of water desalination in Greece. The paper summarizes the current status in southeastern Greece (e.g., Aegean islands and Crete), and investigates the possibility of production of desalinated water from brackish water

Combined ∼10 eV to ∼344 MeV Particle Spectra and Pressures in the Heliosheath along the Voyager 2 Trajectory

We report a unique combination of ~10 eV to ~344 MeV in situ ion measurements from the Plasma Science (PLS), Low Energy Charged Particle (LECP), and Cosmic Ray Subsystem (CRS) experiments on the Voyager 2 (V2) spacecraft, and remotely sensed ~110 eV to ~55 keV energetic neutral atom (ENA) measurements from the Interstellar Boundary Explorer (IBEX) mission and Ion and Neutral Camera (INCA) on the Cassini mission. This combination is done over the time period from 2009 to the end of 2016, along the V2 trajectory, toward assessing the properties of the ion energy spectra inside the heliosheath. The combined energy spectra exhibit a series of softening and hardening breaks, providing important insights on the various ion acceleration processes inside the heliosheath. Ions in the 5.2 keV) provide a significant contribution to the total pressure. With the assumption that all ENAs (~110 eV to 55 keV) are created by charge-exchange interactions inside the heliosheath, we estimate that the magnetic field upstream at the heliopause required to balance the pressure from the heliosheath in the direction of V2 is ~0.67 nT. This number is consistent with the measured magnetic field at V2 from 2018 November, when the spacecraft entered interstellar space

The Discrepancy between Observed and Predicted Heliospheric Energetic Neutral Atoms below Solar Wind Energy

Measuring energetic neutral atoms (ENAs) allows for the remote observation of ion populations from the frontiers of our heliosphere. In this study, we compare the ENAs observed with the IBEX-Lo instrument onboard the Interstellar Boundary Explorer with ENA predictions from two heliosphere models. In contrast to previous studies, this paper presents model-data comparisons for the energy range 50 eV–2 keV over one full solar cycle not only in the upwind direction (Voyager 1 and Voyager 2 sky directions), but also for the north pole, south pole, port tail lobe, and downwind directions. The two heliosphere models produce the same basic result: there is a large gap (1 to 2 orders of magnitude in ENA intensity at 100 eV) between ENA data and model predictions between 100 and 500 eV for all sky directions. The reason for this gap is not understood yet. While some explanations are plausible and will be investigated in future studies, other explanations are excluded

Synergies between interstellar dust and heliospheric science with an interstellar probe

We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavours, and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an interstellar probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute – through measuring dust – to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it ‘rolls’ into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions.ISSN:2752-820