Jupiter’ magnetic field is tilted by ~10º; with respect to the planet’s spin axis, and as a result the Jovian plasma sheet passes over the Galilean satellites at the jovigraphic equator twice per planetary rotation period. The plasma and magnetic field conditions near Ganymede’s magnetosphere therefore change dramatically every ~5 hours, creating a unique magnetosphere-magnetosphere interaction, and on longer time scales as evidenced by orbit-to-orbit variations. In this paper we summarize the typical magnetic field conditions and their variability near Ganymede’s orbit as observed by the Galileo and Juno spacecraft. We fit Juno data from orbit 34, which included the spacecraft’s close Ganymede flyby in June 2021, to a current sheet model and show that the magnetospheric conditions during orbit 34 were very close to the historical average. Our results allow us to infer the upstream conditions at the time of the Juno Ganymede flyby.
This editorial aims to improve awareness of the current best practices in open research, and stimulate discussion on the practical implementation of AGU's data and software policy in key areas of space weather research. We also further aim to encourage authors to take additional steps to ensure clear credit to all contributors to the work, whether that is underlying data, key software, or direct contributions to the manuscript.
Space weather phenomena occur from the Sun to the Earth with damaging impacts on ground-based and space-borne technological infrastructure. The geomagnetic auroral electrojet indices, AU, AL, and AE, have been widely used for monitoring space weather and geomagnetic activities during space storms and substorms. The time series data of solar wind monitored by upstream satellite and ground-based auroral electrojet indices form the input-output system characterizing the dynamic coupling among solar wind, Earth’s magnetosphere, and ionosphere. The data-driven predictions of auroral electrojet indices during geomagnetic storms and substorms face the challenges of capturing the variations of ionospheric electrojet current driven by multiple solar wind variables and are modeled as a coupled complex system with finite and variable memory. The recurrent neural network (RNN) based Long Short-Term Memory (LSTM) machine learning algorithm is well suited to classify, process, and make predictions of the coupled solar wind-magnetosphere-ionosphere system by preserving important information from earlier parts of the coupled time series and carrying it forward. In this study, an RNN-based LSTM model has been built to predict the time series of AE/AL indices with multi-variate solar wind inputs. Both 5-minute and hourly long-term time series data from the NASA OMNI database were used to drive the LSTM model. The coupled time series data are divided into training and testing datasets. The Root-Mean-Square-Error (RMSE) between the predicted and actual AE/AL indices of the testing sets was used to evaluate the roles of the number of layers in the LSTM, memory length of the coupled system, prediction time, and different combinations of solar wind input parameters (magnetic field, velocity, and density). The performance of the LSTM model in predicting AL/AE indices during major geomagnetic storm and substorm events is analyzed. The differences and challenges of applying LSTM to predict 5-min and hourly AE/AL indices are also discussed.
As a rule, the phase velocity of unstable Farley-Buneman waves is found not to exceed the ion-acoustic speed, cs. However, there are known exceptions: under strong electric field conditions, much faster Doppler shifts than expected cs values are sometimes observed with coherent radars at high latitudes. These Doppler shifts are associated with narrow spectral width situations. To find out how much faster than cs these Doppler shifts might be, we developed a proper cs model as a function of altitude and electric field strength based on ion frictional heating and on a recently developed empirical model of the electron temperature under strong electric field conditions. Motivated by the ‘narrow fast’ observations, we then explored how ion drifts in the upper part of the unstable region could add to the Doppler shift observed with coherent radars. While there can be no ion drift contribution for the most unstable modes, and therefore no difference with cs for such modes, under strong electric field conditions, a large ion drift contribution of either sign needs to be added to the Doppler shift of more weakly unstable modes, turning them into ‘fast-‘ or ‘slow-’ narrow spectra. Particularly between 110 and 115 km, the ion drift can alter the Doppler shift of the more weakly unstable modes by several 100 m/s, to the point that their largest phase velocities could approach the ambient E x B drift itself.
Extreme solar particle events (ESPEs) are rare and the most potent known processes of solar eruptive activity. During ESPEs, a vast amount of cosmogenic isotopes (CIs) 10Be, 36Cl and 14C can be produced in the Earth’s atmosphere. Accordingly, CI measurements in natural archives allow us to evaluate particle fluxes during ESPEs. In this work, we present a new method of ESPE fluence (integral flux) reconstruction based on state-of-the-art modeling advances, allowing to fit together different CI data within one model. We represent the ESPE fluence as an ensemble of scaled fluence reconstructions for ground-level enhancement (GLE) events registered by the neutron monitor network since 1956 coupled with satellite and ionospheric measurements data. Reconstructed ESPE fluences appear softer in its spectral shape than earlier estimates, leading to significantly higher estimates of the low-energy (E<100 MeV) fluence. This makes ESPEs even more dangerous for modern technological systems than previously believed. Reconstructed ESPE fluences are fitted with a modified Band function, which eases the use of obtained results in different applications.
The interaction of Io with the co-rotating magnetosphere of Jupiter is known to produce Alfven wings that couple the moon to Jupiter's ionosphere. We present first results from a new numerical model to describe the propagation of these Alfven waves in this system. The model is cast in magnetic dipole coordinates and includes a dense plasma torus that is centered around the centrifugal equator. Results are presented for two density models, showing the dependence of the interaction on the magnetospheric density. Model results are presented for the case when Io is near the centrifugal and magnetic equators as well as when Io is at its northernmost magnetic latitude. The effect of the conductance of Jupiter's ionosphere is considered, showing that a long auroral footprint tail is favored by high Pedersen conductance in the ionosphere. The current patterns in these cases show a U-shaped footprint due to the generation of field-aligned current on the Jupiter-facing and Jupiter-opposed sides of Io, which may be related to the structure in the auroral footprint seen in the infrared by Juno. A model for the development of parallel electric fields is introduced, indicating that the main auroral footprints of Io can generate parallel potentials of up to 100 kV.
We use a 20 year database of Super Dual Auroral Radar Network (SuperDARN) observations to investigate the two component model of ionospheric convection. A convection pattern is included in the database if it is derived from at least 250 radar vectors and has a distribution of electric potential consistent with Dungey-cycle twin vortex flow (a negative potential peak in the dusk cell and a positive potential peak in the dawn cell). We extract the locations of the foci of the convection cells from the SuperDARN convection patterns, and compare their dependencies on the north-south component of the interplanetary magnetic field, IMF Bz, and the auroral electrojet index, AL. We define a quantity, dMLT, as the hour angle between the dawn and dusk convection cell foci, which we use as a proxy for the extent to which the dayside or nightside component of the convection pattern is dominating. We find that at a fixed level of AL, dMLT decreases with increasingly negative IMF Bz, consistent with an increasing dominance of dayside reconnection. We also find that at a fixed level of IMF Bz, dMLT increases with increasingly negative AL, consistent with an increasing dominance of nightside reconnection, but only up to modest values of AL (to ~ −200 nT). As AL becomes further enhanced dMLT decreases again, which we attribute to an inherent dependence of AL on IMF Bz.
Electron temperature anisotropy-driven instabilities such as the electron firehose instability (EFI) are especially significant in space collisionless plasmas, where collisions are so scarce that wave-particle interactions are the leading mechanisms in the isotropization of the distribution function and energy transfer. Observational statistical studies provided convincing evidence in favor of the EFI constraining the electron distribution function and limiting the electron temperature anisotropy. 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. However, in situ observations of the fluctuations generated by the EFI are still lacking and the interplay between magnetic reconnection and EFI is still largely unknown. In this study, we use high-resolution in situ measurements by the Magnetospheric Multiscale (MMS) spacecraft to identify and investigate EFI fluctuations in the magnetic reconnection exhaust in the Earth’s magnetotail. We find that the wave properties of the observed fluctuations largely agree with theoretical predictions of the non-propagating EF mode. These findings are further supported by comparison with the linear kinetic dispersion relation. Our results demonstrate that the magnetic reconnection outflow can be the seedbed of EFI and provide the first direct in situ observations of EFI-generated fluctuations.
On December 04, 2021, a total solar eclipse occurred over west Antarctica. Nearly an hour beforehand, a geomagnetic substorm onset was observed in the northern hemisphere. Eclipses are suggested to influence magnetosphere-ionosphere (MI) coupling dynamics by altering the conductivity structure of the ionosphere by reducing photoionization. This sudden and dramatic change in conductivity is not only likely to alter global MI coupling, but it may also introduce a variety of localized instabilities that appear in both hemispheres. Global navigation satellite system (GNSS) based observations of the total electron content (TEC) in the southern high latitude ionosphere during the December 2021 eclipse show signs of wave activity coincident with the eclipse peak totality. Ground magnetic observations in the same region show similar activity, and our analysis suggest that these observations are due to an “eclipse effect” rather than the prior substorm. We present the first multi-point interhemispheric study of a total south polar eclipse with local TEC observational context in support of this conclusion.
Ionospheric convection patterns from the Super Dual Auroral Radar Network are used to determine the trajectories, transit times and decay rates of three polar cap patches from their creation in the dayside polar cap ionosphere to their end of life on the nightside. The first two polar cap patches were created within 12 minutes of each other and travelled through the dayside convection throat, before entering the nightside auroral oval after 104 and 92 minutes, respectively. When the patches approached the nightside auroral oval, an intensification in the poleward auroral boundary occurred close to their exit point, followed by a decrease in the transit velocity. The airglow decay rates of patches 1 and 2 were found to be ≈0.6% and ≈0.9% per minute, respectively. The third patch decayed completely within the polar cap and had a lifetime of only 78 minutes. After a change in drift direction, patch 3 had a radar backscatter power half-life of 4.23 minutes, which reduced to 1.80 minutes after a stagnation, indicating a variable decay rate. 28 minutes after the change in direction, and 16 minutes after stagnation, patch 3 completely disintegrated. We relate this rapid decay to increased frictional heating, which speeds up the recombination rate. Therefore, we suggest that the stagnation of a polar cap patch is a main determinant to whether or not a polar cap patch can exit through the nightside auroral oval.
Venus today is inhospitable at the surface, its average temperature of 750 K being incompatible to the existence of life as we know it. However, the potential for past surface habitability and upper atmosphere (cloud) habitability at the present day is hotly debated, as the ongoing discussion regarding a possible phosphine signature coming from the clouds shows. We review current understanding about the evolution of Venus with special attention to scenarios where the planet may have been capable of hosting microbial life. We compare the possibility of past habitability on Venus to the case of Earth by reviewing the various hypotheses put forth concerning the origin of habitable conditions and the emergence and evolution of plate tectonics on both planets. Life emerged on Earth during the Hadean when the planet was dominated by higher mantle temperatures (by about 200$^\circ$C), an uncertain tectonic regime that likely included squishy lid/plume-lid and plate tectonics, and proto continents. Despite the lack of well-preserved crust dating from the Hadean-Paleoarchean eons, we attempt to resume current understanding of the environmental conditions during this critical period based on zircon crystals and geochemical signatures from this period, as well as studies of younger, relatively well-preserved rocks from the Paleoarchean. For these early, primitive life forms, the tectonic regime was not critical but it became an important means of nutrient recycling, with possible consequences to the global environment on the long-term, that was essential to the continuation of habitability and the evolution of life. For early Venus, the question of stable surface water is closely related to tectonics. We discuss potential transitions between stagnant lid and (episodic) tectonics with crustal recycling, as well as consequences for volatile cycling between Venus’ interior and atmosphere. In particular, we review insights into Venus’ early climate and examine critical questions about early rotation speed, reflective clouds, and silicate weathering, and summarize implications for Venus’ long-term habitability. Finally, the state of knowledge of the venusian clouds and the proposed detection of phosphine is covered.
In-situ measurements from the Magnetospheric Multiscale (MMS) mission are used to estimate electron density from spacecraft potential and investigate compressive turbulence in the Earth’s magnetosheath. During the MMS Solar Wind Turbulence Campaign in February 2019, the four MMS spacecraft were arranged in a logarithmic line constellation enabling the study of measurements from multiple spacecraft at varying distances. We estimate the electron density from spacecraft potential for a time interval in which the ion emitters actively control the potential. The derived electron density data product has a higher temporal resolution than the plasma instruments, enabling the examination of fluctuation for scales down to the sub-ion range. The inter-spacecraft separations range from 132 km to 916 km; this corresponds to scales of 3.5 to 24.1 ion inertial lengths. The derived density and magnetic field data are used to study fluctuations in the magnetosheath through time lags on a single spacecraft and spatial lags between pairs of spacecraft over almost one decade in scale. The results show an increase in anisotropy as the scale decreases.
The possibility to exploit the muon scattering for the elemental discrimination of materials in a given volume is well known. When more than one material is present along the muon path, it is often important to discern the order in which they are stacked. The scattering angle due to the target volume can be split into two interior angles in the tomographic setups based on the muon scattering, and we call this property as the triangular correlation where the sum of these two interior angles is equal to the scattering angle. In this study, we apply this triangular correlation for a multi-block material configuration that consist of concrete, stainless steel, and uranium. By changing the order of this material set, we employ the GEANT4 simulations and we show that the triangular correlation is valid in the multi-block material setups, thereby providing the possibility of supportive information for the coarse prediction of the material order in such configurations.
Magnetic field draping occurs when the magnetic field lines frozen in a plasma flow wrap around a body or plasma environment. The draping of the interplanetary magnetic field (IMF) around the Earth’s magnetosphere has been confirmed in the early days of space exploration. However, its global and three-dimensional structure is known from modeling only, mostly numerical. Here, this structure in the dayside of the Earth’s magnetosheath is determined as a function of the upstream IMF orientation purely from in-situ spacecraft observations. We show the draping structure can be organized in three regimes depending on how radial the upstream IMF is. Quantitative analysis demonstrates how the draping pattern results from the magnetic field being frozen in the magnetosheath flow, deflected around the magnetopause. The role of the flow is emphasized by a comparison of the draping structure to that predicted to a magnetostatic draping.
Dipolarization events with inductive, radial electric fields are examined, using Van Allen Probes data between 2013 and 2018. Two cases are studied, followed by statistical analyses. These events were observed between evening and premidnight magnetic local times (MLTs) under moderate geomagnetic activities. Radial electric field variations, azimuthal magnetic field variations, and energetic protons were often observed when horizontal magnetic fields started to decrease in the dip region. Magnetic field lines were stretched with their motion similar to the gradient B/curvature drift velocities of energetic protons. Signs of electric fields changed when horizontal magnetic fields started to increase in the dipolarization front (DF). Electric field variations were correlated with magnetic field ones with ~ 90 deg. phase shift. These observations are mainly interpreted in terms of energetic proton structures drifting toward the probe locations, while being accompanied by standing waves.
The Solar Irradiance Science Team #2 (SIST-2) program is a competitively solicited National Aeronautics and Space Administration (NASA) Earth Science Division (ESD) science research program providing three-year awards beginning in July 2018 to quantify and understand the solar irradiance and its variability. A key motivation for the SIST-2 program is to understand the solar radiation variability and implications for Earth’s climate and atmospheric composition. The purpose for the SIST-2 program is limited to the accurate specification of the incoming solar irradiance into the Earth system considering the 43-year satellite data record as well as proxies to which the satellite record can be tied. The SIST-2 program funded eight research grants to study the variability of the total solar irradiance (TSI) and solar spectral irradiance (SSI) and to develop improved space-based data sets, solar proxies, and variability models of the solar irradiance. The SIST-2 projects are briefly introduced.