Homepage of the International Space Science Institute (ISSI) located in Bern, Switzerland
ISSI is a scientifically independent and neutral Space- and Earth Science institute that advances science by facilitating open multi-disciplinary discourse in a stimulating environment, reaching out towards new scientific horizons.
Thirty International Teams have been selected by the ISSI Science Committee for implementation from the proposals received in response to the 2023 call.
As one of ISSI’s and ISSI-BJ’s tools, International Teams of up to 15 scientists address specific self-defined problems in the Space and Earth Sciences, analyzing data and comparing these with models and theories. The teams work together in an efficient and flexible format with typically 2-3 one-week meetings over two years. The results of the studies are published in the peer-reviewed literature.
The next call for proposals will be issued in January 2024.
The Earth’s magnetosphere shields our planet from hazardous space weather effects caused by solar disturbances and energetic particles. However, the global structure of the magnetosphere is still extremely difficult to describe. Major challenges include the scarcity of data sets, as well as the breadth of physical processes that need to be taken into account. Our ISSI Team explores various approaches that help to mitigate these challenges. Recent publications from our ISSI Team provide new insights into how to extract information about global magnetospheric and ionospheric structures, and how to combine global data analysis and global modeling in meaningful ways. The new results suggest potentially transformative ways to work with global datasets, develop new global models, and improve the accuracy of the current global models.
A paper by Samsonov et al. (2022) uses global X-ray imaging of the Earth’s magnetopause as a novel method that will provide us with knowledge about the shape of the magnetopause. The authors use two numerical global MHD models (SWMF and LFM) to simulate the X-ray emissivity in the magnetosheath and cusps, which are sources of soft X-rays due to charge exchange between solar wind ions and exospheric neutrals. Methods developed to extract the information about magnetopause location from synthetic X-ray images will allow to use the data from the future soft X-ray imagers for monitoring of large areas of the magnetopause. This methodology will allow to validate/modify our current modeling tools and approaches and revolutionize the understanding of magnetospheric response to external driving conditions.
A paper by Holappa and Buzulukova (2022) combines 24 years of observations of energetic particle measurements by NOAA POES satellites with simulation results from a global model of the Earth’s magnetosphere to study the effect of the interplanetary magnetic field (IMF) By component on the ring current. The authors showed that there is an explicit By-dependence of the Dst index, which is a measure of the ring current intensity, and that this dependence can be accounted for by a modified solar wind coupling function that includes a correction factor depending on the dipole tilt and IMF By. This study provides a novel contribution to understanding the complex and seasonally varying effects of IMF By on the magnetospheric dynamics by means of combining global datasets and global models.
A recent study by Stephens et al. (2023) uses machine learning techniques for data-mining of 26 years of magnetometer data from multiple satellites to reconstruct the global structure and evolution of reconnection sites, called X-lines, as well as different types of magnetic nulls, called O-lines, in the magnetotail. The study compares the reconstructed location of X-lines and O-lines with observations from MMS mission and finds a good agreement in most cases. The results from the study have potential to revolutionize our understanding of reconnection process on a global level, suggesting that reconnection in the magnetotail is reproducible with historic data sets, and the global 3D structure of the magnetospheric reconnection is reflected in global activity indices, their trends, and the solar wind energy input.
2D histograms of electron density observed by COSMIC data on the test set versus those predicted by the IRI model (a), and the novel neural network NET model (b). (c) Cumulative distribution of ratios between the IRI model and the COSMIC data on the test set; (d) Cumulative distribution of ratios between the developed NET model and the COSMIC data on the test set. Credit: Smirnov et al., 2023, Nature Scientific Reports (CC BY 4.0)
A recent paper by Smirnov et al. (2023) presents a novel neural network model of electron density in the topside ionosphere. The model has been developed and tested using 19 years of GNSS radio occultation data. The model consists of four parameters that describe the shape, height, and gradient of the F2-peak. The model is tested against in situ measurements from several missions and shows excellent agreement with the observations, outperforming the state-of-the-art International Reference Ionosphere (IRI) model by up to an order of magnitude, especially at 100-200 km above the F2-layer peak. This study provides a paradigm shift in ionospheric research, by demonstrating that ionospheric densities can be reconstructed with very high fidelity with the neural network model. The new model could be valuable for a variety of applications, including space weather forecasting, satellite navigation, and communication systems.
Contact: Natalia Buzulukova
References:
Holappa, L., and N. Y. Buzulukova (2022) “Explicit IMF By-dependence of energetic protons and the ring current.” Geophysical Research Letters, 49 (8), https://doi.org/10.1029/2022GL098031
Samsonov, A., Sembay, S., Read, A., Carter, J. A., Branduardi-Raymont, G., Sibeck, D., & Escoubet, P. (2022). Finding magnetopause standoff distance using a Soft X-ray Imager: 2. Methods to analyze 2-D X-ray images. Journal of Geophysical Research: Space Physics, 127, e2022JA030850. https://doi.org/10.1029/2022JA030850
Smirnov, A., Shprits, Y., Prol, F. et al. A novel neural network model of Earth’s topside ionosphere. Sci Rep13, 1303 (2023). https://doi.org/10.1038/s41598-023-28034-z
Stephens, G. K., Sitnov, M. I., Weigel, R. S., Turner, D. L., Tsyganenko, N. A., Rogers, A. J., et al. (2023). Global structure of magnetotail reconnection revealed by mining space magnetometer data. Journal of Geophysical Research: Space Physics, 128, e2022JA031066. https://doi.org/10.1029/2022JA031066
Earth’s magnetic environment is filled with a symphony of sound that we cannot hear. All around our planet, ultralow-frequency waves compose a cacophonous operetta portraying the dramatic relationship between Earth and the Sun. Now, a new citizen science project called HARP – or Heliophysics Audified: Resonances in Plasmas–has turned those once-unheard waves into audible whistles, crunches, and whooshes. Early tests have already made surprising finds, and citizen scientists can join the journey of sonic space exploration to decipher the cosmic vibrations that help sing the song of the Sun and Earth.
When solar plasma strikes Earth, it causes the magnetic field lines and plasma around Earth to vibrate like the plucked strings of a harp, producing ultralow-frequency waves. In 2007, NASA launched five satellites to fly through Earth’s magnetic “harp” – its magnetosphere – as part of the THEMIS mission. Since then, THEMIS has been gathering a bounty of information about plasma waves across Earth’s magnetosphere.
The frequencies of the waves THEMIS measures are too low for our ears to hear, however. So the HARP team sped them up to convert them to audible sound. By using an interactive tool developed by the team, you can listen to these waves and pick out interesting features you hear in the sounds. Humans are often better at picking out interesting wave patterns by ear than by eye – and can even do better than computers at identifying complex patterns that emerge during extreme solar events.
To start exploring these sounds, visit the HARP website.
Above the neutral atmosphere, space is filled with charged particles, which are tied to the Earth’s magnetic field. The particles come from two sources, the solar wind and the Earth’s upper atmosphere. Most of the solar wind particles are deflected by the Earth´s magnetic field, but some can penetrate into near-Earth space. The ionized layer of the upper atmosphere is continuously ejecting particles into space, which have low energies and are difficult to measure. We investigate the relative importance of the two charged particle sources for the dynamics of plasma processes in near-Earth space. In particular, we consider the effects of these sources in magnetic reconnection.
Magnetic reconnection allows initially separated plasma regions to become magnetically connected and mix, and converts magnetic energy to kinetic energy of charged particles. Magnetic reconnection is the main driver of geomagnetic activity in the near-Earth space, and is responsible for the release of energy that drives a variety of space weather effects. We highlight the fact that plasma from the ionized upper atmosphere contributes a significant part of the density in the key regions where magnetic reconnection is at work, and that this contribution is larger when the geomagnetic activity is high.
Main regions of the Earth’s magnetosphere. Ionospheric ions (light blue) escape and fill the outer magnetosphere until they exit the Earth space environment. Credit: Toledo-Redondo et al. (2021)
Thanks to MMS mission, combined with high-performance numerical modelling, we now understand much better how ionospheric ions modify the reconnection process at a microphysical level. Ionospheric ions circulating in the magnetosphere are accelerated at reconnection sites and constitute a significant sink of energy for the reconnection process. In addition, depending on the ion mass, initial energy, and where the ions are entrained in a reconnection site, different energization mechanisms, some of them more efficient than others, come into play.
We still understand relatively little about how these recent discoveries of the magnetic reconnection microphysics shape the magnetosphere system as a whole. The impact of cold ions is still an open field of research, as cold ions introduce a new length-scale and many plasma processes depend on the coupling between different scales.
There is yet another ionospheric population, which is even less understood: cold electrons. They also outflow from the ionosphere, and these are even harder to characterize than cold ions. Electrons play crucial roles on magnetic reconnection and wave generation in the magnetosphere. So far, because of the immense difficulty of observing these low-energy electrons, the effects of cold electrons remain largely unexplored.
References:
Toledo-Redondo, S., André, M., Aunai, N., Chappell, C. R., Dargent, J., Fuselier, S. A., et al. (2021). Impacts of ionospheric ions on magnetic reconnection and Earth’s magnetosphere dynamics. Reviews of Geophysics, 59, e2020RG000707. https://doi.org/10.1029/2020RG000707
Open Access: Toledo, S., M. André, N. Aunai, C.R. Chappell, J. Dargent, S.A. Fuselier, A. Glocer, D.B. Graham, S. Haaland, M. Hesse, L.M. Kistler, B. Lavraud, W. Li, T. E. Moore, P. Tenfjord, and S.K. Vines (2021), Hidden atmospheric particles sculpt near-Earth space environment, Eos, 102, https://doi.org/10.1029/2021EO163314
Plasma waves forming in the turbulent foreshock upstream of Earth’s bow shock have long been known to transmit into Earth’s magnetosphere. Yet the exact mechanism allowing their propagation through the shock remained unknown. A recent paper published in Nature Physics, led by Lucile Turc and initiated within the ISSI Team #448, proposes a new scenario to explain the wave transmission.
This study makes use of state-of-the-art numerical simulations and spacecraft observations to investigate the processes at play when foreshock waves interact with Earth’s bow shock. Numerical simulations were performed with the Vlasiator model, developed at the University of Helsinki. The model describes foreshock waves in their global context and allows tracking the waves on their earthward journey. To confirm the numerical results, observations from the Magnetospheric Multiscale mission (MMS) were analysed upstream and downstream of Earth’s bow shock.
The results of the study show that the transmitted foreshock waves retain similar properties downstream of the shock as in the foreshock, and in particular their fast-magnetosonic nature – fast-magnetosonic waves are a class of plasma waves with correlated variations in plasma density and magnetic field strength. At first glance, it may seem that the waves traverse the shock unchanged, as predicted in early works. However, the direction of the wavevectors reverses across the shock, which is inconsistent with a direct transmission.
Figure 1: Overview of near-Earth space, as simulated by the Vlasiator model. The colour map shows the magnetic field north-south component, out of the plane of the simulation domain. The cyan lines indicate the bow shock and magnetopause positions. (Image Credit: L. Turc/The Vlasiator Team)
To understand the wave transmission, one needs to take a closer look at the processes happening when foreshock waves impinge on the shock. It was found that the waves modulate the plasma properties just upstream of the shock, and in particular the Mach number, which controls the shock strength. This results in a periodic variation of the compression of the plasma as it crosses the shock, which in turn creates regions of enhanced and decreased pressure in the downstream. This pressure imbalance launches compression and rarefaction waves, at the same period as the foreshock waves, which travel all the way to the magnetosphere.
This work provides the missing link in the transmission of foreshock waves from their source region upstream of the shock into the Earth’s magnetosphere, thus improving our understanding of near-Earth space dynamics. Solving this open question was one of the main goals of the ISSI Team #448, which gathered for this purpose experts of plasma waves in the different regions of near-Earth space.
Figure 2: Time-position maps of the (a) magnetic field strength, (b) magnetic field By component, (c) magnetic field Bz component and (d) magnetosonic Mach number, extracted from the simulation along the Sun-Earth line. The solid cyan, black and white lines indicate the bow shock position. The foreshock waves moving towards the shock appear as stripes of alternating colours on the right-hand side of panels a-c. Their counterparts in the downstream are visible in panels a-b. Panel d shows the modulation of the magnetosonic Mach number by the foreshock waves as they approach the shock. (Image Credit: L. Turc, published in Nat. Phys.)
Shocks, such as the bow shock forming ahead of Earth’s magnetosphere, are found everywhere in space, near other planets, supernovae remnants or active galactic nuclei, and are one of the main sources of high energy particles in our universe. Understanding how plasma waves interact with a bow shock, how they modify it and how they are transmitted to the other side of the shock brings us crucial new insight into collisionless shock waves in general.
Reference
Turc, O.W. Roberts, D. Verscharen, A.P. Dimmock, P. Kajdič, M. Palmroth, Y. Pfau-Kempf, A. Johlander, M. Dubart, E.K.J. Kilpua, J. Soucek, K. Takahashi, N. Takahashi, M. Battarbee, U. Ganse: Transmission of foreshock waves through Earth’s bow shock, Nature Physics, 2022, https://doi.org/10.1038/s41567-022-01837-z
ESA’s Comet Interceptor mission (launch in 2029) will, for the first time, visit a long period or dynamically new comet (LPC/DNC), one the most pristine objects in our Solar System. DNCs have been stored in the outermost part of our planetary system since they formed 4.5 billion years ago. From there, they enter the inner Solar System for the first time to reveal their primitive structure and composition.
Comet Interceptor will pass through a potentially hazardous region of such a comet’s inner and outer coma. It is therefore important to assess the dust impact risk to the spacecraft and their scientific instruments to aid hazard mitigation strategies. Though models describing the dust environment for space missions are not new, the Comet Interceptor mission is unique. It is the first mission for which the mission’s precise target (a specific comet) could remain unknown until after launch. Naturally, this is a particular problem for determining the expected dust coma because of the many parameters with a broad range of possible values.
A Team led by team members Vladimir Zakharov and Raphael Marschall developed a new model to address this problem. By simulating tens of thousands of possible scenarios, they could statistically determine the scenarios the space mission could encounter. Figure 1 below shows the number of particles of a particular mass expected to hit the spacecraft during the encounter. The solid line shows the median and the different shaded areas the scatter in possible outcomes. The unknown properties of the comet of Comet Intercepter result in significant uncertainties that can be as large as four orders of magnitude. Once a comet has been chosen and characterised using ground-based telescopes, the relevant comet properties can be fed into the model to reduce uncertainties.
Figure 1: Total number of dust particles encountered according to the EDCM along the spacecraft trajectory of spacecraft A as function dust mass. The shaded areas show different percentile ranges within which cases fall. Additionally the orange curve shows the predicted median densities for a Halley type comet.
This new model also allowed the team to determine some fundamental properties of the activity of comets. One of the most accessible measurements that can be performed on a comet is to determine the brightness of the dust coma. This brightness is usually given in a quantity known as Afρ. Yet one would like to convert this brightness into a dust production rate at the comet’s surface. This most recent work shows that Afρ by itself is a bad predictor of the dust production rate. Yet, if, in addition, the dust’s size distribution can be measured, then we can derive relatively accurate values of the dust production rate from Afρ and the dust size distribution. This relationship is shown in Figure 2.
Figure 2: Dust production rate as a function of Afρ and the power law exponent, β, of the dust size distribution. The values of Afρ are slightly offset depending on the power law exponent to show the overlap resulting from β. By itself Afρ is a poor predictor of the dust production rate of a comet.
A numerical experiment – performed by Daniel Nóbrega Siverio and Fernando Moreno Insertis – has shown for the first time how one of the most abundant structures in the solar atmosphere, the Coronal Bright Points, can be formed, acquire energy, and be disrupted through the action of solar granulation.
When the Sun is observed from space with X-ray or extreme ultraviolet detectors, its atmosphere is seen to be full of roundish bright points with sizes similar to our planet Earth. These Coronal Bright Points (CBPs) are found to be consisted of sets of bright magnetic arcs that confine very hot plasma and emit enormous amounts of energy for hours and even days, typically disappearing after a series of eruptive phenomena.
So far, the existing CBP models have been very idealized, missing crucial aspects of the physics of the Sun such as the energization of the magnetic structures by means of the solar granules and the radiative transfer to explain the coldest solar atmospheric layers. In a paper recently published in the journal Astrophysical Journal Letters, Daniel Nóbrega Siverio and Fernando Moreno Insertis have studied the CBPs using a state-of-the-art numerical code, the Bifrost code, that allows these astrophysicists to model the Sun with the necessary realism to include convective and radiative processes that fundamentally influence the heating of the solar atmosphere.
The two researchers demonstrate for the first time that the action of solar granulation on a magnetic structure of the type expected in many CBPs gives rise to hot and bright arcs, thus being able to explain different features observed with solar space missions for decades. In addition, in the paper, the authors show how new magnetic flux brought from the solar interior to the surface by the granular convective motions even in small scales is enough to destabilize and disrupt the CBP topology, leading to cool ejections (surges) and hot collimated ejections (coronal jets) as frequently detected in observations at the end of the CBP lifetime. The article also includes predictions about the cold regions underneath a CBP and about the small-scale structure that have not yet been approached from an observational point of view. These predictions will require very high-resolution data, such as those from the Swedish 1-m Solar Telescope (SST, in La Palma) and those from the recent Solar Orbiter space mission, in order to be confirmed.
Experiment overview. Top: Main stage of the experiment illustrating the set of hot magnetic arcs that conform the CBP. Bottom: Eruptive stage showing a surge and coronal jet. (a) Temperature. (b) Synthetic SDO/AIA 193 with superimposed magnetic field lines. (c) Synthetic Solar Orbiter/EUI-HRI 174. (d) IRIS Si IV 1393.755 A. Olive line on Panels (b) and (c): T=100000 K isocontour.
The numerical experiment of this work has required thousands of hours of calculation in two of the most advanced supercomputing facilities in the world: Betzy (in Norway) and MareNostrum (in Spain). The work is also included within the project: “Unraveling Surges: a joint perspective from numerical models, observations, and machine learning”, this ISSI Team is devoted to analyze the cool chromospheric ejections commonly associated with eruptive phenomena in the Sun.
Reference
Nóbrega-Siverio, D. and Moreno-Insertis, F.: “A 2D Model for Coronal Bright Points: Association with Spicules, UV Bursts, Surges, and EUV Coronal Jets”, 2022, ApJL,
DOI: https://doi.org/10.3847/2041-8213/ac85b6 (Open Access)
Coronal mass ejections (CMEs) represent some of the most energetic processes in the entire solar system. They are often associated with Solar Energetic Particle Events (SEP events) and are major concerns of space weather studies. When CMEs happen, they drive shock waves in front of them and charged particles are accelerated at the shock front through the diffusive shock acceleration mechanism. Protons and ions can be accelerated to the energy beyond 1 GeV/nuc in some of the most energetic SEP events. Understanding how particles are accelerated in these events and how these accelerated particles propagate to the Earth has been a central problem for space plasma physics.
Members in ISSI Team #469, including team leader Dr. G. Li and team member Dr. L. Zhao has recently won a National Science Foundation (NSF) grant through the ANSWERS program. This four-year, $2.301 million grant from the NSF started in July 2022 and will assist the PI and his team to develop a comprehensive scientific model to understand and predict how CMEs influence the energetic particle radiation environment in the inner solar system and Earth’s magnetosphere, and compare those results with measurements at the Earth’s surface. The grant supports a multidisciplinary team including UAH, the University of Michigan, the University of Wisconsin-River Falls, and the National Solar Observatory. Dr Li and Dr. Zhao, from UAH and UM are PI and Co-PI of this grant. The propagation of energetic protons and ions in the solar wind follow the same interplanetary magnetic field (IMF) lines as those energetic electrons, and studying the configuration of the IMFs is the goal of the ISSI team 469. We expect our ISSI study will be of great value to the newly funded NSF ANSWERS program.
Twenty-five International Teams have been selected by the ISSI Science Committee for implementation from the proposals received in response to the 2022 call.
As one of ISSI’s and ISSI-BJ’s tools, International Teams of up to 15 scientists address specific self-defined problems in the Space and Earth Sciences, analyzing data and comparing these with models and theories. The teams work together in an efficient and flexible format with typically 2-3 one-week meetings over two years. The results of the studies are published in the peer-reviewed literature.
The next call for proposals will be issued in January 2023.
Astronomers have known for a long time that large galaxies grow through accretion and merging of smaller systems. A recent study published in Nature Astronomy demonstrates that this fundamental pattern of structure formation also applies to galactic satellites on small scales. A team of Italian researchers and members of the ISSI/ISSI-BJ Team #444 has discovered an old star cluster in the Large Magellanic Cloud (LMC) whose chemical composition is unambiguously pointing to an external origin.
The Large Magellanic Cloud. In the inset: zooming in the globular cluster NGC 2005. Image Credits: A. Mucciarelli / University of Bologna / Italian National Institute for Astrophysics (INAF)
How do galaxies grow? It is well known that large galaxies become larger and larger by accreting small satellite systems. The team has now found evidence that this is true also on small scales, for the satellites themselves. By examining the chemical properties of a sample of 11 globular clusters in the Large Magellanic Cloud (LMC), they noticed that one of those old groupings of stars had a very different chemical composition than the others. Using high-resolution stellar spectra obtained with the ESO (European Southern Observatory) Very Large Telescope and with the Magellan Telescope in Las Campanas Observatory, Chile, the astronomers discovered that NGC 2005’s stars have less silicon, calcium, copper and zinc than any other star in the targeted LMC clusters. By performing numerical simulations, they demonstrated that the peculiar chemical composition observed in NGC 2005 is best explained if this cluster is the remnant of an ancient, small stellar system that was swallowed by the LMC long ago.
“The chemical composition of a star is like its DNA and there is no way to change it” says Professor Alessio Mucciarelli, first author of the study. “Therefore, the chemistry of a star tells us about the genealogy of this star, namely, the chemical composition of the gas from which it formed. Our discovery demonstrates that NGC 2005 was born outside the LMC.”
Donatella Romano, co-author of the study and co-leader of the ISSI/ISSI-BJ team “Chemical abundances in the ISM: the litmus test of stellar IMF variations in galaxies across cosmic time”, performed the numerical simulations. “NGC 2005 must have been born in a peculiar environment, characterized by a low-level star formation rate and by a stellar initial mass function (IMF) skewed against the most massive stars,” she says. “A clear indication in favor of this interpretation is provided by the extremely low zinc abundance of NGC 2005’s stars: zinc is produced mostly by hypernovae that have stellar progenitors 30-40 times as massive as the Sun, or even more. Hence, a low abundance of this element strongly suggests that the formation of its main stellar producers was somehow suppressed or, at least, strongly reduced.”
Reference:
Mucciarelli, A., Massari, D., Minelli, A. et al.A relic from a past merger event in the Large Magellanic Cloud. Nat Astron (2021). https://doi.org/10.1038/s41550-021-01493-y
