Periodic Reporting for period 1 - FRoST (The Foreshock and its Role in Solar-Terrestrial relations)
Período documentado: 2017-03-15 hasta 2019-03-14
In our modern society relying massively on space-based assets, the effects of solar activity on near-Earth space have become a major concern. Just like hurricanes on the ground, solar storms can disturb the conditions in space and cause harmful space weather. The vulnerability of critical technologies such as global navigation satellite systems or power grids calls for reliable forecasting of adverse space weather, so that its effects can be mitigated. One of the main sources of adverse space weather at Earth are magnetic clouds, giant clouds of solar particles and magnetic fields originating from tremendous eruptions in the Sun’s atmosphere. Understanding how these magnetic clouds affect the different regions of near-Earth space is key to accurate space weather forecasting.
In FRoST, we focus on the interaction of magnetic clouds with the first region of near-Earth space that they encounter on their journey earthward: the foreshock, a region characterised by intense electromagnetic wave activity [see Figure]. Recent studies have shown that processes occurring in the foreshock can have important effects in the Earth’s magnetic domain, the magnetosphere, and even down to the Earth’s surface. Our main goal with this project is to assess for the first time whether the foreshock plays a significant role in the interaction of magnetic clouds with near-Earth space, and thus whether it should be taken into account in space weather models.
Our results show that magnetic clouds affect strongly the foreshock, and in particular the properties of waves in this region. However, these changes do not appear to affect notably the global intensity of the disturbances triggered by the magnetic clouds closer to Earth. The foreshock may have more localised effects, for example enhancing wave activity in some parts of the magnetosphere. This needs to be further investigated if refined, more regional, space weather forecasts are to be developed.
In FRoST, we focus on the interaction of magnetic clouds with the first region of near-Earth space that they encounter on their journey earthward: the foreshock, a region characterised by intense electromagnetic wave activity [see Figure]. Recent studies have shown that processes occurring in the foreshock can have important effects in the Earth’s magnetic domain, the magnetosphere, and even down to the Earth’s surface. Our main goal with this project is to assess for the first time whether the foreshock plays a significant role in the interaction of magnetic clouds with near-Earth space, and thus whether it should be taken into account in space weather models.
Our results show that magnetic clouds affect strongly the foreshock, and in particular the properties of waves in this region. However, these changes do not appear to affect notably the global intensity of the disturbances triggered by the magnetic clouds closer to Earth. The foreshock may have more localised effects, for example enhancing wave activity in some parts of the magnetosphere. This needs to be further investigated if refined, more regional, space weather forecasts are to be developed.
In this project, we have used a combination of computer simulations and observations from scientific spacecraft orbiting the Earth to understand what happens in the foreshock when a magnetic cloud arrives at Earth. The numerical simulations were performed with the Vlasiator code, which provides global simulations of near-Earth space in which small-scale (ion-scale) processes are also included. The latter are crucial to describe the processes occurring in the foreshock. Spacecraft measurements were obtained mostly from the Cluster mission, as its four spacecraft flying in formation allow to determine accurately the wave properties in the foreshock.
Our work revealed that the foreshock wave properties are strongly modified during magnetic clouds, both at the small scales and on the large scales. As a result, we also found changes in the wave properties in the region downstream of the foreshock (relative to the flow of particles coming from the Sun), the magnetosheath [see Figure]. When using global indices to quantify the intensity of space weather disturbances in near-Earth space, we did not find compelling evidence of the influence of the foreshock, suggesting that its effects are either more localised, or not taken into account in these so-called geomagnetic indices. In particular, there are no proxies of wave activity, while it is know that foreshock waves propagate into the magnetosphere, and can thus be a significant source of disturbances.
These results are the topic of one published peer-reviewed paper, another under review, and two manuscripts in preparation. They have been presented at 7 scientific conferences, out of which 3 presentations were invited talks. 3 more invited presentations and one contributed talk are planned later in 2019. The published results have been advertised on social media, and more online advertisement is planned to accompany the upcoming publications.
Our work revealed that the foreshock wave properties are strongly modified during magnetic clouds, both at the small scales and on the large scales. As a result, we also found changes in the wave properties in the region downstream of the foreshock (relative to the flow of particles coming from the Sun), the magnetosheath [see Figure]. When using global indices to quantify the intensity of space weather disturbances in near-Earth space, we did not find compelling evidence of the influence of the foreshock, suggesting that its effects are either more localised, or not taken into account in these so-called geomagnetic indices. In particular, there are no proxies of wave activity, while it is know that foreshock waves propagate into the magnetosphere, and can thus be a significant source of disturbances.
These results are the topic of one published peer-reviewed paper, another under review, and two manuscripts in preparation. They have been presented at 7 scientific conferences, out of which 3 presentations were invited talks. 3 more invited presentations and one contributed talk are planned later in 2019. The published results have been advertised on social media, and more online advertisement is planned to accompany the upcoming publications.
This project has allowed us to make significant progress beyond the state of the art. We have presented the first evidence of the effects of magnetic clouds on foreshock waves, revealing a more complex wave activity in the foreshock during magnetic clouds, and a more intricate large-scale structuring of the foreshock wave field. This unexpected result is well supported by the excellent agreement between numerical simulations and multi-spacecraft measurements. We have further shown that these waves are observed in conjunction with atypical ion velocity distribution functions. We have also performed the first investigation of the magnetosheath properties during magnetic clouds, showing that they are also modified during such events.
These changes of the wave properties in the foreshock and magnetosheath are likely to affect wave activity in the magnetosphere, which is the source of important space weather effects, such as particle acceleration in the Earth’s radiation belts, heating of the upper atmosphere, and enhanced satellite drag. Our results shed new light on the possible sources of these space weather effects, as foreshock waves have unusual signatures during magnetic cloud events.
The modifications of the foreshock wave properties have also significant implications for processes occurring at the bow shock. Foreshock waves are known to cause ripples at the bow shock surface. The changes in the structuring of the foreshock wave field is likely to affect the bow shock, and thus particle reflection which strongly depends on the shock shape. Shock processes and particle reflection and acceleration at collisionless shocks are universal processes, taking place in many different environments, from the Sun’s atmosphere to supernovae. A better understanding of foreshock processes can therefore foster progress in the study of other shocks in the universe.
It has been known for a very long time that foreshock waves can be transmitted into the magnetosphere. However, how they cross the magnetosheath, which acts as a transition region between the foreshock and the magnetosphere, is still outstanding. To solve this long-standing science question, we joined forces with other experts of waves in near-Earth space to constitute an ISSI team (team leader: Lucile Turc) and work together during workshops organised at the International Space Science Institute in Bern (Switzerland). The first team meeting will take place in May 2019, and the team’s activities will continue until 2020. The present project has therefore fostered ideal conditions to finally answer this unsolved question in magnetospheric physics.
On a broader scope, the conditions encountered during magnetic clouds are extreme at Earth, but they can be more common in other planetary environments. Outside of our solar system, exoplanets orbiting close to their host stars are immersed in intense magnetic fields, similar to or even larger than that associated with magnetic clouds at Earth. Considering our findings for the Earth’s foreshock, it is possible that their magnetic environment is much more turbulent than expected. Understanding the interaction of the stellar wind with an exoplanet’s magnetosphere is crucial in order to estimate the magnitude of atmospheric escape due to stellar activity, which is key to assessing the exoplanet’s habitability.
These changes of the wave properties in the foreshock and magnetosheath are likely to affect wave activity in the magnetosphere, which is the source of important space weather effects, such as particle acceleration in the Earth’s radiation belts, heating of the upper atmosphere, and enhanced satellite drag. Our results shed new light on the possible sources of these space weather effects, as foreshock waves have unusual signatures during magnetic cloud events.
The modifications of the foreshock wave properties have also significant implications for processes occurring at the bow shock. Foreshock waves are known to cause ripples at the bow shock surface. The changes in the structuring of the foreshock wave field is likely to affect the bow shock, and thus particle reflection which strongly depends on the shock shape. Shock processes and particle reflection and acceleration at collisionless shocks are universal processes, taking place in many different environments, from the Sun’s atmosphere to supernovae. A better understanding of foreshock processes can therefore foster progress in the study of other shocks in the universe.
It has been known for a very long time that foreshock waves can be transmitted into the magnetosphere. However, how they cross the magnetosheath, which acts as a transition region between the foreshock and the magnetosphere, is still outstanding. To solve this long-standing science question, we joined forces with other experts of waves in near-Earth space to constitute an ISSI team (team leader: Lucile Turc) and work together during workshops organised at the International Space Science Institute in Bern (Switzerland). The first team meeting will take place in May 2019, and the team’s activities will continue until 2020. The present project has therefore fostered ideal conditions to finally answer this unsolved question in magnetospheric physics.
On a broader scope, the conditions encountered during magnetic clouds are extreme at Earth, but they can be more common in other planetary environments. Outside of our solar system, exoplanets orbiting close to their host stars are immersed in intense magnetic fields, similar to or even larger than that associated with magnetic clouds at Earth. Considering our findings for the Earth’s foreshock, it is possible that their magnetic environment is much more turbulent than expected. Understanding the interaction of the stellar wind with an exoplanet’s magnetosphere is crucial in order to estimate the magnitude of atmospheric escape due to stellar activity, which is key to assessing the exoplanet’s habitability.