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.
