PS4.3

The interaction between the interplanetary medium and planetary environments gives rise to different phenomena on several temporal and spatial scales. Here we use the Hilbert-Huang Transform (HHT) to characterize both local and global properties of Mercury's environment as seen during two MESSENGER flybys with different upstream solar wind conditions. Hence, we may infer that the near-Mercury environment presents some different local features with respect to the ambient solar wind, due to both interaction processes and intrinsic structures of the Hermean environment. Our findings support the ion kinetic nature of the Hermean plasma structures, with the magnetosheath being characterized by inhomogeneous ion-kinetic intermittent fluctuations, superimposed to both MHD fluctuations and large-scale field structure. We show that the HHT analysis allow to capture and reproduce some interesting features of the Hermean environment as flux transfer events, Kelvin-Helmholtz vortices, and ULF wave activity, thus providing a suitable method for characterizing physical processes of different nature. Our approach demonstrate to be very promising for the characterization of the structure and dynamics of planetary magnetic field at different scales, for the identification of boundaries, and for discriminating the different scale-dependent features of global and local source processes that can be used for modelling purposes.

How to cite: Milillo, A., Alberti, T., Ivanovski, S. L., Laurenza, M., Massetti, S., Mangano, V., Mura, A., Ippolito, A., Plainaki, C., De Angelis, E., Orsini, S., and Rispoli, R.: Dynamical features of the near-Hermean environment under different solar wind conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8215, https://doi.org/10.5194/egusphere-egu21-8215, 2021.

Mercury’s magnetosphere is considered to be a unique and dynamic system, primarily due to the proximity of the planet to the Sun. The interaction between solar wind and embedded Interplanetary Magnetic Field (IMF) and the dayside Hermean magnetosphere drive an electric current on the magnetopause boundary of the system. The influence of the time-dependent magnetic field generated by this magnetopause current on Mercury’s interior is key to understanding the subsurface structure of the planet, as electromagnetic induction is a valuable technique for delineating electrical properties of planetary interiors. Here we assess the impact a changing IMF direction has on the Hermean magnetopause currents, and the resulting inducing magnetic field. Analytical models of conditions at the magnetopause are combined with measurements made by MESSENGER’s magnetometer as the spacecraft crossed the subsolar magnetopause boundary during the first ‘hot season’.

These MESSENGER magnetopause boundary crossings show that the introduction of the external IMF changes the direction of the magnetopause current by ~50°, compared to the case where only the internal planetary field is considered. Analytical modelling suggests that for a heliospheric current sheet crossing without any change in solar wind dynamic pressure (an east-west reversal of the IMF polarity typical at Mercury), the inducing field at Mercury’s surface caused by the resulting magnetopause current sheet dynamics is of the order of 10% of the global planetary field. The results suggest that variability of the IMF alone can have an appreciable effect on Mercury’s magnetopause current direction and generate a significant inducing magnetic field around the planet. The arrival of the BepiColombo mission will allow this response to be further explored as a method of probing Mercury’s interior.

How to cite: Zomerdijk-Russell, S. and Masters, A.: Variability of the interplanetary magnetic field as a driver of electromagnetic induction in Mercury’s interior, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8339, https://doi.org/10.5194/egusphere-egu21-8339, 2021.

Mercury’s magnetic cusp allows solar wind plasma to precipitate into the magnetosphere, exosphere, and directly to the surface. This precipitation of solar wind leads to the production of neutrals in the exosphere and/or ions in the magnetosphere and thus it has an important role in shaping Mercury’s space environment. Characterizing the ion properties in the cusp region is important for obtaining a better understanding of the Sun-planet interactions and assessing the solar wind penetration in Mercury’s magnetosphere.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has observed the northern cusp regularly during its orbital phase. We have analyzed plasma data obtained by the Fast Imaging Plasma Spectrometer (FIPS) onboard MESSENGER under extreme solar wind events and compared the resulting ion properties in the northern cusp with those under non-extreme solar wind events for the first time. We found that (1) flux enhancement is confirmed under the extreme solar wind, and (2) the ion distribution in the cusp has a smaller kappa value than in the magnetosheath, suggesting ion acceleration occurs in the magnetosphere.

How to cite: Aizawa, S., André, N., and Raines, J.: Ion properties of Mercury’s northern cusp under extreme solar wind observed by MESSENGER, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11897, https://doi.org/10.5194/egusphere-egu21-11897, 2021.

We explore the dynamic magnetosphere of Mercury by employing a three‐dimensional hybrid particle-in-cell (particle ions and massless fluid electrons) code – hybrid-VPIC. The newly developed hybrid-VPIC code (based on the high-performance fully kinetic Vector Particle-In-Cell, VPIC code) incorporates ion kinetics (beam and anisotropy driven instabilities) that are critical for foreshock and magnetosheath physics, as well as the Hall effect which is important for collisionless magnetic reconnection; therefore, it is particularly well suited for investigating the kinetic physics of Mercury's dynamic magnetosphere. The simulation results are in good agreement with MESSENGER’s magnetic field measurements during its second Mercury flyby. We will investigate collisionless magnetic reconnection (including flux transfer events or FTEs and ion velocity distribution functions) and foreshock physics (including plasma turbulence and particle acceleration) in this study.

How to cite: Dong, C., Le, A., Wang, L., Stanier, A., Wetherton, B., Daughton, W., Bhattacharjee, A., Slavin, J., and DiBraccio, G.: Global Hybrid-VPIC Simulations of the Solar Wind Interaction with Mercury's Dynamic Magnetosphere: Reconnection and Foreshock, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12954, https://doi.org/10.5194/egusphere-egu21-12954, 2021.

We inspect the evolution of stream interaction regions from Earth to Mars for the declining solar cycle 24. In particular, the opposition phases of the two planets are analyzed in more detail. So far, there is no study comparing the long-term properties of stream interaction regions and accompanying high-speed streams at both planets for the same time period. We build a catalogue covering a dataset of all measured stream interaction regions at Earth and Mars for the time period December 2014 – November 2018. The number of events (>120) allows for a strong statistical basis. To build the catalogue we use near-earth OMNI data as well as measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. For the opposition phase, we additionally use image data from the Solar Dynamics Observatory to complement the in-situ observations. Bulk speed, proton density, temperature, magnetic field magnitude and total perpendicular pressure are statistically evaluated using a superposed epoch analysis. For the opposition phase, coronal holes that are linked to individual streams are identified. The extracted coronal hole areas (using CATCH) and their longitudinal/latitudinal extension are correlated to the duration and maximum bulk speed of the high-speed stream following the passage of a stream interaction region. We find that an expansion of the stream interface from 1 to 1.5 AU is most visible in magnetic field and total perpendicular pressure. The duration of the high-speed stream does not increase significantly from Earth to Mars, however, the stream crest seems to increase. The amplitudes of the SW parameters are found to only slightly increase or stagnate from 1 – 1.5 AU. We arrive at similar correlation coefficients for both planets with the properties of the related coronal holes. There is a stronger linking of maximum bulk speed to latitudinal extent of the coronal hole than to the longitudinal. On average, the occurrence rate of fast forward shocks increases from Earth to Mars.

How to cite: Geyer, P., Temmer, M., Guo, J., and Heinemann, S.: Evolution of stream interaction regions from 1 to 1.5 AU, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12513, https://doi.org/10.5194/egusphere-egu21-12513, 2021.

The Martian interaction with the solar wind is unique due to the influence of multiple internal and external drivers, including remanent crustal magnetic fields that make the interaction unique. In this work we focus on the analysis of the dynamics of the plasma boundaries that shape the interaction of the planet with its environment, and in particular of the shock whose location varies in a complex way. We use multi spacecraft datasets from three missions (Mars Global Surveyor, Mars Express, Mars Atm-osphere and Volatile Evolution) to provide a coherent picture of the shock drivers. We show how the use of different statistical parameters or cross correlations may modify conclusions. We thus propose the use of refined methods, such as partial correlation analysis or Akaike Information Criterion approach to analyse the multiple drivers of the shock location and rank their relative importance: solar wind dynamic pressure, extreme ultraviolet fluxes, magnetosonic mach number, crustal magnetic fields, but also solar wind orientation parameters. Seasonal effects of crustal fields on the shock, through ionospheric coupling, are also investigated.

How to cite: Garnier, P., Jacquey, C., Génot, V., Sanchez-Cano, B., Gendre, X., Mazelle, C., Fang, X., Gruesbeck, J. R., Hall, B., Halekas, J. S., and Jakosky, B. M.: Dynamics of the Martian bow shock location, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9157, https://doi.org/10.5194/egusphere-egu21-9157, 2021.

High-Mach-number collisionless shocks are found in planetary systems and supernova remnants (SNRs). Electrons are heated at these shocks to temperatures well above the Rankine–Hugoniot prediction. However, the processes responsible for causing the electron heating are still not well understood. We use a set of large-scale particle-in-cell simulations of nonrelativistic shocks in the high-Mach-number regime to clarify the electron heating processes. The physical behavior of these shocks is defined by ion reflection at the shock ramp. Further interactions between the reflected ions and the upstream plasma excites electrostatic Buneman and two-stream ion–ion Weibel instabilities. Electrons are heated via shock surfing acceleration, the shock potential, magnetic reconnection, stochastic Fermi scattering, and shock compression. The main contributor is the shock potential. The magnetic field lines become tangled due to the Weibel instability, which allows for parallel electron heating by the shock potential. The constrained model of electron heating predicts an ion-to-electron temperature ratio within observed values at SNR shocks and in Saturn’s bow shock. We also present evidence for field amplification by the Weibel instability. The normalized magnetic field strength strongly correlates with the Alfvenic Mach number, as is in-situ observed at Saturn's bow shock.

How to cite: Bohdan, A., Pohl, M., Niemiec, J., Morris, P. J., Matsumoto, Y., Amano, T., Hoshino, M., and Sulaiman, A.: Kinetic simulations of high Mach shocks: PIC simulations vs in-situ measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-556, https://doi.org/10.5194/egusphere-egu21-556, 2021.