Electric current systems at Mars and Venus

Mapping Intimacies ◽

10.5194/epsc2020-1017 ◽

2020 ◽

Author(s):

Markus Fränz ◽

Eduard Dubinin ◽

Lukas Maes

Keyword(s):

Solar Wind ◽

Electric Current ◽

Dynamic Models ◽

Bow Shock ◽

Dynamic Effects ◽

Current Configuration ◽

Ion Escape ◽

Shock Location ◽

Physical Effects ◽

Current Systems

The physics of the interaction of unmagnetized planets with the Solar wind has been investigated since the first Mariner spacecraft did reach Mars and Venus more than 50 years ago. Recent observations of the magnetic fields at Mars allowed&#160; to derive the global electric current configuration in the Martian system. Earlier magneto hydro-dynamic models were able to predict the formation and location of the bowshock in front of the planets. More sophisticated models&#160; of the interaction with the magnetized solar wind later could demonstrate the global static picture of the plasma environment of Mars and Venus. But earlier models were rarely able to model dynamic effects and the timing of physical process in this interaction. We here use the open source PLUTO code in its 3D spherical hydrodynamic and magneto-hydrodynamic version.&#160; We also develop a multi-species extension of this code.&#160; We investigate the interaction of the solar wind with the ionospheres of Mars and Venus with the aim to understand the&#160; importance of &#160;different physical effects on bow shock location, ion escape and specifically the electric current structures.&#160; We compare these simulations to observations by the VEX and MAVEN spacecraft.

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Modulation of the solar wind driven ion escape from unmagnetized planets by ultra-low-frequency foreshock waves in a global hybrid simulation

10.5194/egusphere-egu2020-6891 ◽

2020 ◽

Author(s):

Riku Jarvinen ◽

Esa Kallio ◽

Tuija Pulkkinen

Keyword(s):

Solar Wind ◽

Large Scale ◽

Low Frequency ◽

Hybrid Simulation ◽

Bow Shock ◽

Upstream Region ◽

Ulf Waves ◽

Solar Wind Interaction ◽

Ion Escape ◽

A Charge

We study the solar wind interaction with Venus in a 3-dimensional global hybrid model where ions are treated as particles and electrons are a charge-neutralizing fluid. We concentrate on large-scale ultra-low frequency (ULF) waves in the ion foreshock and how they affect the energization and escape of planetary ions. The ion foreshock forms in the upstream region ahead of the quasi-parallel bow shock, where the angle between the shock normal and the magnetic field is smaller than about 45 degrees. The magnetic connection with the bow shock allows backstreaming of the solar wind ions leading to the formation of the ion foreshock. This kind of beam-plasma configuration is a source of free energy for the excitation of plasma waves. The foreshock ULF waves convect downstream with the solar wind flow and encounter the bow shock and transmit in the downstream region. We analyze the coupling of the ULF waves with the planetary ion acceleration and compare Venus and Mars in a global hybrid simulation.

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Estimation of a planetary magnetic field using a reduced magnetohydrodynamic model

Annales Geophysicae ◽

10.5194/angeo-35-465-2017 ◽

2017 ◽

Vol 35 (3) ◽

pp. 465-474

Author(s):

Christian Nabert ◽

Daniel Heyner ◽

Karl-Heinz Glassmeier

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Dipole Moment ◽

Statistical Error ◽

Solar Wind Plasma ◽

Bow Shock ◽

Data Sets ◽

Abstract Knowledge ◽

Planetary Magnetic Fields ◽

Shock Location

Abstract. Knowledge of planetary magnetic fields provides deep insights into the structure and dynamics of planets. Due to the interaction of a planet with the solar wind plasma, a rather complex magnetic environment is generated. The situation at planet Mercury is an example of the complexities occurring as this planet's field is rather weak and the magnetosphere rather small. New methods are presented to separate interior and exterior magnetic field contributions which are based on a dynamic inversion approach using a reduced magnetohydrodynamic (MHD) model and time-varying spacecraft observations. The methods select different data such as bow shock location information or magnetosheath magnetic field data. Our investigations are carried out in preparation for the upcoming dual-spacecraft BepiColombo mission set out to precisely estimate Mercury's intrinsic magnetic field. To validate our new approaches, we use THEMIS magnetosheath observations to estimate the known terrestrial dipole moment. The terrestrial magnetosheath provides observations from a strongly disturbed magnetic environment, comparable to the situation at Mercury. Statistical and systematic errors are considered and their dependence on the selected data sets are examined. Including time-dependent upstream solar wind variations rather than averaged conditions significantly reduces the statistical error of the estimation. Taking the entire magnetosheath data along the spacecraft's trajectory instead of only the bow shock location into account further improves accuracy of the estimated dipole moment.

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The responses of the earth’s magnetopause and bow shock to the IMF Bz and the solar wind dynamic pressure: a parametric study using the AMR-CESE-MHD model

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2018030 ◽

2018 ◽

Vol 8 ◽

pp. A41 ◽

Cited By ~ 4

Author(s):

Juan Wang ◽

Zhifang Guo ◽

Yasong S. Ge ◽

Aimin Du ◽

Can Huang ◽

...

Keyword(s):

Solar Wind ◽

Mach Number ◽

Dynamic Pressure ◽

Bow Shock ◽

Solar Wind Dynamic Pressure ◽

The Earth ◽

Shock Location ◽

Mhd Model ◽

Upstream Solar Wind ◽

The Imf

We have used the AMR-CESE-MHD model to investigate the influences of the IMF Bz and the upstream solar wind dynamic pressure (Dp) on Earth’s magnetopause and bow shock. Our results present that the earthward displacement of the magnetopause increases with the intensity of the IMF Bz. The increase of the northward IMF Bz also brings the magnetopause closer to the Earth even though with a small distance. Our simulation results show that the subsolar bow shock during the southward IMF is much closer to the Earth than during the northward IMF. As the intensity of IMF Bz increases (also the total field strength), the subsolar bow shock moves sunward as the solar wind magnetosonic Mach number decreases. The sunward movement of the subsolar bow shock during southward IMF are much smaller than that during northward IMF, which indicates that the decrease of solar wind magnetosonic Mach number hardly changes the subsolar bow shock location during southward IMF. Our simulations also show that the effects of upstream solar wind dynamic pressure (Dp) changes on both the subsolar magnetopause and bow shock locations are much more significant than those due to the IMF changes, which is consistent with previous studies. However, in our simulations the earthward displacement of the subsolar magnetopause during high solar wind Dp is greater than that predicted by the empirical models.

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Estimating Ion Escape from Unmagnetized Planets

10.5194/angeo-2021-40 ◽

2021 ◽

Author(s):

Mats Holmstrom

Keyword(s):

Solar Wind ◽

Heavy Ion ◽

Mass Loading ◽

Early Solar System ◽

Ion Escape ◽

Ion Production ◽

Hybrid Plasma ◽

Shock Location ◽

Upstream Solar Wind ◽

Best Fit

Abstract. We propose a new method to estimate ion escape from unmagnetized planets that combines observations and models. Assuming that upstream solar wind conditions are known, a computer model of the interaction between the solar wind and the planet is executed for different ionospheric ion production rates. This results in different amounts of mass loading of the solar wind. Then we obtain the ion escape rate from the model run that best fit observations of the bow shock location. As an example of the method we estimate the heavy ion escape from Mars on 2015-03-01 to be 2 · 1024 ions per second, using a hybrid plasma model and observations by MAVEN and Mars Express. This method enables studies of how escape depend on different parameters, and also escape rates during extreme solar wind conditions, applicable to studies of escape in the early solar system, and at exoplanets.

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Energy conversion at the terrestrial bow shock

10.5194/egusphere-egu2020-5246 ◽

2020 ◽

Author(s):

Maria Hamrin ◽

Ramon Lopez ◽

Pauline Dredger ◽

Herbert Gunell ◽

Oleksandr Goncharov ◽

...

Keyword(s):

Solar Wind ◽

Particle Acceleration ◽

Energy Conversion ◽

Mechanical Energy ◽

Bow Shock ◽

Passive Element ◽

Magnetospheric Multiscale ◽

Bow Shocks ◽

Current Systems ◽

The Magnetic Field

At Earth&#8217;s bow shock, the supersonic solar wind is slowed down and deflected around the magnetosphere. To many this is "just a bow shock", a simple and quite passive element of solar-terrestrial physics. However, it has recently been realized that the bow shock plays a significantly more important role with currents on the bow shock connecting through the magnetosheath to the magnetospheric current systems. The bow shock current cannot close locally, since the magnetic field compression in the magnetosheath cannot be maintained globally. The bow shock current is inevitably a generator current extracting mechanical energy from the supersonic solar wind, and feeding it to other processes such as acceleration of the magnetosheath flow, local particle acceleration at the bow shock and dissipation in the distant ionosphere. Here we use data from the first dayside season of the Magnetospheric Multiscale (MMS) mission to investigate the generator properties of the terrestrial bow shock. Typically, the main shock ramp shows clear generator properties, but for some of the more turbulent bow shocks, generator properties may also be observed slightly downstream the ramp. This may be due to effects from shock motions and shock nonstationaity and reformation. Moreover, sometimes a weaker load can be seen in the upstream foot region due to local particle acceleration. We also find that the generator capacity of the bow shock decreases with decreasing bow shock angle as well as with increasing upstream plasma beta and solar Mach number. A better understanding of the energy conversion properties of the terrestrial bow shock will be useful also for the understanding of other astrophysical shock currents. The currents must close somewhere and deposit energy somewhere.

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The influence of crustal magnetic fields on the Martian bow shock : a statistical analysis of Mars Volatile EvolutioN and Mars Express observations

10.5194/epsc2020-819 ◽

2020 ◽

Author(s):

Philippe Garnier ◽

Christian Jacquey ◽

Christian Mazelle ◽

Xiaohua Fang ◽

Jacob Gruesbeck ◽

...

Keyword(s):

Solar Wind ◽

Magnetic Fields ◽

Extreme Ultraviolet ◽

Dynamic Pressure ◽

Bow Shock ◽

Machine Learning Techniques ◽

Mars Atmosphere ◽

Mars Express ◽

Shock Location ◽

The Impact

The Martian interaction with the solar wind is unique due to the influence of remanent crustal magnetic fields. The recent studies by the Mars Express and Mars Atmosphere and Volatile Evolution missions underline the strong and complex influence of the crustal magnetic fields on the Martian environment and its interaction with the solar wind. Among them is the influence on the dynamic plasma boundaries that shape this interaction and on the bow shock in particular. Compared to other drivers of the shock location (e.g. solar dynamic pressure, extreme ultraviolet fluxes), the influence of crustal magnetic fields are less understood, with essentially differences observed between the southern and northern hemispheres attributed to the crustal fields. In this presentation we analyze in detail the influence of the crustal fields on the Martian shock location by combining for the first time datasets from two different spacecraft (MAVEN/MEX). An application of machine learning techniques will also be used to increase the list of MAVEN shocks published to date. We show in particular the importance for analyzing biases due to multiple parameters of influence through a partial correlation approach. We also compare the impact of crustal fields with the other parameters of influence, and show that the main drivers of the shock location are by order of importance extreme ultraviolet fluxes and magnetosonic Mach number, crustal fields and then solar wind dynamic pressure.

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