author = {{Dyadechkin}, S. and {Kallio}, E. and {Wurz}, P.},
  title = {{New fully kinetic model for the study of electric potential, plasma and dust above lunar landscapes}},
  journal = {Journal of Geophysical Research (Space Physics)},
  keywords = {New electrostatic 1-D/2-D/3-D model developed to study direct plasma-surface interaction. 

             The model was used to study plasma above various 2-D lunar surfaces. Landscape shape dominates

             properties of plasma above the surface, electric field, and dust},
  year = 2015,
  month = mar,
  volume = 120,
  pages = {1589-1606},
  abstract = {{We have developed a new fully kinetic electrostatic simulation, HYBes, to study how the lunar 

landscape affects the electric potential and plasma distributions near the surface, and the properties of lifted dust. The 

model embodies new techniques that can be used in various types of physical 

environments and situations. We demonstrate the applicability of the new model in a situation 

involving three charged-particle species, which are solar wind electrons and protons, and lunar photoelectrons.

Properties of dust are studied with test particle simulations by using the electric 

fields derived from the HYBes model. 

Simulations show the high importance of the plasma and the electric potential 

near the surface. For comparison, the electric potential gradients near 

the landscapes with feature sizes of the order of the Debye length are much larger than

those near a flat surface at different solar zenith angles.

Furthermore, dust test particle simulations indicate that the landscape relief influences the dust location over the surface. 

The study suggests that the local landscape has to be taken into account when the distributions of plasma 

and dust above lunar surface are studied. The HYBes model can 

be applied not only at the Moon but also on a wide range of airless planetary objects such as 

Mercury, other planetary moons, asteroids and non-active comets.

  doi = {10.1002/2014JA020511},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Semenov}, V.~S. and {Dyadechkin}, S.~A. and {Heyn}, M.~F.},
  title = {{Buoyancy and the Penrose process produce jets from rotating black holes}},
  journal = {Physica Scripta},
  archiveprefix = {arXiv},
  eprint = {1404.2474},
  primaryclass = {astro-ph.HE},
  year = 2014,
  month = apr,
  volume = 89,
  number = 4,
  eid = {045003},
  pages = {045003},
  abstract = {{The exact mechanism by which astrophysical jets are formed is still unknown. 

It is believed that the necessary elements consist of a rotating (Kerr) black hole and a 

magnetized accreting plasma. We model the accreting plasma as a collection of magnetic 

flux tubes/strings. If such a tube falls into a Kerr black hole, then the leading portion 

loses angular momentum and energy as the string brakes. To compensate for this loss, 

momentum and energy is redistributed to the trailing portion of the tube. We found that 

buoyancy creates a pronounced helical magnetic field structure aligned with the spin axis. 

Along the field lines, the plasma is centrifugally accelerated close to the speed of light. 

This process leads to unlimited stretching of the flux tube since one part of the tube 

continues to fall into the black hole and, simultaneously, the other part of the string 

is pushed outward. Eventually, reconnection cuts the tube. The inner part is filled with 

new material and the outer part forms a collimated bubble-structured relativistic jet. 

Each plasmoid can be considered as an outgoing particle in the Penrose mechanism: it 

carries extracted rotational energy away from the black hole while the falling part, 

with corresponding negative energy, is left inside the ergosphere. 

  doi = {10.1088/0031-8949/89/04/045003},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Dyadechkin}, S. and {Kallio}, E. and {Jarvinen}, R.},
  title = {{A new 3-D spherical hybrid model for solar wind interaction studies}},
  journal = {Journal of Geophysical Research (Space Physics)},
  keywords = {new 3-D global spherical coordinate hybrid model},
  year = 2013,
  month = aug,
  volume = 118,
  pages = {5157-5168},
  abstract = {{A 3-D spherical hybrid model has been developed to study 

how the solar wind interacts with various solar system bodies. The main 

advantages of the new spherical model, called the HYB-s, compared with 

traditional Cartesian models are that the spherical model allows significantly 

reduced radial cell size and, consequently, a smaller total number of cells 

and particles in the simulation. The high radial resolution makes it possible 

to use the new model for 3-D physical studies that have not been feasible before. 

Especially, the spherical model allows the inclusion of self-consistent ionospheric 

photochemistry in global hybrid simulations of the solar wind interaction with 

terrestrial planets Venus and Mars. In this paper we describe the main aspects 

of the developed spherical hybrid model. We also study the solar wind interaction 

with Venus in a global hybrid simulation using the spherical hybrid model and our 

already published Cartesian hybrid model. The comparison between the two models 

suggests the high potential of the developed spherical hybrid model in studies 

of planetary plasma interactions. 

  doi = {10.1002/jgra.50497},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Jarvinen}, R. and {Kallio}, E. and {Dyadechkin}, S.},
  title = {{Hemispheric asymmetries of the Venus plasma environment}},
  journal = {Journal of Geophysical Research (Space Physics)},
  keywords = {Venus, plasma environment, induced magnetosphere, solar wind, interplanetary magnetic field, hybrid simulation},
  year = 2013,
  month = jul,
  volume = 118,
  pages = {4551-4563},
  abstract = {{We study the Venus-solar wind interaction and the hemispheric 

asymmetries of the Venus plasma environment in the global HYB-Venus hybrid 

simulation. We concentrate especially on the role of the flow-aligned 

interplanetary magnetic field (IMF) component (i.e., the Parker spiral angle 

or the IMF cone angle) and analyze the dawn-dusk and Esw asymmetries between 

four magnetic quadrants around Venus. Using the simulation model, we study 

two upstream condition cases in detail: the perpendicular IMF to the solar 

wind flow case and the nominal Parker spiral case (dominant flow-aligned IMF 

component). Several differences and similarities were found in these two 

simulation runs. Common features of the Venus plasma environment between 

the two cases include asymmetric magnetic barrier and tail lobes and asymmetric 

planetary ion escape in the direction of the solar wind convection electric 

field. Further, protons of planetary origin and of solar wind origin were 

found to follow similar velocity patterns in the Venus plasma wake in both 

cases. The differences when the IMF flow-aligned component is dominating 

compared to the perpendicular IMF case, the so-called (magnetic) dawn-dusk 

asymmetries, include the parallel bow shock and the foreshock region, 

the asymmetric magnetic barrier, the asymmetric tail current system, and 

the asymmetric central tail current sheet. Further, the escaping planetary 

H+ and O+ ion fluxes are concentrated more on the hemisphere of the parallel 

bow shock. When interpreting in situ plasma and magnetic observations from 

Venus, the features of at least these two basic IMF configurations should 

be considered. 

  doi = {10.1002/jgra.50387},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Kallio}, E. and {Jarvinen}, R. and {Dyadechkin}, S. and {Wurz}, P. and 

	{Barabash}, S. and {Alvarez}, F. and {Fernandes}, V.~A. and 

	{Futaana}, Y. and {Harri}, A.-M. and {Heilimo}, J. and {Lue}, C. and 

	{M{\"a}kel{\"a}}, J. and {Porjo}, N. and {Schmidt}, W. and {Siili}, T.

  title = {{Kinetic simulations of finite gyroradius effects in the lunar plasma environment on global, meso, and microscales}},
  journal = {Planetary and Space Science},
  year = 2012,
  month = dec,
  volume = 74,
  pages = {146-155},
  abstract = {{The recent in situ particle measurements near the Moon by 

Chandrayaan-1 and Kaguya missions as well as the earlier observation by 

the Lunar Prospector have shown that the Moon-solar wind interaction is 

more complicated than believed earlier. The new observations have arisen 

the need for a detailed modelling of the near surface plasma-surface 

processes and regions near the lunar magnetic anomalies. Especially, 

interpretation of ion, electron, and energetic neutral atoms (ENA) 

observations have shown that the plasma cannot be treated as a single 

fluid but that kinetic effects have to be taken into account. We have 

studied the kinetic effects and, especially, the role of finite gyro-radius 

effects at the Moon by kinetic plasma simulations at three different 

length-scales which exist in the Moon-solar wind interaction. The solar 

wind interaction with a magnetic dipole, which mimics the lunar magnetic 

anomalies in this study, is investigated by a 3D self-consistent hybrid 

model (HYB-Moon) where protons are particles and electrons form a charge 

neutralizing mass less fluid. This study shows that the particle flux and 

density and the bulk velocity of the solar wind protons that hit the lunar 

surface just above the dipole are decreased compared to their undisturbed 

values. In addition, a particle "halo" region was identified in the 

simulation, a region around the dipole where the proton density and the 

particle flux are higher than in the solar wind, qualitatively in agreement 

with energetic hydrogen atom observations made by the Chandrayaan-1 mission. 

The near surface plasma within the magnetic anomaly within a Debye sheath 

is studied by an electromagnetic Particle-in-Cell, PIC, simulation (HYB-es). 

In the PIC simulation both ions and electrons are treated as particles. 

Further, we assume in the PIC simulation that the magnetic anomaly blocks 

away all solar wind particles and the simulation contains only photo-electrons. 

The analysis shows that the increased magnetic field decreases the strength 

of the electric potential and results in a thinner potential sheath than 

without the magnetic field. Overall, the simulations give support for the 

suggestions that kinetic effects play an important role on the properties 

of the lunar plasma environment. 

  doi = {10.1016/j.pss.2012.09.012},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Kallio}, E. and {McKenna-Lawlor}, S. and {Alho}, M. and {Jarvinen}, R. and 

	{Dyadechkin}, S. and {Afonin}, V.~V.},
  title = {{Energetic protons at Mars: interpretation of SLED/Phobos-2 observations by a kinetic model}},
  journal = {Annales Geophysicae},
  year = 2012,
  month = nov,
  volume = 30,
  pages = {1595-1609},
  abstract = {{Mars has neither a significant global intrinsic magnetic field nor a

dense atmosphere. Therefore, solar energetic particles (SEPs) from the

Sun can penetrate close to the planet (under some circumstances reaching

the surface). On 13 March 1989 the SLED instrument aboard the Phobos-2

spacecraft recorded the presence of SEPs near Mars while traversing a

circular orbit (at 2.8 R$_{M}$). In the present study the response

of the Martian plasma environment to SEP impingement on 13 March was

simulated using a kinetic model. The electric and magnetic fields were

derived using a 3-D self-consistent hybrid model (HYB-Mars) where ions

are modelled as particles while electrons form a massless charge

neutralizing fluid. The case study shows that the model successfully

reproduced several of the observed features of the in situ observations:

(1) a flux enhancement near the inbound bow shock, (2) the formation of

a magnetic shadow where the energetic particle flux was decreased

relative to its solar wind values, (3) the energy dependency of the flux

enhancement near the bow shock and (4) how the size of the magnetic

shadow depends on the incident particle energy. Overall, it is

demonstrated that the Martian magnetic field environment resulting from

the Mars-solar wind interaction significantly modulated the Martian

energetic particle environment.

  doi = {10.5194/angeo-30-1595-2012},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Jarvinen}, R. and {Kallio}, E. and {Dyadechkin}, S. and {Janhunen}, P. and 

	{Sillanp{\"a}{\"a}}, I.},
  title = {{Widely different characteristics of oxygen and hydrogen ion escape from Venus}},
  journal = {Geophysical Research Letters},
  keywords = {Magnetospheric Physics: Solar wind interactions with unmagnetized bodies, Planetary Sciences: Solar System Objects: 
  year = 2010,
  month = aug,
  volume = 37,
  eid = {L16201},
  pages = {16201},
  abstract = {{We study the solar wind induced escape of O+ and H+ ions from Venus' 

atmosphere in the HYB-Venus hybrid simulation. Most of the previous Venus global 

plasma modelling studies have concentrated only on the O+ escape. According to 

the hybrid simulation, planetary O+ and H+ ions behave very differently from 

each other in the Venusian induced magnetosphere. Both species are asymmetrically 

distributed in the direction of the interplanetary electric field and in the 

dawn-dusk plane. The H+ flow can be understood by E × B drift motion but finite 

Larmor radius (FLR) effects are essential to the behavior of O+ ions. These 

differences result in different H+/O+ escape ratios globally and in the plasma 

wake. Further, the energy ratio of the escaping planetary ions was found to be 

consistent with the observations made in the near Venus wake by the ASPERA-4 

instrument onboard the Venus Express spacecraft. 

  doi = {10.1029/2010GL044062},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Dyadechkin}, S.~A. and {Semenov}, V.~S. and {Biernat}, H.~K. and 

	{Penz}, T.},
  title = {{Comparison of magnetic flux tube and cosmic string behavior in Kerr metric}},
  journal = {Advances in Space Research},
  year = 2008,
  month = aug,
  volume = 42,
  pages = {565-571},
  abstract = {{Cosmic strings are topological defects which were generated at a 

transition phase of the very early Universe and are probably responsible for 

large-scale structure forming. However, they may pull through all history and 

exist in the recent epoch. Thus, they can have influence for the recent Universe 

interacting with different objects. We consider the cosmic string behavior in the 

vicinity of a spinning black hole by means of a numerical simulation. Here we 

present preliminary results of this work via a comparison of cosmic string and 

magnetic flux tube behavior in the Kerr metric. Such an approach follows from 

the similarity of the equations which describe these objects. Therefore, many 

aspects of this behavior may be comparable. It turns out that the cosmic string 

behavior at an early stage copies the flux tube movement in some degree. Involved 

in differential rotation, the central part of the cosmic string starts to lose 

energy and angular momentum due to string braking. Stretching and twisting around 

the event horizon, the central part of the string gains negative energy in the 

ergosphere. To compensate these losses, positive energy is subsequently generated 

and apparently can be extracted from the ergosphere as in the flux tube case. 

Because of an increase of the numerical errors the code breaks down near the 

event horizon and only initial stages of the negative energy creation can be 

observed. In comparison with the cosmic string, further simulations of the flux 

tube behavior clearly demonstrate an energy extraction process which is attended 

by relativistic jet forming. Consequently, within the frame of direct analogy, 

we consider our result as the very beginning of cosmic string jet formation in 

Kerr geometry. 

  doi = {10.1016/j.asr.2007.06.065},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Semenov}, V. and {Dyadechkin}, S. and {Punsly}, B.},
  title = {{Simulations of Jets Driven by Black Hole Rotation}},
  journal = {Science},
  eprint = {astro-ph/0408371},
  year = 2004,
  month = aug,
  volume = 305,
  pages = {978-980},
  abstract = {{The origin of jets emitted from black holes is not well 

understood; however, there are two possible energy sources: the accretion 

disk or the rotating black hole. Magnetohydrodynamic simulations show a 

well-defined jet that extracts energy from a black hole. If plasma near the 

black hole is threaded by large-scale magnetic flux, it will rotate with 

respect to asymptotic infinity, creating large magnetic stresses. These 

stresses are released as a relativistic jet at the expense of black hole 

rotational energy. The physics of the jet initiation in the simulations 

is described by the theory of black hole gravitohydromagnetics. 

  doi = {10.1126/science.1100638},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Semenov}, V.~S. and {Dyadechkin}, S.~A. and {Ivanov}, I.~B. and 

	{Biernat}, H.~K.},
  title = {{Energy Confinement for a Relativistic Magnetic Flux Tube in the Ergosphere of a Kerr Black Hole}},
  journal = {Physica Scripta},
  eprint = {astro-ph/0110168},
  keywords = {04.70.-s, 04.70.Bw, 98.38.Fs, 98.62.Nx},
  year = 2002,
  volume = 65,
  pages = {13-24},
  abstract = {{In the MHD description of plasma phenomena the concept of magnetic 

field lines frozen into the plasma turns out to be very useful. We present here 

a method of introducing Lagrangian coordinates into relativistic MHD equations in 

general relativity, which enables a convenient mathematical formulation for the 

behaviour of flux tubes. With the introduction of these Lagrangian, so-called 

``frozen-in'' coordinates, the relativistic MHD equations reduce to a set of 

nonlinear 1D string equations, and the plasma may therefore be regarded as a 

gas of nonlinear strings corresponding to flux tubes. Numerical simulation shows 

that if such a tube/string falls into a Kerr black hole, then the leading portion 

loses angular momentum and energy as the string brakes, and to compensate for this 

loss, momentum and energy is radiated to infinity to conserve energy and momentum for 

the tube. Inside the ergosphere the energy of the leading part turns out to be negative 

after some time, and the rest of the tube then gets energy from the hole. In our 

simulations most of the compensated positive energy is also localized inside the 

ergosphere because the inward speed of the plasma is approximately equal to the velocity 

of the MHD wave which transports energy outside. Therefore, an additional physical 

process has to be included which can remove energy from the ergophere. Magnetic 

reconnection seems to fill this role releasing Maxwellian stresses and producing a 

relativistic jet. 

  doi = {10.1238/Physica.Regular.065a00013},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}

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