ISSI Team on modeling cometary environments in the context of the heritage of the Giotto mission to comet Halley and of forthcoming new observations at Comet 67P/Churyumov-Gerasimenko First Workshop, Bern, November 2012 Single fluid approach for modeling solar wind – ionized coma interaction Valentina Keremidarska, Monio Kartalev, Murray Dryer

Outline  Introduction to the single fluid gas-dynamic approach for modeling solar wind interaction with planetospheres and comet exospheres  Briefly about approach implementation to magnetic / nonmagnetic planets  Some general results in modeling SW interaction with Halley ionized coma Attempt to address some of the Target Project’s QUESTIONS  Attempt to address some of the Target Project’s QUESTIONS  Attempt to formulate possible contribution for solving these questions questions  Attempt topossible coordination / cooperation  Attempt to start discussion on possible coordination / cooperation of Sofia group with other Project Groups as a part of the mutual of Sofia group with other Project Groups as a part of the mutual coordination between research groups presented in the Project coordination between research groups presented in the Project

Questions  Q1: Scope of the applicability of different modeling approaches  Some simple but effective enough modeling approaches could be useful for express data analysis, fast evaluation of different hypothesis and interpretations etc  They could be also useful as ingredients of more complex models, saving time and computational cost.  Here is an attempt to inform you (supplementing the talks of Michail Lebedev and Vladimir Baranov) about some forgotten in the era of fast computers capabilities of single fluid models of SW interaction with comets and planets as well.

Specificities and common properties of the interaction regions Magnetic planet Nonmagnetic planet: Ionosphere (planetosphere)- plasma of planetary origin Comet: Regions C and D contain predominantly plasma of comet origin Everywhere: “Outer shocked region”, containing predominantly solar wind plasma Differences in the inner (“near-bodies”) regions of interaction

Physical specificities in the comet and nonmagnetic planets’ cases Source and sink processes in the mass-loaded solar wind and cometary/ planetary plasmas ( in the most general problem statement )

Comet case: The most complex problem statement:  Region A (mass-loaded, preshocked solar wind): photoionisation  Region B (shocked solar wind): photoionisation, charge exchange (together with Region C)  Region C (shocked plasma of cometary origin): photoionisation, charge transfer, dissociative recombination, frictional force Region D (Domain of the supersonic radial flow of cometary ions): constant radial velocity w, constant Mach number M, radial density distribution ~ 1/r Nonmagnetic planet (Venus) case: Mass-loading effect due to the photoionisation of the neutrals of the “hot oxigen corona” is taken into account in both: ionosphere and ionosheath (planetosphere, planetosheath) Magnetic planet (Earth) case: The simplest gasdynamic problem statement classic Euler equation with zero right-hand sides

Equations in comet case

Equations in Venus case ( e.g. Breus et al. Planet. Space Sci., 1987 )

 The 3D gasdynamic numerical procedure utilizes “grid-characteristics” numerical scheme (Magomedov and Holodov, 1988; also e.g. Zapryanov, Minostcev, 1965)  This is explicit first – order nonconservative difference scheme  A “MODULAR APPROACH” is applied in the complex solution of the problems  The solution in all the regions is sought self-consistently, satisfying Rankine- Hugoniot relations on the boundaries  The shapes and positions of these boundaries (shock waves, contact and tangential discontinuities) are obtained also as a part of the solution (discontinuity – fitting scheme ) Idea about the used numerical mesh grid

This animation is from the 3D magnetosheath problem, demonstrating the performance of the used time- marching scheme In the comet case the solution is for 3 domains and for the shapes and positions of the outer and inner shocks and the contact surface The convergence is reached for several thousand iterations. This takes 5-10 min on conventional PC

In the cases of comets and nonmagnetic planets the interaction is described completely in terms of fluid dynamics:  The developed models are gasdynamic for all the regions of interaction. A specific approach is elaborated for the case of the solar wind - Earth interaction This approach comprises in a self-consistent way: Empirical magnetosphere model, modified by numerically inferred 3D magnetopause and MP shielding field The magnetosphere can be closed or open with “prescribed” external to the model magnetic field penetration Numerical 3D magnetosheath Numerical 3D magnetosheath, obtained in gasdynamic approach The magnetosheath magnetic field can be obtained additionally, solving magnetic induction equation by use of the velocity distribution Different meaning of “gas-dynamics” for neutral and ionized coma

The model of the solar wind – Earths magnetosphere interaction was developed with the substantial participation of Polya Dobreva and Detelin Koichev

Twofold results of the model running under some conditions: solar wind (plasma, IMF) and magnetosphere (dipole tilt, Dst)  Modification of the Tsyganenko 3D empirical model with  realistic, pressure balanced numerical magnetopause and  corresponding new numerically inferred shielding field distribution  3D numerical magnetosheath with  Plasma parameters distributions  Self-consistently obtained shapes and positions of  the magnetopause and  the shock wave

Finite element grid, containing 1505 elements), utilized in problem solving Magnetosphere magnetic field model Chapman – Ferraro problem for the m-pause shielding field

Models’ performance  Outer (shocked solar wind) regions of interaction  The obtained results are in general in good agreement with results of other modeling approaches  Numerous comparisons with spacecraft measurements confirmed the models’ correct performance including  Crossings of the Earth’ bow shock and magnetopause, as well parameters’ variations along magnetosheath orbits  Measurements of Giotto spacecraft during Halley mission  Pioneer Venus Orbiter observations  Inner regions of interaction (especially in Venusian and Comet Halley cases)  There are some good coincidences with experiments which are probably not achieved in the interpretation of other models  Probably: new insights in understanding the inner regions of interaction

Suppositions:  Static neutral oxygen exosphere around the planet with distribution of the number density N o (Breus et al. 87) where N ex = 10 7 cm -3 is the density at the exobase (sphere with r ex = 200 km ) constant temperature T o = 350 o K of the exosphere neutrals  Mass - loading effect due to photoionization is taken into account in both regions  On the exobase (200 km): condition Vn=0  Especially in the ionosphere the photoionization is the only source of the considered ionized gas ! (as supposed by Vaisberg and Zeleny, Icarus, 1984)  The influence of the magnetic field is omitted in both regions – this is important, as soon as some of the effects, obtained here as a consequence of only of the dynamics of the mass-loaded ionized gas, have been explained by other authors by the influence of the magnetic field!!  The governing equations are the same with the mentioned specification of the right hand sides Venusian results

Some results:  Expected results about the ionosheath  The results about the ionosphere (planetosphere) are obtained under only one additional supposition: NO photo-ionization in the “planet shadow” No introduced heat inflows! Venusian results Common picture of the numerically obtained planetosphere and planetosheath (in real scales).  Mach number isolines. Here: Dp=4; p= 0.11 nPa. planetosphere planetosheath Mach number isolines

Some results: Venusian results  Dependence of the shapes and positions of the bow shock and planetopause on the solar wind dynamic pressure Dp.  Solar wind thermal pressure p=0.11 nPa

Some results: Venusian results A comparison between  the experimentally obtained (Brace et al., Pioneer Venus Orbiter ) – dashed line and  numerical (solid line) dependence of  the altitude of the planetopause (ionopause) subsolar point  versus the solar wind dynamic pressure

Some results: Venusian results Isolines of a typical number density distribution in the planetosphere region.

Solar wind – comet interaction (for Halley case) No intrigue about the outer region of interaction: The outer shock wave position, as well as the parameter's distribution in the outer region are in good coincidence with the Giotto experimental data and other model predictions For instance, a comprehensive comparison between experimental and model results in this outer region is done in: Baranov V.B. and Lebedev M.G. (1993) The interaction between the solar wind and the comet Halley atmosphere: observations versus theoretical predictions, Astron. Astrophys., 273, 659. Coincidence with MHD results too

(not in scale here!) Very fast program performance

Questions  Q5: How to couple the neutral coma model and MHD (or other used fluid approach of the ionized coma) There are at least two aspects of this problem:  Global interaction between neutral and ionized coma   Formation of the inner side conditions of the ionized coma model as a result of the processes in the neutral coma

Is it possible and is it necessary instead of simplified neutrals distribution to utilize solutions like this:

Possible activity of our group in Sofia till the next team meeting and beyond :  Developing the single fluid model of solar wind-comet interaction to 3D approach  Including (in convection approach) the magnetic field in the model  Contacts and discussions with neutral coma groups  Possible collaborative work with these groups

Questions  Q10: How to establish a community service center for numerical modeling if necessary ( Wing-Huen Ip )

 There is already such kind of Center, especially devoted to serve Rosetta mission (ICES) and even some of he team members substantially contribute to this center performance.  Nevertheless there is a very important, probably still free, niche: While ICES is concentrated on huge models, requiring extremely expensive infrastructure and maintenance, the community (both – experimentalists and theoreticians) will often need convenient and reliable, easily accessible tools (better on their PC) in consideration new data, express interpretations and so on.  It is an advantage of the team that it is compound of :  specialists, experienced in developing easy to use models  specialists, capable to verify them on more complex models  experimentalists, that may focus their efforts into useful and specifically needed problems

Example: If you need to analyze the results of magnetopause crossing, you may order magnetosheath modeling in CCMC (NASA) and will have it in ~3 days. You may however do practically the same on your PC.

Possible activity of our group in Sofia till the next team meeting and beyond :  Active participation in developing easily accessible models  Getting experience in utilization of more complex models, provided by specialized community centers  Participation in the establishment (probably..?) of some kind of consulting center for using and interpreting models.

Thank you!