TheInteraction of Non-Magnetic Solar System Bodies with Fast Moving Plasma.

Transcription

1 TheInteraction of Non-Magnetic Solar System Bodies with Fast Moving Plasma. Andrew F. Nagy 1, Dalal Najib 1,2, Gabor Toth 1, and Yingjuan Ma 3 1) Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, 48109, United States 2) National Research Council, Washington, D. C., United States 3) Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA, 90025, United States.

2 Fluid models: Different Model Approaches: Multi-dimensional gas-dynamic, single-fluid and multi-fluid MHD models. Hybrid models: These models use kinetic equations for the ions, but assume that the electrons are fluids. Kinetic models: These models use the magnetic field and velocity vector information from either MHD or hybrid models and then apply the equations of motion to the ions (not selfconsistent calculations). Mostly used for escape or deposition calculations. Monte Carlo (DSMC) models: Fully kinetic calculations, but no relevant, fully 3D calculations have yet been published (to my knowledge).

3 Previous Mars/Venus/Titan studies (not all inclusive!!) MHD models: 2D model: Shinagawa and Bougher [1999] 2D two-fluid MHD model: Sauer and Dubinin [2000] 3D model: Bauske et al. [2000] 3D multi-species model: Liu et al. [1999], Ma et al.,[2004, 2007, 2011] 3D multi-species: Terada et al. [2009] 3D non-ideal, multi-fluid MHD model: Harnett and Winglee [2003, 2007] Hybrid models: 3D: Kallio and Janhunen [2002] 3D: Brecht and Ledvina [2006]; [2011] 3D: Simon et al. [2006] 3D: Modolo et al. [2005] Kinetic models: 3D: Fang et al. [2010]

4 (neglecting resistive and Hall terms): t ρ s t +. ( ρ s u s ) = S ρ 4 ρ u + 4 ρ uu + p+ 1 B2 I BB = S i i i=1 i=1 2 ρu Že Žt +. u e+p+ 1 2 B2 [ B.u ]B = S e B t u B ( )= 0

5 For each ion fluid, s, we obtain (neglecting resistive and Hall terms): ρ s t +. ( ρ s u s ) = S ρ ρ s u s n q s +. ( ρ s s u s u s + Ip s )= n s q s ( u s u + ) B + t ne e (J B p )+ S e ρ s u s p s t +. ( p su s )= ( γ 1)p s.u s + S p B t u + B ( )= 0

6 General Picture of Solar Wind Interaction with a Non-Magnetic Body.

7 The Ma, Najib and Terada multi-species and multi-fluid MHD models are the only MHD ones which have a meaningful/realistic ionosphere incorporated in their model. Why is this important? The answer is that the obstacle to the flow is the ionosphere. Some of the other models handle this issue by placing their inner boundary above the effective ionosphere, so that to a large degree their results are determined by their chosen lower boundary conditions. There is a reason For trying to avoid the ionosphere from a practical point of view. To get a realistic ionosphere for Mars (as an example) one needs a radial spatial resolution of about 10 km, which increases the the needed computational resources very significantly, so there is a price to pay.

8 List of chemical reactions and rates considered in the model: Reaction Rate coefficient References CO 2 + hv CO 2+ + e O + hv O + + e H + hv H + + e s -1 (solar max) s -1 (solar min) s -1 (solar max) s -1 (solar min) s -1 (solar max) s -1 (solar min) Schunk&Nagy, 2000 Schunk&Nagy, 2000 Fox [private communication] CO O O 2 + CO cm s Schunk&Nagy, 2000 CO 2+ + O O + + CO cm -3 s -1 Schunk&Nagy, 2000 O + + CO 2 O CO (800/Ti) 0.39 cm -3 s -1 Fox and Sung, 2001, JGR O + + H H + + O cm -3 s -1 Schunk&Nagy, 2000 H + + O O + + H cm -3 s -1 Fox and Sung, 2001, JGR O 2+ + e O + O (1200/Te) 0.56 cm -3 s -1 Schunk&Nagy, 2000 CO 2+ + e CO + O (300/Te) 0.5 cm -3 s -1 Schunk&Nagy, 2000

9 Spherical grids: Radial resolution is 10 km Angular resolution is to Solar wind parameters n sw =4cm -3 ;U sw =485km/s B IMF in the X-Y plane (-1.677, 2.487, 0.0) B=B 0 + B 1, where Simulation Details(A) B 0 is the crustal magnetic field (60-order spherical harmonic model of Arkani-Hamed [2001]) U sw B IMF

10 Simulation details (B) Inner Boundary Conditions Inner boundary at 100 km [O 2+ ], [O + ] and [CO 2+ ] are in photochemical equilibrium Optical depth considered; corresponding photoionization rates used [Schunk & Nagy, 2009]

11 O 2+ Density (solar min; no crustal field; B y only and corona) Single Fluid Multi Fluid

12 Magnetic field: XZ-plan (solar min; no crustal field, B y only and corona) Single Fluid Multi Fluid E conv

13 Multi Fluid ( Solar min, Parker spiral; with crustal field and corona) X-Z plane X-Y plane

14 Pressure profiles along the Sun-Mars line for solar maximum conditions.

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17 MPBand Bow Shock locations Solar minimum no crustal Single Fluid Multi-Fluid Solar minimum with crustal Solar maximum with crustal Observed subsolar bow shock location (1.64 ± 0.08) R M, subsolar magnetic pileup boundary location (1.29±0.04)R M [Vignes et al. 2000]

18 Recent Mars Express Results: Nilsson et al., 2011 Average solar min. escape flux ~ 2x10 24

19 Calculated Escape Fluxes (in s -1 ) O + O 2 + CO 2 + Total Solar Min (Viking) 1.6x x x x10 24 Solar Max 7.7x x x x10 24

20 Reduced Titan Ionospheric Chemistry (7 ion species) No. Name Components Mass(amu) Mass Range(amu) 1 L + H +, H 2 +, H M + CH , N,CH4,CH3,CH2, CH +,C +, O H1 + + C 2 H H2 + HCNH MHC + C 3 H +, C 3 H 2+, C 3 H 3+, C 3 H 4+, C 3 H 5+, C 4 H 3+, C 4 H 5+,... 6 HHC + C 5 H 3+, C 5 H 5+, C 5 H 7+, C 5 H 9+, C 6 H 5+, C 6 H 7+, C 7 H 5+, HNI + C 3 H 2 N +, C 5 H 5 N +, C 3 HN

21 Titan Escape Escape Rates (per sec) at Different SLTs No. Name 6SLT 12SLT 18SLT 0SLT 1 L + 6.5E E E E+24 2 M + 5.5E E E E+24 3 H E E E E+24 4 H E E E E+24 5 MHC + 7.2E E E E+23 6 HHC + 2.0E E E E+23 7 HNI + 6.1E E E E+22 Total (amu/s) 234.0(g/s) (amu/s) 265.1(g/s) (amu/s) 209.6(g/s) (amu/s) 290.9(g/s)

22 Ma et al and Najib et al. the multi-species and multi-fluid MHD models use a spherical grid structure with a good radial resolution. The models include realistic ionospheres with the main chemical reactions considered. The models also include mass loading and ion-neutral collision effects. The two Mars models give similar bow shock and MPB locations for the same input conditions. The Mars multi-fluid MHD models show that the crustal magnetic field increases the bow shock and pileup boundary locations. Crustal magnetic field, interplanetary magnetic field orientation and solar radiation strength all cause changes in the trans-terminator and escape fluxes. The multi-fluid model is able to reproduce the asymmetries resulting from the convection electric field. The calculated ion escape rates are consistent with the measured values.