Shock waves

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Shock waves

normal gas:collisionstransgfer momentumand energy


Shock: transition from super- to sub-sonic flowaccompanied by compression and dissipation


Bow shocks• supersonic motion relativelyto gas• CME, planetary bow shocks,heliospheric, comets• frame of reference!Blast waves• sudden release of thermalenergy• flare, supernova


B (nT)V (km/s)N (cm -3 )T (K)upstreamdownstream


Magnetized plasma• several modes can transform information• Alfven speed:• magnetosonic speed:• collisionless shocks• MHD discontinuities-properties of plasma change- only bulk properties


Rankine-Hugoniot relations:• Jump conditions across MHD shock/discontinuity in ideal MHD• conservation of mass, ,momentum and energy (RH1-RH4)RH1RH2RH3adiabatic equation of stateassumedRH4RH5RH6


a) contact discontinuity (B n 0)- n,T may change, all other quantities constantb) tangential discontinuity (B n =0)- n, B t change- total pressure conserveda) intermediate/Alfven shock (B rotates 180°)- n changes only in anisotropy plasma- special case: rotational discontinuity (flow, but no change in n)b) slow mode shock- B t decreasesc) fast mode shock- B t increaseS d > S u


Shock angle• parallel shock B t =0- no change in field direction or magnitude, only compression• perpendicular shock B n =0- plasma pressure and B increasequasi-parallelquasi-perpendicular


Shock Mach number: ”strength” of the shockV i : sonic, Alfven, magnetosonic speedcritical Mach number (when u d =c sd )• subcritical; dissipation due to dispersion/anomalous resistivity• Supercritical: additional dissipation mechanism (ion reflection)supercriticald=383 kmsubcriticald=109 km


fastforward-reverseshock pairCo-rotating interaction regions• slow - fast solar streams• fast-reverse shock pair• shocks not fully formed at 1AU


CME shockfrontBemporad andManucuso, 2010fast CME-driven shocks• Common at 1 AU• Recentrly ”discovered ” in white-light- combined remote data r, plasmaparameters, B• radio tracking shock speedupstreamdownstream


Coutersy: M. Pulupasolar energetic particles (SEP) acceleration• few tens keV to tens of MeV• diffusive shock acceleration• particles cross shock many times


fast CMEQS: Quiet SunAR: Active RegionSW: Solar WIndslow CME• CME or flare?Moretron and EIT waves


Voyager 2 termination shock• at 84 AU Aug 30-Sep 1, 2007• several crossings• supersonic to subsonic• weak, quasi-perpendicular shockRichardson et al, 2008 Nature


new IBEX data• no helispheric bow shock• heliosphere slower than previously thought• stronger IS field larger c MS

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