Magnetosphere-Ionosphere- Thermosphere coupling and the aurora UV Ingo Müller-Wodarg 1 Space & Atmospheric Physics Group Imperial College London i.mueller-wodarg@imperial.ac.uk
Ionosphere of Earth The ionosphere on Earth is subdivided into layers of plasma peaks named D, E, F1, F2 (historically) Peak densities are often named Nm*, peak heights hm* Most layers disappear at night, only the F2 layer is maintained at night Peak densities vary also with sunspot numbers NmF2 hmf2 I. Müller-Wodarg 2 STFC Advanced Summer School 2016
Mars ionosphere Benna et al. (2015) I. Müller-Wodarg 3 STFC Advanced Summer School 2016
Saturn ionosphere Cassini RSS Kliore et al. (2009) Low Latitude Mid Latitude High Latitude Horizontal structure (Lat & local time) Variability: Causes and time scales I. Müller-Wodarg 4 STFC Advanced Summer School 2016
Ionospheres in the solar system Mendillo et al. (2002) I. Müller-Wodarg 5 STFC Advanced Summer School 2016
Magnetosphere-Ionosphere coupling at Earth Geomagnetic disturbances are carried by the solar wind into the magnetosphere, and from the magnetosphere via the ionosphere into the Earth s upper atmosphere... I. Müller-Wodarg 6 causing substantial changes which can be seen also from the ground. STFC Advanced Summer School 2016
The Dungey Cycle Dungey [1961] proposed that reconnection drove plasma convection (ExB drift) in the ionosphere: Dayside reconnection in the magnetosphere (requires southward B y ) (1) Solar wind plasma drags B field of Earth towards the tail (2-5) Tailside reconnection (6): acceleration of electrons along field lines aurora Transport of field lines towards Earth and towards dayside (7-9) This plasma and B field convection is mapped into the high latitude ionosphere I. Müller-Wodarg 7 STFC Advanced Summer School 2016
Aurora on Earth I. Müller-Wodarg 8 STFC Advanced Summer School 2016
Space weather at Earth Rishbeth et al. (2010) I. Müller-Wodarg 9 STFC Advanced Summer School 2016
Space weather response of thermosphere Exosphere temperature change Earth The thermosphere responds to changes in electric fields and particle precipitation from the magnetosphere Temperatures are enhanced at polar regions and the disturbances travel equatorward from both poles, giving a global response CTIP Model I. Müller-Wodarg 10 STFC Advanced Summer School 2016
Aurora on Jupiter Bunce et al. (2005) I. Müller-Wodarg 11 STFC Advanced Summer School 2016
Changing aurora on Saturn Feb 2008 Saturn Clarke et al. (2009) I. Müller-Wodarg 12 STFC Advanced Summer School 2016
Jupiter Cowley and Bunce (2002) idian cross-section through the jovian magnetosphere, showing the principal features of the inner an I. Müller-Wodarg 13 STFC Advanced Summer School 2016
M-I-T coupling on giant planets I. Müller-Wodarg s * s Fig. 1. Sketch of ajoule meridian heating cross section Q Joule through = 1 E ~E Saturn s + quasiaxisymmetric inner & and ion middle dragmagnetosphere, extending to dis- ~u B ~ tances of 15 20 R S in the equatorial plane. a idrag = The 1 arrowed J ~ B ~ solid lines indicate magnetic field lines, which are modestly distended outward from the planet by azimuthal currents (the ring-current ) flowing in the near-equatorial plasma. The rotating plasma is shown V, U J B B Rotating plasma Hill (1979) Cowley and Bunce (2003) sion. Furthe et al. (1998). observed ov dayside hem between 07: latitude rang tent with the SKR radio e and Genova, tions, the aur sity between ing from no emissions pe ~E The main around both Prangé et al STFC Advanced Summer School 2016
Space weather in the solar system Prangé et al. (2004) I. Müller-Wodarg 15 STFC Advanced Summer School 2016
Saturn Space Weather Solar wind at 1 AU http://stereo.ssl.berkeley.edu/sac2012/ I. Müller-Wodarg 16 STFC Advanced Summer School 2016
What and why? Magnetosphere-Ionosphere coupling on Earth is a mature discipline, thanks to efforts over the past 50 years Giant planets have magnetospheres and ionospheres as well, the study of their coupling is still "exploration science" Some of many open questions for Giant planets: Energy crisis in the thermospheres Highly variable ionosphere structure Saturn's changing magnetosphere rotation rate Scientifically, both sides (Earth and planetary) can learn from one another - yes, planets also teach us about Earth! Obvious benefit also for exoplanet studies I. Müller-Wodarg 17 STFC Advanced Summer School 2016
Energy & momentum drivers in upper atmospheres Solar/stellar radiation Magnetosphere Angular momentum Reduced in atmosphere Waves JxB X JxB Angular momentum Increased in magnetosphere I. Müller-Wodarg 18 STFC Advanced Summer School 2016
masstransport.upon combiningthesetwo resultswe obtain differential equation whose solution gives thecorotation laga Magnetosphere-atmosphere coupling FigureI illustrates thebirkeland currentgeometry andth coordinate system usedhere.for simplicitywe treatthe cas a functionof distance in themagnetosphere. af a spin-aligned dipolemagnetic field,alignedwiththe ax af ourspherical (r, 0, q )coordinate system. Notein Figure Ihatthej x B forceis directed soasto increase theangu a omentum of theoutermagnetosphere at theexpense of th ngularmomentumof the atmosphere. Atmospheric torque.ion-neutralcollisions exerta dra :orce Foperunitvolume thatisbalanced, ina steady state, b.hej x B force: Angular momentum Reduced in atmosphere Hill (1979) JxB Towards Saturn 20 RS 15 RS 10 RS 5 RS Distance X JxB after Smith and Aylward (2008) Angular momentum Increased in magnetosphere Fig. 1. Illustration of thecoordinate system andfieldgeome mployedin the calculation.the senseof the electriccurrentflow is adicatedby openarrowheads. Ion drag: 1/ρ (jxb) Effect on atmosphere: Joule ( Ohmic ) heating: 1/ρ (jxe) I. Müller-Wodarg 19 STFC Advanced Summer School 2016
M-I-T Coupling Magnetosphere MHD/Hybrid Model Electric field Magnetic field Energetic particles Atmosphere Collisional Fluid Model I. Müller-Wodarg 20 STFC Advanced Summer School 2016
Saturn Thermosphere Ionosphere Model (STIM) Thermosphere GCM (Mueller-Wodarg et al. 2006; 2012) Ionosphere Model (Moore et al., 2004; 2010) Electron flux Electric field Suprathermal Electron Transport Model (Galand et al., 2009; 2011) BATS-R-US (Jia et al., 2012) I. Müller-Wodarg 21 STFC Advanced Summer School 2016
Saturn Thermosphere-Ionosphere Model (STIM) Coupled 3-D thermosphere-ionosphere model Solar production & chemistry Plasma dynamics: winds & diffusion Full neutral-ion dynamical & chemical coupling Self-consistent calculation of conductivity & Joule heat. High latitude particle precipitation & ionisation High latitude electric field from BATS-R-US (Jia et al.) SPV B-field model H 3 + IR cooling Further reading: Mueller-Wodarg et al. (Icarus, 2006; 2012) Moore et al. (Icarus, 2004; JGR, 2012, 2012) Galand et al. (JGR, 2009; 2011) I. Müller-Wodarg 22 STFC Advanced Summer School 2016
Ionosphere Saturn Mueller-Wodarg et al. (2012) I. Müller-Wodarg 23 STFC Advanced Summer School 2016
Auroral forcing & response Lat=78 Saturn Electron influx STIM-GCM I. Müller-Wodarg 24 STFC Advanced Summer School 2016
Exospheric Temperatures Lines: STIM Model Dots: Measurements Saturn I. Müller-Wodarg 25 STFC Advanced Summer School 2016
Energy balance Direct thermal heating Saturn Dynamical redistribution QEUV=0.04 mw/m 2 Energy balance dominated by dynamics 1D thermal models not usable I. Müller-Wodarg 26 STFC Advanced Summer School 2016
Resolution matters Saturn 2 lat x 10 lon x 0.4 H 1200 km 1 lat x 4 lon x 0.2 H Uzon Uz I. Müller-Wodarg 27 STFC Advanced Summer School 2016
MHD simulations of magnetosphere BATS-R-US Jia et al. (2012) Saturn I. Müller-Wodarg 28 STFC Advanced Summer School 2016
Feb 2008 Auroral activity Saturn Clarke et al. (2009) I. Müller-Wodarg 29 STFC Advanced Summer School 2016
Electric field Saturn Normal SW Pressure High SW Pressure Jia et al. (2012) Upstream solar wind input (96 RS) I. Müller-Wodarg 30 STFC Advanced Summer School 2016 1
Pedersen conductance Quiet Disturbed Saturn Quiet: ɸ10 kev, aver = 1.6 mw/m 2, Emax 42 mv/m Disturbed: ɸ10 kev, aver = 4.0 mw/m 2, Emax 63 mv/m I. Müller-Wodarg 31 STFC Advanced Summer School 2016 2
TEC Saturn "Quiet" "Disturbed" I. Müller-Wodarg 32 STFC Advanced Summer School 2016
Joule heating Saturn Quiet Disturbed I. Müller-Wodarg 33 STFC Advanced Summer School 2016
Temperature response to pulses Saturn I. Müller-Wodarg 34 STFC Advanced Summer School 2016
Time-dependent response Meridional wind Zonal wind Saturn I. Müller-Wodarg 35 STFC Advanced Summer School 2016
Response time scales: Zonal winds Saturn V exo 70 V H3+ I. Müller-Wodarg 36 STFC Advanced Summer School 2016
Thermal relaxation time scale Saturn T exo T H3+ 70 50 200h 10 I. Müller-Wodarg 37 STFC Advanced Summer School 2016
Dynamical time scale V exo V H3+ Saturn I. Müller-Wodarg 38 STFC Advanced Summer School 2016
Concluding comments Magnetosphere-Ionosphere-Thermosphere coupling represents transfer of solar wind energy & momentum into ionosphere & thermosphere Energy & momentum at high latitudes is dominated by this coupling Earth s upper atmosphere variability ( Space Weather ) is of interest scientifically and technologically We have recently developed the capability of simulating M-I coupling also on Saturn Models allow to understand response and relaxation time scales in atmosphere: validity of steady state assumptions? I. Müller-Wodarg 39 STFC Advanced Summer School 2016