Slide 1

Coupling of the Magnetosphere and Ionosphere by Alfvn Waves at High and Mid-LatitudesBob Lysak, Yan Song, University of Minnesota, MN, USAMurray Sciffer, Colin Waters, University of Newcastle, NSW, Australia

Dynamic coupling the magnetosphere and ionosphere is achieved by the propagation of ULF wavesShear Alfvn waves mediate changes in the field-aligned currentFast mode waves mediate changes in the pressure balanceNote that electric fields and currents do not map or penetrate: transport of fields and currents requires wave propagation.A model for ULF wave propagation in the strongly inhomogeneous dipole magnetosphere has been developed to describe these processes: 1Pi1/2 Propagation in Inner MagnetosphereNew model developed in dipole geometry to describe ULF wave propagation and interaction with ionosphere (Waters et al., 2013; Lysak et al., 2013)Height-resolved ionospheric model gives more realistic ionospheric fields. Ground magnetic fields calculated from spherical harmonic expansion.Region from L = 1.5 to L = 10 modeled. Plasmapause at L=4.Model is 3d, with 128x64x318 cells in L-shell, MLT, radial distance, using staggered Yee grid, suitable for modeling Maxwells equations.Compressional driver on outer boundary, Gaussian in latitude and longitude. Inner L-shell uses B= 0 boundary condition (no compression).2Density and Alfvn speed profilesModel based on ionospheric model as in Kelley (1989), plasmasphere model of Chappell (1972), 1/r density dependence along high-latitude field lines.Plasmapause at L=4, width of transition 0.1 RE

Alfvn travel time profileModel is driven with a damped 50 sec wave trainFundamental resonances at L= 3 and 5.5; third harmonic (150 sec) at L = 8.5Note range of frequencies at plasmapause: easy to excite plasmapause surface waves

Results: Bz and Ex in meridian and equatorEx, Shear Alfvn modeBz, Compressional modeMidnight meridianEquatorial plane

018126Magnetic fields at GroundBxByNorthSouth

018126Time Development of Bz

Compressional magnetic field on the equator at 0 MLTEach curve offset by 2 nTLowest 3 curves (plasmasphere) oscillate in phase: plasmasphere resonanceL=10

8643.532.52Arrival of signal at ground

Ground magnetic fields at 21 MLT plotted at 5 intervals in latitudeLowest latitudes on bottomEach curve offset by 2 nT (Bx) or 0.2 nT (By)Peak signals arrive within 10s of seconds of each otherNote this does not imply propagation in latitude, but differences in travel time from source.

Equatorial electric field as function of MLTZonal electric field (E) at equator at L=1.5 (inner boundary)This field gives vertical ExB drift of equatorial plasma5 mV/m offset for each curveTime differences are 10s of seconds, but amplitude on dayside is reduced

MLT=211815129630Effect of Hall conductivityHall conductivity breaks dawn-dusk symmetry in convectionRadial electric field (positive outward) implies azimuthal flowGreen and red are westward flow, blue and purple eastward

With Hall conductivityWithout Hall conductivityConclusions and Future WorkNumerical ULF wave model can be used to describe ULF propagation in the inner magnetosphere.Wave arrives at all latitudes in inner magnetosphere within a minute or so.Plenty of future possibilities: Day-night asymmetry in the ionosphereDawn-dusk asymmetry in plasmasphere (plumes)Stretching of model geometry on nightside