Transcript CEDAR2014
Dynamic Coupling between the Magnetosphere and the Ionosphere P. Song1, and V. M. Vasyliūnas1,2 1. Space Science Laboratory and Physics Department University of Massachusetts Lowell 2. Max-Planck-Institut für Sonnensystemforschung, Germany Dynamic Coupling: processes t<30 min, such as substorms and auroral brightening Ionosphere is driven from the magnetosphere by the magnetic tension force: not by electric field or field-aligned currents Eugene Parker (2007): “It is here that a fundamental misunderstanding has become widely accepted, mistaking the electric current j and electric field E to be fundamental physical entities… Magnetospheric physics has suffered severely from this misdirection…” The new model/theory has been developed based on BV paradigm During Dynamic Processes: • • No steady state ionospheric Pederson and Hall currents exist Steady state Ohm’s law is not applicable J || E||b P (E u n B) H b (E u n B) • Steady state field-aligned currents are not established by height-integration J || p (E u n B) • • • • • The inertia of the ionosphere/thermosphere plays an important role More driving force is needed to push the ionosphere into motion An overshoot in disturbance is expected: substorm onset/brightening (it is not necessary that the magnetospheric source is explosive) Wave reflections between the ionosphere and magnetosphere are expected: oscillations are seen on top of an overall substorm profile (noting the AE index is the envelop of oscillations, ~100 min) Mode conversion: field-aligned Alfvenic perturbations from the magnetosphere are converted mostly to horizontal propagating fast mode in the ionosphere (whole ionosphere responds to solar wind changes very quickly ~ 1 min after the time delay to dayside cusp) Global Consequence of A Poleward Motion • Antisunward motion of field line in the open-closed boundary creates – a high pressure (compressional wave) region in the direction of acceleration, and – a low pressure (rarefaction wave) region beyond the accelerated region • • • Continuity requirement produces convection cells through fast mode waves in the ionosphere and motion in closed field regions. Poleward motion of the feet of the flux tube propagates to equator and produces upward motion in the equator. Ionospheric convection will drive/modify magnetospheric convection Expected Heating Distribution sun • For uniform conductivity, velocity pattern coincides with the magnetic perturbation. • FAC forms at the center of the convection cells • Poynting flux is proportional to V2, weakest at the center of convection cells • Neglecting the heating from precipitation particles, – Conventional model (EJ paradigm): driver is the FAC on dawn-dusk sides – New model (BV paradigm): driver is in dayside and nightside cusps and strong along the noon-midnight meridian Whole Ionospheric Response Time (from dayside cusp to nightside cusp) to An Upstream Change • A time delay to solar wind to the subsolar magnetopause • A time delay from magnetopause to dayside cusp • If the ionosphere is driven passively by the magnetospheric convection: convection time ~20 min • Driving by ionospheric fast mode ~ 1 min Conclusions • Based on 13 years of theoretical investigations and E. N Parker’s enlightening comment • A theoretical model of the M-I coupling has been developed based on collisional MHD • It explains self-consistently or predicts – Ionospheric heating as heavily damped Alfvén waves via frictional and Ohmic heating – The damping is not strongly dependent on frequency for ULF waves – Heating is proportional to the Poynting flux, not field-aligned current – Heating is strong where flow is strong (along noon-midnight) and is weak in flow reversals (Dawn-dusk polar caps) – Enhanced temperature and upward motion along noon-midnight meridian – Fast mode transmission is dominant and couple to different latitudes via ionosphere – Whole ionosphere responds in fast mode time scale ~ 1 min – Overshoot in ionospheric response: ionospheric inertia =>substorm – Oscillations of ~100 min in ionospheric or ground measurements: wave reflections