07/11/2007ESSW4, Brussels1 Coupling between magnetospheric and auroral ionospheric scales during space weather events M. ECHIM (1,2), M. ROTH(1) and J. DE KEYSER(1) (1) Belgian Institute for Space Aeronomy, Brussels, Belgium (2) Institute for Space Sciences, Bucharest, Romania

07/11/2007ESSW4, Brussels2 Outline of the talk Auroral activity and space weather events Dayside auroral arcs and coupling to magnetospheric boundary layers and SW properties Tangential discontinuities with sheared flows as auroral generators; typical scales Current continuity in the ionosphere; feedback effects Quasi-static coupling model: numerical results Conclusions, future research

07/11/2007ESSW4, Brussels3 Auroral activity and space weather events Image courtesy of LESIA, Meudon, Paris

07/11/2007ESSW4, Brussels4 Auroral activity and space weather events Close to solar maximum (May 1998)

07/11/2007ESSW4, Brussels5 Auroral activity and space weather events At solar minimum (September 2007)

07/11/2007ESSW4, Brussels6 Dayside auroral arcs and coupling to magnetospheric boundary layers and SW properties Credit: sci.esa.int/cluster

07/11/2007ESSW4, Brussels7 Dayside auroral arcs and coupling to magnetospheric boundary layers and SW properties Newell et al., 2004 Moen et al., 1994 Vo and Murphree, 2001

07/11/2007ESSW4, Brussels8 The inverted V-event The parallel electric fields can easily account for the peak generally observed in the differential flux versus energy spectra of electrons that produce the arcs 

07/11/2007ESSW4, Brussels9 Tangential discontinuities with sheared flows as auroral generators Planar surface in the y-z plane Variations along the x m coordinate normal to the TD plane. E along the x-axis, B along the z-axis, a,V and J along the y- axis

07/11/2007ESSW4, Brussels10 Tangential discontinuities with sheared flows as auroral generators piecewise Maxwellian VDFs (Roth et al., 1996) analytical moments of the VDF Φ m and a computed numerically from the Maxwell’s equations The model can describe simultaneous shears in B and V flow Convergent electric field

07/11/2007ESSW4, Brussels11 Current continuity in the ionosphere; feedback effects Current continuity in the ionosphere: Ionospheric feedback: Self-consistent  m ; ad-hoc models in previous studies (Lyons, 1980, 1981)

07/11/2007ESSW4, Brussels12 Quasi-static coupling model: numerical results

07/11/2007ESSW4, Brussels13 Quasi-static coupling model: numerical results – effects of LLBL/SW speed Solid line : non-uniform  P with  P0 =0.5 S Dashed line : non-uniform  P with  P0 =5.0 S Dotted line : uniform  P = P0 =5.0 S and feedback

07/11/2007ESSW4, Brussels14 Quasi-static coupling model: numerical results – effects of LLBL/SW density Solid line : non-uniform  P with  P0 =0.5 S Dashed line : non-uniform  P with  P0 =5.0 S Dotted line : uniform  P = P0 =5.0 S and feedback

07/11/2007ESSW4, Brussels15 Quasi-static coupling model: numerical results – effects of e - temperature Solid line : non-uniform  P with  P0 =0.5 S Dashed line : non-uniform  P with  P0 =5.0 S Dotted line : uniform  P = P0 =5.0 S and feedback

07/11/2007ESSW4, Brussels16 Summary, Conclusions Larger SW/LLBL velocity larger shear more power Increased luminosity of the auroral arc Larger SW/LLBL density thinner auroral structures Ionospheric feedback Larger potential difference energy flux Low  P0 thinner structures smaller energy flux

07/11/2007ESSW4, Brussels17 The auroral current circuit Left: a negatively charged potential structure is representative of the aurora. Right: a positively charged potential structure is representative of the auroral return current. The two branches close at typical altitudes of 5,000−8,000 km in the upward-current region above the aurora and at 1,500−3,000 km in the auroral return-current region. Together with the ionospheric closure current and the magnetospheric generator the field-aligned currents form the complete auroral current circuit. The figure shows a north−south section that usually extend several hundreds of kilometres in the east−west direction. From Markund et al., Nature 414, , 2001

07/11/2007ESSW4, Brussels18 Summary, Conclusions – Uniform  P the arc tends to be brighter and wider when the convection in the LLBL is faster; the arc tends to become thinner and more intense when the density of the LLBL plasma increases (and the LLBL velocity remains unchanged); the arc keeps the same luminosity but expands in width when the LLBL electron temperature increases while the LLBL density and velocity remain unchanged the region where the energy precipitation reaches significant values corresponds to discrete auroral arcs of the order of 1-10 km in latitudinal extent.