1. 17th Cluster Workshop 12-15 May 2009 R. Maggiolo 1, M. Echim 1,2, M. Roth 1, J. De Keyser 1 1 BIRA-IASB Brussels, Belgium 2 ISS Bucharest, Romania Quasi-stationary acceleration of auroral electrons and ions from conjugated Cluster- DMSP observations and a magnetosphere- ionosphere coupling model

2. OUTLINE  Introduction Auroral structures and magnetospheric discontinuities  Model Self consistent modeling of the coupling of a magnetospheric plasma discontinuity with the auroral ionosphere  Cluster-DMSP conjunction Comparison between data and model 17th Cluster Workshop 12-15 May 2009

3. H +,O +, e - E E E Plasma discontinuity Ionospheric O +, H + 2 1 H +,O +, e - J // INTRODUCTION Modeling Magnetospheric Tangential Discontinuities (TD) can generate convergent electric fields with scales typical for discrete aurora (Roth et al. 1993) Coupling TD model with ionosphere: generation of current system and field aligned potential drop consistent with discrete auroral arcs (Echim et al. 2007, 2008) Observations Observation of intense auroral electric fields and auroral current system at magnetospheric boundaries with Cluster (Vaivads et al. 2003 ; Marklund et al. 2004, 2007; Johansson et al. 2006, 2007) 17th Cluster Workshop 12-15 May 2009 e-e-

4. MODEL H +,O +, e - IONOSPHERIC LOAD E E E Plasma discontinuity 2 1 MAGNETOSPHERIC GENERATOR H +,O +, e - J // Coupling of a magnetospheric discontinuity with the auroral ionosphere Echim et al. 2007  Kinetic model of TD  Current continuity on topside ionosphere  Adiabatic current-voltage relation 17th Cluster Workshop 12-15 May 2009

5. MODEL TD  Kinetic model of TD (Roth et al. 1996) MAGNETOSPHERIC GENERATOR 1 2 ZMZM B XMXM Planar TD surface in the X-Z plane,  Time stationarity, B N =0  Gradients of plasma bulk properties along X M, normal to the TD plane.  Vlasov and Maxwell equations to describe the transition between 2 asymptotic states  Asymptotic populations: piecewise Maxwellian VDFs (Roth et al., 1996)  The Vlasov solution depends on the constant of motion  The moments of the distribution function are computed analytically  They are used to compute the charge density and currents in the Maxwell equations  Poisson’s equation replaced by quasineutrality equation Z 17th Cluster Workshop 12-15 May 2009

6. MODEL  Conservation of the magnetic moment  Conservation of the total energy  Monotonic variation of the potential  Magnetospheric and ionospheric populations taken separately Electrons (Knight 1973; Lemaire&Scherer 1973) Ions (Lemaire & Scherer 1971)  Kinetic model of TD (Roth et al. 1996) J pedersen J // MAGNETOSPHERIC GENERATOR IONOSPHERIC LOAD ZIZI B XIXI  Adiabatic current-voltage relation TD 1 2 ZMZM XMXM Z  Current continuity on topside ionosphere 17th Cluster Workshop 12-15 May 2009

7. MODEL  Current continuity on topside ionosphere  Kinetic model of TD (Roth et al. 1996) (Harel et al. 1977)  Uniform ionospheric densities and temperatures: e -, H +, O +, He +  Ionospheric feedback: energy dependent conductance J pedersen J // MAGNETOSPHERIC GENERATOR IONOSPHERIC LOAD ZIZI B XIXI  Adiabatic current-voltage relation TD 1 2 ZMZM XMXM Z 17th Cluster Workshop 12-15 May 2009

8. MODEL Magnetospheric generator input parameters Asymptotic plasma parameters at each side of the discontinuity B M, N M, T M, V M Ionospheric load input parameters Ionospheric parameters N I, T I,  P Tangential Discontinuity model Adiabatic current-voltage relationship Current continuity on topside ionosphere Output inside the magnetospheric discontinuity  M (x M ), N(x M ), J // (x M ) Output at ionospheric altitude  I (x I ), J // (x I ),  (x I ) 17th Cluster Workshop 12-15 May 2009

9. Cluster-DMSP conjunction (Vaivads et al. 2003 GRL) Southern Hemisphere, 20H MLT Altitudes: Cluster 3.7 R E DMSP 850 km CLUSTER DMSP CONJUNCTION: in situ data VS model 17th Cluster Workshop 12-15 May 2009 19h17:03 19h18:10 19h15:09 19h16:54 19h18:10

10. Plasma discontinuity Upgoing O + ~3 keV Bipolar electric field structure Potential drop ~3.5 kV  V=  E.dl 17th Cluster Workshop 12-15 May 2009 CLUSTER DMSP CONJUNCTION: in situ data VS model Precipitating electrons ~100 eV (not shown) H+H+ O+O+

11. CLUSTER DMSP CONJUNCTION: in situ data VS model Structure stationary at a time scale of a few minutes 1- CLUSTER data SC1 SC2 SC3 SC4 17th Cluster Workshop 12-15 May 2009

12. CLUSTER DMSP CONJUNCTION : in situ data VS model In the region I current Thickness ~ 30 km Precipitating electrons: ~3.5 keV 2- DMSP data 17th Cluster Workshop 12-15 May 2009

13. CLUSTER DMSP CONJUNCTION : in situ data VS model - H + and e - on both sides of the discontinuity - center : upgoing O + and downgoing e - 1- Cluster measurements as input parameters for the TD model DMSP (850 km) H +, e - e-e- IONOSPHERIC LOAD E E E Plasma discontinuity Ionospheric O + 2 1 MAGNETOSPHERIC GENERATOR CLUSTER (4,7 R E ) H +, e - 17th Cluster Workshop 12-15 May 2009

14. CLUSTER DMSP CONJUNCTION : in situ data VS model The spatial scale of the structure (200 km) The field-aligned potential drop (3.5 kV) An upward current sheet (0.3 µA/m²) The density overshoot due to both: - upgoing O + ions - interpenetration of magnetospheric plasma from the left and right sides of the TD 2- Comparison between the TD model profiles and Cluster data inside the magnetospheric discontinuity The model reproduces: 17th Cluster Workshop 12-15 May 2009

15. CLUSTER DMSP CONJUNCTION : in situ data VS model The spatial scale of the structure Model ~20-25 km DMSP ~30 km The field aligned potential drop Model 3.2-3.9 kV DMSP ~3.5 kV The field aligned current Model 4-6 µA/m² DMSP ~6 µA/m The peak electron energy flux Model 12-26 mW/m² DMSP 20 mW/m² 3- Comparison between DMSP data and the model predictions at ionospheric altitude The model reproduces: 17th Cluster Workshop 12-15 May 2009

16. CONCLUSION Cluster and DMSP data during a conjunction above the Southern auroral oval are well reproduced by a quasi-static model coupling a magnetospheric plasma discontinuity with the ionosphere. The convergent electric field formed inside a magnetospheric plasma discontinuity can sustain the auroral current system associated with discrete auroral arcs This mechanism generates a quasi-static electric field/acceleration The electromotive force is due to: i) thermoelectric effects due to kinetic pressure gradients ii) convective effects due to shears of plasma bulk velocity 17th Cluster Workshop 12-15 May 2009

19. SC3 E B 17th Cluster Workshop 12-15 May 2009

20. Plasma discontinuity Field aligned O + ~2 keV Bipolar electric field structure Potential drop ~2kV J // =1/  0 rot(B)  V=  E.dl Upward field aligned current 17th Cluster Workshop 12-15 May 2009