1. A. Vaivads, M. André, S. Buchert, N. Cornilleau-Wehrlin, A. Eriksson, A. Fazakerley, Y. Khotyaintsev, B. Lavraud, C. Mouikis, T. Phan, B. N. Rogers, J.-E. Wahlund STAMMS Workshop Orleans, France, 2003 The magnetopause on electron scales Current layers and waves

2. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 2 Outline Small scale current sheets at the magnetopause Comparison to numerical simulations Lower hybrid drift waves and whistlers Comparison to laboratory observations Particle diffusion Summary Why small scales? What is their structure? What is their role? May affect large scale phenomena Decoupling of particles from field lines often on small scales. Efficient energy conversion from electromagnetic to kinetic energy often on small scales Waves They transport energy and particles, heat particles, they also can be used as remote or local sensing tools of plasma.

3. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 3 Scales ParameterMagnetosheathMagnetosphere B,n,Te,Ti30nT, 10cm -3, 150eV, 1keV30nT, 1cm -3, 1keV, 10keV GyroradiusH+ 150km, e- 1.4 kmH+ 480km, e- 3.5km Inertial lengthH+ 72km, e- 1.7kmH+ 230km, e- 5.3km GyrofequencyH+ 0.46Hz, e- 840Hz Lower hybrid20Hz Small spatial scales  between ion and electron scales and smaller  a few tens of km and below

4. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 4 High latitude, northern hemisphere MP crossing 100km Cluster separation s/c in burst mode

5. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 5 There is a narrow current sheet (yellow) Parallel current within the current sheet is in opposite direction to magnet-opause current Significant differences among s/c in E and B.

6. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 6 Generalized Ohms law and Cluster At spin resolution B 3D[FGM], E [EFW,EDI], n [CIS, PEACE, WHISPER], p e [PEACE], v [CIS], j [PEACE+CIS, curlometer] At high time resolution (5 S/s and higher) B 3D[FGM,STAFF], E [EFW,EDI], sometimes n [WBD] n satellite potential [EFW] j [curlometer, planar current sheet assumption] T e v

7. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 7 Narrow current sheet (~20km, 5-10 e,  e ) in both j perp and j II Jump in magnetic field magnitude coincides with density gradient E~j x B Electron pressure gradient not important In addition to gradient, the electron beam carrying parallel current can be a source of free energy for wave generation

8. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 8 E~j x B Potential drop across the current sheet of a few hundred V

9. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 9 Numerical simulations of reconnection Two fluid simulations of reconnection with a guide field No electron pressure and partial time derivative included Width of separatrix is a few times electron inertial length Electric field is strong along the whole separatrix E ~j x B, in most of the system [Rogers]

10. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 10 Waves strongest in the narrow current sheet (gradient in n and B) Broad band spectra in E and B Spectral peaks in E and B close to f LH ’LHD’ Spectral peaks in E and B at ~100 Hz, ’whistlers’ Strong Poynting flux associated to both ’whistlers’ and ’LHD’ Waves generated by gradients or electron beams? E B S

11. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 11 EFW internal burst In internal burst separate signal for every probe available (9000 S/s) Cross-correlation gives phase speed in the spin plane

12. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 12

13. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 13 Laboratory observations [Carter et al. 2002] Reconnection is driven by increasing the magnetic flux around Flux cores Lower hybrid drift waves near the low-  edge LHD waves have low coherence and have no clear correlation with reconnection rate Analysis of magnetic field fluctuations and narrow current sheets in progress MRX – magnetic reconnection experiment

14. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 14 LHD waves in laboratory vs. space LaboratorySpace Broadband, f max ~ f LH  ~  e  Strongest at low-  edge  Low coherence  Fast growth rate & damping  The propagation directionv De along MP e  max ~ 5% T e   ? The next step is to compare magnetic field observations (current sheets, whistlers) in laboratory and space.

15. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 15 Particle diffusion, effective collision frequency In the diffusion approximation diffusion coefficient is given by The effective collision frequency is given by [Carter et al. 2002] Fluctuation correlations can be estimated using analytical estimates of density fluctuations if the electric field fluctuation spectrum is known. EFW instrument allows simultaneous estimate of the density and electric field fluctuations under assumption that fluctuations in spacecraft potential can be interpreted as density variations

16. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 16

17. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 17 Narrow strong current sheets (width 5-10 e,  e, j~1-5  A/m 2 ) at the magnetospheric side of the magnetopause Coincides with density gradients, strong E fields and wave activity E~jxB, electron pressure gradients are not important Similarities with separatrixes in numerical simulations of reconnection LHD waves similar to those in lab-experiments of reconnection Narrow regions of whistler emission within the current sheet. Diffusion across the current sheets, D~ 10 9 m 2 /s, outside D<10 8 m 2 /s. Continue comparisons with 3D numerical simulations Identify reconnection events where Cluster are at small separation and close to the diffusion region (poster by Yuri Khotyaintsev) Look for the events where measurements of E II are possible Summary Future

18. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 18 Other eventE B  S || 2001-03-02

19. Swedish Institute of Space Physics Uppsala STAMMS, Orleans 15 May 2003 slide 19 Aurora vs Magnetopause Aurora mainly ion scale phenomena but can have scales down to electron scales Auroral field lines – strong parallel current sheets, particle acceleration, different plasma waves, often boundary phenomena (PSBL) Infering E II from measurements of E perp There are many similarities but are physics similar? cause vs. effect