Transcript power point
STAMMS Workshop Orleans, France, 2003 The magnetopause on electron scales Current layers and waves 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 Outline Swedish Institute of Space Physics Uppsala 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? slide 2 STAMMS, Orleans 15 May 2003 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. Scales Swedish Institute of Space Physics Uppsala Parameter Magnetosheath Magnetosphere B,n,Te,Ti 30nT, 10cm-3, 150eV, 1keV 30nT, 1cm-3, 1keV, 10keV Gyroradius H+ 150km, e- 1.4 km H+ 480km, e- 3.5km Inertial length H+ 72km, e- 1.7km H+ 230km, e- 5.3km Gyrofequency H+ 0.46Hz, e- 840Hz H+ 0.46Hz, e- 840Hz Lower hybrid 20Hz 20Hz Small spatial scales between ion and electron scales and smaller a few tens of km and below slide 3 STAMMS, Orleans 15 May 2003 Swedish Institute of Space Physics Uppsala slide 4 STAMMS, Orleans 15 May 2003 High latitude, northern hemisphere MP crossing 100km Cluster separation s/c in burst mode Swedish Institute of Space Physics Uppsala slide 5 STAMMS, Orleans 15 May 2003 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. Generalized Ohms law and Cluster Swedish Institute of Space Physics Uppsala 1 1 m ( j B ) p e 2 d tj j ne ne ne 1 m EII pe 2 dtj j ne ne E v B At spin resolution •B 3D[FGM], E [EFW,EDI], n [CIS, PEACE, WHISPER], pe [PEACE], v [CIS], j [PEACE+CIS, curlometer] slide 6 STAMMS, Orleans 15 May 2003 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] •Te •v Swedish Institute of Space Physics Uppsala slide 7 STAMMS, Orleans 15 May 2003 Narrow current sheet (~20km, 5-10 le,re) in both jperp and jII 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 s/c4. vMP=105 [-0.76 -0.35 -0.54] km/s GSE, Te=150eV. E low pass filtered at 30 Hz N - normal to MP, towards MSh, L - closest to the mean direction of B, M=LxN. dt= [0 0.19 0.72 -0.17] s. 5 a) s/c1 s/c2 s/c3 s/c4 4 3 Swedish Institute of Space Physics Uppsala 2 s/c1, E [mV/m] 1 20 b) s/c 1 E jxB/ne - Te dx n/n c) s/c 2 E jxB/ne - Te dx n/n d) s/c 3 E jxB/ne - Te dx n/n e) s/c 4 E jxB/ne - Te dx n/n 0 -20 -40 s/c2, E [mV/m] 20 0 -20 -40 s/c3, E [mV/m] 20 0 -20 -40 s/c4, E [mV/m] 20 0 -20 -40 slide 8 STAMMS, Orleans 15 May 2003 p1039 14-May-2003 23:02:33 08:11:56 08:11:57 08:11:58 08:11:59 06-Feb-2002 08:12:00 E~j x B Potential drop across the current sheet of a few hundred V Numerical simulations of reconnection [Rogers] Swedish Institute of Space Physics Uppsala slide 9 STAMMS, Orleans 15 May 2003 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 Swedish Institute of Space Physics Uppsala E B S slide 10 STAMMS, Orleans 15 May 2003 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 fLH ’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? EFW internal burst Swedish Institute of Space Physics Uppsala slide 11 STAMMS, Orleans 15 May 2003 In internal burst separate signal for every probe available (9000 S/s) Cross-correlation gives phase speed in the spin plane Swedish Institute of Space Physics Uppsala slide 12 STAMMS, Orleans 15 May 2003 Laboratory observations [Carter et al. 2002] MRX – magnetic reconnection experiment Swedish Institute of Space Physics Uppsala slide 13 STAMMS, Orleans 15 May 2003 Reconnection is driven by increasing the magnetic flux around Flux cores Lower hybrid drift waves near the low-b 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 LHD waves in laboratory vs. space Swedish Institute of Space Physics Uppsala Laboratory Space Broadband, fmax ~ fLH l ~ re Strongest at low-b edge Low coherence Fast growth rate & damping vDe along MP ? The propagation direction efmax ~ 5% Te slide 14 STAMMS, Orleans 15 May 2003 The next step is to compare magnetic field observations (current sheets, whistlers) in laboratory and space. Particle diffusion, effective collision frequency Swedish Institute of Space Physics Uppsala In the diffusion approximation diffusion coefficient is given by D njv j nj The effective collision frequency is given by veff slide 15 STAMMS, Orleans 15 May 2003 qj n j m jV y , j [Carter et al. 2002] E yn j 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 Swedish Institute of Space Physics Uppsala E [mV/m] DS s/c4, filter [15 40] Hz 20 x y 0 -20 - dn [cm 3] E [mV/m] DS D=<nv>/ <n> [m2 /s] 0.2 0 9 -0.2 x 10 3 2 1 0 -1 50 x y 0 [cm-3 ] -50 2.5 Vps 2 N 1.5 slide 16 STAMMS, Orleans 15 May 2003 1 08:11:57.0 .5 08:11:58.0 06-Feb-2002 .5 Summary Swedish Institute of Space Physics Uppsala Narrow strong current sheets (width 5-10 le,re , j~1-5mA/m2) 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~ 109 m2/s, outside D<108 m2/s. Future slide 17 STAMMS, Orleans 15 May 2003 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 EII are possible Other event 2001-03-02 Swedish Institute of Space Physics Uppsala E B S|| slide 18 STAMMS, Orleans 15 May 2003 F Aurora vs Magnetopause Swedish Institute of Space Physics Uppsala slide 19 STAMMS, Orleans 15 May 2003 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 EII from measurements of Eperp There are many similarities but are physics similar? cause vs. effect