Thanks to : S. Dubyagin, D. Sormakov, S.Apatenkov (SPbU), Y.Asano, A. Runov, W. Baumjohann, R. Nakamura, T. Zhang (IWF), A.Petrukovich (IKI), P. Louarn , J.-A. Sauvaud (CESR), A.Fazakerley, C.Owen (MSSL), T. Nagai (TITECH), T. Mukai (ISAS)

1
????? ???????? ? ????????? ? ????????
?????????????? ??????? ?????

• ?. ?. ??????? (?????),

Thanks to S. Dubyagin, D. Sormakov, S.Apatenkov
(SPbU), Y.Asano, A. Runov, W. Baumjohann, R.
Nakamura, T. Zhang (IWF), A.Petrukovich (IKI),
P. Louarn , J.-A. Sauvaud (CESR), A.Fazakerley,
C.Owen (MSSL), T. Nagai (TITECH), T. Mukai
(ISAS) INTAS grant 03-51-3738
2
??????? ????????????

• ??????? ???? ?????? ? ?? ???????? ????????? ???
  ?????? ?????????, Cluster, Geotail
• ?????? ?????? INTAS (2003)
• ???????? ? ????????????? ?????????? ???????
  ????? (flapping motions)
• ????????? ?????
• ??????????? ?? ?????? ??????? ??????????????
• ?? ???? ????? ?? ????????????? ???????. ???????
  ???????????? (XY GSM),
• ???????? ???.?????? ???? ??????? (Bn0),
  ?????????? ?? ?????? Bngt0 ??? ?????????? 1d
  ?????????????
• ??????????? ????? ??????????? ????? ???????????
  ???????? ??? ??????? ???????????? (flapping)
  ???????? ????
• Cluster, Geotail

3

• I. ??????????????
• flapping ??????? ?????

4
Data base of rapid CS crossings / Methods

• CLUSTER ?r 1800,1000, 300km
• FGM CIS data 2001, 2004, 2003
• Data set 1 (186189 events)
• Jump Bx ?Bx gt 15 nT
• Duration 30slt t lt 300 s
• No special selection of plasma properties.
• Data set 2 (57 events, reliable normals)
• Baricenter cross the neutral sheet
• Smooth crossings, similar traces at all SC,
  stable timing
• Good curlometer results (DivB/Curl B lt 0.3 in gt
  60 of points)
• Tilt determination
• 1/ MinVarAnalysis (1SC) ? n1 , n2 (j), n3
  (n) in 1d CS
• 2/ Current-based (4SC) nj n1 x jNS / n1
  x jNS
• 3/ Timing (4SC)

5
Methods How accurate are tilt determinations ??
No a priori reason why MVA should work in 1D
current sheets.. Comparison of CS normal
directions determined with timing (TIM), current
(CUR) and MVA are in good agreement
(n1n2)gt0.9 ? ? lt 25o for gt80 cases
TIM/CUR, MVA is less accurate gt
Confirm local planar approximation as reasonable
starting choice.
Practical criteria for MVA in tail CS ?2 / ?3
gt 4 ????25o, (incl 75
events)
Sergeev et al., Ann.Geophys.,p. , 2006
6
Example October 20, 2001 CL at -13, 12,-1 Re
Z Y
j , n NS

• Multiple NS crossings during substorm (onset
  0920UT), slow flow Vx,y (passive CS), all time
  inside PS (Sergeev et al.,2004 GRL)
• Consistence of n determinations from T and MVA
  very large tilt toward Y !!
• Consistent alternating nz (see Table)
• Alternating signs jz (B,-b, etc) and nz
  variations under positive jy jz ? jy
  large tilts
• Propagate duskward
• Large tilts, YZ Kink mode with strong folds

7
20040805 Cluster TC-1, Kink mode confirmed
TC-1 -10.7 -6.8 2.6
Cluster -15.4 -8.9 3.4

• Cluster Timing MVA
• Normals swinging in YZ plane
• Kinks propagating dawnward
• at V30 km/s

• 8 NS crossings, timescale 150 500 s ,
• weak substorms
• Similar phased variations of Bx (1320-15 UT)
• Cluster TC-1 ? kinks with length gt5 Re
  along the tail

Zhang et al., Ann Geo, 2005
8
Appearance of Flapping Structures

• SHAPE (reconstructed from probing small parts !)
  
• appear as parts of oscillation pattern or
  solitary structures parts of plane not uncommon
• ?Y ? AZ ? h CS
• ?1-3Re 0.5-2Re 0.2-1Re
• Large tilts of CS parts (up to 90o to nominal Z)
• Large-amplitude Nonlinear
• Structures (Waves)
• LIFETIME
  Only lower estimates are
  possible in examples
• with slow propagation which give
• TL can be ? 5 min

5 min
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Guide- versus normal B-field components
B vector is averaged over BX
lt3nT region. a - angle between n and Z GSM
BJ/Bn
Tilted sheets possess large guide
B-field as distinct from sheets with
standard tilt.
Standard Tilted CS
Dubyagin et al., AnnGeo, 2007 subm
10
Kink Propagation and Ion flows along normal
direction

• ION FLOWS (from CIS)
• Problems effect of same order of magnitude as
  possible instrumental Z-offsets and errors
  transient effects and changing tilts easily ruin
  any correlation only Vn is available from
  timing
• Special subset 42 events with nT??nJ??nMVA
  within 20o
• RESULTS
• Plasma flows in the same direction with same
  velocity along the normal
• Most of flapping Kink structures can be the
  structures nearly standing in the flow

Dubyagin et al., AnnGeo, 2007 subm
11
Timing propagation direction velocities
VT B1

• Propagation from center to flanks,
  perpendicular to magnetic field plane
• Zone of mixed direction near midnight (esp.
  premidnight) where X-line observations are
  most frequent at substorm onset (Nagai et 1998)
  
• Propagation speeds 20-300 km/s,
• median 50 km/s
• Larger speeds near MReconnection site and in
  BBFs
• Propagation pattern reminds the pattern of
  cross-tail average flow, could be structures
  standing in the flow???

Runov et al., AG 2005
Sergeev et al., GRL 2004
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Occurrence of Fast CS crossings

• Geotail
• 3 years data set, 3s B-field from DARTS
• 1100 fast crossings (occurrence)
• MVA with ?2/?3gt4 and Ngt15 to get normals (480
  events, for tilts study)
• Results
• n3 ? 0, nY, nZ like at Cluster
  ? confirm YZ-kink mode
• duration depends on local flows
  (short during fast flows and in reconnection
  regions)
• Sergeev et al. AnnGeophys, 2006

MVA normals Dawn
Dusk
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Occurrence of Fast CS crossings, 2

• Results
• n3 ? 0, nY, nZ
  ? confirm kink mode
• duration - short
  during local fast flows)
• occurrence frequency increases
  downtail and in Y -5..10 Re
• consistent with flankward propagation,
  confirm magnetospheric origin
• occurrence resemble occurrence of BBFs and MR
  at substorm onsets (Nagai et al.,1998)
• Sergeev et al.
  AnnGeophys, 2006

14
Flapping Activity Dependence

• Dependence on AE and auroral activity
• Common during substorms, but sometimes met
  during quiet AE
• Usually associated with auroral brightenings or
  poleward arcs (PC or streamer?), but clear
  one-to-one relationship occur rarely
• few events with NO auroral brightenings
  (all CDPS events).
• Dependence on Local activity
• flapping appear within the whole range of PS
  parameters
• sharp crossings with large tilts and large Vz
  and VT are frequently noticed near MR region, and
  in BBFs (?)
• Needs more (quantitative) study
• Dubyagin et al., paper IAGA2005-A-00302

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Parameters of flapping current sheets

• duration lt30 - gt300s, depends on local flows
  (short in BBFs and near MR)
• in the neutral sheet Bns 4 nT (1..18nT),
  usually BjgtBn
• curvature Earthward (closed FL-90) in CL data
  set
• B-curvature radius Rc 5 Lcp (Lcp -gyroradius
  in BL field)
• halfthickness h10 Lcp (1..20 Lcp), weak
  correlation with Rc
• adiabaticity parameter ? Rc BL/ (Lcp Bns)1/2
  0.6 (0.2..2)
• 
  - non-adiabatic ions
• any local (density/temperature/velocity)
  conditions
• plasma velocity BBFs only in 25, gt60
  Vplt100km/s

Runov et al. AnnGeo, 2005, p.1391, also Shen et
al JGR, 2003, p.1168
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Summary of Flapping-related structures

• Large-amplitude Nonlinear Structures (Waves or
  Solitary structures)
• Very large tilts (gt45o from Z in 50 of events)
• Fast CS crossings due to kink waves with
  normals rotated ?B (in YZ)
• Propagated center?flanks , ion speeds 20-300
  km/s, median 50km/s
• Occur 10-gt30 Re, frequency increases with
  distance, peaks premidnight
• Associated with auroral brightenings and
  substorms, exceptions exist
• Ion flow includes
• Vz corresponding to up/down CS motions
• Vpn flow have same sign/magnitude as the
  propagation velocity
  for low speed events (?)

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Mechanisms of Flapping ?

• MHD effect of localized reconnection with
  magnetic shear (Semenov et al.,1994, Shirataki,
  Fujimoto et al 2006)
• Kinetic (KH or drift) instability
  (Nakagawa-Nishida, 1989, Karimabadi et al.,
  2003,. )
• Standing modes in (neutral Harris) sheet (Fruit
  et 2002, Volverk et al., 2003)
• Eigenmodes in finite Bz current sheet
  (Golovchanskaya, Maltsev, 2004)
• PIC simulations of CS instability (e.g. with
  real hcs, Sitnov et al 2004), association with
  other instabilities (e.g. LHDI, etc)
• Different initial models and parameters,
  different detailness of predictions - difficult
  to compare
• critical issues to answer
• MHD or kinetic effects? Instability or
  generation by reconnection? - ???
• Propagation velocity (in dHT frame) ? -typically
  small
• CS parameters/structures favourable for
  generation?
• - no obvious preference..
• Different mechanisms could be involved???

18

• II. ?????????
• flapping ??????? ?????

19
October 20, 2001 Oscillation amplitude and CS
structure

• Vz integration vertical PS/plasma motions
• consistent variations Vc Vp
• ?z1-2 Re
• CS structure of individual crossings, from B (z)
  (Vc and average tilts used)
• different shapes (single peaks, flat,
  bifurcated, symm/asym, time-dependent?,)
• CS scale-sizes vary between 1000 km and 4000
  km
• All crossings are different !

Thin embedded, Bifurcated, 1 asymmetric, etc
A B b C c D d E e
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Survey of structures , comparison to Harris
distributions

• Reconstruction of 30 suitable crossings (tilts,
  coord.system, Zscales)
• Identify
• central embedded sheets
• bifurcated sheets
• asymmetric sheets
• Non-Harris distributions !!
• j shape deviate from Harris
• Density and j- profiles are different, flat
  density distributions
• (Runov et al., AnnGeo 2006)

21
Parameters of Current sheet structures

• 55 Central peak, main part of the current is
  concentrated in Bxlt0.5BL, BL(B22µ0Pi)½
• Typical half-thickness of the central peak
  1000 - 2000 km 3 7 Lcp,
• Shoulders
• 10 Bifurcated Local minimum of the current
  density at Z 0 (Bx0)
• Typical half-thickness 3000 km 10 Lcp
• Thicknesses of peaks of 1000 - 2000 km
• 35 Asymmetric Off-equatorial maximum of the
  current density
• Typical half-thickness 1500 - 3000 km
• No big difference in parameters !
• Also - No significant differences
  in ion anisotropy/ nongyrotropy

22
Current sheet structures

• Are non-Harris features special for
  flapping sheets only (e.g.
  transient effect??)
• Asano et al 2005 (GRL, L03108)
• Other approach and method (no preference to
  flapping sheets)
• Large tilts excluded
• Results
• Harris distributions rare !
• Central embedded sheets - 40
• Bifurcated/off-center peaks - 17
• comparable to in flapping sheet survey!
• of bifurcated sheets slightly increases during
  BBFs
• similar conclusion by Thompson, Kivelson et
  JGR2006

Harris
?B ?B
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Inconsistence of rotB and ion currents

• Expected Ti/Tegtgt1 ? jpgtgtje and main contribution
  from jp to jTOT
• Observed large discrepancies
• different signs jC and jplt0, jp gt jC Implies
• electrons as main current carriers ?
• Explanation dawnward convection, implies
  converging En and negative e-charge in the sheet
  
• (Runov et al., AnnGeo 2006)

jC n e (ltVpgt - ltVegt)
24
Comparisons including electron contribution
Calibration of electron spectrometer at required
accuracy appeared to be very difficult
instrumental problem Results are yet available
only for 1 long event in 2001, Seem to be
consistent with electrons to be dominant current
carrier..
B1, nT
25
CS in/near Reconnection Region

• Recent findings (CLUSTER)
• Hall B-fields and current/carriers mostly
  following predictions
• Thin sheets 1 c/?pi (400-800km) directly
  confirmed, j 30-50 (up to 120) nA/m2
• may be very short (seconds)
• large tilts are common (!?)
• may include small FRope-like structures etc,
• entire picture sometimes looks like strong
  turbulence
• Nakamura et al., JGR , A11206, 2006,
• Wygant et al., JGR, 2004

jzgsm
10sec CSheet in XZ gsm plane
flapping-like?
X-15Re
26

• IV. ??? ?? ???????

27
Discussion Z-????????? ?? 1d or 2d effect?

• ?? ???? ????? ?? ????????????? ???????
  ????????????, 1d ???? ??????? (Bn0), ??????????
  ?? ?????? Bngt0
• ??????? 1d ???????? ?????? ?????????
• ?/?z gtgt?/?x ?????? ??? BxgtgtBn ? 0
• ?Xgtgt?Z (Tail approximation) ? ?????????????
• ?(z), j(z) ???????????? ?? ?-???????????????

?X
? ???????????? (???????. flapping ??)
-?????????\??????? ???????????????? ?????
????????? (20\10\01, Nakamura et 2006),
-???????? NS-?????????? (t -? ??? ?????????-?),
-???????? ?????????? ????????? gt?????
????????? ???????? ????????????? 1-2 ????????
??????????? ????? ?
28
Discussion Z-????????? ?? 1d or 2d effect?
(2)

• ? ???????????? (???????. flapping ??)
• -?????????\??????? ???????????????? ?????
• ????????? (20\10\01, Nakamura et 2006), ?????
  ??????? ? Z- ????????? ????????
• -???????? NS-?????????? (t -? ??? ?????????-?),
• -???????? ?????????? ?????????
• gt????? ????????? ???????? ????????????? 1-2
  ???????? ??????????? ????? ?

3D M?? ????????????? - YZ-kink ???????????
????? - ?????? ??????????????? ???????? ???????
???? (?? X ? Y!!) ??????? ?Y ? Z, ???????
???? - ??????? ????????? ??
??????? ???-??????? ?????????? ????????????
???????? ???????. ?? ???? 2d (??????.)
???????? ?????????? ?????????????? ??.?????
Thompson, Kivelson et al., JGR 2006
29
Future work
30
Curlometer and proton current comparisons
YZ plane

• Explanation requires dawnward convection (50
  km/s),
• implies converging En ( earthward E in NS) and
  negative e-charge in the sheet
• origin of dawnward convection on duskside???
  inconsistent with average convection
• consistent with Wygant et al JGR 2005 Cluster
  event analyses but obtained in
  thin electron-scale CS, charge separation near MR
  as compared to relatively thick
  (hfew Lcp) events in our survey (?)
• A challenge
• to confirm this explanation by studying
  electron contributions and
• to understand origin/mechanisms of dawnward
  convection in the sheet

Hori et al.,2000, also Kauffmann et 2001,
Asano et 2003 etc