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Embedded current sheet in the Earth’s magnetotail A.A. Petrukovich , A.V. Artemyev , L.M. Zelenyi Space Research Institute, Moscow R. Nakamura Space Research Institute, Graz. Outline 1. Thin embedded sheets are frequently observed 2. How sheets can be quantified ? - PowerPoint PPT Presentation
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Embedded current sheet in the Earth’s magnetotail
A.A. Petrukovich, A.V. Artemyev, L.M. Zelenyi Space Research Institute, Moscow
R. NakamuraSpace Research Institute, Graz
Outline
1. Thin embedded sheets are frequently observed
2. How sheets can be quantified ?
3. Embedded sheets in the magnetotail context
4. Implications for substorms
Вложенный токовый слой в хвосте магнитосферы
A.A. Petrukovich, A.V. Artemyev, L.M. Zelenyi Space Research Institute, Moscow
R. NakamuraSpace Research Institute, Graz
1. Тонкие вложенные слои – характерный объект в хвосте
2. Количественное описание вложенных слоев
3. Вложенные слои в контексте плазменного слоя
4. Вложенные слои в контексте суббури
Runov et al., 2006, AnGeo
Embedding: spatial scale of current is smaller than
spatial scale of density
Asano et al 2005, GRL
ISEE-1,2: thin current sheet (with small Bz) is embedded in a thicker plasma sheet
Mitchell et al, 1990, Sergeev et al, 1993
Cluster:
Observations
Embedded sheet profile
Harris sheet: Be and Je: He=Be/Je
Embedded sheet: J0 and B0: H0=B0/J0
Total: Jmax, B0, BeJe<<J0 , Je is not resolved by Cluster
at distances 15-20 Re
Jmax ~J0
Jmax=J0+Je, Je<<J0
B0 Be
Harris profile
Je
Embedded sheet in theory
essentially embedded sheet in thin anisotropic current sheet
model by Zelenyi et al.
B0 is less definite:
embedding is often created just adding background plasmas.
Thin current sheets have typical thickness ~ Larmor radiusin boundary magnetic field B0
Cluster 2001-2004 cases: thin (almost) horizontal single-peaked symmetric sheets
Cluster view on embedding
Theory predicts thickness of the order of ion Larmor in B0!
L=B0/J0~B0/Jmax
Cluster view on embedding
1. Large current densities areunderestimated
2. Small current densitiesare overestimated: J0~Je
3. Particle sorts add scatter
Cluster view on embedding: uncertainties
1. L0 ~ 1-3 * RL0
2. Range of B0
=> J0 ~ B0^2 with larger B0 sheets are thinner!
=> Magnetic flux F0 ~ B0 * RL0 = pc/e/B0 * B0 = const (B0) - “quantum” flux
Most of the flux is in wings but
Harris sheet has infinite range!
Make J=0 at finite Z“finite” Harris (Veltri et al 1998)
F0=(0.5-2)B0*L0 ~ 1-5 *B0*RL0
Quantify embedded sheet
Embedding in the magnetotail context
F0 ~ (1-5) * 0.02 Wb/m (4000 eV) << Fe ~ 0.5 Wb/m 10 times!
1. Extreme case smallest possible B0 so that J0 >= Je
B0/Be >= sqrt(F0/Fe) ~ .3-.25
2. Extreme case B0 ~ Be: if F0<<Fe
singular thin sheet in empty plasma sheet Drop all plasma from plasma sheet
Or much smaller Fe~F0
At 15 Re – post-plasmoid plasma sheet ?
Total plasma sheet flux Fe is much larger than F0 at 15-20 Re
Embedding in the magnetotail context
Minimum embeddingis indeed B0 > 0.25-0.3 Be
8 of 10 cases of B0 > 0.5 Be are after tailward plasmoids!
Example->
Depleted magnetic flux in the post-plasmoid plasma sheet Hones, 1984
Embedding in the magnetotail context
Distant tail
Fe~F0
B0~Be
Be – small
thin sheets are almost Harris
Near tailBoundaryWhen Bz ~ B0
1D approximationIs not valid
Middle tailFe is growing to E
Be is growing
B0 and J ?
Embedding in the magnetotail context
Embedding parameters inTsyganenko modelsdepend on tail stretching
Latitude 70 used as boundary of PS
Embedding in the magnetotail context
Implications for substorms
1. Criterion of being inside embedded sheet when considering onset flows:in a regular quiet sheet: F0/Fe < 1/10 B0/Be ~ 1/3, => 0 ~ 10
2. Plasma sheet with embedding is thinner for the same Fe and Be
than Harris sheet (it contains more flux and less plasma):
Re_new = Re_harris * (1+aF0/Fe)/(1+aB0/Be) = Re_harris *0.9
Leaving more space for increase of open magnetic flux even when Be=const
3. Total cross-tail current I grows towards Earth and during growth phase, but local current density J is controlled by embeddingwhere and why current density peaks (at onset)?
4. During growth phase embedded sheet intensifies.Flux is removed or plasma is removed to allow larger B0
Sergeev et al, 1993
Implications for substorms
Petrukovich et al, 2007
5. Stability
Burkhart, 1992, suggestedfor an embedded sheet
The growth rate scales asB0/Be *(1- (B0/Be)2)
Zelenyi et al model predicts instabilityzone related with Bz
Implications for substorms
Conclusions
Thin ion scale embedded sheets are frequent especially during substorms
Thickness is controlled by local larmor (as in theory) and plasma properties
Crucial internal parameter is B0, magnetic flux is constant.
Sheet in the magnetotail is controlled by B0/Be and F0/Fe
Quiet sheets have deep embedding B0<< Be (at 15-20 Re) and slowly
evolve with increase of B0 during growth phase
Largest embedding B0~Be requires plasma sheet magnetic flux drop –
after onset or in the distant tail
Plasma sheet is thinner when embedded and less stable.
Embedding should be taken into account in analyses of ion kinetics,global convection, stability, etc.