Презентация на тему: " С.П. Савин, Л.М. Зеленый, Е.А. Кузнецов (ИКИ РАН) О взаимосвязи 2 фундаментальных явлений: концентрированных плазменных струй и альвеновского коллапса." — Транскрипт:
С.П. Савин, Л.М. Зеленый, Е.А. Кузнецов (ИКИ РАН) О взаимосвязи 2 фундаментальных явлений: концентрированных плазменных струй и альвеновского коллапса
From: EGU06-A Kartalev, M.; Savin, S. ; Dobreva, P.; Amata, E.; Shevyrev, N. EGU06-A From: EGU06-A Kartalev, M.; Savin, S. ; Dobreva, P.; Amata, E.; Shevyrev, N. EGU06-A From: EGU06-A Kartalev, M.; Savin, S. ; Dobreva, P.; Amata, E.; Shevyrev, N. EGU06-A February 13, 2001, CLUSTER
arcsin(Vz/|V|) arcsin(Vy/|V|) W kin nV i V X Y Z MP indentation
MP Jets in SW? BS |V|, [km/s] N i, [cm -3 ] V Ti In most jets nV rises mostly due to n, for W k inputs of n and V 2 are comparable
- (a) Cluster 3, W k – ram pressure, W t –ion thermal pressure, W b – magnetic pressure, lagged W k in SW (ACE); - (b) Cluster 3, angles sin -1 (V z /|V|), sin -1 (Vy/|V|), GDCF – model prediction; Insert: jet directions in XZ plane; V=(-26;15;7) km/s – GSE velocity of the outermost jet as a whole; V=(-117;-37;31) km/s – velocity of the innermost jet. Dashed lines – the most deflected jets at UT and at UT.; - (c) comparison of W k, [keV/cm 3 ], ion density N, [1/cm 3 ], and ion velocity (|V|/20, [(km/s)/20]), Cluster 3; - (d) the GSE electric component E y from 4 Clusters
Jet going to SW? Jet inside MP? decay? Deflected jets with compara- ble input from N i and V 2 as a probable result of the MSH flow decay GDCF angle V_XY From magnetic disturbance at leading jet front (-196;-230;90) km/s (-185;106;-219)km/s Cluster 3, February 13, Jet width ~ 200 km ~ (2-3) i
A summary plot of the Cluster data during the cusp interval 05: :00 UT on March 17, The panels show, from top to bottom, the HIA ion omni-directional energy fluxes, the HIA ion density, velocity and temperature, the FGM magnetic field, all from spacecraft 1, and the lagged IMF from the ACE spacecraft. (Figure provided by B. Lavraud) [ISSI book: CLUSTER AT THE MAGNETOSPHERIC CUSPS] GSE, 6-12 UT IMF B z >0
GSE, 6-12 UT Possible source jet MP jet IMF B z >0 Proxy for MSH:
Ion flux nV from Cluster1 on March 17, 2001 (black) versus that of WIND in SW, (-22;-189;-40) R E GSM. 1.5*nV from WIND would be a proxy for the ion flux in MSH (with nearly the same averaged flux ~3.3 along the orbit) Possible source jet MP jet
Cluster 1, March 17, 2001 Possible source jet Post-BS jets result from density rise. Further in MSH velocity starts to do comparable input in the jets flux, slightly dominating at the MP. MP jet BS jets
(a)Comparison of |B| on 4 SC (colors for SC 1-4: black, blue, violet, red) on March 17, 2001 associated with the MP jets (see Fig. 1); (b) Ram pressure W k from 3 SC and that of SC1 at UT (source jet, dashed line, lagged); (c) Cluster 1: W k (black), W t – thermal ion pressure (blue), W b – magnetic pressure (violet) and W k in SW from Wind (magenta); (d) E y from 4 Clusters.
60-75 nT Direction of MP jets versus that of the flow ahead MP and source one
Cluster 1, March 17, 2001 Comparison of velocity and density in the possible source sonic jet (right) with that of MP supersonic jet (left) : at MP velocity rises and jumps stronger, density is slightly less and time-lagged. Vx Vz MP jets source jet ~2 i
5N i 30W k 100W b VzVz VyVy VxVx Standing E n -wave? 1st BS BS jets (Y_GSE=0)
n i M i V i 2 /2 < k (B max ) 2 / 0 [k ~ (0.5-1) – geometric factor] n i M i V i 2 /2 > k (B max ) 2 / 0 The plasma jets, accelerated sunward, often are regarded as proof for a macroreconnection; while every jet, accelerated in MSH should be reflected by a magnetic barrier for n i M i V i 2 < (B max ) 2 / 0 in the absence of effective dissipation (that is well known in laboratory plasma physics) Plasma jet interaction with MP
In the jets kinetic energy W kin rises from ~ 5.5 to 16.5 keV/cm 3 For a reconnection acceleration till Alfvenic speed V A it is foreseen W kA ~ n i V A 2 /2 ~ const |B| 2 that requires magnetic field of 66 nT (120 nT inside MP if averaged with MSH) [Merka, Safrankova, Nemecek, Fedorov, Borodkova, Savin, Adv. Space Res., 25, No. 7/8, pp , (2000)]
23/ , MHD model, magnetic field at 22:30 UT; blue – Earth field; red - SW; yellow - reconnected; right bottom slide – plasma density; I- Interball-1 G- Geotail; P- Polar X X Reconnection X X
Cluster1, February 2, 2003Cluster3, February 2, 2003 WkWk WbWb WtWt [eV/cc] UT MP W b,t,k - cross-correlation < 0.35 Supersonic flow Magnetic barrier with ~sonic flow stagnant turbulent boundary layer (closer to the Earth) cusp plasma ball
For collapse at ion gyroradius scale we estimate equilibrium from We estimate D H from characteristic shift by squared ion gyroradius i 2 at ion gyroperiod for the gradient scale ~ ion gyroradius The Alfvenic collapse would stop at the scales of ~ ion gyroradius (i.e. at the MHD validity breaking), when magnetic field diffusion due to the finite ion gyroradius effects can neutralize the field growth
Interball-1 MSH/stagnation region border encounter on April 21, Comparison with switch-off slow shock [Karimabadi et al., 1995] displays strong magnetic barrier with pressure of the order of the MSH ram pressure. Inside diamagnetic bubble ion temperature balances the external pressure
Locations in Geocentric Solar Magnetospheric (GSM) coordinates of 208 magnetic barriers detected in Interball-1 magnetic field data between 1995 and 2000.
Alfven wave filamentation: Self-focusing instability [Bugnon, G., R. Goswami, T. Passot and P.L. Sulem, TOWARDS FLUID SIMULATIONS OF DISPERSIVEM HDWAVES IN A WARM COLLISIONLE SS PLASMA, Adv, Space Res., in press (2006)]
Alfven wave filamentation: Self-focusing instability [T. Passot et P.L. Sulem, Landau fluids for space plasmas]
Mechanisms for acceleration of plasma jets Besides macroreconnection of anti-parallel magnetic fields (where the magnetic stress can accelerate the plasma till n i M i V iA 2 ~ B 2 /8 ), there are experimental evidences for: -Fermi-type acceleration by moving (relative the incident flow) boundary of outer boundary layer; - acceleration at similar boundaries by inertial (polarization) drift.
From: EGU06-A Kartalev, M.; Savin, S. ; Dobreva, P.; Amata, E.; Shevyrev, N. EGU06-A Plasma acceleration by pressure gradients at cusp throat tailward edge Model V z in MSH (right) and along Cluster 3 orbit on February 13, 2001 (top, brown curve) versus Cluster 3 data (blue line) with structured jets
Time traces (in microseconds) in turbulent boundary layer in tokamak T-10, r=34 cm, (a)electric field E p, [Volts] (a) (b) plasma density fluctuations n(t) [1/cm 3 ] (b) particle flux due to ExB drift across magnetic field [1/(cm 2 sec)]
Jet types and generation mechanisms (1) BS (just inside, density-produced, cant hit MP) : Magnetosonic (MS) collapse? Beams/ electric standing structures? (2) Postshock/MSH: - Alfvenic collapse/structuring; - Decay (deflected jets can cross MP and BS ) - Entropy wave/non-uniform eigen mode? - Transformation of BS jets (cant hit MP)? (3) Transient: Decay? Alfvenic collapse/structuring? Cleaning way for moving boundaries? (4) Near-MP: -(2); -(3); - Reconnection; - Interaction with reflected waves [Savin et al., JETPh Lett., 2004]: (a) Local decay of MS waves, amplified by the reflected waves (b) Inertial drift in standing interference structures - Pressure gradients at cusp throat (providing structured outflow of stagnant plasma along MP tailward of the over-cusp indentation) - Substructures of secondary shocks/ discontinuities, cf. (1) ? - Oppositely directed normal electric field at charged current sheets (first of all MP), including moving boundaries (cf. 3)
'Plasma jets' are regularly detected in the magnetosheath (MSH) with preference of occurrence behind the bow shock (BS). The typical jet duration is up to several tens of seconds. They appear intermittently, exhibiting as their main feature an increase in the dynamic pressure of 2-3 times above the solar wind (SW) pressure. Jets are seen also in the boundary layers and even outside the BS. Some of the jets carry the momentum excess during MSH transition towards a state of smaller dynamic pressure. They also appear as a result of transient MSH reactions on SW disturbances, e.g. cleaning the way for approaching BS or MP. Transient jets are followed by decelerated flows having speeds near or below the Alfvén velocity. The magnetic stress balance is satisfied in the sub-Alfvénic/Alfvénic flows, unlike the super-Alfvénic MSH ones. Thus, the interacting flow-obstacle system would have lower potential energy after the jets emitting (this reminds one to a peculiar maser-like transition from the meta-stable to a stable state).
In the presence of postshock jets the flux in the middle of MSH tends towards the SW one, which is in contrast to model predictions. Averaging of the flux along spacecraft orbits in time gives a flow deficit of 20-40% with respect to the gasdynamic model. But averaging in space, taking into account the jet motion across the spacecraft at average MSH speed, lets the data and models converge. Being statistically confirmed, it suggests that the jets must be considered in the flow balance of the MSH. Such intermittent/ transient flow concentrations are opposite to the predictions of gasdynamics and MHD for the transformation of SW kinetic energy into thermal energy at the BS since in the jets the dynamic pressure is rising instead of falling. We infer supporting of the local energy conservation by the (quasi) standing in the obstacle frame electric structures, stored the energy at intensity maximums in the MSH wave interference pattern, which re-distributes the energy of the incident flow.
The typical jet velocity approaches the sound speed in the MSH. Supersonic jets are found in the mantle/LLBL. Presumably they are caused by the Laval-nozzle effect. The high-dynamic pressure jets can skew the MP, being able to drive secondary reconnection at the deformed MP. Four jet types are discussed versus possible mechanisms of their generation, including inertial drift, Alfven wave filamentation, 3- wave decay, Alfven collapse, pressure gradients, charged current sheets and reconnection. The reconnection does not seem to be the dominant jet source even in boundary layers. The jets occur to be nonlinear structures detected for decades. But understanding of their properties and origin could essentially modify the approach to the SW- magnetosphere interaction and should also shed light on heliospheric and astrophysical plasma streamlinings along withTOKAMAK boundary layers. This work was supported by INTAS grant and ISSI.
В ы в о д ы «Плазменные струи», редко объясняемые пересоединением магнитных силовых линий, регулярно наблюдаются в магнитослое между ударной волной и магнитопаузой, их длительность ~ десятков секунд, рост их динамического давления на фоне невозмущенного солнечного ветра - до 2-3 раз. - Примерно 20% струй пронизывают высокоширотную магнитопаузу, вызывая вторичное пересоединение и пролетая в межпланетное пространство через плазменную мантию или низкоширотный погранслой. - Некоторые их них отражаются геомагнитным полем независимо от межпланетного магнитного поля. - Одной из функций струй в магнитослое является «сброс» вниз по потоку до 40% импульса как в стационарном случае, так и при динамическом росте или падении внешнего динамического давления. При этом локальный баланс энергии поддерживается квази-покоящимися электромагнитными структурами в магнитослое. вытесняет плазму вдоль силовых линий - Одним из источников ускорения струй является Альвеновский коллапс, в котором взрывообразный рост магнитного поля опрокидывающихся силовых линий вытесняет плазму вдоль силовых линий