2009 ILWS Workshop, Ubatuba, October 4-9, 2009

Transverse magnetospheric currents and great

geomagnetic stormsE.E.Antonova (1,2),

M. V. Stepanova (3), I.P. Kirpichev (2,1), K. G. Orlova (1), S.S. Pulinets (1),

(1) Skobeltsyn Institute of Nuclear Physics Moscow State University, Moscow(2) Space Research Institute RAS, Moscow, Russia

(3) Physics Department, Universidad de Santiago de Chile, Chile.

Outline of talk•Topology of high latitude magnetospheric domains. •Daytime transverse currents.•CRC – high latitude continuation of the ordinary ring current.•Radial plasma pressure distributions and the sources of Dst variation.•Problem of acceleration of relativistic electrons.•Local plasma traps and local electron radiation belts to the pole of the external boundary of the external radiation belt.

Region from ~7 till ~10RE is ordinarily considered as the region of quasitrapping. Particle trajectories for particles with pitch angles <90 are closed inside the magnetosphere (Shabanskiy and Antonova [1968] effect)

-12.00 -8 .00 -4.00 0 .00 4.00 8 .00 12.00

X , R e

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e

E p = 1 0 k e V

Antonova A.E. and Malova H.V. [2004]

[Delcourt and Sauvaud, 1999]Öztürk and Wolf [2007]

Hori et al. [2003]

Effect of drift echo is observed till ~13RE

near midnight [Hori et al., 2003].

12

00

0618

60 0

80 0

Yagodkina and Vorobjev, (2004)

Themis D magnetopause crossing at subsolar point 18 July 2007

It is well known also that plasma sheet-like plasma population surround the Earth and is constantly observed near noon when satellite cross the magnetopause and LLBL at the subsolar point.

Themis observations support this picture.

Obtained by DeMichelis et al. [1998] picture of current densities does not take into account the daytime magnetic field configuration in which minimal values of magnetic field on the field line take place far from the equatorial plane. Therefore the distribution of current densities at the equatorial plane does not show the distribution of integral current in the flux tube.

At the same time it is ordinarily suggested that daytime part of the magnetosphere from ~7 till ~10RE does not have great transverse currents and nighttime currents are closed by magnetopause currents (tail current) or field-aligned currents (partial ring current).

Example of calculation of isolines B=const (for 100 nT, 90 nT, …) in accordance with Tsyganenko-2004 model at SW Pdin=2 нПа, IMF Bz=-5нТ, By= Bx=0.

Daytime magnetospheric compression leads to distortion of magnetic field. Minimal values of magnetic field take place far from the equatorial plane. Analysis of the configuration of B=const isolines leads to the conclusion that most part of daytime transverse current can be concentrated far from the equatorial plane.

First results of the calculation of current densities on dayside auroral field lines using obtained by Lui and Hamilton [1992] radial plasma pressure profile and Tsyganenko-2001 magnetic field model [Antonova et al., 2009] lead to values comparable with nighttime current densities at the same geocentric distances. The distribution of plasma pressure from 9 till 10RE was approximated by exponential dependence. Integral daytime current between 7.5 and 10 RE constitute ~105-106 A. The direction of daytime transverse current is opposite to the direction of magnetopause current.

Themis multisatellite project measurements near the equatorial plane (see http://www.nasa.gov/missions_pages/themis/) give possibility to obtain radial plasma pressure distribution at geocentric distances from 7 till 10RE.

All Themis-B observations for the period 02.06-29.10.2007 at the geocentric distances 7 < r < 12 RE with 20 longitude deviation were analyzed. The position of the magnetopause was obtained using Bz IMF and Psw measured by Wind satellite.

Distribution of maximal current densities at the daytime field lines obtained using averaged distribution of plasma pressure and Tsyganenko-2001 magnetic field model for solar wind parameters Bz=-5 nT, By=0, solar wind dynamic pressure equal to 2.5 nPa and Dst=-5 nT. Integral current in both hemispheres constitute in studied case 5.8105 A.

The center of transverse currents.

Therefore it is possible to modify existing models of magnetospheric transverse currents and include the high latitude continuation of ordinary ring current – cut ring current (CRC).

Transverse current at geocentric distance ~11RE can be closed not by magnetopause currents but currents of the same nature connected with the existence of radial plasma pressure gradients.

It is necessary to take into account that CRC disturbs not only Bz component of the magnetic field near the Earth but also the Bx component. Such distortion can be evaluated using simple model of two oblique rings.

J=107 A

The introduction of high latitude continuation of the ordinary ring current leads to definite modification of the problem of Dst formation and acceleration of relativistic electrons. Most part of auroral oval is probably mapped on the CRC region. Auroral oval dynamics has the intimate connection with processes during magnetic storm.

Relativistic electrons as a rule appear during recovery phase of magnetic storm. The localization of the place of there appearance is connected with the minimum value of Dst variation by relation of Tverskaya (1986), Tverskaya et al. (2003) and coincide with the most equatorial localization of westward electrojet.

transport from the tail

transport from the ionosphere

avalanche-like behavior

If p(L)=pex(Lex/L)7 and 02 2/ lobeex Bp

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eq

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critst LL

B

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nTl 1075.2 4max

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max

LDst

The dependence

obtains the theoretical explanation (see Tverskoy, 1997) including the value of coefficient (Antonova, 2005) in azimuthally symmetric case:

It was taken into account that upper limit of the inner magnetospheric particle feeling is determined by the stability of the distribution of the plasma pressure. This limit exists in spite of the action of different acceleration and transport mechanisms of plasma particles.

Comparison of theory predictions with the results of experimental observations

pL-s

Tverskaya et al. (2005)

Antonova and Stepanova (2005)

However symmetric ring current does not produce great magnetic field distortion and plasma parameter <1. An order of magnitude larger with >1 magnetic field distortions are connected with asymmetric ring current

The position of the source of the acceleration of relativistic electrons at the latitudes of auroral oval requires the analysis of two important effects:•Stochastic acceleration due to interaction with auroral turbulence•Regular acceleration due to the increase of the magnetic field during storm recovery phase.

Inhomogeneous radial plasma pressure distribution can be observed

Results of Interball/Tail probe observations (Kirpichev, 2007)

Results of CRRES observations (Kozelova et al., 2008)

Complicated picture of transverse currents and possibility of the formation of local plasma traps.

The asymmetric ring current is an example of such inhomogeneous pressure distribution. It is observed in the high latitude magnetosphere. Its intensity is greatly increased during magnetic storms.

Results of IMAGE observations

Plasma pressure gradients in the asymmetric ring current are directed to its center Eastward transverse current is developed in accordance with the condition of magnetostatic equilibrium

[jB]=p

Current loops and B=const loops can be formed at definite conditions.

The possibility of closed Bmin=const loops formation is supported even in the case of using Tsyganeno models.

An example of calculation Bmin isolines using Tsyganenko-2005 model.

Energetic electrons can be trapped in such local regions forming local radiation belts.

Results of CORONAS-F observations show the existence of comparatively stable regions of increased fluxes of relativistic electrons to the pole from the external boundary of the external radiation belt (Myagkova et al., 2008, in press). 412 crossings of polar region at altitude 400-450 km were analyzed using low altitude 500 km polar orbiting Russian satellite CORONAS-F data. Electron precipitations at L>8 were observed in 248 cases.

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1 - 2003/07/15 23:45 M LT 10:152 - 2003/07/16 01:20 M LT 11:003 - 2003/07/16 02:55 M LT 11:40

Electron precipitations observed during 4.5 hours (3 orbits) 15-16 July, 2003

This hypothesis is supported by CORONAS-F satellite observations.

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84 polar crossings with electron precipitations observed during December 2003 and January 2004 were compared with auroral oval position using Meteor-3M data. The time of observations, coordinates and MLT- sectors were suitable for 32 of them.

Practically all of observed increases of relativistic electron fluxes were localized inside the auroral oval.

Conclusions:• Daytime transverse currents connected with the existence of radial plasma pressure gradients flow at geocentric distances ~7-10RE far from the equatorial plane.•The value of integral dayside transverse current is comparable with the value of nighttime transverse current at the same geocentric distances. This means the possibility of the existence of surrounding the Earth current loops constituting cut ring current (CRC). CRC is the high latitude continuation of ordinary ring current and has the same nature. •Regular and stochastic acceleration mechanisms can produce definite contribution in the acceleration of relativistic electrons. The contribution of stochastic mechanisms can be obtained only after extraction of the contribution of regular mechanisms. •Local plasma traps for relativistic electrons can be formed in the high latitude magnetosphere.•The solution of the problem of acceleration of relativistic electrons requires the analysis of the processes at the geocentric distances mapped on the auroral oval.

Thank you for your attention