E.E. Antonova1,2, I.P. Kirpichev2,1, Yu.I. Yermolaev2 Interaction of the solar wind with the magnetosphere of the Earth and the formation of magnetospheric boundary layers S.S. Rossolenko1,2, E.E. Antonova1,2, I.P. Kirpichev2,1, Yu.I. Yermolaev2 1. Skobeltsyn Institute of Nuclear Physics Moscow State University, Moscow, Russia 2. Space Research Institute RAS, Moscow, Russia

Outline Magnetosphere boundary layers Low Latitude Boundary Layer (LLBL) properties The LLBL formation processes The investigation of the problem of pressure balance on the magnetopause The ΘBn angle and it’s dependence from the IMF orientation The dependence of LLBL thickness from the bow shock type The model of turbulent transport across the LLBL

The Earth’s magnetosphere

Under southward IMF conditions LLBL properties • mixing region of cold plasma of the solar wind and hot plasma of magnetosphere • control the rate of mass, momentum and energy transfer between the magnetosheath and the magnetosphere •along LLBL from noon to the tail, the flow moves faster and the layer becomes thicker • under northward IMF conditions LLBL is thicker, then under southward Under northward IMF conditions

Satellites data Interball/Tail: • Corall - low-energy ion experiment (velocity, density, temperature, magnetic field) • Electron - low-energy electron experiment Wind: • solar wind parameters (pressure, velocity, IMF) Geotail: • plasma and magnetic field parameters THEMIS: • ESA - ions and electrons data • FGM - magnetic field parameters The THEMIS data is available on http://www.cdaweb.gsfc.nasa.gov

LLBL properties from INTERBALL/Tail observations Mixing region of cold dense ions of the solar wind and hot ions of magnetosphere with the plasma energies averaged between PS and MSH plasma energies Plasma sheet LLBL Magnetosheath Magnetosheath LLBL Plasma sheet 11 January 1997 Different plasma mixing of ions and electrons 20 September 1995

The event of 21 September 1995: INTERBAL/Tail observatons Thick LLBL from 00:15 till ~02:25 UT and plural magnetopause intersections after 02:25 UT are observed.

Opened questions about the LLBL The plasma penetration inside the LLBL under different IMF conditions The formation of LLBL thickness (the dependence from geomagnetic and interplanetary parameters) The LLBL parameters under IMF Bz>0 more than for 4 houres The structure of LLBL

LLBL formation processes • magnetic reconnection • magnetosheath plasma penetration inside the magnetosphere in the near cusp regions • diffusion through the magnetopause The possibility of local pressure disbalance due to the high level of magnetic field fluctuations (inhomogenuities of plasma parameters) was not considered. Usually used LLBL formation scheme

The A, B, C - THEMIS - satellites data for 8 November 2007 THEMIS-A crossed magnetosheath, LLBL, plasma sheet THEMIS-B observed solar wind plasma and magnetic filed parameters THEMIS-C – crossed the magnetosheath in the time interval 0000-0350 UT

THEMIS-A Low Latitude Boundary Layer crossing The satellite crossed LLBL at 01:42:07-01:43:10 UT Magnetosheath LLBL Plasma Sheet

THEMIS-B solar wind observations The interplanetary magnetic field fluctuations constitute ~3 nT Rather stable solar wind parameters

THEMIS-C magnetosheath observations Magnetosheath magnetic field fluctuations constitute ~10-20 nТ Turbulent magnetosheath conditions

The role of turbulent fluctuations of plasma and magnetic field in LLBL formation • Values of magnetic field fluctuations exceed the value of magnetic field inside the magnetosphere in the near cusp regions. • It is necessary to include such fluctuations in the pressure balance on the magnetopause. • Different conditions of pressure balance take place at different places of the magnetopause. • Local disruption of pressure balance will lead to plasma jets penetration inside the magnetosphere. Results of calculations of positions of the daytime magnetic configuration in accordance with Tsyganenko-1996 magnetic field model for the 8 November 2997

The pecularity of discussed mechanism • J. Lemair (1977) suggested the mechanism of plasma penetration inside the magnetosphere connected with space inhomogeneity of the solar wind dynamic pressure. • Suggested mechanism of boundary layer formation considers the great inhomogeneity of magnetosheath magnetic field. • Both mechanisms consider inhomogenuities of plasma parameters near the magnetopause as the main condition of plasma penetration inside the magnetosphere. It is necessary to mention that popular mechanisms of plasma penetration – reconnection and diffusion consider cases of homogenous plasma flow in the magnetosheath.

The parameter influencing on the magnetosheath magnetic field fluctuations: the ΘBn angle and it’s dependence from the IMF orientation The ΘBn angle (between the vectors of IMF and the bow shock perpendicular) influence on the part of the particles of imbricate solar wind flow, that can penetrate inside the magnetosheath or can be reflected, and on the magnetic field variations at the dayside magnetosphere (Kuncic et al., 2002, Luhmann et al., 1986, Nemecek et al. 2002). Ion flow and magnetic field variations in magnetosheath decrease with the ΘBn angle increasing (diss. of Sheviryev N.N.) If ΘBn < 45 the behind lying bow shock is quasiparallel, the reflected from the shock solar wind and the penetrated througth the bow shock energetic particles of the magnetosphere and magnetosheath can flow far upward the solar wind flow, reeled in the magnetic field lines (Fuselier, 1994). If ΘBn > 45 the bow shock is quasiperpendicular, the magnetic filed is oriented nearly tangent to the bow shock, the reflected particles, reeled in the magnetic field lines, cannot flow far from the bow shock and the vibrations are generated on it or behind it.

The dependence of bow shock types from the IMF orientation On the scheme the IMF is oriented at the angle 45° to the Earth-Sun line and lyes at the equatorial plane. The perpendiculars to the bow shock and the ΘBn angles are shown at the dusk and down flanks. The bow shock parts located at the upper half plane (at the dusk flank of the magnetosphere) are quasiperpendicular, the angle ΘBn> 45 °. The regions in front of the down flank (the lower half plane) are quasiparallel, the angle ΘBn < 45 °.

The dependence of LLBL thickness from the bow shock type The ions flow and magnetic field variations decrease with the ΘBn angle growth. At the quasiparallel bow shock (ΘBn < 45°) the plasma parameter and the magnetic field fluctuations in the magnetosheath exceed the fluctuations behind the quasiperpendicular bow shock (ΘBn > 45°). The pressure balance on the magnetopause should be more often disrupt at the quasiparallel bow shock due to the high level of plasma parameters and magnetic field fluctuations, that can lead to the LLBL plasma jets formation. The LLBL thickness increases at the quasiparallel bow shock??

The LLBL crossing on 19 August 1997 at the quasiparallel bow shock LLBL is observed at 12:33:30-12:34:20 UT, the time of LLBL crossing – 60 sec. ΘBn ≈ 14° LLBL is observed at 12:35:30-12:37:30 UT, the time of LLBL crossing – 120 sec. ΘBn ≈10° IMF: Bx ≈ -5,5 nТ, By ≈ 2,5 nТ, Bz ≈ 0,5 nТ

The LLBL crossing on 13 February 1998 at the quasiperpendicular bow shock LLBL is observed at 19:49:30-19:51:10 UT, the time of LLBL crossing – 100 sec. ΘBn ≈ 86° IMF: Bx ≈ 3nТ, By ≈ -2nТ, Bz ≈ 1nТ

The dependence of the LLBL crossing time from the ΘBn angle for the dayside magnetosphere and the tail Is there a tendency to LLBL thickness increasing with the ΘBn angle growth? Pink – nightsight (tail) (Х<0), black – daysight of the magnetosphere (Х>0)

The dependence of the LLBL crossing time from the ΘBn angle (from 35° to 70°) for the dayside magnetosphere and the tail The dependence of the LLBL thickness from the bow shock type was not found on the received material.

Hypothesis, explaining the absence of the dependence of LLBL crossing time from the ΘBn angle LLBL is usually forming due to the magnetosheath particles penetration inside the magnetosphere in the near cusp regions, where the high level of fluctuatios is constantly observed. The LLBL thickness is determined by the processes inside the magnetosphere, as it was introduced in the paper Antonova, 2005, and not by the processes in the magnetosheath or in the near cusp regions. It is necessary to mention that the processes of plasma structures flow and penetration inside the LLBL are still not enough investigated, that can introduce some errors into the method. The increasing of the statistics perhaps will also clarify the picture.

The flow of plasma in turbulent region The model of turbulent transport across the LLBL The convection and diffusive transport in Y-direction The increasing of the average convection velocity <vy> leads to LLBL thinning, the decreasing of <vy> leads to growth of LLBL thickness, if the diffusion coefficient is constant The flow of plasma in turbulent region The theory explains the dependence of LLBL thickness from the IMF Antonova E.E., 2005

Results It is shown that 1) amplitudes of magnetic field fluctuations can exceed the magnetic field in the near cusp region. 2) magnetic field fluctuations can be the source of the violation of the magnetopause pressure balance. 3) magnetosheath parameter fluctuations can be considered as the source of plasma jets in LLBL. The dependence of the time of LLBL crossing from the bow shock type was investigated in order to prove the hypothesis about the role of magnetosheath magnetic filed fluctuations in the LLBL thickness formation. But the dependence was not observed. The investigated results confirm the estimation about the formation of LLBL due to the plasma penetration in the near cusp regions, where we usually observe high level of magnetic field fluctuations. The results connected with the proofed dependence can be explained taking into account the role of the processes in the magnetosphere in the thick LLBL formation.

Thank you for the attention!