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Ann. Geophys., 22, 183-212, 2004
www.ann-geophys.net/22/183/2004/
© European Geosciences Union 2004
Magnetosheath-cusp interface
S. Savin1, L. Zelenyi1, S. Romanov1, I. Sandahl2, J. Pickett13, E. Amata6, L. Avanov1, J. Blecki9, E. Budnik1, J. Büchner10, C. Cattell15, G. Consolini6, J. Fedder11, S. Fuselier7, H. Kawano4, S. Klimov1, V. Korepanov16, D. Lagoutte12, F. Marcucci6, M. Mogilevsky1, Z. Nemecek8, B. Nikutowski10, M. Nozdrachev1, M. Parrot12, J. L. Rauch12, V. Romanov1, T. Romantsova1, C. T. Russell5, J. Safrankova8, J. A. Sauvaud14, A. Skalsky1, V. Smirnov1, K. Stasiewicz3,9, J. G. Trotignon12, and YU. Yermolaev1
1Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, Moscow, 117810, Russia
2Swedish Inst. Space Physics, Kiruna, Sweden
3Swedish Inst. Space Physics, Uppsala, Sweden
4Kyushu University, Japan
5IGPP, UCLA, USA
6Interplanetary Space Phys. Inst., CNR, Roma, Italy
7Lockheed Martin Alto Res. Lab., CA, USA
8Faculty Math. Phys., Charles U., Praha, Czech Republic
9Space Res. Center, Polish Academy Sci., Warsaw, Poland
10Max-Planck Inst. Aeronomie, Katlenburg-Lindau, Germany
11Naval Research Lab., Washington, USA
12Laboratory Phys. Chemistry Environment, Orleans, France
13University of Iowa, USA
14Centre d’Etude Spatiale des Rayonnements, Toulouse, France
15University of Minnesota, USA
16Lviv Center for Space Researches, Ukraine
Abstract. We advance the achievements of Interball-1 and other contemporary missions in exploration of the
magnetosheath-cusp interface. Extensive discussion of published results is accompanied by
presentation of new data from a case study and a comparison of those data within the broader
context of three-year magnetopause (MP) crossings by Interball-1. Multi-spacecraft boundary
layer studies reveal that in ∼80% of the cases the interaction of the magnetosheath (MSH) flow
with the high latitude MP produces a layer containing strong nonlinear turbulence, called the
turbulent boundary layer (TBL). The TBL contains wave trains with flows at approximately the
Alfvén speed along field lines and "diamagnetic bubbles" with small magnetic fields inside. A
comparison of the multi-point measurements obtained on 29 May 1996 with a global MHD model
indicates that three types of populating processes should be operative:
- large-scale (∼few RE) anti-parallel merging at sites remote from the cusp;
- medium-scale (few thousandkm) local TBL-merging of fields that are anti-parallel on average;
- small-scale (few hundredkm) bursty reconnection of fluctuating magnetic fields, representing a
continuous mechanism for MSH plasma inflow into the magnetosphere, which could dominate in
quasi-steady cases.
The lowest frequency (∼1–2mHz) TBL fluctuations are traced throughout the magnetosheath
from the post-bow shock region up to the inner magnetopause border. The resonance of these
fluctuations with dayside flux tubes might provide an effective correlative link for the entire
dayside region of the solar wind interaction with the magnetopause and cusp ionosphere.
The TBL disturbances are characterized by kinked, double-sloped wave power spectra and, most
probably, three-wave cascading. Both elliptical polarization and nearly Alfvénic phase velocities
with characteristic dispersion indicate the kinetic Alfvénic nature of the TBL waves. The three-wave
phase coupling could effectively support the self-organization of the TBL plasma by means
of coherent resonant-like structures. The estimated characteristic scale of the "resonator" is of the
order of the TBL dimension over the cusps. Inverse cascades of kinetic Alfvén waves are proposed
for forming the larger scale "organizing" structures, which in turn synchronize all nonlinear
cascades within the TBL in a self-consistent manner. This infers a qualitative difference from the
traditional approach, wherein the MSH/cusp interaction is regarded as a linear superposition of
magnetospheric responses on the solar wind or MSH disturbances.
Key words. Magnetospheric physics (magnetopause, cusp,
and boundary layers) – Space plasma physics (turbulence;
nonlinear phenomena)
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