The geopause in relation to the plasma sheet and the low‐latitude boundary layer: Comparison between Wind observations and multifluid simulations

Wind observations during the May 10, 1996 perigee are used in conjunction with multifluid global simulations to investigate the mixing of magnetosheath-like plasma and ionospheric plasma in the dawn current sheet. Magnetosheath-like plasma can play important roles in the formation of the low-latitude boundary layer (LLBL) and the cold, dense plasma sheet (CDPS) identified previously in Geotail studies where the magnetosheath component is seen as a low energy component. The Wind observations show that this cold component can be seen well inside the nominal position of the magnetopause and even the CDPS, and is most pronounced near the magnetic equator. This cold plasma provides an important tracer for the geopause where the dynamics of the region inside the boundary is controlled by ionospheric plasma arid the region outside is dominated by plasma of solar wind origin. The geopause position in the present case appears be about halfway between the noon-midnight meridian and the magnetopause. In addition, it is shown that the cold magnetosheath-like plasma has significant asymmetries between the northern and southern sides of the current sheet with enhanced cold plasma being observed in the Northern Hemisphere relative to that seen in the Southern Hemisphere. This asymmetry which is also seen in the modeling and is associated with the high dipole (> 20°) tilt during the event which allows enhanced entry of magnetosheath plasma in the Northern (summer) Hemisphere and enhanced ionospheric plasma outflows in the Southern (winter) Hemisphere. Flow asymmetries in the particle distributions that have properties similar to the magnetosheath boundary layer are also observed. However, the characteristics of the distributions indicate that the flow is between the LLBL and the CDPS as opposed to the LLBL and the magnetosheath.

[1]  R. Winglee,et al.  Multi‐fluid simulations of the magnetosphere: The identification of the geopause and its variation with IMF , 1998 .

[2]  M. Fujimoto,et al.  Plasma entry from the flanks of the near‐Earth magnetotail: Geotail observations , 1998 .

[3]  M. Fujimoto,et al.  Structure of the low‐latitude boundary layer: A case study with Geotail data , 1998 .

[4]  J. Borovsky,et al.  The superdense plasma sheet: Plasmaspheric origin, solar wind origin, or ionospheric origin? , 1997 .

[5]  T. Sanderson,et al.  Low-latitude dusk flank magnetosheath, magnetopause, and boundary layer for low magnetic shear: Wind observations , 1997 .

[6]  M. Fujimoto,et al.  Solar wind control of density and temperature in the near‐Earth plasma sheet: WIND/GEOTAIL collaboration , 1997 .

[7]  G. Paschmann.  Observational Evidence for Transfer of Plasma Across the Magnetopause , 1997 .

[8]  R. Winglee,et al.  The average shape of the Magnetopause: A comparison of three‐dimensional global MHD and empirical models , 1997 .

[9]  B. Anderson,et al.  Electron and ion signatures of field line topology at the low-shear magnetopause , 1997 .

[10]  J. M. Bosqued,et al.  A three-dimensional plasma and energetic particle investigation for the wind spacecraft , 1995 .

[11]  F. Mariani,et al.  The WIND magnetic field investigation , 1995 .

[12]  David G. Sibeck,et al.  Magnetopause shape as a bivariate function of interplanetary magnetic field Bz and solar wind dynamic pressure , 1993 .

[13]  C. Russell,et al.  Structure and properties of the subsolar magnetopause for northward interplanetary magnetic field - Multiple-instrument particle observations , 1993 .

[14]  J. Sauvaud,et al.  Polar wind ion dynamics in the magnetotail , 1993 .

[15]  W. Lennartsson.  A scenario for solar wind penetration of earth's magnetic tail based on ion composition data from the ISEE 1 spacecraft , 1992 .

[16]  T. Moore.  Origins of magnetospheric plasma , 1991 .

[17]  C. Russell,et al.  Structure and properties of the subsolar magnetopause for northward IMF: ISEE observations , 1990 .

[18]  T. Moore,et al.  A three‐dimensional numerical model of ionospheric plasma in the magnetosphere , 1989 .

[19]  W. Lennartsson.  Plasma sheet ion composition at various levels of geomagnetic and solar activity , 1987 .

[20]  T. Moore,et al.  The ionosphere as a fully adequate source of plasma for the Earth's magnetosphere , 1987 .

[21]  T. Eastman,et al.  Energetic Particle Observations in the Low‐Latitude Boundary Layer , 1985 .

[22]  E. W. Hones,et al.  Structure of the low‐latitude boundary layer , 1980 .

[23]  I. Papamastorakis,et al.  Plasma acceleration at the Earth's magnetopause: evidence for reconnection , 1979, Nature.