A statistical study on the shape and position of the magnetotail neutral sheet

Abstract. We study the average shape and position of the magnetotail neutral sheet based on magnetic field data obtained by Cluster, Geotail, TC-1, and THEMIS from the years 1995 to 2013. All data in the aberrated GSM (geocentric solar magnetospheric) coordinate system are normalized to the same solar wind pressure 2 nPa and downtail distance X ∼ −20RE. Our results show characteristics of the neutral sheet, as follows. (1) The neutral sheet assumes a greater degree of curve in the YZ cross section when the dipole tilt increases, the Earth dipole tilt angle affects the neutral sheet configuration not only in the YZ cross section but also in the XY cross section, and the neutral sheet assumes a more significant degree of tilt in the XY cross section when the dipole tilt increases. (2) Counterclockwise twisting of the neutral sheet with 3.10° is observed, looking along the downtail direction, for the positive interplanetary magnetic field (IMF) BY with a value of 3 to 8 nT, and clockwise twisting of the neutral sheet with 3.37° for the negative IMF BY with a value of −8 to −3 nT, and a northward IMF can result in a greater twisting of the near-tail neutral sheet than southward. The above results can be a reference to the neutral sheet model. Our large database also shows that the displaced ellipse model is effective to study the average shape of the neutral sheet with proper parameters when the dipole tilt angle is larger (less) than 10° (−10° ).

[1]  N. Tsyganenko,et al.  Internally and externally induced deformations of the magnetospheric equatorial current as inferred from spacecraft data , 2015 .

[2]  T. Hori,et al.  The Distant Magnetotail: Its Structure, IMF Dependence, and Thermal Properties , 2013 .

[3]  Werner Magnes,et al.  The THEMIS Fluxgate Magnetometer , 2008 .

[4]  Werner Magnes,et al.  The Double Star magnetic field investigation: instrument design, performance and highlights of the first year's observations , 2005 .

[5]  N. Tsyganenko,et al.  Global shape of the magnetotail current sheet as derived from Geotail and Polar data , 2004 .

[6]  M. W. Dunlop,et al.  The Cluster Magnetic Field Investigation: overview of in-flight performance and initial results , 2001 .

[7]  Wolfgang Baumjohann,et al.  Basic Space Plasma Physics , 1996 .

[8]  J. Slavin,et al.  Average motion, structure and orientation of the distant magnetotail determined from remote sensing of the edge of the plasma sheet boundary layer with E > 35 keV ions , 1995 .

[9]  C. M. Hammond,et al.  Imaging the effect of dipole tilt on magnetotail boundaries , 1994 .

[10]  Hideaki Kawano,et al.  The GEOTAIL Magnetic Field Experiment. , 1994 .

[11]  J. Slavin,et al.  The distant magnetotail's response to a strong interplanetary magnetic field By - Twisting, flattening, and field line bending , 1985 .

[12]  J. Slavin,et al.  Average configuration of the distant (<220 Re) magnetotail: Initial ISEE‐3 magnetic field results , 1983 .

[13]  Stanley W. H. Cowley,et al.  Magnetospheric asymmetries associated with the y-component of the IMF , 1981 .

[14]  D. Fairfield.  A statistical determination of the shape and position of the geomagnetic neutral sheet , 1980 .

[15]  C. Russell.  Comments on the paper ‘The internal structure of the geomagnetic neutral sheet’ by K. Schindler and N. F. Ness , 1973 .

[16]  J. Binsack,et al.  Explorer 33 and 35 plasma observations of magnetosheath flow , 1972 .

[17]  C. Russell,et al.  Some remarks on the position and shape of the neutral sheet , 1967 .

[18]  T. Murayama.  Spatial distribution of energetic electrons in the geomagnetic tail , 1966 .

[19]  N. Ness.  THE EARTH'S MAGNETIC TAIL* , 1965 .