PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
regions of magnetotail current sheet and magnetopause. The tilt of the magnetic dipole to the ecliptic plane
was 0 degrees during the whole run (5 hours), the coordinate system GSE was used. Three simulations
(Victor_Sergeev_040607_1, Victor_Sergeev_010907_1, VictorSergeev_031307_1; further refered to as run1,
run2, run3 accordingly) with various initial conditions in a solar wind have been considered.
In the interplanetary environment for run1 we have set initial conditions as follows. The parameters Vx
=-450 km/s, Vy = 0, density of solar wind n = 2 cm -3 , temperature 6000 K, Bx = 0 and By = 0 nT have been
kept constant during the run. The Bz-component during the first hour of simulation was put -5 nT, then it
sharply changed to +2 nT and was kept the same till the end of simulation. We have also set the changes of
Vz-components of solar wind speed from -30 to 30 km/s starting from ST = 01:40 of the simulation time
(ST). For simulation runs 2 and 3 the initial conditions were similar except for Vx = -600 km/s and n = 5 cm -3
for run2 and Vx = -300 km/s with n = 20 cm -3 for run3.
a)
b)
c)
Figure 1: Results of 3D MHD modeling for Run1 at 01:56ST. The figuresa,b,d show the distribution of
parameters in the neutral sheetsurface. a) colors indicates Ey = -[VxB]y, contours indicate the ratio Jz/Jy>
0.7 (from fig.1b); b) color shows the ratio Jz /Jy ; d) colour shows Zns. In figure 1c red, black and blue lines
indicate Zns(Y) profiles at distances 12, 18 and 26 RE. Crosses in figures c) and d) indicate points of a
neutral sheet where the surface is not reliably determined (correlation coefficient Bx & Z is less than 0.85).
In figures b, d the arrows show the vectors of horizontal plasma flow .
Computed parameters from the tail current sheet area interesting to us were taken by using the
interpolation procedure with step 0.5 RE in X gse (from -30 to -10 RE), with the step 0.2 RE in Y gse (from -
15 to 15 RE), and with the step 0.2 RE in Z gse (from -6 to 6 RE). For any [X,Y] we obtained the coordinate
of a neutral sheet (ZNS) by analyzing the regression Bx(Z) as the point, where the corresponding regression
line crosses the axis Bx=0. The reliability of so defined neutral sheet position ZNS can be controlled by the
value of the correlation coefficient between Bx and Z: points XY characterized by low correlation coefficient
(CC