The structure and dynamics of a large-scale plasmoid generated by fast reconnection in the geomagnetic tail

Abstract

Abstract. As a sequence of Ugai (2010b), the present paper studies in detail the structure and dynamics of large-scale (principal) plasmoid, generated by the fast reconnection evolution in a sheared current sheet with no initial northward field component. The overall plasmoid domain is divided into the plasmoid reconnection region P and the plasmoid core region C. In the region P, the magnetized plasma with reconnected field lines are accumulated, whereas in the region C, the plasma, which was intially embedded in the current sheet and has been ejected away by the reconnection jet, is compressed and accumulated. In the presence of the sheared magnetic field in the east-west direction in the current sheet, the upper and lower parts of the reconnection region P are inversely shifted in the east-west directions. Accordingly, the plasmoid core region C with the accumulated sheared field lines is bent in the north-south direction just ahead of the plasmoid center x = X C , causing the magnetic field component in the north-south direction, whose sign is always opposite to that of the reconnected field lines. Therefore, independently of the sign of the initial sheared field, the magnetic field component B z in the north-south direction has the definite bipolar profile around X C along the x-axis. At x = X C , the sheared field component has the peak value, and as the sheared fields accumulated in the region C become larger, the bipolar field profile becomes more distinct.

Virtual satellite observations of plasmoids generated by fast reconnection in the geomagnetic tail

“…On the other hand, we recently studied the plasmoid structure and dynamics, generated by the fast reconnection mechanism, and demonstrated that the field lines inside the plasmoid are not helical nor closed (Ugai, 2010(Ugai, , 2011. A similar conclusion is also suggested on the basis of satellite observations (Sormakov and Sergeev, 2008;Sergeev et al, 1992).…”

“…In previous papers (Ugai, 2010(Ugai, , 2011, the structure and dynamics of the plasmoid generated by the fast reconnection mechanism are generally studied for three cases (1) B y0 = 0.1 and α = 0.1, (2) B y0 = 0.1 and α = 0.2 and (3) B y0 = 0.2 and α = 0. In the present paper, these simulation results are employed for virtual satellite observations.…”

“…The computational region is taken to be a rectangular box, 0 ≤ x ≤ L x , 0 ≤ z ≤ L z , and −L y ≤ y ≤ L y , and the axis symmetry boundary conditions are assumed with respect to the x-and z-axes (Ugai, 2011). On the other boundary planes…”

“…Hence, the main theme of the present paper is to examine this controversial issue by virtual satellite observations. On the basis of Ugai (2011), Fig. 2a shows the schematic drawing of a plasmoid travelling in the earthward direction, where the x-, y-and z-axes are directed to the earthward, duskward and northward directions, consistent with the GSM coordinates; also, the origin x = 0 is taken to be the initial X line location, where magnetic reconnection starts.…”

“…Figure 2b shows the magnetic field lines passing through the plasmoid, which indicate that they are not helical inside the plasmoid. In this case, the region P above and below region C is inversely shifted in the y-direction to bend the field lines accumulated in region C, marked by the letter B, in the z-direction (Ugai, 2011).…”