Distribution of X-type magnetic neutral lines in the magnetotail with Geotail observations

摘要

We obtained the distribution of the X-type magnetic neutral lines in the magnetotail from X_(GSM) = 0 to -210 R_E with Geotail observations. For the detection of the neutral lines, we adopted simultaneous reversals of magnetic field from north to south (south to north) and ion bulk velocity from earthward to tailward (tailward to earthward). In the near-tail region (0 greater than or equal X_(GSM)>-30 R_E), the occurrence rate of the reversal events had a peak at Y_(GSM) approximately equals +9 R_E and was characterized by a very asymmetric form in the YGSM direction. The region of the reversal events appeared to expand in the Y_(GSM) direction up to a 50 R_E width at X_(GSM) approximately equals -50 R_E. This width was maintained in the region further downtail (X_(GSM)<-50 R_E). The occurrence rate integrated in the Y_(GSM) direction was found to have a maximum at X_(GSM) approximately equals -60 R_E.