TY - JOUR

T1 - A statistical study of magnetopause structures

T2 - Tangential versus rotational discontinuities

AU - Chou, Y. C.

AU - Hau, L. N.

PY - 2012

Y1 - 2012

N2 - A statistical study of the structure of Earth's magnetopause is carried out by analyzing two-year AMPTE/IRM plasma and magnetic field data. The analyses are based on the minimum variance analysis (MVA), the deHoffmann-Teller (HT) frame analysis and the Walén relation. A total of 328 magnetopause crossings are identified and error estimates associated with MVA and HT frame analyses are performed for each case. In 142 out of 328 events both MVA and HT frame analyses yield high quality results which are classified as either tangential-discontinuity (TD) or rotational-discontinuity (RD) structures based only on the Walén relation: Events with SWA 0.4 (S WA 0.5) are classified as TD (RD), and rest (with 0.4 < S WA < 0.5) is classified as "uncertain," where S WA refers to the Walén slope. With this criterion, 84% of 142 events are TDs, 12% are RDs, and 4% are uncertain events. There are a large portion of TD events which exhibit a finite normal magnetic field component Bn but have insignificant flow as compared to the Alfvén velocity in the HT frame. Two-dimensional Grad-Shafranov reconstruction of forty selected TD and RD events show that single or multiple X-line accompanied with magnetic islands are common feature of magnetopause current. A survey plot of the HT velocity associated with TD structures projected onto the magnetopause shows that the flow is diverted at the subsolar point and accelerated toward the dawn and dusk flanks.

AB - A statistical study of the structure of Earth's magnetopause is carried out by analyzing two-year AMPTE/IRM plasma and magnetic field data. The analyses are based on the minimum variance analysis (MVA), the deHoffmann-Teller (HT) frame analysis and the Walén relation. A total of 328 magnetopause crossings are identified and error estimates associated with MVA and HT frame analyses are performed for each case. In 142 out of 328 events both MVA and HT frame analyses yield high quality results which are classified as either tangential-discontinuity (TD) or rotational-discontinuity (RD) structures based only on the Walén relation: Events with SWA 0.4 (S WA 0.5) are classified as TD (RD), and rest (with 0.4 < S WA < 0.5) is classified as "uncertain," where S WA refers to the Walén slope. With this criterion, 84% of 142 events are TDs, 12% are RDs, and 4% are uncertain events. There are a large portion of TD events which exhibit a finite normal magnetic field component Bn but have insignificant flow as compared to the Alfvén velocity in the HT frame. Two-dimensional Grad-Shafranov reconstruction of forty selected TD and RD events show that single or multiple X-line accompanied with magnetic islands are common feature of magnetopause current. A survey plot of the HT velocity associated with TD structures projected onto the magnetopause shows that the flow is diverted at the subsolar point and accelerated toward the dawn and dusk flanks.

UR - http://www.scopus.com/inward/record.url?scp=84865975587&partnerID=8YFLogxK

U2 - 10.1029/2011JA017155

DO - 10.1029/2011JA017155

M3 - 期刊論文

AN - SCOPUS:84865975587

SN - 2169-9380

VL - 117

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

IS - 8

M1 - A08232

ER -