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Observations of an interplanetary switch‐on shock driven by a magnetic cloud
Author(s) -
Feng H. Q.,
Lin C. C.,
Chao J. K.,
Wu D. J.,
Lyu L. H.,
Lee L. C.
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl037354
Subject(s) - shock (circulatory) , physics , mach number , oblique shock , magnetohydrodynamics , mechanics , magnetic field , moving shock , bow shock (aerodynamics) , plasma , magnetic cloud , computational physics , interplanetary spaceflight , shock wave , solar wind , nuclear physics , medicine , quantum mechanics
A possible interplanetary switch‐on shock event prior to a trailing magnetic cloud was observed on August 1, 2002 at 1 AU. We fit the data with the Rankine‐Hugoniot (R‐H) relations based on both oblique and switch‐on shock models. It is found that both models are consistent with the observed data, and the best fit solutions of the two models are close to one another. For the oblique shock model, the best fit upstream shock normal angle, θ BN1 (= cos −1 (B t1 /B 1 )), is as small as 5.55°. The shock has the following characteristics: (1) plasma density, plasma temperature, and the magnetic field strength all increase across the shock, (2) protons are thermalized very efficiently across the shock, but it is not the case for electrons, (3) the fast‐mode Mach number is greater than unity in the preshock region and less than unity in the postshock region, and (4) from the oblique shock model we find that the normal Alfvén Mach number is very close to unity in the postshock region, while from the switch‐on shock model we obtain a solution of unity normal Alfvén Mach number. Our results clearly demonstrate the MHD character of a fast shock propagating along the ambient magnetic field.